MOLECULAR ELECTRONICS—

SCIENCE AND TECHNOLOGY

AIP CONFERENCE PROCEEDINGS 262

MOLECULAR ELECTRONICS—

SCIENCE AND TECHNOLOGY

ST. THOMAS, VIRGIN ISLANDS 1991

EDITOR:

AM AVI RAM IDM/WATSON RESEARCH CENTER

AIP American Institute of Physics New York

CONTENTS

Preface ix Acknowledgments xi

A. Aviram I. T H E O R E T I C A L S T U D I E S O F S W I T C H E S A N D C O N D U C T I V I T Y

I N M O L E C U L A R D E V I C E S Molecular Orbital Studies of Electric Field-Controlled Electron Transfer 3

M. Dupuis and A. Marquez Soliton, Charge-Density Wave Structure and Band Gaps in Odd Polyene and Symmetrical Polymethinecyanine (Brooker) Ions and in f-Polyacetylene: Implications for Molecular Electronics 11

J. R. Reimers, J. S. Craw, and N. S. Hush Formation and Stabilization of Organic Charge States in Conjugated Systems: Are There Limits to the Synthesis of Conducting Molecular Wires of Known Delocalization Length? 28

C. W. Spangler, P.-K. Liu, and E. G. Nickel

IL MOLECULAR DEVICES Rectification of Scanning Tunneling Microscope Current Due to CU Phthalocyanine on Graphite 39

M. Pomerantz, A. Aviram, R. A. McCorkle, P. A. Roland, and A. G. Schrott Caroviologens: Towards Molecular Wires 48

M. Blanchard-Desce, T. S. Arrhenius, M. DvolaTtzky, S.-I. Kugimiya, T. Lazrak, and J.-M. Lehn

Characterization of a Cellular Array of Dipoles for Molecular Information Processing 58

S. Cincotti, M. Parodi, A. Chiabrera, A. Delfino, E. DiZitti, and S. Ridella Tailoring Organic Molecules for Electron Transfer 68

M. Baumgarten, U. Müller, and K. Müllen Orthogonally Fused Conducting Oligomers for Molecular Electronic Devices 77

J. M. Tour, R. Wu, and J. S. Schümm The Search for Organic Unimolecular Rectifiers 85

R. M. Metzger Poly(2-Ethylaniline) in Zeolite Hosts: Conjugated Nanometer Size Filaments 93

P. Enzel and T. Bein III . C O N T R O L O F I N T R A M O L E C U L A R E L E C T R O N T R A N S F E R

A Model Conformational Flip-Flop Molecular Switch 107 C. Joachim, G. Treboux, and H. Tang v

vi

Control of Intramolecular Electron Transfer by Protonation: Dimers and Polymers Containing Ruthenium II/III and 44' Azopyridine 118

J.-P. Launay and V. Marvaud Functionalizations of Conducting Polymers Towards Organic Superlattice and Molecular Device 129

T. Shimidzu Molecular Wire and Interface for Bioelectronic Molecular Devices 139

M. Aizawa, G. F. Khan, H. Shinohara, and Y. Ikariyama IV. N A N O L I T H O G R A P H Y A N D N A N O F A B R I C A T I O N

Nanolithography and Direct Exposure of S i 0 2 Layers 151 A. N. Broers, X. Pan, D. R. Allee, and C. P. Umbach

Modified Lithium Fluoride Films as a Resist for Nanometer Electron Beam Lithography 163

W. Langheinrich and H. Beneking Two-Dimensional Protein Crystals as Patterning Elements in Molecular Nanotechnology 167

U. B. Sleytr, D. Pum, M. Sara, and P. Messner V. O P T I C A L M O L E C U L A R S W I T C H E S

Bacteriorhodopsin Variants for Optical Information Processing: A New Approach in Material Science 181

N. Hampp, R. Rhoma, C. Bräuchle, F.-H. Kreuzer, R. Maurer, and D . Oesterhelt

Theoretical Analysis of Third-Order Polarizability Enhancement of Disubstituted Diphenyl Polyenes via Oxidative Doping 191

J. R. Tallent, R. R. Birge, C. W. Spangler, and K. O. Havelka Modifying the Photoelectric Behavior of Bacteriorhodopsin by Site-Directed Mutagenesis: Electrochemical and Genetic Engineering Approaches to Molecular Devices 204

F. T. Hong, F. H. Hong, R. B. Needleman, B. Ni, and M. Chang Photoelectrochemical Memory System Using Azo Compound LB Film 218

Z. F. Liu, K. Hashimoto, and A. Fujishima Re-Engineering Photosynthetic Reaction Centers 226

S. G. Boxer, J. Stocker, S. Franzen, and J. Salafsky Molecules for Energy Transfer and Switching 237

H. C. Wolf VI . N O N L I N E A R O P T I C A L P R O P E R T I E S O F M A T E R I A L S

Calculations of Nonlinear Optical Properties of Model Langmuir-Blodgett Films 245

R. W. Munn and M. M. Shabat Structure/Property Relationships for Molecular Second-Order Nonlinear Optics 252

S. R. Marder, L.-T. Cheng, D. N. Beratan

vii

VII. MESOSCOPIC PHYSICS A N D DEVICE THEORY Noise Properties of the Resonant Tunneling Structure 267

D. V. Averin Coulomb Blockade Effects in Disordered Wires 275

R. A. Webb, V. Chandrasekhar, and Z. Ovadyahu Electronic Devices in Large Systems 285

R. W. Keyes Will There be True Nm Scale Lithographie Circuits? 298

G. J. Dolan VIII. SPECTROSCOPY OF SINGLE MOLECULES

High-Resolution Spectroscopy on Single Molecules in Solids 305 M. Orrit and J. Bernard

Fixation of Protein Molecules for STM Measurement 311 M. Hara, H. Sasabe, M. Miyazawa, and K. Niki

Interpretation of STM Images: Xe on Cu(110), Eigler Atomic Switch and Xe Writing 319

C. Joachim, P. Sautet, and A. Altibelli Author Index 333

P O L Y ( 2 - E T H Y L A N I L I N E ) IN Z E O L I T E H O S T S : C O N J U G A T E D N A N O M E T E R S I Z E F I L A M E N T S

Patr ic ia Enzel and Thomas Be in* Depar tmen t of Chemis t ry , P u r d u e U n i v e r s i t y ,

Wes t Lafayet te , IN 4 7 9 0 7 , U S A

A B S T R A C T P o l y ( 2 - e t h y l a n i l i n e ) cha ins w e r e s y n t h e s i z e d w i th in the three-

d i m e n s i o n a l Channels of dehydrated z e o l i t e s X and Y. The Na- and acidic f orms of the zeo l i t e h o s t s were loaded w i th the m o n o m e r f rom h e x a n e So lu t ion , w h i c h w a s s u b s e q u e n t l y o x i d i z e d wi th a q u e o u s ( N H 4 ) 2 S 2 0 8 - The s ter ic d e m a n d s for the p o l y m e r i z a t i o n are i l lus trated by the inabi l i ty of the p o l y m e r to form in the o n e - d i m e n s i o n a l Channel S y s t e m of morden i t e . S ince pro tons are not n e c e s s a r y for the p o l y m e r i z a t i o n to occur , the p o l y m e r is f ormed in the acid form of the z e o l i t e s as w e l l as in the N a - f o r m s . Po lymer iza t ion o c c u r s a l s o at the outer s u r f a c e s o f the zeo l i t e c r y s t a l s . The external po lymer can be r e m o v e d w i t h Chloroform after it w a s c o n v e r t e d to the so lub le base form. The in trazeo l i t e po lymer chain l ength p e a k s at about 0 .1 | im (de termined from ge l permeat ion c h r o m a t o g r a p h y ) , and is subs tant ia l l y greater than that ob ta ined in bulk p o l y m e r i z a t i o n s .

I N T R O D U C T I O N If taken to the e x t r e m e , the des ign of ' m o l e c u l a r e lec t ron ics '

c o m p o n e n t s such as in t e rconnec t s , rec t i f ie rs , and s t o rage funct ions s e e k s to u t i l i ze true m o l e c u l a r s p e c i e s . 1 ' 2 Organic c o n d u c t i n g p o l y m e r s are p r o m i s i n g candidates for this goa l b e c a u s e they are l o w - d i m e n s i o n a l wi th d irec t iona l b o n d i n g , can pr inc ipa l ly be s y n t h e s i z e d to des i red l e n g t h s , and b e c a u s e they have adjustable conductivity.3»4»5 It i s o f great in teres t to e x p l o r e the p h y s i c a l p r o p e r t i e s , part icularly the c o n d u c t i v i t y , o f separated , ordered f i laments of conduc t i ng p o l y m e r s at nanometer d i m e n s i o n s .

Our research e f for t s have recent ly d e m o n s t r a t e d the e n c a p s u l a t i o n o f c o n j u g a t e d p o l y m e r s such as p o l y p y r r o l e , p o l y a n i l i n e and p o l y t h i o p h e n e in the crys ta l l ine Channel S y s t e m s 6 of z e o l i t e s . 7 P r e c u r s o r m o n o m e r s are in troduced into the z e o l i t e h o s t and are s u b s e q u e n t l y p o l y m e r i z e d by appropriate o x i d a n t s in the p o r e Sys tem. The s y n t h e s i s of t h e s e and related Sys tems represent s an important Step t o w a r d s s tab i l i zed and or iented "molecular wires", that c o u l d in pr inc ip le a l l o w to p r o c e s s s i g n a l s or to störe informat ion i n s ide Channel S y s t e m s wi th nanometer d i m e n s i o n s .

With the goa l o f a c h i e v i n g mo lecu lar a l i g n m e n t o f c o n j u g a t e d p o l y m e r c h a i n s , s evera l g r o u p s h a v e de s igned route s to ei ther s y n t h e s i z e the p o l y m e r s in ordered S y s t e m s , s u c h as l iqu id c r y s t a l s 8 , or to e n c a p s u l a t e c o n j u g a t e d p o l y m e r i c cha ins i ns ide c r y s t a l l i n e i n o r g a n i c h o s t mater ia ls by in - s i tu p o l y m e r i z a t i o n .

P o l y p y r r o l e and p o l y t h i o p h e n e fibers of only 30 n m in wid th have been g r o w n e l e c t r o c h e m i c a l l y wi th in m i c r o p o r o u s m e m b r a n e s , such as

© 1992 American Institute of Physics 93

94 Poly (2-Ethylani l ine) in Zeolite Hos t s

A n o p o r e a lumina fi l trat ion m e m b r a n e s 9 . The h igher conduc t iv i ty of these f ibers was assoc ia ted with the high degree of or ien ta t ion of the po lymer s a long the fiber ax is .

P y r r o l e , t h iophene , and ani l ine were in tercala ted and in-s i tu po lymer ized in the in ter layer space of i r o n - o x y c h l o r i d e ( F e O C l ) 1 0 and vanad ium ox ide ( V 2 O 5 . n H 2 0 ) 1 1 . Po lyan i l i ne in terca la tes were a l so formed by po lymer iza t ion of ani l ine in the gal ler ies of Cu-exchanged f luo rohec to r i t e 1 2 .

P y r r o l e has been spon taneous ly ox id ized and in-s i tu po lymer ized in 6 .8 Ä Channels of the t h ree -d imens iona l coord ina t ion po lymer [ (Me3Sn)3FeHI (CN)6]oo 1 3. Methy lace ty lene gas reacts with the acid si tes in zeol i tes L, Y, beta, Z S M - 5 , omega , morden i t e , and S A P O - 5 to form reac t ive , conjugated o l i g o m e r s 1 4 . Shor t - cha in o l igomers of p o l y t h i o p h e n e were p repa red , ox ida t ive ly doped to the conduc t ing State and s tabi l ized in Na-pen tas i l zeo l i t e s 1 5 .

The e lec t ronic p roper t i e s of the encapsu la ted S ing le cha ins of conjugated po lymers as a function of s t ruc tu re and in te rac t ions with the hos t are of par t icu lar in teres t . In the first phys ica l s tudy of spin and Charge car r ie rs in zeo l i te -encapsula ted po lypyr ro l e 1 6 , we find that a l though the cha ins are fully ox id ized and conta in b ipo la ron ic Charge ca r r i e r s , they do not exhibi t s ignif icant a . c conduc t iv i ty at 1 G H z . This Observat ion as wel l as the re la t ive ly l a rge l inewid th of the E S R s ignal can be expla ined with t rapping of po la rons and b ipo la rons by the pe r iod ic zeol i te f r amework .

P o l y m e r chain length is an impor tan t i s sue in the cor re la t ion of e lec t ronic p roper t i e s of the encapsu la ted po lymers with s t ruc ture . It was therefore of in teres t to form conjugated po lymers that are k n o w n to be so lub le in the bulk , so that t echn iques such as gel permeat ion c h r o m a t o g r a p h y could be employed for the chain length de te rmina t ion . This ar t ic le desc r ibes recent resu l t s on the in t razeol i te syn thes i s of po ly (2 -e thy l an i l i ne ) , and init ial chain length de te rmina t ions of the r e su l t ing molecu la r f i laments .

Po lyan i l i ne ( P A N I ) is un ique among the conduc t ing p o l y m e r s . Its conduc t iv i ty depends mainly on two va r i ab le s : a) the ox ida t ion State of the po lymer and b) the degree of p ro tona t ion of the n i t rogen a toms in the b a c k b o n e 1 7 . The chemical ox ida t ion of ani l ine in acidic aqueous Solut ion y ie lds the "emera ld ine s a h " form of bulk P A N I as a dark b lue-green prec ip i ta t e 1 8 . It is bel ieved to cons i s t at a pro tonat ion level of 0 .5 H + / N of equal number s of r educed , and ox id ized , p ro tona ted q u i n o n e d i imine repeat un i t s .

P A N I can a lso be formed upon ' dop ing ' the c o r r e s p o n d i n g ' e m e r a l d i n e base ' form of po lyan i l ine with aqueous H C l . This r e su l t s in a large inc rease in the number of unpa i red s p i n s 1 9 , p robab ly as d i a m i n o b e n z e n e radical c a t i o n s 2 0 . P ro tona t ion of P A N I in the emera ld ine oxida t ion State leads to a dramat ic change in conduc t iv i ty from 1 0 - 1 0 Sem"1 for the unpro tona ted po lymer to ~5 S e m - 1 when p ro tona t ed .

Po lyan i l i ne is not comple te ly so lub le in common o rgan ic so lven t s because of the s t i f fness of its backbone . The inco rpora t ion of po lar funct ional g r o u p s or long f lexible alkyl cha ins in the po lymer backbone

P. Enze l a n d T. Bein 95

is a c o m m o n techn ique to p repa re , r e spec t ive ly , water or o rgan ic so lven t s o l u b l e p o l y m e r s . This concep t was success fu l ly appl ied to po lyan i l ine . A lky l r i n g - s u b s t i t u t e d an i l ines , w h e r e the a lkyl g roup is e i ther methyl , e thy l or p r o p y l , have been po lymer ized by chemica l and e lec t rochemica l m e t h o d s 2 1 . The chemica l syn thes i s invo lves the ox ida t ion of the subs t i t u t ed m o n o m e r with ammonium pe roxod i su l f a t e in acidic aqueous med ia , ana logous to po lyan i l ine .

A s - s y n t h e s i z e d po lyan i l ine der iva t ives are i n s o l u b l e in common o r g a n i c so lven ts but become comple te ly so lub le in Chloroform or t e t r ahydro fu ran after depro tona t ion in 0 . 5 M N H 4 O H . S ince one o r tho Pos i t i on is b locked in 2 - subs t i tu ted an i l ines , a lower con ten t of o r tho c o u p l i n g s can be expec ted to lead to a more regulär head- to- ta i l po lymer s t ruc tu re and the reby , to h igher po lymer iza t ion y i e ld s . The conduc t iv i t i e s of the alkyl r i ng - subs t i t u t ed po lyan i l ines are lower than t h o s e of the paren t po lyan i l ine , by two Orders of magn i tude . This is c o n s i s t e n t wi th a reduc t ion of the rc-conjugation of the a lkyl der iva t ives caused pr imar i ly by s ter ic e f fec t s 2 2 . The s ter ic d e m a n d s of the s ide cha ins wi l l d i s to r t the p lanar a r rangement that is mos t favorab le for the con juga ted Sys tem.

Chemica l ly syn thes ized po ly (2 -e thy lan i l ine ) h y d r o c h l o r i d e salt is a g reen p o w d e r . Its base form is b lue . The salt form is be l ieved to ex i s t p r imar i ly as a p o l y s e m i q u i n o n e radical ca t ion, s imilar to the paren t p o l y a n i l i n e 2 4 .

E X P E R I M E N T A L The dehydra ted Na- and acidic forms of the z e o l i t e hos t were

loaded w i th 2 - e t h y l a n i l i n e from a hexane So lut ion of the m o n o m e r . The in t razeo l i t e 2 -e thy lan i l ine was oxid ized with aqueous a m m o n i u m p e r o x o d i s u l f a t e with s to ich iomet ry ox idan t : m o n o m e r = 1 . 5 . This ra t io w a s adop ted from l i tera ture p r o c e d u r e s 2 8 .

T h e po lymer was extracted from the h o s t f r amework by d i s s o l u t i o n of the zeol i tes with ci tr ic acid. Depro tona t ion of in t razeol i te p o l y ( 2 - e t h y l a n i l i n e ) was per formed by t reat ing the s ample w i th an a q u e o u s So lut ion of N H 4 O H .

R E S U L T S A N D D I S C U S S I O N T h e p o l y m e r i z a t i o n r e a c t i o n as a f u n c t i o n o f h o s t a n d o x i d a n t . Table 1 summar izes the resu l t s of m o n o m e r load ing and po lymer i za t ion with different ox idan t s and h o s t s . It can be not iced that ox ida t ion with pe roxod i su l f a t e y ie lds po lymer r ega rd l e s s of the p ro ton concen t r a t i on p resen t in the zeol i te . 2 -e thy lan i l ine is more easi ly ox id i zed than the unsubs t i t u t ed ani l ine . The anodic peak poten t ia l for the ox ida t ion of ani l ine appears at 0 .8 V v s . Standard ca lomel e lec t rode ( S C E ) , and for the ox ida t ion of 2-e thy lan i l ine the peak potent ia l appears at 0 . 4 1 V v s . S C E 2 9 . The m o n o m e r can be po lymer i zed in the bulk in the absence of p r o t o n s . H o w e v e r , oxida t ion with o ther ox idan t s such as h y d r o g e n pe rox ide So lut ion , oxygen t rea tment at 100°C for 12 h o u r s , or an acidic Solut ion of i odate did not resu l t in po lymer f o r m a t i o n . In the ca se of sample HöY-ETAN oxid ized with H 2 O 2 , an o range p r o d u c t is

96 Poly (2-Ethylani l ine) in Zeolite Hos t s

o b t a i n e d , apparent ly due to the format ion of an azo Compound a n a l o g o u s to a z o b e n z e n e .

The z e o l i t e / p o l y m e r adducts w e r e treated wi th base So lu t ion , and r i n s e d t h o r o u g h l y wi th Chloroform, to r e m o v e any p o s s i b l e ex terna l p o l y m e r . All the zeo l i t e p o w d e r s remained b lue after this treatment c o n f i r m i n g that the base form o f the p o l y m e r remained e n c a p s u l a t e d w i th in the zeo l i t e Channels . A l though the Chloroform So lu t ions w e r e b l u e , c o n f i r m i n g the p r e s e n c e o f s o m e r e m o v a b l e p o l y m e r , or o l i g o m e r c h a i n s , no attempts to quant i fy the amount o f p o l y m e r p r e s e n t w e r e m a d e due to the e x t r e m e l y smal l amounts of material that w a s ex trac ted .

2-Ethy lan i l ine did not p o l y m e r i z e in m o r d e n i t e e v e n t h o u g h a c o n s i d e r a b l e amount of m o n o m e r w a s loaded in to it (Table 1). T a k i n g in to account the ease with which the m o n o m e r p o l y m e r i z e s in the o the r h o s t s , it can be c o n c l u d e d that the o n e - d i m e n s i o n a l f r a m e w o r k o f m o r d e n i t e in t roduces s ter ic res tr i c t ions and p r ec ludes p o l y m e r i z a t i o n due to g e o m e t r i c c o n s t r a i n t s .

Citr ic acid w a s u s e d to d i s s o l v e the f r a m e w o r k , s i n c e it is a m u c h mi lder acid than H F , and is k n o w n to c o m p l e x a lumina te s p e c i e s in Solut ion . A l though it d i s s o l v e s the f r a m e w o r k , this p r o c e s s i s v e r y s l o w and i n v o l v e s s u c c e s s i v e e x t r a c t i o n s , w h i c h makes e s t a b l i s h i n g a quant i ta t ive m a s s ba lance d i f f icul t .

Table 1: In t razeol i te P o l y ^ - e t h y l a n i l i n e ^ as a funct ion of zeol i te hos t and ox idan t .

Sample Monomers^ Oxidant P r o d u c t a N a Y - E T A N c 33 (46) persu l fa te + b lue

ioda te , H+ - w h i t e d H 6 Y - E T A N c 2 7 , 3 2 e (46) persu l fa te + b lue

ioda te , H + - w h i t e d H 2 0 2 - o r a n g e ^ 0 2 , ioo°c - w h i t e d

N a X - E T A N c 22 (35) persu l fa te + b lue ioda te , H + - w h i t e d

H 3 5 N a 5 3 X - E T A N c 26 (35) persu l fa te + b lue ioda te , H+ - w h i t e d

H 8 M - E T A N C 6.5 (8) persu l fa te - b lu i sh H 2 0 2 - w h i t e d

0 2 , ioo°c - w h i t e d

a Molecu les of 2 -e thy lan i l ine adsorbed per uni t cell of zeol i te . N u m b e r s in pa r en the se s c o r r e s p o n d to the amount of m o n o m e r s offered in the load ing Solut ions . b Po lymer i za t ion is obse rved (+) or not (-) . c ETAN = 2 -e thy lan i l i ne . d Whi te is the or ig ina l co lor of the parent zeol i te . e A m o u n t of loading can vary from batch to ba tch . f Orange byp roduc t .

P. Enzel a n d T. Bein 97

S p e c t r o s c o p i c c h a r a c t e r i z a t i o n . The FTIR spec t ra of the zeo l i t e /po ly (2 -e thy lan i l ine ) samples are s h o w n in F i g u r e 1. Band p o s i t i o n s and their a s s i g n m e n t s are summar ized in Table 2 . The infrared spec t ra of sample H Ö Y - E T A N and of the ex t rac ted po lymer show bands s imilar to those of the bulk po lymer . The band a round 1598 cm"1 indica tes p robab ly the ex i s tence of q u i n o n e d i imine species as in p o l y a n i l i n e 2 3 . The absorp t ion at 1642 cm*1 is charac te r i s t i c of zeol i t ic water . The spect ra of o ther zeoli te samples (Table 2) are very s imi lar to that of H Ö Y - E T A N .

The s t rong absorp t ion s tar t ing at 1600 c m - 1 and ex tend ing to the nea r - IR , a t t r ibuted to the p r e sence of free car r iers in the bulk po lymer , is no t o b s e r v a b l e in the zeoli te sample , and only s l ight ly in the ext rac ted in t razeol i te po lymer . These obse rva t i ons indica te a different dop ing level of the encapsu la ted chain .

The in tens i ty of all the po lymer bands in the zeol i tes spec t ra is d imin i shed (by 30 % ) , by the t rea tment with an aqueous base So lut ion and s u b s e q u e n t w a s h i n g with Chloroform. This indica tes that p o l y ( 2 -e thy lan i l ine) was w a s h e d from the external c rys ta l su r faces .

Table 2. FTIR spec t ra of the p o l y ^ - e t h y l a n i l i n e ^ samples

H g Y - E T A N 3 (cm- l )

Recovered P E T A N 3 (cm- l )

P E T A N bulka (cm- l ) A s s i g n m e n t

2971 2 9 6 6 2 9 7 2 Uas C H 3 2 9 3 4 2933 2 9 3 6 X>as C H 2

2876 1642 1593 1500 1455

2873 1598 1498 1457

2 8 7 6 1594 1504 1457

VS C H 3 zeoli t ic H 2 O qu ino id benzeno id - C H 2 - C = C -

1404 1335 1345 1331

5 a s C H 3 b y p r o d u c t b P h e n y l - N (qu ino id )

a ETAN = 2-e thy lan i l ine , PETAN = po ly (2 -e thy lan i l i ne ) . b Due p robab ly to overox ida t ion of the ani l ine r ing with pe roxod i su l f a t e .

The e lec t ronic absorp t ion spect ra of the zeo l i t e /po ly(2-e thy lan i l ine) inc lus ion Compounds (F igure 2) d i sp lay features s imi lar to those o b s e r v e d in po lyan i l ine adduc t s . The band a round 800 nm ( 1 . 5 5 eV) is a t t r ibuted to the p re sence of radical ca t ions , wh i l e that a round

98 Poly (2-Ethylani l ine) in Zeolite Hos t s

600 nm (2 .1 eV) is a s s igned to q u i n o n e d i imine moie t ies in the b a s e po lymer . Depro tona t ion wi th an aqueous Solut ion of N H 4 O H causes the d i sappea rance of the radical cat ion bands and an inc rease of the ba se band , as expec ted . S u b s e q u e n t w a s h i n g with Chloroform re t r ieves the peak a round 800 nm of the po lymer salt . P r o b a b l y , the in t razeol i te po ly (2 -e thy lan i l ine ) in the emera ld ine salt form is inaccess ib le to the base s ince the zeoli te crys ta ls are covered with an ex te rna l layer of po lymer . The coat ing of base po lymer is d i s s o l v e d with Chloroform, leaving behind only zeoli te with encapsu la ted po lymer . C h a i n l e n g t h d e t e r m i n a t i o n . F i g u r e 3 s h o w s the molecular s ize d i s t r ibu t ion curves for po ly (2-e thy lan i l ine ) bulk and the p o l y m e r ext rac ted from H g Y - E T A N , obta ined from gel pe rmea t ion c h r o m a t o g r a p h y ( G P C ) m e a s u r e m e n t s wi th p o l y s t y r e n e Standards. T h e d i s t r ibu t ions are b imoda l . Fo r po ly (2 -e thy lan i l ine ) bulk , the main fraction d i sp l ays a molecu la r we igh t ( re la t ive to po ly s ty r ene ) of 5 0 0 0 as r e p o r t e d 2 9 , and a minor fraction with a molecular we igh t of 6 3 0 0 0 . F o r the po lymer extracted from the zeoli te , this t rend is inver ted , with the main fraction c o r r e s p o n d i n g to a molecular we igh t of 5 6 0 0 0 , and a smal ler one with molecu la r we igh t of 320 .

In o rde r to de te rmine accurate molecu la r we igh t s with G P C , the ca l ibra t ion Standard used shou ld be of the same s t ruc ture as the p o l y m e r of u n k n o w n molecular w e i g h t . S ince po ly (2 -e thy lan i l ine ) does not have the same s t ruc ture as po ly s ty r ene , a cor rec t ion factor has to be taken in to account . For po lyan i l ine , a cor rec t ion with a te t ramer of ani l ine was s u g g e s t e d 2 4 . The ra t io of the real molecular we igh t and the p o l y s t y r e n e - b a s e d G P C molecular we igh t of the te t ramer is cons ide red as a cor rec t ion factor . As the confo rmat ions of po lyan i l i ne and p o l y ( 2 -e t h y l a n i l i n e ) are p robab ly s imilar in a So lut ion of T H F , a cor rec t ion with the same factor shou ld p rov ide a r ea sonab le es t imate for the chain l eng ths . The molecular we igh t of po ly (2 -e thy lan i l ine ) r ecovered from sample H ^ Y - E T A N , obta ined from the p o l y s t y r e n e ca l ibra t ion with the cor rec t ion factor of 0 . 3 8 3 2 , is 2 1 2 8 0 . This va lue c o r r e s p o n d s to an ex tended po lymer about 0 .1 | im long . This is j u s t about 10 t imes shor te r than the average size of zeol i te c rys ta l s ut i l ized in this s tudy . It can be conc luded that the po lymer ex tends t h r o u g h o u t a subs tan t i a l fraction of the c rys ta l s .

Cor rec t ing the G P C resu l t s with the same factor , a length of on ly 9 nm is obta ined for the main fraction of the bulk po lymer . The s t r ik ing d i f ferences in molecular we igh t be tween the bulk po lymer and the o n e ext rac ted from the zeoli te could be a t t r ibuted to different mechan i sms of po lymer iza t ion in both media . One might env i s ion that in the bulk there are many poss ib i l i t i e s for radical encoun te r s r e su l t ing in q u e n c h i n g of the po lymer iza t ion . In the conf ined Spaces of the zeoli te Channels , t h e s e e n c o u n t e r s s h o u l d be great ly reduced , and the po lymer ob ta ined in the zeoli te can grow much longer .

A C K N O W L E D G E M E N T The authors a c k n o w l e d g e part ial funding from S p r a g u e Elec t r ic

C o m p a n y for this w o r k .

P. Enzel a n d T. Bein 99

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100 Poly (2-Ethylani l ine) in Zeolite Hos t s

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P. Enzel and T. Bein 101

F i g u r e 1. FTIR spectra of po ly (2 -e thy lan i l ine ) s amp le s . A ) H Ö Y - E T A N , B ) po ly (2 -e thy lan i l ine ) recovered from A , and C ) po ly (2 -e thy lan i l i ne ) bu lk .

102 Poly (2-Ethylani l ine) in Zeoli te Hos t s

F i g u r e 2 . Elec t ronic abso rp t ion spec t ra of zeo l i t e /po ly(2-e thy lan i l ine ) s a m p l e s . A) N a Y - E T A N , B) sample A + base , C) s ample B washed with Chloroform, D) HöY-ETAN, E) sample D + base , and F) sample E w a s h e d wi th Chloroform.

P. Enzel and T. Bein 103

F i g u r e 3 . Molecu la r s ize d is t r ibut ion curves for po ly (2 -e thy lan i l ine ) s a m p l e s . A ) bulk po ly (2 -e thy lan i l ine ) , and B) po ly (2 -e thy lan i l ine ) ex t rac ted f rom H Ö Y - E T A N .