Inter-American Photochemical Society Newsletter · This newsletter is available in PDF format from the website. I-APS Newsletter Volume 24 Number 2, Fall 2001 1 I-APS Officers (2000–2002)

Inside this issue:I-APS Officers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1Advisory Committee Members . . . . . . . . . . . . . . . . . . 1Letter from the President . . . . . . . . . . . . . . . . . . . . . . . 2Note from the Editor . . . . . . . . . . . . . . . . . . . . . . . . . . 3Award Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Symposium Honoring George S. Hammond,

Jack Saltiel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5XIIth Inter-American Photochemical

Society Conference Report . . . . . . . . . . . . . . . . . . . 10Organic Photosensitizers to Probe Macromolecular

Structure and Dynamics, Lisa A. Kelly . . . . . . . . . . 14Celebration of Michael Kasha’s 80th Birthday,

Edwin F. Hilinski . . . . . . . . . . . . . . . . . . . . . . . . . . . 20Glossary of Terms in Photocatalysis

and Radiocatalysis . . . . . . . . . . . . . . . . . . . . . . . . . . 22Positions Available . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23Upcoming Meeting Information . . . . . . . . . . . . . . . . . 23Society Application Form . . . . . . . . . . . . . . . . . . . . . . 25

Inter-American Photochemical Society NewsletterVolume 24 Number 2, Fall 2001

I-APS Internet Address:http://www.chemistry.mcmaster.ca/~iapsThis newsletter is available in PDF format from the website.

I-APS Newsletter Volume 24 Number 2, Fall 2001 1

I-APS Officers(2000–2002)PresidentFrederick D. LewisDepartment of Chemistry2145 Sheridan RoadEvanston, IL [email protected]

Vice-PresidentEdwin F. HilinskiDepartment of ChemistryFlorida State UniversityTallahassee, FL [email protected]

SecretarySteven A. FlemingDepartment of ChemistryBrigham Young UniversityProvo, UT [email protected]

TreasurersLisa A. Kelly(USA)Department of Chemistry andBiochemistryUniversity of MarylandBaltimore County1000 Hilltop CircleBaltimore, MD [email protected]

Cornelia Bohne(Canada)Department of ChemistryUniversity of VictoriaP.O. Box 3065Victoria, BC V8W [email protected]

Frank H. Quina(South America)Instituto de QuimicaUniversidade de Sao PauloSao Carlos, Sao PauloCEP 13560 [email protected]

Advisory BoardCornelia BohneDepartment of ChemistryUniversity of VictoriaP.O. Box 3065Victoria, BC V8W [email protected]

Ian R. GouldDepartment of Chemistry& BiochemistryArizona State UniversityBox 871604Tempe, AZ [email protected]

Irene KochevarDepartment of DermatologyMassachusetts GeneralHospital WEL-224Harvard Medical SchoolBoston, MA [email protected]

Pedro F. AramendiaINQUIMAE. Departamento deQuímica InorgánicaFCEN. Universidad deBuenos AiresPabellón 2. Ciudad Universitaria1428 Buenos [email protected]

Mary K. BoydDepartment of ChemistryLoyola University Chicago6525 N. Sheridan RoadChicago, IL [email protected]

Gerald J. MeyerDepartment of ChemistryThe Johns Hopkins University3400 North Charles StreetBaltimore, MD [email protected]

Newsletter EditorLinda A. PeteanuDepartment of ChemistryCarnegie Mellon University4400 Fifth AvenuePittsburgh, PA [email protected]

WebmasterWilliam J. LeighDepartment of ChemistryMcMaster UniversityHamilton, ON L8S [email protected]

2 I-APS Newsletter Volume 24 Number 2, Fall 2001

August 1, 2001

Dear Colleagues:In my last letter to you, dated 19 October 2001, I concluded by forecasting that the coming year would be an

exciting one for our Society. Events have borne this out. In the intervening nine months there have been no fewerthan five photochemistry conferences in the Americas, including the highly successful 12th I-APS Conference inCórdoba, Argentina. Plans are in place for the 13th I-APS Conference to be held in Tempe, Arizona, January 2-6,2002. Our new Secretary, Steve Fleming, and Newsletter Editor, Linda Peteanu, are in the process restructuring ourmembership rolls and newsletter. In cooperation with the European Photochemical Association (EPA) and JapanesePhotochemical Association (JPA) we have established an Inter-Society Committee on Photochemistry (I-SCP). Weare also in discussion with EPA and JPA concerning new journals sponsored by those societies.

Let me begin by thanking the co-chairs Pedro Aramendia and Miguel Garcia-Garibay and all the members ofthe organizing committee for the 12th I-APS Conference, particularly our local hosts Gerardo Argüello and GustavoArgüello, for their considerable efforts in what proved to be a stimulating meeting in a most agreeable, secludedlocation. Pacifichem 2000 attracted many I-APS and JPA members to Honolulu for multiple large symposia. Aspecial symposia at the San Diego ACS meeting honoring George Hammond on the occasion of his 80th birthdaywas organized by Carl Wamser. And Michael Kasha’s friends and colleagues gathered in Tallahassee for a symposiumin celebration of Michael Kasha’s 80th birthday. The most recent gathering of photochemists was at the 20th GordonResearch Conference on Organic Photochemistry in New London, CT. Jack Saltiel has the distinction of havingattended all five of these meetings. Society members have promised reviews of several of these conferences for thisissue of the Newsletter.

Society Secretary, Steve Fleming, has undertaken the on-going task of updating our membership rolls. Last yearwe moved our membership renewal date to January 1. Those of you whose memberships expire at the end of this yearcan expect to receive dues notices from Steve during the Fall. I-APS membership is a real bargain, especially forpostdocs and students. Please renew your membership and encourage your students and photochemical colleagues tobecome I-APS members. Several significant decisions have been made with respect to our Newsletter. At the suggestionof our new Editor, Linda Peteanu, the publication schedule has been changed from May and November to Februaryand August. This will allow us to provide more timely announcements of meetings and society awards. The Newsletterwill also be significantly reduced in size by moving the text of solicited scientific articles to our web site. Abstracts ofarticles will continue to appear in the Newsletter along with news and other items of interest to I-APS members.The reduction in size will significantly reduce production time and publication and mailing costs. Watch for the firstissue of the reformatted Newsletter which should appear at the end of the summer both in your mailbox and on ourweb site.

On the international front, Dick Weiss and Cornelia Bohne are serving as I-APS representatives on the newlyformed I-SCP which will represent the three societies (I-APS, EPA, JPA) in dealings with the restructured IUPACand other issues of interest to the three societies. Last year Elsevier began publication of J. Photochem. Photobiol. C.Reviews under the editorial control of the JPA. Next January the Royal Society of Chemistry will begin publicationof Photochem. Photobiol. Sciences (PPS) on behalf of the EPA and the European Society for Photobiology. I wouldpersonally encourage I-APS members to support these society-published journals as well as Photochem. Photobiol.which is published by the American Society for Photobiology. Support would entail submission of articles andsubscription to personal and library copies. The existence of strong, society-controlled journals will benefit theinternational photochemistry community and may render superfluous high priced commercial journals of questionablequality.

Letter from Frederick D. Lewis

Frederick D. LewisDepartment of ChemistryNorthwestern UniversityEvanston, IL 60208-3113 [email protected]

Phone: 847-491-3441Fax: 847-467-2184


In closing, let me encourage all society members to attend the 13th I-APS Conference in Tempe, AZ, January 2-6, 2002. Co-chairs Ian Gould and Peter Ford have assembled an impressive list of invited speakers, which can beviewed on our web site. Moreover, they guarantee flawless Arizona weather. This will be the Society’s first NorthAmerican meeting west of the Sewanee River and an opportunity for increased participation by colleagues in thewestern states. Postdocs and students are always welcome at I-APS meetings. So plan on attending — and bring acolleague or your students. I look forward to seeing you in Tempe.

Best regards,

Fred Lewis

With this issue, I will be taking over the editorial duties for the I-APS Newsletter from William Jenks. I first thankWilliam for doing a great job during his tenure and for giving me a lot of help and advice. Secondly, I will describesome changes that are planned for the Newsletter and solicit your input.

The first change you may notice is that the Newsletter that you have received is considerably ‘streamlined’ in aneffort to use space as efficiently as possible. The I-APS treasury funds, generated via modest membership dues, willbe saved in the production and mailing of this reformatted Newsletter so that more money can be used in supportother important Society activities such as conferences and student travel awards. In the future, the focus of theNewsletter will be on Society news, conference announcements, and contributed summaries of recent photochemicalconferences. General scientific review articles, submitted by the readership, will also be included as opportunitiesarise. The second upcoming change will be that some of the longer pieces will be abstracted in the Newsletter withthe remaining content published on the web. Each abstract will contain an easy-to-use link to the appropriate webpage. Eventually, we hope that most, if not all, of the Newsletter will be entirely web-based, saving both paper andexpense.

I recognize that many of these changes may initially appear quite drastic, but I hope that the membership willgrow comfortable with the print-and web format. Furthermore, I ask for your indulgence as we implement thesechanges because we will certainly be facing a bit of a learning curve. Please feel free to contact me with any questionsand/or comments that you may have regarding the format and content of the Newsletter.

Best regards,

Linda Peteanu

Note from the Editor

Linda PeteanuDepartment of ChemistryCarnegie Mellon University4400 Fifth AvenuePittsburgh, PA [email protected]


2002 I-APS Award inPhotochemistry: Paul F. BarbaraProfessor Paul F. Barbara of the University of Texasat Austin is the winner of the 2002 I-APS Award inPhotochemistry. This Award is given in recognition ofPaul’s outstanding contributions to the advancement ofphotochemical and photophysical sciences during the lastten years. These contributions include detailed studiesthat use ultrafast spectroscopy, single moleculespectroscopy, and near field scanning optical microscopyand spectroscopy. As noted in the nominating materials,a hallmark of Paul’s research is the use of state-of-the-artexperimental strategies to investigate theoreticallyaccessible chemical prototypes, many of which his grouphas introduced. Paul’s descriptions of condensed phasephysical and chemical phenomena are well based infundamental principles and are well received by scientistsacross the range of photosciences because of Paul’s abilityto make the significance understandable to a broadaudience.

2002 I-APS Fellowship:Donald R. ArnoldDonald R. Arnold, Professor Emeritus of DalhousieUniversity, has been elected to Fellowship in the Inter-American Photochemical Society. I-APS Fellowship ingeneral is awarded on the basis of lifetime scientificachievements in photochemistry or contributions to thescience of photochemistry as a discipline or service tothe Society. The nomination cites Don’s pioneeringinvestigations in several areas of organic photochemistryincluding the following: photoinduced electron-transferreactions; exciplexes; the photochemistry of charge-transfer complexes; the capto-dative effect in free radicals;triplets, and radical ions; the [2 + 2] photoadditionof ketones to alkenes; the reactivity and spectroscopy ofaryl- and vinylcarbenes; free radical chemistry;electrochemistry; and the photochemistry of small ringcompounds such as cyclopropanes, cyclopropenes, andoxiranes. Don served as the first I-APS President (1980-83). He has been a regular participant in the I-APSWinter Conference and Gordon Research Conference onOrganic Photochemistry.

2002 I-APS Awards and Fellowships

2002 Cilento Award:Claudio D. BorsarelliClaudio D. Borsarelli of the Universidad Nacional deSantiago del Estero, Argentina is the winner of the 2002Cilento Award. This Award is presented to a scientist,aged 35 or younger, working in Latin America in order toencourage participation in the I-APS Winter Conference.Dr. Borsarelli is an assistant professor at the UniversidadNacional de Santiago del Estero and an assistantresearcher at the Consejo de Investigaciones Científicasy Técnicas de la República Argentina (CONICET) atthe university. His research interests are chemical andphotochemical reactivity of natural and artificial pigmentsin organized media, reactions of singlet oxygen withnatural pigments, photostability of pharmaceuticals, andelectron-transfer and proton-transfer reactions inhomogeneous and heterogeneous media.

2002 Closs Award:Tracy L. MorkinTracy L. Morkin from McMaster University is the winnerof the 2002 Closs Award. The Closs Award is given toa student in recognition of high quality research that isto be presented orally at the I-APS Winter Conference.Ms. Morkin is a graduate student working with ProfessorWilliam J. Leigh. She has been investigating thephotochemistry of ∀-silyl-substituted diazo compounds,diazirines, and ketenes with the ultimate goal ofcharacterizing the reactivity of transient silenes thatare formed via rearrangements of their precursor∀-silylcarbenes.


Organized by Carl C. Wamser (Portland State University)and sponsored by the organic and physical chemistrydivisions, this symposium was held on April 2 and 3, 2001in San Diego, as part of the 221st National Meeting ofthe American Chemical Society. It was a personally andscientifically rewarding, heart-warming affair that broughtto this attendee particularly strong nostalgia for theCaltech days in George Hammond’s laboratory. A largeappreciative audience included a fine representation ofthose of us who had the good fortune to be touched byGeorge as he blazed through the different stages of hiscareer. The Iowa State years, the Caltech years, the UC,Santa Cruz years, the Allied Chemical years, and, afterhis retirement, the Bowling Green, GeorgetownUniversity and now Portland State University years wereall represented.

Carl Wamser (Ph.D., Caltech) opened the firstafternoon session of the symposium with biographicalcomments about George’s early years, running the familydairy farm in Auburn, Maine at 13 after his father’s deathand then attending nearby Bates College. The firstspeaker, Jay Kochi (University of Houston, Ph.D., IowaState), prefaced his scientific lecture with a tribute toGeorge, and his seminal contributions to physical organicchemistry and photochemistry in particular, and his abilityto influence his colleagues and students at all levels. Jayspoke of George’s gift of imagination, his generousintellect and his superb ability for zeroing in on theessential. A quote from Orville Chapman “George nevermet an idea he did not like” struck a cord with all of uswho knew him. Jay knew George before hisphotochemistry years. He met him first as a UCLAundergraduate some 53 years ago, when George gave asubstitute lecture for Saul Winstein, with whom he was apostdoctoral fellow after earning his Ph.D. with PaulBartlett at Harvard. He was so impressed that he followedGeorge to Iowa State, where George had a profound effectin helping assemble a dynamic group of faculty thatincluded Ernie Wenkert, Chuck Depuy and OrvilleChapman. Jay spoke of the Chinese tradition of revering,honoring, and respecting longevity, and presented Georgewith a classical Chinese poem, that George is to have

translated in time for his 100th birthday celebration. Jaythen announced the permanent establishment of theGeorge S. Hammond Lectureship at Bates College.Former Iowa State colleagues accomplished this throughcontributions to George’s alma mater, a wonderful gesturethat touched George deeply.

The scientific part of Jay’s lecture (Charge transferphotochemistry via electron donor/acceptor organizations)began with examples illustrating the ubiquitous, alasunheralded, involvement of colored charge transfercomplexes in “garden variety” organic reactions, such asbromine addition to alkenes, electrophilic aromaticsubstitution and the Diels-Alder reaction. Contact ionradical pair (CIRP) intermediates, although verycommon, are not mentioned in Organic Chemistrytextbooks. Jay reviewed incisive contributions from hisown research, concentrating on those for which CIRPformation is induced by light absorption into the CTband. He emphasized the importance of includingsolvation energies in correlations of reaction rateconstants with the electronic transition energy (hνCT) ofthe CT band. For instance, rate constants foroxymercuration of aromatic hydrocarbons show randomcorrelation with corresponding hνCTs but yield to adramatically linear correlation when solvation energiesare included.

Nick Turro (Columbia University, Ph.D. Caltech)was the second speaker. Nick was my classmate at Caltechhaving arrived there in the summer of 1960. He spoke ofthe decisively shaping influence of the late PeterLeermakers (Ph.D. Caltech) in bringing him to Georgeand to Caltech, and how, on being labeled by George an“anti-photochemist” when, in a public lecture, hedemonstrated for him the luminol chemiluminescencereaction, he rose to the challenge by changing researchdirections. Nick turned from seeking entry into tripletstates thermally via transition metal ion catalysis tophotochemistry and triplet photosensitization. WithPeter’s participation this transition immediately bore fruitin the benzophenone-photosensitized photolysis of ethylpyruvate and launched Nick’s remarkable career inphotochemistry. Nick credits George for having given us

Photochemistry Becomes More Complex: A SymposiumHonoring George S. Hammond On His 80th Birthday

Jack SaltielDepartment of ChemistryFlorida State UniversityTallahassee, FL [email protected]


the tools to unravel photochemical mechanisms byshowing how triplet sensitization could be appliedgenerally in the unambiguous study of triplet statereactivity. Then, in the early 60s, at the dawn of modernmolecular photochemistry, when each breakthrough cameclose on the heels of another, it was a heady atmospherein the Hammond research group and with George’sencouragement his co-workers would long maintain“photochemical highs”.

Apparently, not entirely satisfied with the title of hislecture “Supramolecular and magnetic control effects inorganic photochemistry”, Nick tried “Super dupermolecular photochemistry” and “Better things and betterliving through complexity”. Supramolecularphotochemistry, the study of photochemical reactions inthe confining media of zeolites, cyclodextrins, micelles,and complex fluids, brings into play noncovalentinteractions between substrate and environment thathave a controlling influence on the outcome ofphotochemical reactions. Nick described the photolysisof symmetrical (ACOA) and unsymmetrical (ACOB)dibenzyl ketones in the super cage environments ofzeolites. Because of different size restrictions, substratesin different locations in the zeolite (framework, holes,internal pores) behave as isomers with different relativemobility, as revealed by 2H NMR measurements onstrategically deuterated substrates. Conditions weredescribed that allow control of cage products on photolysisof ACOB from 100% cage effect, CE, (AB product only)to 0% CE (statistical AA/AB/BB ratio) and to –100%CE (AA and BB products only). Enormous effects onradical lifetimes were established by transient EPRmeasurements (compare microseconds outside withseconds and hours within supracages). Depending onradical size, supracage size restrictions dramatically inhibitradical dimerization and favor disproportionation. Inzeolites providing larger cages, cage reactions of theprimary radical pairs (e.g., A/COB) could be studied andthe effect of 13C in the carbonyl carbon on triplet → singletradical pair conversion and of external magnetic fieldswere described. At the end of this spectacular lecture Nickexpressed our gratitude to George: “George we all thankyou and love you for your mentoring insights, dedication,and your ability to imprint your scientific attributes onall your students and collaborators”.

After a break and a chance to greet old friends, itwas Nate S. Lewis’ turn to speak. Perhaps Nate illustratesbest the intricate scientific ties between many of theSymposium participants. Now a professor at Caltech, hehad started out as an undergraduate there. Encouraged in1976 by Kent Mann, a graduate student, he was “suckedinto” the research collaboration between the Harry Grayand George Hammond groups, without knowing at the

time that that decision would have a profound effect onhis future. It led him to MIT for his Ph. D. studies withMark Wrighton (Florida State B. S., Caltech Ph. D.),who was the first to set the Hammond/Gray collaborationon fire, and then back to Caltech.

The title of Nate’s lecture was “Nanocrystallinetitanium dioxide solar cells sensitized with ruthenium orosmium polypyridyl complexes: Photoelectrochemical studiesand electron transfer dynamics”. He described the use ofosmium polypyridyl complexes as sensitizers ofnanoporous TiO2 electrodes to solar illumination. Spectralresponses of TiO2 solar cells are extended to longerwavelengths with the use of OsII(H2L)2(CN)2, (where Lis 4,4’-dicarboxylato-2,2’-bipyridine) or OsII(H2L)3

2+ thanwith the use of RuII(H2L)2(NCS)2 and all produce veryhigh external quantum yields for photocurrent flow.Singlet and triplet MLCT states of the ruthenium andosmium bipyridyl complexes RuII(H2L)2(CN)2,OsII(H2L)2(CN)2, RuII(H2L)2(NCS)2 andOsII(H2L)2(NCS)2 inject electrons into the semiconductorwith rate constants in the 1010 – 1013 s-1 range. The muchslower rates of charge recombination decrease withincreasing driving force, indicating that they fall in theMarcus inverted region. Solar cell efficiencies over 5%were achieved. Higher efficiencies may result by designingsensitizers in nanocrystalline solar cells that takeadvantage of the Marcus inverted region behavior ofcharge recombination. This augurs well, because anefficiency increase to 15% is likely to lead to commerciallyfeasible applications.

Tom Penner (Caltech Ph. D.) was the first industrialspeaker of the Symposium (Imaging Materials and Media,Eastman Kodak Company). In his Ph.D. studies duringthe late 1960s, Tom had inherited David Whitten’s(Caltech postdoctoral) research project concerningrelationships between photochemistry and radiationchemistry. The fact that Tom’s presentation was co-authored by Dave Whitten is testimony to the lastingnature of research collaborations between George’s co-workers. Tom spoke of George’s view that the teachingof chemistry in terms of the traditional divisions presentsan impediment to learning the subject. In his talk, JayKochi had also mentioned the Hammond/Gray paradigmof organizing the teaching of chemistry according tofunction: Synthesis, analysis, structure, and “the heart ofchemistry” dynamics.

Tom’s topic, “Photoprocesses in ordered thin films”,concerned the design of materials for optical and photonicapplications. Achieving desired performance depends, inpart, on including functionality to control intermolecularinteractions for large-scale organization. Chromophoresthat interact with light in a specified way are essentialcomponents. Systems consisting of deliberately

Photochemistry Becomes More Complex: A Symposium Honoring George S. Hammond On His 80th Birthday


interactive multiple components offer opportunities andchallenges for optimizing conditions to maximizeperformance. Energy migration in dye-polymer/clay filmswas described. Formation of J-aggregates by cyanines andother dyes incorporated in polymers allows layer-by-layerfabrication of films on anionic clays. Efficient energytransfer from dye to dye and from layer to layer producesan antenna function for harvesting light energy. The effectof increasing the number of layers is not completelyunderstood. For instance, a case was described for whichenergy migration is very efficient for the first six dye layers,but further layers (up to ten total) are non-contributing.This antenna effect has practical applications in silverhalide imaging. An effective absorbance of 0.15 for amonolayer of dye coating on a silver halide crystal leadsto a large fraction of wasted incident light. The antennaeffect of multilayer dye assemblies markedly increases lightabsorption efficiency in photographic films. The orderedantenna dye on the silver halide grain acts as a templatefor the formation of J-aggregates with their characteristiclarge absorbances.

Dick Weiss (Caltech postdoctoral) presented the lasttalk of the first session of the symposium. As a graduatestudent with Eugene Snyder at the University ofConnecticut in the late sixties, the Woodward andHoffmann concept of orbital symmetry conservation inelectrocyclic reactions had intrigued Dick, who knew thatits application to photochemical reactions wasproblematic. The draw of California and photochemistry,in that order, brought Dick to Caltech, armed withEugene’s advice to bet George that he could not stopsmoking. Dick has enjoyed a close association withGeorge that extended well beyond the initial twopostdoctoral years. It continued through Dick’s three-yearappointment as an NAS Overseas Fellow at theUniversidade de Sao Paulo in Brazil, a program in whichGeorge was intimately involved, and more recently,through George’s highly positive association with Dick’sresearch group at Georgetown University. He finished theintroduction to his talk with two GSH quotations. Thefirst was George’s enthusiastic “Gee that’s great” reactionto new results which had an exhilarating effect onstudents, and the second was from George’s reflective side“Any scientific (or other) discipline when put into a smallbox will surely shrivel and die”. Dick has been studyingthe control of photochemical reactions by polymer media.He took comfort in the fact that although thephotochemistry was confined to small boxes (cages), theyhave flexible walls.

The title of Dick’s contribution was “Extractingfundamental (simple) photochemical and photophysicalinformation from reactions of guest molecules in complexpolymeric media”. Results were presented for the photo-

Fries reactions of 1-naphthyl esters in unstretched andstretched polyethylene. Stretching the polymer leads toa transition in structure from spheralytic organization ofthe crystalline portion to aligned microcrystallites andcauses a decrease of mean free ‘hole’ volumes of 10-20Å3. The free volume change influences the fate of cagedsinglet radical pairs. For instance, the ortho/para ratio ofthe acetylnaphthol products formed on photolysis of 1-naphthyl acetate changes from 4.2 in unstretched to 4.9in stretched polyethylene. For the bulkier myristate, onlyortho product is observed in either unstretched orstretched polyethylene. The confinement of the polymerenvironment prevents the relative reorientation of theinitial radical pair that is required for para coupling.Decarbonylation of the initial alkanoyl radical in the cagegives a new radical pair whose fate is also influenced bythe medium. The second part of the talk concernedcovalent attachment of aromatic hydrocarbons to thepolymer backbone via proton bombardment. Accordingto Dick, Marshall McLuhan’s 1964 aphorism, “Themedium is the message”, although made in a differentcontext, aptly describes the controlling influence ofpolymeric media on photochemical processes, with thecaveat that “To understand the message, first understandthe medium” (Richard Weiss, 1984 unpublished).

Harry Gray (Caltech) was the first speaker of thesecond afternoon session on Tuesday, April 3. Harry spokeof George’s enormous influence on his life, on his researchcareer and on the inorganic and organometallic chemicalcommunity, generally. “I was a decent inorganic chemist,and then I met George”, he joked. George was responsiblefor Harry’s conversion to photochemistry and for his movefrom Columbia to Caltech, but when Harry turned toGeorge and said “Thank you” he was speaking for all of us.

The title of Harry’s contribution was “Probing enzymeswith photosensitizers linked to substrates”. He spoke first ofthe enormous barrier to electron transfer between metalions in water due to the extremely high waterreorganization energy and how the low reorganizationenergy of the protein medium leads to a reduced, friendlyto life, barrier. For instance, electron transfer betweenFe2+ and Fe3+, an identity reaction, occurs within 100 msin water at a separation of 6.5 Å but would require 1016

years at a separation of 20 Å. In a protein environmentelectron transfer between Fe2+ and Ru2+ at a separation of20 Å occurs within 0.5 µs! A series of cytochrome P450cam

(P450) substrates tethered to luminescent Ru sensitizersbind the enzyme with comparable or greater affinities thanthose of the unmodified substrates. Ru-Fe(heme) energytransfer in the bound complex dramatically acceleratesexcited state decay. Analyses of luminescence decaykinetics yield dissociation constants for P-450/Ru-substrate complexes and similar Ru/Fe distances are



extracted for a variety of complexes from the energytransfer parameters. The similarity of the distancessuggests a common substrate binding access channel.Confirmation of the validity of the calculated distanceswas obtained by x-ray crystallography of the crystal ofone complex. Selective binding of the modified substratesto P450 was inferred from the luminescence kinetics inthe presence of other heme proteins, indicating that suchsubstrates could form the basis for a new class of opticallydetected in situ biosensors. The use of fluorinatedbiphenyl linkers instead of methylene chains enhancesbinding 100-fold.

The second speaker, Doug Neckers (Bowling Green)started with a tribute to George: “We honor GeorgeHammond, the man who brought light to an organicchemistry laboratory”. As a graduate student with EarlHuyser at the University of Kansas, Doug had studiedthermally and photochemically induced free radicalreductions of ketones. Influenced by fellow postdoctoralfellow Nick Turro in Paul Bartlett’s laboratory at Harvard,he settled on photochemistry as a career. Doug was thedriving force that created The Center of PhotochemicalSciences at Bowling Green in 1985 and brought Georgethere as a Senior McMaster Institute Research Fellow in1988. Through George’s frequent visits to the center,Doug has maintained a close relationship with him.

Doug spoke of his photopolymerization studies thatevolved into three-dimensional imaging and photo-stereolithography. His 3-D photochemistry has had asignificant impact on paleontology through theremarkable achievement of producing a 3-D polymer copyof the skull of a 2800-year old Egyptian mummy from theCT scan. Doug’s formal contribution was on“Photoreactions studied by step-scan transient IRspectroscopy”. He described how this technique has beenapplied to elucidate long-standing mechanistic questionsin photochemistry. For instance, dating back to Doug’sPh.D. studies, intramolecular γ-H abstraction in the tripletstate of alkyl phenylglyoxylates had been postulated toyield a biradical that dissociates to a ketone, derived fromthe alkoxy group of the ester, and 1-hydroxy-1-phenylketene as a reactive intermediate. Step-scantransient IR spectroscopy provides IR spectra in a time-window of 20 ns to 5 µs following excitation and allowsdirect detection of ketene formation (400 ns rise-time)from the triplet state (389 ns decay time). The shortlifetime of the biradical intermediate (15 ns) precludesits observation in the IR spectra. The ketene is trappedas the methyl mandelate when benzene or cyclohexanesolutions of the phenylglyoxylates are irradiated in thepresence of methanol. In another example, dating backto work carried out in collaboration with Nick Turro inPaul Bartlett’s laboratory, Doug described the IR detection

of tetramethylcyclopropanone formed as a transient onphotolysis of tetramethyl-1,4-cyclobutanedione.

Next was Dave Eaton (DuPont iTechnologies) whowas George’s last Caltech Ph.D. as a full Caltech resident,before George moved to Santa Cruz. In his Ph.D. workhe had examined pyrazoline precursors to possiblediradical intermediates that could potentially be involvedin diene photorearrangements and photoisomerization,partly with Bob Bergman as a collaborator. After joiningDuPont, Dave was able to observe George in his role as aconsultant. George contributed intellectually as well asin his traditional role as cheerleader to the many technicaldevelopments involved in commercialization ofphotopolymer films for electronics and printingapplications and in the process has gained many friendsat DuPont. In fact, it was early collaborations among CarlWamser, George and two DuPonters (Cathy Chang andCharlie Baylor) that led to an understanding of theexciplex nature of the interactions betweenbenzophenone and Michler’s ketone and to thecommercial use of this “synergistic” photoinitiator. It wasDave’s pleasure to convey DuPont’s salute to George onhis 80th birthday!

In his talk, “Photochemical industry becomes complex,too” Dave elaborated on the historical aspects ofphotopolymer technology, from its invention at DuPontby Louis Plambeck in the 1950’s through its introductioninto commercial use in the 60’s and 70’s. During this timethe use of photopolymers revolutionized the ways thatthe printing process was accomplished and led, along withmany other innovations, to the microelectronicsrevolution we have experienced over the last 40 years.Photopolymer printing plates and photoresists for themanufacture of printed wiring boards are nowcommonplace. New commercial laser-based systems takeadvantage of the digital data streams that are thebackbone of our information exchange processes today.Dave concluded with predictions of uses of photopolymermaterials in future optical communication networkapplications, as waveguide materials and opticalcomponents. The message: though photopolymers arenow 50 years old, they continue to show promise forimportant new innovations for a long time to come. Inthis respect, they are just like George who continues toamaze us all after all these years.

Jim Yardley (Columbia Radiation Laboratory) spokeon “Laser photochemistry: 25 years toward a fulfilledpromise?” In 1977, the lure of laser chemistry promptedJim’s move from the University of Illinois to AlliedChemical. He was there in 1978 to witness George’s moveto AlliedSignal, Inc. and to experience the remarkableresearch reorganization under his leadership.



Jim pointed out that initial attempts to develop laseractivated “synthons”, starting for instance, with ironpentacarbonyl and seeking through photolysis atincreasing laser intensities to form tetra- and tricarbonylreactive intermediates, failed to yield the desiredselectivity. Such initial failures, coupled with the highcost of laser photochemistry, led the scientific world toturn to “high value chemistry”: isotopic separation,pharmaceuticals, and catalysis, but again commercialviability proved elusive. Early successes were realized inthe realm of semiconductor processing, including thedevelopment of new photoresist materials. Another areaof laser photochemistry in which George played a crucialrole at Allied concerned the development of guided waveoptical devices. Through photochemistry, it is possibleto define the spatial variation of refractive index withina polymeric medium and thus direct and control thepropagation of light within that medium. This requiredthe development of chromophore/polymer combinationsthat were not opaque in the UV. Photochemicaltransformations in the chromophore have yieldedenormous changes in refractive index. Looking into thefuture, laser photochemistry holds the key fordevelopment of the next several generations ofsemiconductor devices through short wavelength laserlithography. Fabrication of low cost optical devices fortelecommunications and for a host of data communicationapplications is also likely to depend on laserphotochemistry. Jim concluded that the future of laserphotochemistry is bright in ways not widely appreciated25 years ago.

Fittingly, George’s wife, Eve L. Menger (PortlandState University) gave the last scheduled talk of theSymposium. Eve’s talk “Leitmotif from the life of aphotochemist”, liberally sprinkled with quotations fromGeorge’s talks, was a retrospective of George’s career.George’s scientific and teaching genius and his philosophywere revealed to the audience in his own words. WhenGeorge left Caltech for UC, Santa Cruz in 1972, many ofhis friends thought he had taken leave of his senses.George had been drawn by the new challenges and thepredictions that Santa Cruz was destined soon to becomea UCLA or a Berkeley. As Vice Chancellor of all sciences,he had the opportunity and authority to implement hisnew ideas in the less rigid environment of a new placeand, thus to work against artificial divisions in scienceand to emphasize instead its unity. After an exciting first18 months in which several of George’s ideas were broughtto fruition (some, e.g., a technical writing program, haveblossomed and are still in existence), growth at SantaCruz, and the flexibility it allowed, came to an abrupthalt. His appointment as Foreign Secretary for theNational Academy of Sciences provided new

opportunities, which George whole-heartedly embracedwithout sacrificing his teaching commitments. Georgemanaged to keep everything going under circumstanceswhere the “urgent takes priority over the important”. Inhis classes at Santa Cruz, the students’ admiration of theway he “ordered molecules around” earned him thenickname General George. Unfortunately, among theconsequences of the mistaken demographic projectionswere the inability to continue hiring young faculty, and acontinuous struggle to get existing research laboratoriesproperly outfitted. On top of this, some colleagues wereopposed to the creation of a Photochemistry Center,viewing it as an unnecessary dilution of diminishedresources. When George left Santa Cruz for AlliedChemical in 1978, friends viewed the decision as beyondthe pale, but the years at Allied proved exciting andproductive.

George, the thinker/philosopher was revealed inexcerpts from a series of remarkable speeches on topicsranging from chemical education, to chemistry in general,and to research management. According to George, theway chemistry was generally taught left much to bedesired. Freshman chemistry delivered a hodgepodge oftopics and organic chemistry placed a premium on thememorization of a bunch of name reactions. He advocatedthe restructuring of chemistry along functional lines:structural chemistry, dynamics and chemical synthesiswith sensible examples of the contributions of chemistryto other sciences. This would involve the integration of,for instance, organic and inorganic chemistry and wouldavoid existing divisional lines with their terribly stylizedtraditional courses and their devastating effect on thelearning of chemistry. He called for careful scrutiny ofwhat was taught and described our current divisionalsystem as artificial, incoherent, redundant and harmfulto its most important element, the students. In a 1971speech to the American Institute of American Engineers,George criticized the notion that teachers shouldmotivate students. According to George, motivationcomes from within. He attacked still another artificialteaching boundary by stressing that chemical science andengineering form a continuum. He called for a moreinclusive, open style of teaching, while recognizinglimitations imposed on teachers by their own experiences:“My own experience of open style teaching is limited—Iam a product of my own experience”. In another talk hecautioned that the rapid growth of science is not reflectedin what is taught. He advised that the fact that a particulartopic had been included in a course for a long time wasnot necessarily an indication that it was basic!Furthermore, if a topic were included in a course becauseit was ’basic’, one should be prepared to say to what it isbasic.



The XIIth IAPS conference was held at the beautifulsetting of Ascochinga, Córdoba, Argentina between May20th and May 25th 2001. This was the second IAPSmeeting in South America. The co-chairs of the meeting(Pedro Armendia and Miguel Garcia-Garibay), as wellas the local organizers, did a superb job in putting togetheran excellent scientific program. On the entertainmentside we all enjoyed the social activities during the weekand the Argentinean hospitality.

The scientific program started on Monday morningwith a lecture by A. Moore (Arizona State University,Tempe, USA) where she described the strategies for thestructural design and photophysical characterization ofthe various components of mimetic antenna systems. Shealso described systems for proton transfer acrossmembranes, where the key feature is the organization ofthe reaction centers in liposomes. This proton transportwas then coupled to Ca2+ transport. The second talk ofthe morning was given by F.D. Saeva (Eastman KodakCompany, Rochester, USA) who presented the behaviorof electron acceptors with a σ* LUMO. Thesecompounds, which have a light absorbing chromophoreand sulfonium salt moieties, lead to efficientphotogeneration of protons. The session was followed byJ.C. Scaiano’s (University of Ottawa, Ottawa, Canada)lecture on a new fluorescent method to assess DNAdamage. Dyes where the fluorescence responds to mobilityrestrictions were employed because they are able todiscriminate between single- and double-stranded DNA.This discrimination is based on lifetime measurementsand the application of this method as an analytical toolwas described. The last lecture of the morning was givenby C.P. Kubiak (University of California San Diego, LaJolla, USA). He spoke about the use of conductancespectroscopy, where the STM tip is brought into closecontact with a monolayer of organic compounds on gold.The conductance was shown to depend on the electronicstructure and length of the molecules in the monolayer.This technique can be employed to determine the energyof the HOMO level of organic molecules with respect tothe Fermi level of gold.

Conference Report: XIIth Inter-AmericanPhotochemical Society Conference

Cornelia Bohne Lisa KellyDepartment of Chemistry Department of Chemistry and BiochemistryUniversity of Victoria University of Maryland, Baltimore CountyVictoria, BC Baltimore, MDCANADA USA

The Monday afternoon session started with thelecture by M. R. Wasielewski (Northwestern University,Evanston, USA) on processes involving electronmovements in organic nanostructures. He discussed hisresults on the modulation of the electronic properties ofbridge molecules used as photoswitches, followed by thepresentation of an assembled system, containing both anantenna and electron acceptor, where the direction ofcharge transport was photoswitched. L. A. Monteiro(Universidad de La Habana, La Habana, Cuba) presentedtheoretical studies on the photochemistry of glyoxal. Heshowed the various possible deactivation channels, anddiscussed in detail the decomposition into CO and H2.Mechanistic studies on the stereospecific ring opening ofcyclobutene were the subject of W.J. Leigh’s (McMasterUniversity, Hamilton, Canada) talk. The photochemicalring opening occurs adiabatically from the Rydberg statewith conrotatory stereochemistry. The reaction involvestwisting and rotation. When rotation is inhibited, a π,π*state is populated and disrotatory stereochemistry isobserved. The next lecture was given by T.D.Z. Atvars(Universidade Estadual de Campinas, Campinas, Brasil)on her studies using fluorescence spectroscopy andmicroscopy to characterize dye-polymer interactions andto study polymer properties. Protic sites in the polymerswere characterized and various relaxation processes wereidentified. Fluorescence microscopy was employed tostudy the miscibility and phase separation mechanismsof polymers. The last speaker of the afternoon’s sessionwas L.A. Bagatolli (Universidad Nacional de Córdoba,Córdoba, Argentina). He spoke about the use of two-photon excitation spectroscopy to investigate the gel-phase coexistence in membranes. The experiments wereperformed with single, giant unilamellar vesicles, onwhich images of the different microdomains wereobtained. A fluorescent probe was employed that issensitive to the state of the lipid phase. This techniquewas also employed to visualize protein-lipid interactions.The first poster session was held before dinner and gaveeveryone one more opportunity to socialize and discussscience.


The session on Tuesday morning started with F. M.Winnik’s (Université de Montréal, Montréal, Canada)lecture on her use of fluorescence to characterize polymer-liposome interactions. The polymers were tagged withfluorescent probes. The interaction of cationic polymerswith liposomes covered with anionic polymers showedthat the anionic polymers were not removed from thesurface of the liposomes when the anionic polymerscontained a hydrophobic anchor. In addition, shediscussed drug delivery systems that were prepared bycoating liposomes with pH sensitive polymers. The nexttalk, by M.V. Encinas (Universidad de Santiago de Chile,Santiago, Chile), covered the characterization of newphotoinitiator systems for free radical polymerization. Theflavine/amine photoinitiator system was investigated withthe objective of optimizing the efficiency of radicalformation. In methanol, a significant amount of radicalsis formed from the singlet excited state, but this channelis absent in water. S. E. Braslavsky (Max-Planck Institutfür Strahlenchemie, Mülheim an der Ruhr, Germany)presented work on the application of photoacousticspectroscopy to understand how the nature of the mediumaffects the volume changes in the ring opening/closingof spiropyrans in water and cycloalkanes. The volumechanges in water are mainly related to proton transfer,whereas electrostriction is the primary effect incycloalkanes. The final lecture of this session was givenby C. D. Borsarelli (Universidad Nacional de Santiagodel Estero, Santiago del Estero, Argentina). He presentedhow photoacoustic spectroscopy was employed to obtainthe partial volume changes of ionic species. The enthalpyand volume changes were obtained simultaneously for thequenching of 3[Ru(bpy)3

2+]* by Fe3+ in the presence ofdifferent counterions. An expansion or contraction wasobserved depending on the nature of the couterions, andthis effect was explained by the formation of a complexbetween Fe3+ and the couterions. In addition, he showedresults on the determination of the partial molar volumefor protons and for electrons in water.

The afternoon session started with the presentationof the Cilento award and the award lecture by E. Wolcan(Universidad Nacional de La Plata, La Plata, Argentina).He presented his work on the photochemistry andphotophysics of Rhenium dicarbonyl compounds asmonomers and when they are part of polymers. Thephotophysical behavior in different solvents and polymerswere discussed. The results were complemented with pulseradiolysis studies to confirm the identity of the transientsseen in the laser flash photolysis experiments. J. M.Riveros (Universidade de São Paulo, São Paulo, Brasil)spoke on the photodissociation of gas-phase ions. Severalexamples were presented where photodissociation wasstudied by multi-photon IR dissociation. With this

technique, the structure of isomeric ions can bedistinguished. Blackbody dissociation kineticsexperiments, applied to the photodissociation ofacetophenone, were also discussed. The next talk wasgiven by C.S. Foote (University of California, LosAngeles, Los Angeles, USA) on the photooxidation ofguanosine and some model compounds. Mechanisticstudies at low temperature were performed on modelcompounds in order to identify the primary products ofthe photooxidation reaction. Several products wereobserved, which were unstable. These products werecharacterized spectroscopically, and mechanisticpossibilities were proposed. The topic of P.F. Barbara’s(University of Texas, Austin, USA) lecture was the studyof conjugated polymers by single molecule spectroscopy.He showed that a detailed picture of the MEH-PPVpolymer structure can be obtained by studying thefluorescence behavior of a single molecule of the polymer.He proposed that MEH-PPV adopts a highly orderedcollapsed conformation. The last talk of the afternoonwas given by S.B. Yamaki (Universidade Estadual deCampinas, Campinas, Brasil). She described how EVAcopolymers are labeled with pyrene by thephotoirradiation of 1-pyrenyl-diazomethane. Bycomparing the photophysical properties of pyrene labeledPE and PVA, she concluded that, for EVA, the labelingoccurred mainly on the PE moieties. Finally, the secondposter session was held after the talks. After dinner,Michael Kasha (Florida State University, Tallahassee,USA) gave a talk entitled “Four Great Personalities ofScience: G.N. Lewis, J. Franck, R.S. Mulliken and A.Szent-Gyorgyi”. His recollection inspired everyone in theaudience.

The Wednesday morning session started with alecture by I.E. Kochevar (Havard Medical School, Boston,USA) on the use of photochemistry to understand hownormal oxidizing species react in biological systems.Singlet oxygen was generated close to the cell membraneby irradiating a sensitizer with an evanescent wave.Apoptosis was induced by singlet oxygen production inor near the plasma membrane, but lipid peroxidation isnot involved in this process. J.R. Scheffer (University ofBritish Columbia, Vancouver, Canada) followed with hislecture on photochemical processes in the solid state. Hecovered the strategies to achieve asymmetric inductionin crystals, followed by a description of several reactionsin the solid state that lead to unusual products. Examplesincluded the formation of oxetanes from the reaction ofcyclic ketones and 1,3 phenyl migration for acyclicketones. The last talk of the morning was given by B.B.Craig (Spectra-Physics, Mountain View, USA) onultrafast laser sources and their commercial applications.He described the latest laser technologies with regards to

Conference Report: XIIth Inter-American Photochemical Society Conference


ultrafast pulses. The afternoon was spent on an excursionthrough the scenic landscape of CÛrdoba, followed bytea. During the dinner party we were treated to a localbarbeque with dancing extending through the night.

The session on Thursday morning started with alecture by E.A. Jares-Erijman (Universidad de BuenosAires, Buenos Aires, Argentina) on how fluorescenceenergy transfer processes, studied using a microscope, canbe employed to evaluate molecular proximity in thenanometer range. The FRET modulation was achievedusing a photochromic compound with a good fatigueresistance. In addition, time- and spectrally-resolvedmicroscopy was performed using lanthanide chelates. M.S.Platz (Ohio State University, Columbus, USA) followedwith a lecture on the photochemistry of blood products.He described his studies on photosensitized methods toinactivate bacteria and viruses in blood. The targets forthe photosensitized reactions were nucleic acids, sinceblood products contain very little nucleic material.Riboflavin was employed for mechanistic studies usingtime-resolved infra-red spectroscopy and calculations.

The 2001 IAPS award was presented by Fred Lewis,the President of the Society, to M.A.J. Rodgers (BowlingGreen State University, Bowling Green, USA). MikeRodgers dedicated his award lecture to his graduatestudents, post docs and all young researchers whorepresent the future of science. He presented work onredox reactions in complexes of metalloporphyrins withnative proteins or synthetic peptides. Photoinducedelectron transfer was studied in complexes held togetherby electrostatic interactions. Several donor/acceptor pairswere used in order to change the free energy for thereactions. The results were explained by thereorganizational needs of the donor and acceptor forelectron transfer to occur. Molecular dynamics wereperformed to relate the calculated electron transfer rateconstants with the distance between acceptors and donorsin the complexes. A good correlation was obtained. Thelast lecture of the morning was given by H.E. Toma(Universidade de São Paulo, São Paulo, Brasil). He spokeon photophysical and photochemical studies tocharacterize tetraruthenated porphirins and porphyrazinesupramolecular systems. These systems were characterizedby Raman spectroscopy, luminescence spectra andelectrochemical studies. The compounds described wereused for several applications, such as photooxidation ofDNA and electrostatic assembly of bilayers. The lattersystem was used as a sulfite sensor in wine.

After lunch, a lively last poster session was held.Participants enjoyed the beautiful weather as theymingled and discussed photochemistry. The afternoonsession started with the presentation of the Closs awardto M. Khajehpour (University of Missouri-Columbia,

Columbia, USA). The award lecture dealt with thecontribution of the solvent quadrupole moment to thesolvent reorganization energy studied in an anthracene-dimetylamine derivative. The quenching reaction wasstudied in various solvents and was shown to be anactivated process. In dipolar and quadrupolar solvents,the rate constant is enhanced when compared to alkanes.This difference was explained to be due to differences inthe barrier crossing frequencies. G.L. Indig’s (Universityof Wisconsin, Madison, USA) lecture was on chemicalaspects of mitochondrial targeting in photochemoterapy.Instead of targeting the tumor vascular system, hisapproach targets tumor cells directly. The fact that themitochondria of the tumor cell have a membranepotential that is higher than for normal cells was exploredto selectively incorporate the photosensitizers in themalignant cells. The key feature is to use molecules(Crystal-Violet derivatives) that are hydrophilic enoughonly to partition into the tumor cells. The next lecturewas given by D. Whitten (QTL Biosystems, Santa Fe,USA). He described the superquenching of fluorescentpolyelectrolytes. Negatively charged fluorescent polymersare quenched much more efficiently by positively chargedquenchers due to the strong, but non-specific, associationof the quencher with the polymer. This type ofsuperquenching was seen for a variety of polymers.Applications of this phenomenon to biosensors werediscussed. T.J. Wallington (Ford Motor Company, USA)talked about the formation of organic aerosols during theatmospheric oxidation of toluene. These studies arerelated to the formation of smog in urban areas. Toluenewas used as a model compound, and the mechanisticstudies performed suggest that the oxidation of toluene isinvolved in a secondary process of smog formation. Thenext lecture was given by R.J. McMahon (University ofWisconsin, Madison, USA) on possible reactiveintermediates, in particular carbenes, that are relevantto the chemistry of interstellar space. Numerous organiccompounds have been detected in interstellar space bymicrowave spectroscopy. Matrix isolation experimentswere described where molecules found in space have beenspectrocopically detected and characterized. The last talkof the day was given by L. Otero (Universidad Nacionalde Rio Cuarto, Rio Cuarto, Argentina). He describedexperiments on the photoelectronic effects in thin SNO2

films generated in the photoinduced charge separationin a porphyrin-C60 dyad. This project focuses onimproving the efficiency of solar cells. The synthesis andspectroscopic characterization were described and theefficiency of the photoelectric effect was evaluated.

On Friday morning, L. Kelly (University of Maryland,Baltimore County, Baltimore, USA) described the utilityof dually luminescent polymers as temperature and



pressure sensors. The materials were prepared as randomcopolymers of aromatic hydrocarbons and dialkylaniline.The ratiometric changes in excimer to monomerluminescence as a function of temperature and appliedpressure were discussed, and their utility in mappingdynamic flow and temperature fluctuations on 2D surfacesdescribed. O. Martinez (Universidad de Buenos Aires,Buenos Aires, Argentina) presented a new form of high-resolution spectroscopy: field enhanced scanning opticalmicroscopy or FESOM. The field enhancement toscanning optical microscopy was provided by a modulatedlaser. Optical images with vertical resolution of 0.1 nmwere obtained, suggesting the technique may approachatomic resolution. In the next lecture, J. Toscano (JohnsHopkins University, Baltimore, USA) described howtime-resolved infrared spectroscopy is used to probeorganic reaction dynamics. The technique has been usedto probe the mechanism of NO release upon pulsedexcitation of diazeniumdiolates. Toscano showed that, bytuning the covalently attached substituents, the undesiredformation of nitrosamine was minimized. In the final talkof the conference, M. de Oliveira (Universidade Estadualde Campinas, Campinas, Brasil) continued the theme ofphotochemical NO release. The photolysis of sodiumnitroprusside or SNP produced both NO and cyanide.When the compound was irradiated in poly(ethyleneglycol) matrices, the photochemical production ofcyanide was inhibited and NO production was selectivelyfavored.



Charge transfer reactions involving DNA have receiveda considerable amount of attention in the literature. Anumber of published reports have discussed the factorsthat control the distance dependence of electrontransfer.1,2,3,4 I will not attempt to engage in a discussionlong-range electron transfer in DNA in this report.Instead, I wish to provide a perspective on the utility ofelectronically excited states as structural probes of DNAand proteins. Specifically: “What are the strategies andutilities of developing light-activated compounds tocleave DNA and proteins?” On more occasions than Iwould like to admit, my friends and colleagues have posedthe question: “Why does everyone want to cleave DNA?”While some members of the IAPS community are awareof the relevant strategies and issues, I wish to direct thisarticle to “non-experts” in the community. In thiscontribution, I will attempt to answer that question andprovide a chemical basis for how to carry the reactionout. Specific challenges that lie ahead of us will bediscussed. Readers are also referred to an excellent reviewof “photonucleases” that has recently appeared.5

Let’s start with the “why.” Knowledge of the structureof biological macromolecules is crucial to elucidating theirfunction and modifying their reactivity (e.g. for drugdesign). Aside from diffraction techniques, spectroscopy(nuclear magnetic resonance, fluorescence, UV/Viselectronic, and vibrational) has long been the techniqueof choice to evaluate static structure and understanddynamic processes. As structures become large,crystallization becomes difficult and resolving overlappingspectroscopic transitions is challenging. An alternativeapproach is used in molecular biology. Genomic mappingand sequencing have been made possible using naturalenzymatic agents to cleave nucleic acids and proteins.These reagents, when used as structural probes, willrecognize and cut the target at a specific restrictionfragment, leaving manageable fragments to be sequencedand reconstructed. The recent sequencing of the humangenome is an example of this familiar to all.6 Imagine asynthetic system that can mimic the action of nucleasesand proteases only after being “triggered” by theabsorption of a photon. When successfully developed,

Organic Photosensitizers to Probe MacromolecularStructure and Dynamics

Lisa A. KellyDepartment of Chemistry and Biochemistry

activation of the structural probe can be “timed” withrespect to a mixing or folding event. Suddenly, theprospect of studying dynamic processes of large,macromlecuar systems unfolds

Footprinting experiments are commonly used toelucidate the protein-binding site in nucleic acidpolymers. Typically, diffusible oxygen radicals that willcleave the nucleic acid at “exposed” sites are chemicallyproduced. Hydroxyl radical-like species are mostcommonly used and are produced from the Fentonreaction of iron (II) with hydrogen peroxide.7 While theterm is often used loosely, the footprinting “reagent”should initiate DNA strand cleavage non-specifically andspontaneously. In other words, all sites should be equallyviable targets, and breaking of the strand should notrequire the addition of post-footprinting reagents. To carryout the footprinting reaction in a time-resolved fashion,the production of the reactive species should be “turnedon” at controlled times. In this way, structural dynamicsinvolving the macromolecular complex may be obtained.In fact, it works! Such a strategy has been implementedusing pulsed X-ray irradiation synchronized to a stopped-flow mixing device.8 The method uses hydroxyl radicalsthat are produced from the radiolysis of water by pulsedX-rays from a synchrotron storage ring. Since the sourceis pulsed, hydroxyl radical production occurs at fixed timeswith respect to initiating the folding or mixing event.Although the work has shown great promise, the practicallimitations of accessing pulsed X-ray sources has limitedthe applicability in biophysical chemistry. This is wherewe come in! As photochemists, we can think aboutstrategies to design a molecule, that can be light-activatedby a benchtop laser, to generate reactive and diffusibleintermediates. Strategies for doing this and challengesthat lie ahead are discussed in this article.

Mechanisms of DNA Damage.The principle pathways of DNA photocleavage involvedirect interactions with the deoxyribose or base, indirectdamage following energy transfer to molecular oxygen,or photogeneration of a reactive oxygen species (e.g.hydroxyl radicals). Direct interactions of thephotosensitizer excited state (PS*) with DNA may lead


to damage following (i)hydrogen atom abstractionfrom deoxyribose or (ii)electron transfer from thenucleic acid base (redox-initiated damage). These areshown in Scheme 1. In thefirst case, spontaneous scission of the nucleic acid strandwill occur. Damage will be redox-initiated if the freeenergy is favorable:

∆G = -[(E1/2 (PS*/PS.-) - (E1/2 (B.+/B)]

While the individual base oxidation potentials areknown,9 they remain undetermined in DNA, wherestacking interactions and solvation will certainly play arole in modifying their values. It is, however, well-established that guanine is the most easily oxidized of allof the bases. Moreover, adjacent –GG- or –GGG- steps,are more easily oxidized, at the 5’-side, than isolatedguanines. As a consequence, oxidizing equivalents thatare placed on duplex DNA (e.g. by oxidizing any of thenucleobases) will migrate to a guanine trap site. Resultantstrand cleavage is not spontaneous, but is induced or“visualized” upon alkali (usually hot piperidine)treatment. In summary, the two mechanisms of damageare quite different and can have different utility asstructural probes. The thermal chemistry of the oxidativestrand scission of nucleic acids is discussed elsewhere.10,11

Atom abstraction reactions.Hydrogen atom abstraction is initiated by a variety ofreactive intermediates. It is useful to consider the bonddissociation energies shown in Table 1.12 Footprintingexperiments are generally carried out by initiatinghydrogen atom abstraction from deoxyribose. From Table1, it is apparent that the reaction:

OH. + RH → H2O + R.

is driven by an exothermicity of ca.64 kJ/mole. To time-resolve thefootprinting reactions, thephotochemically produced speciesshould: (1) be produced rapidlyfollowing pulsed excitation and (ii)possess sufficient reactivity to initiatethe atom abstraction event. Reportsof the photoinitiated hydroxyl radicalproduction via homolytic bondcleavage of aromatic hydroperoxides have appeared.Specifically, the utility of the hydroperoxide derivativeof 1,8-naphthalimide (Shown in Figure 1) as a

“photofootprinting” reagent hasbeen described.13 Upon UVirradiation, hydroxyl radicals wereformed. While hydroxyl radicalswere implicated in the DNAdamage, the photoinitiateddamage did not target thenucleotides in a sequence-neutralfashion, as expected for hydroxylradical damage.

Aside from hydroxyl radicals,chlorine atoms are viable reactiveintermediates for initiatinghydrogen atom abstraction from aH-C bond. From Table 1, it isapparent that the energetics for this process are modestlyfavorable. The analogous reaction with bromine or iodineatoms is energetically uphill. Armitage and Schuster haveshown that UV irradiation of anthraquinone in anaqueous solution of sodium chloride induces non-selective, spontaneous cleavage of DNA.14 A mechanisminvolving chloride oxidation by the anthraquinone tripletstate, followed by hydrogen atom abstraction by freechlorine atoms, was provided. In other work,photoactivated chlorobithiozoles have been shown toeffectively initiate DNA strand cleavage following C-Clbond homolysis.15

Finally, n-π* excited states are well-known toundergo hydrogen atom abstraction processes.16 Thesimilarity to alkoxy radicals is often used to explain thereactivity observed by n-π* excited states.

Excited states of uranyl (UO22+) ion,17 rhodium

chelates,18 cobalt(III) bleomycin,19 anthraquinonederivatives,20 nitro-substituted imides,21 andphotosensitizer-linked nitrobenzamides.22,23,24 have shownto be effective at initiating hydrogen atom abstracting.

Nucleobase Oxidation.As shown in Scheme 1, the direct interaction of anelectronically excited state with DNA can initiate singleelectron transfer from a DNA nucleobase. Among theclasses of molecules that have been shown to initiateDNA photooxidation are metallointercalators,25

riboflavin,26 imide,21,27 and anthraquinone derivatives.28

To date, redox-initiated cleavage has been shown to occuronly at guanine-rich sites. Results from Barton’slaboratory, using metallointercalators, have indicated thatthe final site of damage is generally at the 5’-side of –GG- steps.25,29 Computational studies have supported thehypothesis that these sites are the most readily oxidized.30

Singlet excited states of certain planar aromaticsystems have been used to carry out nucleotideoxidation.31,32 Since the excitation energy of singlet states

Organic Photosensitizers to Probe Macromolecular Structure and Dynamics

Bond DissociationEnthalpy(kJ/mole)

H-OH 498H-CH3 434H-Cl 432H-Br 366H-I 298

Table 1.

Scheme 1.

Figure 1.


is inherently higher than that of triplet states, singletstates are better electron acceptors. However, a majorchallenge in using singlet excited states is the rapidcharge-recombination that “short-circuits” the redoxreaction. If the lifetime of the charge-separated state isnot sufficiently long to allow for thermal strand cleavage,the activity of the structural probe is substantiallydiminished.

In summary, the utility of chromophores that reactwith DNA via electron transfer is limited: (a) Thestructural probe is limited to targeting guanine-rich sites;(b) the strand cleavage will not occur spontaneously; and(c) the quantum yield of the process is diminished bycharge recombination.

Naphthalimide-Derived Photosensitizers for Specificand Non-Specific Damage.Having provided an overview of the “why” and “how,” Iwill indulge myself by discussing the photochemistry ofnaphthalene derived imides and their potential utility asdiverse structural probes. The naphthalene-derived imideand diimide compounds are shown in Figure 2. Thesecompounds possess a number of desirable properties: (i)they can be readily synthesized from commerciallyavailable aromatic anhydrides; (ii) a variety of functionalgroups can be appended to the imide nitrogen to providefor molecular recognition; and (iii) they possess desirableand tunable redox properties that make them viable forinitiating oxidativedamage to DNA. It hasbeen shown that L-lysinesubstituted naphthaleneimides, when photolyzedin the presence of DNA,initiate oxidative damagepreferentially at the 5’-sideof GG steps in duplexDNA.27 Saito et al. showed that thymine-selectivecleavage is initiated by a nitro-substituted 1,8-naphthalimide chromophores.21 Site-specific cleavage wasattributed to hydrogen atom abstraction from the thyminemethyl group, not to abstraction from the DNA sugarbackbone or electron transfer. In other work, laser flashphotolysis of a solution of the naphthalimide derivativeand a duplex hexamer revealed production of the imideradical anion concomitant with the decay of the imidetriplet.27 The production of the radical anion wasattributed to simple electron transfer to the electronicallyexcited triplet state from a DNA nucleotide (eq 1).

3 .NI* + DNA → NI - . + DNA + (eq 1)

The quantum yield of damage, initiated by thisreaction, was small (< 10-3) . Subsequent to the reportby Matsugo et al., a detailed mechanistic study describingthe photochemical deactivation pathways of thehydroperox-substituted naphthalene imides waspublished.33 Both reports provided strong evidence for theproduction of HO. Following γ-hydrogen abstraction and–O-OH homolytic bond cleavage. Significantly, this latterreport described a competitive and efficient triplet-statedeactivation pathway (eq 2).

3 .Imide* + Imide → Imide - . + Imide + (eq 2)

Wishing to take advantage of the redox tunability ofthe aromatic imides, we embarked on a detailed study ofthe photoinitiated redox reactions of these compounds.After characterizing the photoredox kinetics for thereactions of triplet state of these compounds with theindividual nucleotides, we modified the structures to bewater soluble and positively charged. The compoundsshown in Figure 2 with cationic substituents R (shownbelow) were prepared.

The compounds bind very strongly to the anionicbackbone of DNA (Kb = 2.5 x 104 M-1 and 7.8 x 105 M-1

for NI and NDI, respectively). When bound, theintersystem crossing yield is significantly diminishedrelative to free solution ( '

ISCö 4

= 0.08 and 0.004 for NIand NDI, respectively).34 No long-lived redox productswere observed on time scales longer than 30 ps. Weattribute the negligible triplet-state yield and lack of redoxproducts to the rapid “static” quenching of the singletexcited state by the nearby nucleotide bases. Since thecharge recombination is rapid, no “usable” redoxequivalents are produced from DNA-boundnaphthalimide or naphthaldiimide. A survey of publishedreports reveals that, in general, the quantum yield ofredox-initiated damage by cationic DNA-boundchromophores is quite low.26,32

Consistent with the report by Matsugo et al., we alsoobserved a diffusional process that resulted in theproduction of the naphthalimide radical anion. Weinitially attributed this species to the diffusional reactionof imide triplet state with DNA (process (i) in Scheme2). Upon closer inspection and a detailed kinetic study,we found that the primary source of imide radical anionswas from the bimolecular self-quenching reaction in bulkaqueous solution (process (ii) in Scheme 2 and eq 2).With the measured bimolecular rate constants forprocesses (i) and (ii) differing by nearly 2 orders ofmagnitude, the reaction of the NI triplet state with DNA


Figure 2.


is not a viable damage pathway. After an initial reactionof despondence and talk of abandoning naphthalimidephotochemistry, we suddenly realized that all is not lost.We have produced, with high quantum efficiency, anoxidizing equivalent … NI.+. The quest for this speciesbegan.

The radical cation of 1,8-naphthalimide is spectrallyinvisible in the UV and visible region and could not bedirectly observed. However, we have verified it’sproduction using tetramethyl-1,4-phenylenediamine(TMPD) as a radical trap:

NI.+ + TMPD ' NI + TMPD.+ (eq 3)

The spectrum of TMPD.+ is characterized by spectralfeatures at565 and 610nm.35 Asshown inFigure 3, theoxidized trapis observed inthe transientspectrum ofs p e c i e sp r o d u c e dunder “self-quenching” conditions.36

The kinetics of DNA damage were investigated underconditions where a variety of reactive intermediates wereproduced.36 The observed rate of DNA damage was fastestwhen production of the radical cation was favored. Inaddition, preliminary data show that the damage inducedby this species is not guanine-specific and isspontaneous.In summary, the self-quenching reaction that is usuallydeemed to be an annoyance to photochemists appears tobe a viable route to the efficient production ofphotofootprinting reagents!

Promising Pathways to Increasing Long-LivedRadical Yield from Singlet-State Quenching.As discussed above, the rapid static quenching of singletstates by nearby nucleotides in DNA-bound systems oftenshort-circuits the reaction. As a promising solution to

this problem, the addition of a secondary electronacceptor may increase charge separation efficiency byspatially separating the electron and hole. This“cosensitization” approach has proven effective.29,32 Thepresence of a “secondary” electron acceptor (usuallymethyl viologen) has been shown to increase the yieldphotoredox products by a factor of 10,000.29 The effect isattributed to the spatial separation of the electron andhole that slows the charge recombination. However, theenhancement generally requires large concentrations ofcosensitizer to be present. In the case of our cationicnaphthalimide compounds, the chromophores dissociatedfrom DNA upon addition of the cosensitizer. Taking alesson from photosynthetic reaction centers and artificialp h o t o s y n t h e t i csystems,37 we haveused a two-component donor-acceptor system toincrease the yield oflong-lived chargeseparated states,while keeping then o n - c o v a l e n tg r o u n d - s t a t ecomplex intact.38

The compounds areshown in Figure 4 (x = 2 – 6).

In aqueous solution, the singlet excited state of the1,8-naphthalimide is rapidly quenched by electrontransfer to the covalently attached viologen (k2 = 1.5 x1010 s-1 (x = 2) – 8.3 x 107 s-1 (x = 6)).39 Chargerecombination is rapid, and no redox products areobserved by nanosecond laser flash. As DNA is added tothe solution, viologen radical is observed in the spectrum(Figure 5), suggesting that nucleobase oxidation by thenaphthalimideradical cationis competitivewith chargerecombination.

The yieldof viologenr a d i c a lincreases asthe additionof DNAf a v o r sformation ofthe associatedcomplex. Insummary, theuse of


Scheme 2. Deactivation processes of “free” and DNA-bound naphthalimide(rate constants shown are those measured for N-(ethylpyridinium)-1,8-naphthalimide).

Figure 3. Transient absorption spectra observed 50ms after 355 nm excitation of argon-saturatedsolutions of 100 mM NI (left) and 100 mM NI with 10mM TMPD (right).

Figure 4. Schematic of NI-vio dyads toincrease charge-separation yield of DNA-boundchromophores.

Figure 5. Production of bipyridinium radical cationupon 355-nm excitation of Ni-vio (x = 4) in thepresence of 370 µM calf-thymus DNA (0, 0.6, 2, and10 µs (decreasing ∆A) after the laser pulse). Insetshows the increase in the radical yield with theaddition of DNA. Solutions are argon-saturated andcontain 10 mM pH 7.0 phosphate buffer.


covalently attached chromophore-cosensitizer dyadsystems provides a strategy for increasing the charge-separation yield as the chromophore/DNA ground-statecomplex is formed.

To conclude, I hope that I have provided aperspective of the biophysical applications and strategiesof photoinitiating macromolecular damage. Thedevelopment of a photofootprinting assay that can betime-resolved to probe dynamic processes should focuson the rapid and efficient generation of reactiveintermediates. The reactive species should possesssufficient reactivity to damage all sites equivalently andspontaneously. In contrast, the one-electron oxidationof nucleotide bases will favor guanine-rich sites. Strategiesfor overcoming efficient charge recombination should bedeveloped to increase the quantum efficiency of region-specific damage.

Acknowledgements.We would like to thank the American Cancer Society,Maryland Division, and the National Science Foundationfor support of this work.

References.(1) Schuster, G. B. Acc. Chem. Res. 2000, 33, 253-260.

Kan, Y. and Schuster, G. B. J. Am. Chem. Soc. 1999,121, 11607–11614; Henderson, P. T.; Jones, D.;Hampikian, Y. K.; Schuster, G. B. Proc. Natl. Acad. Sci.1999, 96, 8353–8358.

(2) Hall, D. B.; Holmlin, R. E.; Barton, J. K. Nature 1996,382, 731–735; Núnez, M. E.; Hall, D. B.; Barton, J. K.Chem. Biol. 1999, 6, 85–97.

(3) R. D.; Wu, T.; Liu, X.; Letsinger, R. L.; Greenfield, S. R.;Miller, S. E.; Wasielewski, M. R. J. Am. Chem. Soc.2000, 122, 2889–2902.

(4) Giese, B.; Wessley, S.; Spormann, M.; Lindemann, U.;Meggers, E.; Michel-Beyerle, M. E. Angew. Chem. Int.Ed. 1999, 38, 996–999.

(5) Armitage, B. Chem. Rev. 1998, 98, 1171–1200.

(6) Venter, et al. Science 2001, 1304–1351; Nature 2001,409, 860–921.

(7) Tullius, T. D.; Dombroski, B. A.; Churchill, M. E.; Kam,L. Methods Enzymol. 1987, 155, 537; Tulius, T. D.;Dombraski, B. A. Proc. Natl. Acad. Sci. USA 1986, 83,5469; Dixon, W. J.; Hayes, J. J.; Levin, J. R.; Weidner,M. F.; Dombroski, B. A.; Tullius, T. D. Methods Enzymol.1991, 208, 380.

(8) Ralston, C. Y.; Sclavi, B.; Sullivan, M.; Deras, M. L.;Woodson, S. A.; Chance, M. R.; Brenowitz, M. MethodsEnzymol. 2000, 317, 353–368.

(9) Steenken, S. and Jovanovich, S. V. J. Am. Chem. Soc.1997, 119, 617– 618.

(10) Pogozelski, W. K.; Tullius, T. D. Chem. Rev. 1998, 98,1089–1107.

(11) Burrows, C.; Muller, J. G. Chem. Rev. 1998, 98, 1109–1152.

(12) Lide, David R., Ed. (1998) CRC Handbook ofChemistry and Physics 79th Edition, pp. 9–51 CRCPress, Boca Raton, Fl.

(13) Matsugo, S.; Kawanishi, S.; Yamamoto, K.; Sugiyama,H.; Matsuura, T.; Saito, I. Angew. Chem., Int. Ed. Engl.1991, 30, 1351–1352.

(14) Armitage, B. and Schuster, G. B. Photochem. Photobiol.1997, 66, 164–170.

(15) Quada, J. C., Levy, M. J and Hecht, S. M. J. Am. Chem.Soc. 1993, 115, 12171–12172.

(16) Turro, N. J. Modern Molecular Photochemistry; Benjamin/Cummings: Menlo Park, California, 1978, Chp. 10.

(17) Nielsen, P. E.; Hiort, C.; Sönnichsen, S. H.; Buchardt,O.; Dahl, O.; Nordèn, B. J. Am. Chem. Soc., 1992, 114,4967– 4975.

(18) Sitlani, A.; Long, E. C.; Pyle, A. M.; Barton, J., K. J.Am. Chem. Soc. 1992, 114, 2303–2312;

(19) Chang, C. –H. Meares, C. F. Biochemistry 1982, 21,6332– 6334; Saito, I.; Morii, T.; Sugiyama, H.; Matsuura,T.; Meares, C. F.; Hecht, S. M. J. Am. Chem. Soc. 1989,111, 2307–2308.

(20) Breslin, D. T.; Coury, J. E.; Anderson, J. R.; McFail-Isom, L; Kan, Y.; Williams, L. D.; Bottomley, L. A.;Schuster, G. B. J. Am. Chem. Soc. 1997, 119,5043–5044.

(21) Saito, I.; Takayama, M.; Kawanishi, S. J. Am. Chem.Soc. 1995, 117, 5590–5591.

(22) Nielsen, P. E.; Jeppesen, C.; Egholm, M.; Buchardt, O.Biochemistry 1988, 27, 6338–6343; Buchardt, O.;Egholm, M.; Karup, G.; Nielsen, P. E. J. Chem. Soc.,Chem. Commun. 1987, 1696–1697.

(23) Kuroda, R.; Shinomiya, M. Biochem. Biophys. Res.Commun. 1991, 181, 1266–1272.

(24) Karup, G.; Meldal, M.; Nielsen, P. E.; Buchardt, O. Int.J. Pept Protein Res. 1988, 32, 331.

(25) Hall, D. B.; Holmlin, R. E.; Barton, J. K. Nature 1996,382, 731–735; Hall, D. B.; Barton, J. K. J. Am. Chem.Soc. 1997, 119, 5045–5046; Stemp, E. D. A.; Arkin, M.A.; Barton, J. K. J. Am. Chem. Soc. 1997, 119,2921 – 2925.

(26) Ito, K.; Inoue, S.; Yamamoto, K.; Kawanishi, S. J. Biol.Chem. 1993, 268, 13221–13227.



(27) Saito, I.; Takayama, M.; Sugiyama, H.; Nakatani, K.;Tsuchida, A.; Yamamoto, M. J. Am. Chem. Soc., 1995,117, 6406–6407.

(28) Armitage, B. Yu, C.; Devadoss, C.; Schuster, G. B. J.Am. Chem. Soc, 1994, 116, 9847– 9859; Breslin, D. T.;Schuster, G. B. J. Am. Chem. Soc. 1996, 118,2311–2319.

(29) Barton, J. K. Pure and Appl. Chem. 1998, 70, 873–879.

(30) Sugiyama, H. and Saito, I. J. Am. Chem. Soc., 1996,118, 7063–7068.

(31) Brun, A. M.; Harriman, A. J. Am. Chem. Soc. 1991,113, 8153–8159.

(32) Dunn, D. A.; Lin, V. H.; Kochevar, I. E. Biochemistry,1992, 31, 11620–11625.

(33) Aveline, B. M.; Matsugo, S.; Redmond, R. W. J. Am.Chem. Soc. 1997, 119, 11785–11795.

(34) Rogers, J. E.; Weiss, S. J.; Kelly, L. A. J. Am. Chem. Soc.2000, 122, 427– 436.

(35) Worrall, D. R.; Williams, S. L.; Wilkinson, F. J. Phys.Chem. B 1997, 101, 4709– 4716; Wimalasena, K.;Wimalasena, D. S. Biochem. Biophys. Res. Comm. 1991,175, 920–927.

(36) Rogers, J. E.; Abraham, B.; Rostkowski, A.; Kelly, L. A.Photochem. Photobiol. In Press.

(37) Gust, D.; Moore, T. A.; Moore, A. L. Acc. Chem. Res.2001, 34, 40– 48.

(38) Rogers, J. E.; Le, T. P.; Kelly, L. A. Photochem. Photobiol.2001, 73, 223–229.

(39) Le, T. P.; Rogers, J. E.; Kelly, L. A. J. Phys. Chem. A2000, 104, 6778–6785.



April 14, 2001 was an overcast butwarm spring day in Tallahassee,Florida. Those gathered for thecelebration of the 80th birthday ofMichael Kasha were, however,engulfed in the bright intellectual andcultural glow generated by the eventshonoring Michael who was born onDecember 6, 1920. This celebrationtook the form of a rich, scientificsymposium in the morning andafternoon followed by a wonderfulbanquet in the evening.

The 2001 Kasha AwardSymposium and Ceremony began at 8:00 a.m. in theTurnbull Conference Center on the campus of FloridaState University (FSU). The Kasha Award, whichrecognizes and stimulates research and promotes qualityscientific writing, has been given annually since 1995 toan FSU graduate student in the Molecular Biophysics(MOB) Graduate Program. Students, who are primaryauthors of papers published in the past two years, areconsidered for the award after nomination by their majorprofessors. This year a special award symposium wasorganized by the MOB graduate students and sponsoredby the MOB Graduate Program, the Institute of MolecularBiophysics, and the Department of Chemistry. Over 80scientists were present to hear the fine slate of speakersinvited by the students.

After a half-hour of mixing during an energizingcontinental breakfast, the participants heard welcomingremarks from W. Ross Ellington, Professor and Directorof the Institute of Molecular Biophysics, from NareshDalal, Professor and Chair of the Department ofChemistry, and from Mohammad Yousef, MOB studentand Vice President of Students for the EffectiveCommunication of Science.

The lead-off speaker was none other than the day’shonored person Michael Kasha who spoke about “Aurorasand Solar Protons.” This topic contained once of the fociof Michael’s researches, namely proton transfer. However,instead of its usual intramolecular context for Michael,

Celebration of Michael Kasha’s 80th Birthday

Edwin F. HilinskiDepartment of Chemistry,Florida State University,Tallahassee, Florida 32306-4390

this lecture involved effects of proton transfer from thesun to the earth.

Each of the remaining guest lecturers were introducedby the MOB student who invited the speaker. PromodMehndiratta introduced Robin M. Hochstrasser of theUniversity of Pennsylvania. Robin, who in the pastworked with Michael Kasha as a postdoctoral researcher,talked about “Infrared Analogues of NMR” andapplications of this spectroscopic approach to biologicalprocesses.

A change in the original order of the programoccurred when Joseph R. Lakowicz of the University ofMaryland at Baltimore, who was not feeling very well,needed to present his lecture before he was forced to returnto his hotel room. Debbie Kelly introduced Joseph whosetalk was entitled “Radiative Decay Engineering.” Hepresented work about the effects metal surfaces onfluorescence and described some biomedical applicationsof systems involving silver islands.

Elena Falvovskaia, who at the time of this symposiumwas a graduate student working with Michael, introducedthe last speaker before lunch. Alexander P. Demchenkoof the A.V. Palladin Institute of Biochemistry, Kiev,Ukraine and of the Tübitak Marmara Research Center,Turkey had been a visiting professor in Michael’slaboratory. Alexander gave his lecture on a “NewGeneration of Fluorescence Probes for Molecular and

Photo by Jim Gattis, Florida State University


Cellular Research.” Afterward the participants adjournedfor the taking of the group photograph and for lunch.

The afternoon session convened at 1:10 p.m. whenGlenn A. Crosby of Washington State University, also apast postdoctoral associate with Michael, was introducedby Cheri Hampton. “Bridging Spectroscopy andChemistry with nd6 Metal Complexes” was the title ofGlenn’s talk about rhenium, rhodium, and rutheniumcomplexes.

Klaus Schulten of the University of Illinois atUrbana-Champaign talked about “How Nature HarvestsSunlight” after being introduced by Sanguk Kim. Hedescribed computational studies on structure anddynamics in photosynthetic systems.

The last guest speaker was Mostafa A. El-Sayed ofthe Georgia Institute of Technology. Mostafa was one ofMichael’s Ph.D. students. Mohammad Yousef introducedMostafa whose topic was “Small is Different: SomeProperties of Material Confined to Nanometer Length.”He discussed the synthesis, characterization, andspectroscopic properties of gold and platinumnanoparticles.

The final event of this daylong symposium waspresentation of the 2001 Kasha Award by Laura Keller,the Director of the MOB Graduate Program, to JunfengWang who is an MOB student working with TimothyCross.

Throughout the day there were lively discussions ofthe research that was presented and fond reminiscencesof time spent in Michael’s laboratory and of associationswith him made across Michael’s broad range of interests.

The festivities associated with the evening banquetcommenced with cocktails at 6:30 p.m. in the third floordining room of the University Center Club on the campusof Florida State University. The program announced thatthis banquet is in celebration of the 40th anniverary ofthe Institute of Molecular Biophysics, the 80th birthdayof Michael Kasha — its founder, and the 50th year ofMichael Kasha’s faculty service. It was sponsored by theInstitute of Molecular Biophysics and the Department ofChemistry.

As he did for the symposium, Ross Ellington, Directorof the Institute of Molecular Biophysics, provided openingremarks to the 235 people gathered from near and far forthe banquet and introduced special guests.

After a very enjoyable hour and a half of dining, wewere treated to a delightful 45-minute concert by Brazilianmaster guitarist Antonio Carlos Barbosa-Lima who playeda Kasha classic guitar to perform twelve works by Villa-Lobos, Bonfá, Lecuona, Madriguera, Yasui, Gershwin,Cordero, Barrios, and Barroso.

Next, Naresh Dalal,Chair of the Departmentof Chemistry, gave a briefintroduction of thehonoree. Michael Kashathen took the stage to endthe day in the manner thathe began it — to give apresentation. This lecturewas much less technicalthan the one given in themorning. It was wellreceived by the diversity offriends, colleagues, andfamily who were present.With that twinkle in his eyes and engaging smile on hisface, Michael treated his audience to thirty minutes ofreminiscences of personal, scientific, and artistic aspectsof his life. We enjoyed it very much. Ross Ellington sentus on our ways with a few closing remarks.

The variety of interests of the speakers andparticipants in the symposium and of the guests at thebanquet along with the range of scientific topics andartistic offerings of this celebration day reflected wellMichaels Kasha’s impact and the appreciation of him byhis friends and associates.

Celebration of Michael Kasha’s 80th Birthday

Photos by Stephen Leukanech, Florida State University


Glossary of Terms in Photocatalysisand RadiocatalysisSynopsis: This document has two principal goals. First,it summarizes some of the issues that pertain to thecomplexities encountered in photocatalysis. Secondly, itpresents a glossary of terms proposed to describe thosephenomena, which fall under the umbrella of“photocatalysis” and “radiocatalysis”. A distinction ismade between the different phenomena that are relatedto either or both photochemistry and photocatalysis, andto radiation chemistry and radiocatalysis. Consistentdefinitions of terms in these areas are given. Definitionsof important parameters that describe photocatalytic andradiocatalytic phenomena quantitatively are alsoproposed. As with the related Glossary of Terms inPhotochemistry, this document is a dynamic workingdocument, which will need to be revisited from time totime as the field progresses and new discoveries reported.Some of the terms used in photochemistry are also givenhere for completion, either verbatim or modified toaddress the issues of photocatalysis.

Glossary of Terms in Photocatalysis and Radiocatalysis1

{A Preliminary Version of IUPAC’s Project # 2001-036-1}

November 21, 2001V. Parmon*, A.V. Emeline†, and N. Serpone†

* Boreskov Institute of Catalysis, Siberian Branch of the Russian Academy of Sciences, Prospekt Akademika Lavrentieva, 5,Novosibirsk 630090, Russia. Email: [email protected]

† Department of Chemistry and Biochemistry, Concordia University, 1455 deMaisonneuve Blvd. West, Montreal (Quebec), CanadaH3G 1M8. Email: [email protected]

Note To The Reader:This preliminary version of the Glossary of Terms inPhotocatalysis and Radiocatalysis is IUPAC’s Project No.2001-036-1. It is being made available to a worldwidereadership through several Journals and Newsletters ofphotochemistry and catalysis. It is also posted on theI-APS web site. The intent of the authors is to seek thecommunity’s (at large) views, comments, and suggestionsthat will improve this document for ultimate submission,acceptance and publication of the final version to theappropriate Division(s) of IUPAC. The authors wouldsincerely appreciate it if the views, comments andsuggestions would be forwarded to both senior authors atthe email addresses indicated no later than June 30, 2002.

(1) People consulted during the preparation of the earlier versions of this document: Yu. Aristov (Russia), D. Bahnemann(Germany), J. Bolton (Canada), A. Cassano (Argentina), L. Koopal (The Netherlands), L. Palmisano (Italy), V.K.Ryabchuk (Russia), E. Savinov (Russia).


Positions AvailableAnyone wishing to post an ad of this type is welcome toemail the editor with the ad information.

Post-doctoral position at Max-Planck-Institutfür StrahlenchemieA post-doctoral position is immediately available for aproject financed by the Volkswagen Foundation onphotoinduced enthalpy and structural changes duringphotoinduced electron transfer reactions in aqueousmedia between redox centers of flavodoxin and azurinmutants bridged by flavin derivatives of various lengthsacting as spacer as well as of xanthene dyes triplets andmetal cyanides, as model reactions. The techniques to beapplied are laser-induced optoacoustic spectroscopy andnanosecond flash photolysis. Complementary techniquessuch as steady-state and time-resolved fluorescencespectroscopy are available in the Institute. Acquaintancewith photochemical techniques and/or with biophysicalmethods applied to protein studies is desirable. Please sendthe curriculum vitae and two reference letters to

Silvia E. BraslavskyMax-Planck-Institut für StrahlenchemiePostfach 10 13 65D 45413 Mülheim an der RuhrGermany

Tel: *49 (208) 306-3681 direct; -0 (switchboard)Fax: *49 (208) 306-3951Email: [email protected]

Information on the past and current work in thelaboratory may be found in

http://www.mpi-muelheim.mpg.de/mpistr_braslavsky.html

Conferences and SymposiaWe would appreciate your help in keeping this serviceup-to-date. If you know of an upcoming meeting whichis of potential interest to photochemists, please send therelevant information (following the format below) toThe I-APS Webmaster ([email protected]).

2002January 2–5XIIIth Inter-American PhotochemicalSociety ConferenceTempe, Arizona

Contact:Ian R. GouldDepartment of Chemistry and BiochemistryArizona State UniversityTempe, AZ 85287-1604Phone: (480) 965-7278Email: [email protected]

Peter C. FordDepartment of ChemistryUniversity of California, Santa BarbaraSanta Barbara, CA 93106Phone: (805) 893-2443Email: [email protected]

January 28 – February 2Photosciencias 2002Havana, Cuba

Contact:Prof. Elena Vigil SantosFacultad de QuimicaUniversidad de La HavanaLa Habana 10400, CubaEmail: [email protected]

July 14–19XIXth IUPAC Conference onPhotochemistryBudapest, Hungary

Contact:Hungarian Chemical Society(MKE) H-1027 Budapest, Fo u. 68. HungaryPhone: 36-1-201-6886; Fax: 36-1-201-8056Email: [email protected]

Documents

Inter-American Photochemical Society Newsletter · This newsletter is available in PDF format from the website. I-APS Newsletter Volume 24 Number 2, Fall 2001 1 I-APS Officers (2000–2002)