Fine-Tuning of Yellow or Red Photo and Electroluminescence of Functional Difluoro-boradiazaindacene Films

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DOI: 10.1002/adfm.200700697
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Fine-Tuning of Yellow or Red Photo- and Electroluminescence ofFunctional Difluoro-boradiazaindacene Films**

By Laure Bonardi, Hani Kanaan, Franck Camerel, Pascale Jolinat, Pascal Retailleau, and Raymond Ziessel*

he present work describes the synthesis of difluoro-boradiazaindacenes (Bodipy) functionalized at the central 8-position by

henylamino moieties easily transformable into phenyl amide scaffoldings. Molecules carrying three linear or branched chains

ere prepared and characterized. AnX-ray crystal structure for the pivotal trimethoxyphenyl-Bodipy derivative was determined,

nd the packing is discussed in terms of molecular interactions; a key feature for the formation of thin films. All of the dyes are

ermally stable up to 170 8C but no liquid-crystalline phases are observed. Reversible reduction and oxidation processes occur

round þ0.97 and �1.34 V, respectively, versus saturated calomel electrode in solution and the electroactivity and photo-

minescence are maintained in thin films produced by vacuum evaporation. Interestingly, two distinct emissions are observed at

50 and 635 nm by electroluminescence of the trimethoxyphenyl-Bodipy derivative, corresponding to the luminescence of

olated molecules and dimers, respectively. Doping Alq3 films with this Bodipy molecule by vacuum evaporation produces

rganic light-emitting diodes (OLEDs) in which very efficient energy transfer from the Alq3 matrix to the Bodipy occurs by a

sonance mechanism involving the first Bodipy excited state. Yellow light (550 nm, 344 cd m�2 at 15 V) is emitted at low doping

ncentration (7 mol %), whereas red light (635 nm, 125 cd m�2 at 15 V) is emitted at higher concentration (19 mol %).

ispersion of the Bodipy into a fluorescent poly(N-vinylcarbazole) polymer (PVK) (�3 mol % per repeating unit of PVK) by

lution processing exclusively produces yellow emission owing to the isolated Bodipyfluorophore (550 nm, 213 cd m�2 at 15 V).

he second excited state of the Bodipy dye is likely involved during energy transfer from the PVK matrix.

1. Introduction

The engineering of robust molecular materials with

improved luminescence, electron exchange, and charge-

transport properties is a fruitful subject, attracting worldwide

interest and undergoing rapid development. This widespread

interest stems from potential applications as light-emitting

films and electroluminescent materials[1,2] and molecular

[*] Dr. R. Ziessel, L. Bonardi, Dr. F. CamerelLaboratoire de Chimie MoleculaireEcole Chimie, Polymeres, Materiaux (ECPM), ULP-CNRS25 rue Becquerel, 67008 Strasbourg Cedex (France)E-mail: [email protected]

H. Kanaan, Dr. P. JolinatLaboratoire Plasma et Conversion d’Energie (LAPLACE)Universite Paul Sabatier, Bat 3R331062 Toulouse Cedex 09 (France)

Dr. P. RetailleauLaboratoire de Cristallochimie, ICSN – CNRS, Bat 271 avenue de la Terrasse, 91198 Gif-sur-Yvette (France)

[**] This work was jointly supported by the Louis Pasteur Universitythrough the European School of Polymer and Materials Chemistry(ECPM), by the Centre National de la Recherche Scientifique (CNRS)of France, and ANR Contract ANR-05-BLAN-0004-01, FCP-OLEDs. Wewarmly thank Dr Bertrand Donnio from the IPCMS in Strasbourg forperforming low- and wide-angle X-ray diffraction experiments on thesenovel compounds. We are also indebted to Professor Jack Harrowfield(ISIS Strasbourg) for careful reading and commenting thismanuscriptprior to journal submission. Supporting information is availableonline from Wiley InterScience or from the author.

Adv. Funct. Mater. 2008, 18, 401–413 � 2008 WILEY-VCH Verlag

probes.[3] Many different electroluminescent, organic, low-

molecular-weight or polymeric materials have been prepared

and tested, among which are tetracene,[4] pentacene,[5]

a-sexithiophene,[6] polyphenylvinylene, polyacetylene, poly-

fluorene, polycarbazole, pyridine- or oxadiazole-containing

conjugated polymers, polyquinolines, polyquinoxalines, and

cyanopolymers.[7] Recently, the harvesting of triplet excitons

using metal-containing complexes (Pt or Ir) has proved to be a

very successful way of making efficient organic light-emitting

diodes (OLEDs), since these devices incorporate a heavy-

metal atom with strong spin–orbit coupling that enhances

intersystem crossing, favoring the triplet state. In this way, the

lowest triplet state is efficiently populated and can produce

phosphorescence. By using a phosphorescent dye that captures

both singlet and triplet excitons, the internal efficiency can be

increased.[8] The doping of Alq3 (q¼ 8-hydroxyquinolate) with

organic dyes has also been found to be a means of increasing

the overall electroluminescence efficiency by allowing efficient

energy transfer from the metal-containing matrix to the

organic light-emitting dye.[9,10]

Of major importance in the field of effective organic

fluorophores are the difluoro-boradiazaindacenes, commonly

named boron-dipyrromethene dyes (Bodipy).[11] These dyes

are widely employed as useful fluorescence probes for labeling

biomolecules[12] and for the sensing of calcium ions,[13] nitric

oxides,[14] protons,[15] or various cations[16,17] by optoelectronic

switching. The attractive features of these dyes stem from

the facile modification of their structures, providing opportu-

nities to fine-tune their properties and to incorporate recog-

GmbH & Co. KGaA, Weinheim 401

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L. Bonardi et al. / Electroluminescence of Functional Difluoro-boradiazaindacene Films

402

nition sites for a variety of analytes. These dyes combine sharp

absorption bands (full width at half-maximum (FWHM)�25–35 nm), high molar absorption coefficients (e¼ 40 000 to

110 000 M�1 cm�1), large fluorescence quantum yields

(f¼ 60–90%), and relatively long excited-state lifetimes

(1 to 10 ns) with excellent chemical and photochemical

stability in solution and in the solid state, and valuable

charge-transfer properties. Furthermore, their optical proper-

ties are sensitive to modifications around the pyrrole core,[18]

the central meso position,[19,20] and the boron atom.[21] In

addition, the dyes have good solubility in organic solvents and

are thus amenable towards chromatography on silica or

alumina. The high purity and neutrality of these molecules

allow vacuum deposition in conventional equipment. Exten-

sive efforts have therefore been devoted to the design and

preparation of sophisticated dyes for use as chromogenic

probes,[22] fluorescent switches,[23] electro-chemiluminescent

molecules (in solution)[24] and electroluminescent materials (in

the solid state),[25] laser dyes,[26] sensitizers for solar cells,[27]

drug-delivery agents,[28] and as electron-transfer probes for

radical ion pairs generated by local electric fields.[29]

In some exceptional cases, Bodipy has been used as an

antenna transferring its excitonic energy to acceptor frame-

works such as zinc porphyrins[30–32] or perylene dyes.[33] Long-

range charge separation induced by photoinduced electron

transfer processes has also been highlighted in different

accounts.[34,35] Such photoinduced electron transfer has been

extensively exploited in chemosensor systems.[36,37] Electro-

luminescence from borodipyrromethene dyes doped into a

polyvinyl–carbazole host polymer[25a] or thin films of alumi-

nium complexes has previously been observed in OLEDs.[25b]

Electrogenerated luminescence has also been investigated in

acetonitrile solution by pulsing the working electrode between

the first oxidation and reduction peaks of the Bodipy.[24] The

well-defined molecular structure of Bodipy makes it relatively

easy to establish firm structure–property relationships. Recen-

tly, novel Bodipy architectures enabled their incorporation

into supramolecular assemblies, such as liquid-crystalline

materials or organo-gelators,[38–40] and luminescent phenol-

pyridyl-boron complexes displaying bright luminescence have been

exploited in white and blue electroluminescent devices.[41]

Scheme 1. i) H2 (1 atm), 5 % Pd/C (0.1 equiv. of Pd), EtOH/CH2Cl2, r.t., 1

www.afm-journal.de � 2008 WILEY-VCH Verlag GmbH

The design of luminescent and photoresponsive liquid

crystals is particularly appealing owing to their potential

applications in photoelectronic devices.[42] Advantages of

liquid crystals are their ease of processing (via solution

techniques), the possibility of alignment by shear forces or by

application of electrical or magnetic fields, and their capacity

for self-healing. For these reasons, we have synthesized new

Bodipy derivatives bearing gallate-substituted residues with

aliphatic chains (8, 10, 12, 16, and 20 carbons) or with methoxy

groups as model compounds, and these were well characterized

by X-ray diffraction on single crystals, NMR, absorption and

fluorescence spectroscopies, and electrochemistry. Their remar-

kable optoelectronic properties led us to test these materials in

electroluminescent devices. The methoxy-substituted deriva-

tive gives stable electroluminescent films as pure material,

while incorporation of the long-chain compounds produces

unstable devices. To improve the efficiency of the methox-

y-derivative device, this compound was sublimated in an Alq3matrix or incorporated by solution-processing in PVK polymer

to produce multilayered electroluminescent devices. Owing to

the propensity of Bodipy to form luminescent aggregates, it

was possible to tune the electrogenerated light from yellow to

red.

2. Results and Discussion

2.1. Synthesis

The starting p-nitrophenyl-4,4-difluoro-4-bora-3a,4a-diaza-

s-indacene derivative 1 was obtained by condensation of

2,4-dimethyl-3-ethylpyrrole (also called Kryptopyrrole) with

the p-nitrophenylacylchloride in dichloromethane at room

temperature, followed by a complexation to a BF2 fragment

after deprotonation with triethylamine.[43] By means of a

catalytic hydrogenation over Pd on charcoal, this nitro

derivative can be easily reduced into the corresponding amine

(Scheme 1).[44] Reaction of the p-aminophenyl-4,4-difluoro-4-

bora-3a,4a-diaza-s-indacene derivative with a series of

3,4,5-tris-alkyloxy-benzoic acids leads to the synthesis of a

wide range of amido-Bodipy derivatives functionalized with

day. ii) 3,4,5-tris-alkyloxy-benzoic acid chloride (1 equiv.), TEA, CH2Cl2, r.t.

& Co. KGaA, Weinheim Adv. Funct. Mater. 2008, 18,401–413

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L. Bonardi et al./Electroluminescence of Functional Difluoro-boradiazaindacene Films

Figure 1. Oak Ridge Thermal Ellipsoid Plot (ORTEP) view of 3 withprincipal atomic numbering (thermal ellipsoids at 50% probability level).

straight or branched paraffin chains. Its formation results from

reacting the amino-Bodipy compound with 3,4,5-tris-alkyloxy-

benzoic acid chlorides in presence of triethylamine (TEA)

(Scheme 1). For the phytol strands a racemic mixture of

3,4,5-tris-(3,7,11,15-tetramethyl-hexadecyl) was used, whereas

for the citronellol strands the pure (S)-(þ)-citronellyl deriva-

tive was used.[45] All compounds were fully characterized by

means of NMR spectroscopy, Fourier transform infrared

(FTIR) spectroscopy, electrospray ionization mass spectro-

metry (ESI-MS), and elemental analysis. The introduction of

long carbon chains improves the solubility in common organic

solvents, facilitates evaporation under high vacuum, and

results in well-organized solid-state phases by microsegrega-

tion between the polar Bodipy core and the apolar chains.

The amide bond connecting the fluorophore to the gallate

platform was especially introduced to control and stabilize the

molecular organization through hydrogen bonding (vide infra).

2.2. X-Ray Characterization

Single-crystals of compound 3 suitable for X-ray structure

determinations were obtained by slow evaporation of a

CH2Cl2/hexane solvent mixture. This compound crystallized

in the monoclinic space group P21/c (a¼ 15.036(1) A; b¼21.641(2) A; c¼ 10.101(1) A; V¼ 3145.8(5) A3, Z¼ 4). Figure 1

shows the atomic numbering and labeling scheme. The

geometry around the boron atom is tetrahedral and the

observed distances and angles compare well with the ones

usually observed on similar compounds (distances being: B-F1,

1.382(4) A; B-F2, 1.388(4) A; B-N1, 1.540(4) A; B-N2, 1.549(4)

A and angles being: N1-B-F1, 110.5(3)8; N1-B-F2, 110.4(2)8;N2-B-N1, 106.8(2)8; N2-B-F2, 109.6(3)8; F1-B-F2, 109.0(3)8and N2-B-F1, 110.4(3)8).[46] The dipyrromethene subunit

(including the two pyrrole rings, the four methyl carbons,

and the two methylene carbons) is planar. The central phenyl

ring Ar1 is almost orthogonal to the Bodipy fragment (angle

Ar1-Bodipy¼ 80.08) and twisted by 39.18 from the plane of the

terminal phenyl ring Ar2. The twist between the Bodipy

fragment and the terminal phenyl ring Ar2 is 42.28.Different views of the crystal packing are presented in

Figures 2 and 3. The molecules are connected by a uniform

unidimensional hydrogen-bonded network running along the c

axis (represented by dashed lines in Fig. 2). These inter-

molecular hydrogen bonds involve the hydrogen atom on N3

on one molecule and the oxygen atom O1 of the adjacent

molecule. In this way, all the molecules are engaged in two

hydrogen bonds pointing in opposite directions (N3H-O1¼2.19 A and N3-H-O1 angle¼ 155.78; Fig. 2a). FTIR spectro-

scopy is a powerful tool to probe hydrogen bonding and,[47–48]

at room temperature, this compound has its amide group

involved in strong hydrogen bonding, as clearly evidenced by

the nNH, nCO stretching vibrations at 3308 and 1650 cm�1

respectively. Note that corresponding values for free amides

usually lie at 3500-3400 cm�1 for nNH and around 1680 cm�1 for

nCO.[38,39] The presence of single nNH, and nCO stretching bands

in the IR spectra confirms a well-organized hydrogen-bonded

Adv. Funct. Mater. 2008, 18, 401–413 � 2008 WILEY-VCH Verlag GmbH &

network in which only one type of hydrogen bond is effective.

The structure determination shows that this supramolecular

hydrogen-bonded edifice adopts a V-shape. These hydrogen-

bonded strands are further connected via the Bodipy fragments

by H . . .F interactions (Fig. 2b), which result in strongly

stabilized zig-zag layers (Fig. 3). Closer examination of the

structure reveals that the Bodipy fragments are dimerized in a

centrosymmetric fashion by the formation of two hydrogen

bonds between one fluorine atom of the BF2 fragments (F2) on

the first molecule and two hydrogen atoms on the phenyl ring

Ar1 of the second molecule (C6AH----F1¼ 2.618 A; C6AHF1

angle¼ 117.38; C5AH----F1¼ 2.502 A; C6AHF1 angle¼122.08; Fig. 2, bold dashed lines). These Bodipy dimers are

further connected by weaker H . . .F interactions along the c

direction (C2AH----F2¼ 3.200 A; C2AHF2 angle¼ 98.38;C3AH----F2¼ 3.375 A; C3AHF2 angle¼ 102.28; Fig. 2, thindashed lines). The formation of Bodipy dimers orients the ethyl

groups of one fluorophore in the same direction. No strong

interactions are apparent between the different zig-zag layers.

2.3. Thermal Properties

All of the compounds display a clear melting point, corres-

ponding to a phase transition from a birefringent powder to an

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Figure 2. a) View of the 1D hydrogen-bonded network, represented by dotted lines, running along the c axis (N3H-O1¼ 2.191(2) A and N3-H-O1angle¼ 155.63(14)8). b) HF bonds observed in intra- and inter-Bodipy dimers: strong interactions are represented as bold dotted lines and weakinteractions by thin dotted lines.

Figure 3. Projection of the crystalline structure of 3 along the c axis (left, hydrogen atoms omitted for clarity) and schematic representation of thisstructure (right). A black rod corresponds to a Bodipy dimer and a black circle to a one-dimensional hydrogen-bonded network viewed from the top.

404 www.afm-journal.de � 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Adv. Funct. Mater. 2008, 18,401–413

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Figure 4. Compound 4 viewed by optical microscopy below 150 8C on cooling from the isotropicliquid (left, without polarizer; right, same area between crossed polarizers).

isotropic liquid. Isotropization temperatures decrease as the

chain lengths increase (Table S1). The high enthalpy values

observed for the last transition upon heating confirmed these

observations. Compounds 7 and 8 directly melt from the crystal

to the isotropic liquid, but the other compounds (4, 5, and 6)

exhibit several successive crystal-to-crystal phase transforma-

tions before melting to the isotropic liquid. Unfortunately,

despite the presence of long carbon chains, none of these

compounds form liquid-crystalline phases. However, on cool-

ing from the isotropic state, it was observed by optical micros-

copy between crossed polarizers that these compounds have a

marked tendency to recrystallize uniformly as thin films. In

this way, large monodomains of well-aligned molecular

assemblies can be formed, as observed in Figure 4 where

three monodomains with different orientations are presented.

The tendency of these fluorophores to form well-organized,

crystalline thin films may be useful for optoelectronic appli-

cations such as OLEDs or solar cells.

2.4. Optical and Electrochemical Properties in Solution

Spectroscopic data for compounds 3 to 8 are gathered in

Table 1 and for compounds 1, 2 in Table S2. All of the

compounds show similar absorption patterns which are

characteristic of Bodipy fluorophores, and a representative

example is depicted in Figure 5. The absorption spectrum is

composed of a strong S0! S1 (p!p�) transition located

around 525 nm, with molar extinction coefficients ranging from

70 000 to 100 000 M�1 cm�1, in keeping with classical Bodipy

Scheme 2. Molecular structures of Bodipy A and reference compound B.

derivatives.[49] A second absorption band

centered around 370 nm, is assigned to

the S0! S2 transition of the Bodipy sub-

unit.[50] The third absorption at around

275 nm is likely due to p-p� and n-p�

transitions localized on the phenyl and

dipyrromethene fragments.[51] The amido

compounds have high fluorescence quantum

yields, ranging from 58 to 75%. The weak

Stokes’ shifts (about 500 cm�1) observed

over the whole series of fluorophores is in

good agreement with a singlet emitting

state. Excitation spectra perfectly match the

Adv. Funct. Mater. 2008, 18, 401–413 � 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

absorption spectra (Fig. 5 as a typical

example), which is in keeping with a

unique excited state, excluding the exis-

tence of a CT transition, despite the

presence of both electron-donating and

electron-attracting fragments on these

fluorophores. Moreover, no quenching

of the luminescence by molecular oxygen

is observed, excluding the presence of a

possible triplet emitting state. The fluor-

escence decay profiles of these molecules

can be fitted by a single exponential decay,

with fluorescence lifetimes ranging from

4.9 to 6.2 ns (Table 1 and in Fig. 5b), in line with a singlet

emissive state. All of the fluorescence spectra exhibit nice

mirror symmetry with the lowest-energy absorption band,

meaning that the corresponding transitions involve the same

excited state.

The electrochemical properties were determined by cyclic

voltammetry in dichloromethane solution. Table 1 lists the

potentials (relative to the saturated chemical electrode (SCE)

reference) for the waves that were observed in the þ1.6 to

�2.0 Vwindow. Firstly, for all of the compounds, the reversible

anodic wave around þ0.97 V is assigned to the (Bodipy/

Bodipyþ�) couple. Note that this wave is less anodic with

respect to phenyl- or toluyl-substituted Bodipy’sA (Scheme 2)

[þ1.11 (60) V and �1.26 (70) V versus SCE].[53] This likely

reflects the fact that the trialkoxy-gallate substituents are

better electron-donating groups compared to the other

derivatives. There is no indication of oxidation to the

(Bodipy2þ) dication within the given electrochemical window

as previously observed for pyridine-linked Bodipy com-

pounds.[53] The second oxidation is irreversible at around

þ1.52 V and is likely localized on the trialkoxyphenyl subunit

in keeping with literature data[54,55] and the electrochemistry of

the reference compound B (Scheme 2) (þ1.55 V irrev.).

The single reduction is attributed to the Bodipy radical

anion (Bodipy��), which was in all cases reversible and more

cathodic compared to the toluyl compound A. This observa-

tion is also in keeping with the increase of electron density

imparted by the trialkoxyphenyl fragments.

Note that the LUMO–HOMO gap (at about 2.30 eV)

remains similar along the series, as reflected by the constancy of

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Table 1. Optical and electrochemical data measured in dichloromethane solution at 298 K.

labs [nm] e [M�1 cm�1] lF [nm] FF [a] tF [ns] kr [b] [108 sS1] knr [b] [10

8 sS1] E-oxy, [c] [V] (DE [mV]) E-red, [c] [V] (DE [mV])

3 525 60 000 540 0.65 6.2 1.04 0.56 þ0.97 (60) �1.33 (70)

þ1.54 (irrv.)

4 525 75 000 540 0.58 5.4 1.07 0.77 þ0.97 (60) �1.35 (70)

þ1.51 (irrv.)

5 525 70 000 540 0.75 5.8 1.29 0.43 þ0.97 (60) �1.34 (70)

þ1.51 (irrv.)

6 525 77 000 540 0.66 5.1 1.29 0.66 þ0.97 (70) �1.33 (60)

þ1.52 (irrv.)

7 525 95 000 540 0.67 4.9 1.37 0.67 þ0.97 (60) �1.34 (70)

þ1.54 (irrv.)

8 525 100 000 541 0.68 5.9 1.15 0.54 þ0.99 (60) �1.29 (70)

þ1.52 (irrv.)

[a] FF was determined in dichloromethane solution (c¼ 5� 10�7M) using Rhodamine 6G as reference (FF¼ 0.78 in water, lexc¼ 488 nm) [52]. All of the FF values have been

corrected for changes in refractive index. [b] kr and knr values were calculated using the following equations: kr¼FF/tF, knr¼ (1 � FF)/tF, assuming that the emitting state is

produced with unit quantum efficiency. [c] Potentials were determined by cyclic voltammetry in deoxygenated CH2Cl2 solutions containing 0.1 M TBAPF6, at a solute

concentration of 10�3M, at 20 8C. Potentials were standardized using ferrocene (Fc) as an internal reference and converted to SCE assuming that E1/2 (Fc/Fc

þ)¼þ0.38 V

(DEp¼ 70 mV) vs. SCE. The error in the half-wave potentials is�10 mV. The scan rate was 200 mV s�1. When the redox process is irreversible the peak potential (Ecp) is quoted.

All of the reversible processes are monoelectronic.

Figure 5. a) Absorption spectra for 3 (absorption in dashed line, excitationin dotted line), and emission spectra in solid line (lexc¼ 525 nm). All of thespectra were measured in CH2Cl2 at r.t. (c¼ 5� 10�7

M). �¼ second orderexcitation. b) Measured intensity decay of 3 at 540 nm (lexc¼ 525 nm) andits corresponding single-exponential fit (solid line).

406 www.afm-journal.de � 2008 WILEY-VCH Verlag GmbH

the emission wavelength (Table 1). Changing the substitution

position or increasing the number of amido fragments does not

significantly change the redox potentials of the concerned

fragments. These results clearly reflect the combined effects of

electron donation and charge delocalization and are in keeping

with previous observations on related molecules.[42]

2.5. Electroluminescent Devices (OLEDs)

These Bodipy molecules exhibit remarkable optoelectronic

properties, with strong absorption in the visible region, high

fluorescence quantum yields, and narrow emission bandwidths

with high peak intensities. These optical properties render

them attractive as organic emitters. Moreover, these neutral

molecules are thermally stable, soluble in common organic

solvents and can be easily deposited on a surface by vacuum

evaporation or spin-coating. Furthermore, the property of

forming well-organized thin films on a surface may lead to

improved emission efficiency in OLED applications. Addi-

tionally, these molecules are redox active, undergoing oxi-

dation and reduction in a convenient potential range, raising

the prospect of their use in OLEDs.

To evaluate the capability of transporting charges and

forming excitons, a simple OLED was fabricated using a pure

layer of these compounds (100 nm) sublimed onto an indium

tin oxide (ITO)-coated glass substrate, and using an aluminum

cathode as contact-electrode. Compounds with long carbon

chains have been tested but, when a potential is applied, the

compounds start to melt and the formation of collapsed

droplets can be observed by optical microscopy, meaning the

OLED is unstable. However, electroluminescence devices with

the methoxy derivative 3 were found to be stable over a period

of hours.

The photoluminescence spectrum of the organic film

presents two maxima at 545 and 633 nm upon excitation at


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390 nm. The first emission peak can be safely attributed, in

regard to the results obtained in solution, to the emission of

monomeric and isolated Bodipy molecules. The second

emission peak at 633 nm is attributed to the formation of

dimers. Based on the crystal structure of the tris-amide

derivative bearing methoxy groups in place of the aliphatic

chains, we suggest that the aggregation process is likely driven

by formation of dimers stabilized by hydrogen bonding. In fact,

in the solid state, strongly stabilized Bodipy dimers are formed

through H-F bonds (Fig. 2b). Such behavior has already been

observed by fluorescencemeasurements performed on gels and

liquid-crystalline materials based on Bodipy cores.[39] It has

been demonstrated that the emission at 635 nm originates from

the formation of excited dimers (excimers). Larger and less-

organized aggregates are virtually not observed because they

should emit at lower energies and the width of the emission

band should be larger. The excitation spectra measured at both

emission wavelengths are identical and perfectly match the

absorption spectra over the entire spectral range.

Electroluminescence spectra were collected for various

applied voltages on this simple ITO/Bodipy(3) (100 nm)/Al

OLED configuration. Interestingly, the electroluminescence

spectra also displayed two intense emission peaks at 550 nm

(yellow) and 635 nm (red; Fig. 6), very similar to the

photoluminescence spectra measured on the same device.

Upon increasing the applied voltage, the electroluminescence

intensity increases but the relative intensity of the two emission

peaks remains constant. This dual emission in the yellow and in

the red part of the visible spectrum explains the orange color

detected with the spectroradiometer. It can be anticipated that

the color of the light emitted by the working OLEDwill mainly

depend on the proportion of monomers and dimers. Unfortu-

nately, this material degrades quickly and dark spots appear on

the device. When a constant voltage is applied over a long time

(1 h), the luminosity gradually decreases until the diode

appears to be extinguished. However, this compound can emit

when simply sandwiched between ITO-coated glass and alu-

minum electrodes. It could, however, not be excluded that

under these working conditions boron/aluminum exchange

might cause the progressive destruction of the device.

Figure 6. Electroluminescence spectra of an OLED structure, ITO/Bod-ipy(3) (100 nm)/Al, for various applied voltages.


To improve the device efficiency and stability, compound 3

was incorporated into an Alq3 matrix, known to behave as an

electron-transporting material,[56] inside a multilayer OLED

device. Two OLEDs with different doping ratios of compound

3 in the Alq3 matrix have been studied (ITO/a-NPD (30 nm)/

Alq3:Bodipy(3) (7 mol %, 60 nm)/BCP(7 nm)/Al and ITO/

a-NPD(30 nm)/Alq3:Bodipy(3) (19 mol %, 100 nm)/BCP(7

nm)/Al). Figure 7 represents a simplified energy diagram for

the ITO/a-NPD/Alq3:Bodipy(3)/BCP/Al structure. The HOMO

and LUMO energies were calculated by a procedure adopted

from the literature.[57] Accordingly, the value for ferrocene

(Fc) oxidation with respect to the zero-vacuum level is esti-

mated as �4.8 eV, determined from �4.6 eV for the standard

electrode potentialE8 of normal hydrogen electrode (NHE) on

the zero vacuum level, and 0.2 V for Fc vs. NHE.[58] In these

devices, a-NPD (N,N0-di-[(1-naphthyl)-N,N0-diphenyl]-1,10-

biphenyl)-4,40-diamine) and BCP (2,9-dimethyl-4,7-diphenyl-

1,10-phenanthroline) act respectively as a hole-transporting

layer and an electron-transporting, hole-blocking layer. Holes

are injected from ITO into a-NPD and blocked at the

Alq3:Bodipy(3)/BCP interface. On the cathode side, electrons

are injected into BCP and blocked at the a-NPD/Alq3:Bo-

dipy(3) interface. Charge confinement promotes the formation

and recombination of excitons inside the Alq3:Bodipy layer,

thus optimizing the OLED operation..

There is a perfect match between the absorption spectrum of

compound 3 in thin films and the photoluminescence of Alq3,

maximum located at 515 nm, FWHM¼ 90 nm (Fig. 8). The

choice of Alq3 as a host matrix for Bodipy seems to be

appropriate since energy transfer from Alq3 to a Bodipy

derivative should be extremely favorable, involving the first

excited state of the Bodipy. This is confirmed in Figure 9a,

showing the excitation and photoluminescence spectra of an

Alq3:Bodipy (7 mol %) film. Clearly, the narrow yellow

emission at 550 nm is assigned to the Bodipymonomer whereas

the weak emission at 635 nm is due to Bodipy dimers. No

residual emission arising from the Alq3 could be detected,

proving complete energy transfer from the Alq3 matrix to the

Bodipy dye. The excitation spectrum (Fig. 9) displays an

intense absorption at 400 nm, proving that full energy transfer

from the Alq3 to the Bodipy is occurring in this device.

On increasing the Bodipy concentration from 7 to 19 mol %

the photoluminescence spectrum showed a major red emission

centered at 635 nm (Fig. 9). This is a clear signature that, at this

concentration, the Bodipy molecules are mainly dimerized.

The absence of an Alq3 emission also confirms the effective-

ness of the energy transfer from Alq3 to the Bodipy dimers, as

found for the lower doping. Thus, the color of the light emitted

by the working OLED depends on the degree of doping of

Bodipy into the Alq3 matrix, which tunes the proportion of

yellow and red emitted light (inset in Fig. 10). The electrol-

uminescence spectra plotted in Figure 10 correspond to devices

with different dopant concentrations (7 mol % and 19 mol %)

of the emitting layer.

As stated above, yellow (550 nm) and red (635 nm)

emissions can be observed and depend on the dopant ratio, i.e.,


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Figure 7. Energy diagram of an ITO/a-NPD/Alq3:Bodipy/BCP/Al structure. The HOMO and LUMO levels of Bodipy are represented by dotted lines andderived from cyclic voltammetry measurements.

408

the aggregation state, inside the layers. A residual yellow

emission (�6% intensity) is, however, observed in the

electroluminescence spectrum of the ITO/Alq3:Bodipy(3)

(19 mol %, 100 nm)/BCP(7 nm)/Al OLED structure and

indicates that a small fraction of Bodipy molecules are

unaggregated. Interestingly, the widths of both emission bands

are virtually similar and in keeping with a monomeric (lem550 nm) and a dimeric (lem 635 nm) species. Formation of

larger aggregates in which a higher number of molecules are

effectively organized would lead to a much wider emission

band, further shifted to lower energy. The presence of addi-

tional functions favoring co-operative effects would help to

further aggregate the molecules by a co-operative effect and

Figure 8. Absorption spectrum of a film of compound 3 (continuous line);absorption spectrum (dashed line) and photoluminescence spectrum(dotted line) of an Alq3 film.


would then increase the local organization and enhance

electronic coupling. As a consequence the spectrum of the

aggregate would then be broader; which has clearly not been

observed in the present case.

The current density–voltage and light intensity–voltage

characteristics of an ITO/a-NPD (30 nm)/Alq3:Bodipy(3)

(7 mol %, 60 nm)/BCP (7 nm)/Al structure are presented in

Figure 11. Log J is linearly dependent on log V above a

threshold voltage, which may correspond to a trap-limited

current (JaVmþ 1, m> 1). When sufficient double charge

injection occurs, light emission can be observed. The increase

of light intensity with voltage is faster than that of current

density, inducing an increase of device external quantum

efficiency (e.g., number of emitted photons per injected charge

carrier); then, this difference decreases for higher voltages. The

maximum luminance value measured for this device was 344

cd m�2, while it was only 10 cd m�2 in the case of the simple

ITO/Bodipy(3) (100 nm)/Al OLED structure.

Solution processing also provides devices by spin-coating

using PVK as the polymermatrix doped with compound 3. This

well-known, hole-transporting polymer[59] displays an emission

spectrum located at 410 nm. With the ITO/PEDOT:PSS (60

nm)/PVK:Bodipy(3) (10 wt %, 100 nm)/Al structure, only a

yellow emission has been observed (Fig. S1). This result

obtained with a dopant concentration of �3 mol % is in

keeping with the absence of Bodipy aggregation (dimer for-

mation) at that concentration level. Here it is assumed, in light

of the spectral overlap between the Bodipy absorption

(Figure 5) and the PVK emission, that complete energy

transfer from the PVK to the second S0! S2 transition of the


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Figure 9. a) Excitation (lem¼ 550 nm) (dotted line) and photolumines-cence spectra of Alq3:Bodipy(3) film at 7 mol % (lexc¼ 400 nm). b)Excitation (lem¼ 635 nm) (dotted line) and photoluminescence spectraof Alq3:Bodipy(3) film at 19 mol % (lexc¼ 400 nm).

Figure 10. Electroluminescence spectra of the OLED structures: ITO/a-NPD (30 nm)/Alq3:Bodipy(3) (7 mol %, 60 nm)/BCP(7 nm)/Al (left,yellow color) and ITO/a-NPD (30 nm)/Alq3:Bodipy(3) (19 mol %, 60 nm)/BCP(7 nm)/Al (right, red color).

Figure 11. Current density (triangles) – voltage and light intensity(circles) – voltage characteristics of the ITO/a-NPD (30 nm)/Alq3:Bodipy(3) (7 mol %, 60 nm)/BCP(7 nm)/Al structure.


Bodipy is occurring. Ultrafast fluorescence up-conversion

studies have demonstrated that vibrational cooling of hot

Bodipy excited states in the S1 state is very efficient and occurs

within a 20 ps timescale.[60] Recent studies in solution have

proven that resonance energy transfer from the S2 state is as

efficient as from the S1 transition of boron dipyrromethene

dyes.[61]

3. Conclusions

Owing to the propensity of functionalized Bodipy dyes to

aggregate in the solid state, thin films incorporating these

materials show emissions in the yellow and red due to

monomer and dimers, respectively. Doping the Alq3 host layer

provides electroluminescent devices in which complete energy

transfer from the Alq3 to the Bodipy dye occurs. Here

the S0! S1 absorption transition of the Bodipy is involved in

the energy transfer process. By increasing the doping of Bodipy

into the Alq3 matrix, dye dimers are formed, providing a

bathochromic shift of the electro-emitted light. It is foreseen

that a fine control of the doping rate will allow a fine-tuning of

the emitted light from yellow to red. This unusual tuning is only

observed in the solid state. By dispersing the Bodipy dye into a

PVK polymer by spin coating, yellow light is solely observed in

the OLED. Complete energy transfer from the PVK to the

Bodipy is occurring, involving in this case the S0!S2 transition

of the Bodipy. Work in progress concerns the addition of

polymerizable groups at the end of the long paraffin chains in

order to better control the stacking of the molecules and to

avoid the demixing problems found with the long carbon

chains.

4. Experimental Section

300.1 (1H) and 75.5MHz (13C) NMR spectra were recorded at roomtemperature using perdeuterated solvents as internal standards: (H) in


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410

ppm relative to residual protiated solvent; (C) in ppm relative to thesolvent. A ZAB-HF-VB-analytical apparatus in FABþ mode was usedwith m-nitrobenzyl alcohol (m-NBA) as the matrix. Chromatographicpurification was conducted using 40–63 mm silica gel. Thin-layerchromatography (TLC) was performed on silica-gel plates coated withfluorescent indicator. FTIR spectra were recorded using a Perki-n-Elmer ‘‘spectrum one’’ spectrometer from thin films deposited ontodry KBr pellets. UV-vis spectra were recorded using a UVIKON 940/941 dual-beam grating spectrophotometer (Kontron Instruments)with a 1 cm quartz cell. Fluorescence spectra were recorded on aPerkin-Elmer LS50B spectrofluorimeter. All of the fluorescencespectra were corrected. The fluorescence quantum yield (Fexp) wascalculated fromEquation 1. In Equation 1, F denotes the integral of thecorrected fluorescence spectrum, A is the absorbance at the excitationwavelength, and n is the refractive index of the medium. The referencesystem used was rhodamine 6G (Fref¼ 0.78, lexc¼ 488 nm) [52] inair-equilibrated water.

Fexp ¼ Fref

Ff1� expð�Aref ln 10Þn2gFref f1� expð�A ln 10Þn2ref g

(1)

Luminescence lifetimes were measured on a PTI QuantaMasterspectrofluorimeter, using TimeMaster software with time-correlatedsingle photon mode coupled to a stroboscopic system. The excitationsource was a thyratron-gated flash lamp filled with nitrogen gas. Nofilter was used for the excitation. An interference filter centred at550 nm selected the emission wavelengths. The instrument responsefunction was determined by using a light-scattering solution(LUDOX). Differential scanning calorimetry (DSC) was performedon a Netzsch DSC 200 PC/1/M/H Phox instrument equipped with anintracooler, allowing measurements from �65 8C up to 450 8C. Thesamples were examined at a scanning rate of 10 K min�1 by applyingtwo heating cycles and one cooling cycle. The apparatus was calibratedwith indium (156.6 8C). Phase behavior was studied by polarized-lightoptical microscopy (POM) on a Leica DMLB microscope equippedwith a Linkam LTS350 hot-stage and a Linkam TMS94 centralprocessor.

OLED devices with pure Bodipy compounds were elaborated bysuccessively evaporating the organic compound and aluminum ontoITO-coated glass substrates (Visiontek Systems Ltd). MultilayerOLEDs of Bodipy compounds incorporated into an Alq3 matrix wereobtained by coevaporation ofAlq3 andBodipy from separate crucibles.The home-made evaporator used was located inside a nitrogen-filledglovebox comprising an oxygen and water-vapor elimination system(Jacomex). The materials were placed into silica crucibles andevaporated under a secondary vacuum (�10�5–10�4 Pa) by Jouleheating. Glass or ITO-coated glass substrates were placed �20 cmabove the evaporation sources. The deposition rates (typically 0.1 nms�1) and thicknesses were measured in situ with a quartz microbalance(InficonXTM/2). Due to the impossibility of simultaneously measuringthe Alq3 and Bodipy deposition rates, the Bodipy concentration in theAlq3 layer was measured after deposition by UV-visible spectroscopy.Prior to evaporation, the substrates were successively cleaned withacetone at 60 8C and ethanol, washed with deionized water and driedwith N2. N,N0-di-[(1-naphthyl)-N,N0-diphenyl]-1,10-biphenyl)-4,40-diamine (a-NPD, a hole-transporting material), tris(8-hydroxyquino-line)aluminium (Alq3, an electron-transporting and emitting material),2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP, a hole-blockinglayer) and poly(N-vinylcarbazole) (PVK) were purchased fromSigma-Aldrich and used as received. Unlike the other organicmaterials, PVK was dissolved in chloroform and deposited by spincoating. The HOMO-LUMO levels of Bodipy were characterized bycyclic voltammetry. The ITO work function was measured with aKelvin probe (McAllister Technical Services KP-6500). MultilayerOLEDs were fabricated by successively depositing the organicmaterials on ITO-coated glass substrates (Visiontek Systems Ltd),


constituting the transparent anode; an aluminium cathode was thendeposited, completing the structure. The electroluminescence intensityvariation versus voltage was measured with a silicon photodiode.Emission spectra and luminance were obtained respectively from aspectroradiometer (Minolta CS-1000) and a luminancemeter (MinoltaLS-110).

The X-ray-diffraction data were recorded from a single crystal ofdimensions 0.35� 0.35� 0.05 mm3, at ambient temperature on anEnraf-Nonius Kappa-CCD diffractometer, using graphite-mono-chromated Mo Ka radiation (l¼ 0.71073 A). Data reduction andcorrection for absorption were carried out using the HKL suite. 3609unique reflections were obtained from a total of 42 252 measuredreflections (Rint¼ 0.0732), in the range of h:�15 to 15; k:�21 to 22; andl: �10 to 10 with umax¼ 21.768. The structure was solved by Pattersonmethods and expanded to all non-hydrogen atoms by the Fouriermethod (PATTY) and refined by full-matrix least-squares on F2 valuesusing SHELX-L97 as implemented into CRYSTALBUILDER GUI.Convergence for 397 variable parameters by least-squares refinementon F2 with w¼ 1/[s2(F2

o)þ (0.0591P)2þ 1.5933P] where P¼(F2

o þ 2F2c)/3, for 2815 reflections with I> 2s (I) was reached at

R¼ 0.0524 and wR¼ 0.1302 with a goodness-of-fit of 1.062. The finaldifference Fourier map was featureless, with maximum positive andnegative peaks of 0.343 and �0.247 eA�3 respectively. CCDC-639641contains the supplementary crystallographic data for this paper. Thesedata can be obtained free of charge from the Cambridge Crystal-lographic Data Centre.

4.1. General Procedure for the Synthesis of

Compounds 3 to 10

Compound 2 and triethylamine (2 equiv.) were added to a

stirred solution of the benzoic acid chloride (1 equiv.) in

distilled CH2Cl2. The resulting mixture was stirred at room

temperature for 12 h, when total consumption of the starting

material was observed. The reaction mixture was then washed

with water, the organic layer dried over anhydrousMgSO4, and

the solvent evaporated. Purification was performed using a

chromatography column packed with silica gel, using CH2Cl2/

petroleum ether and CH2Cl2/MeOH as the eluents, and then

recrystallization from CH2Cl2/CH3CN, CH2Cl2/MeOH

or CH2Cl2/hexane.

Compound 3: The compound was prepared from 0.072 g of

3,4,5-tris-methoxy-benzoic acid (0.34 mmol), 3 mL of SOCl2,

0.0134 g of 2 (0.34 mmol), 0.09 mL of distilled triethylamine

(0.68 mmol) and 20 mL of distilled CH2Cl2 to give 0.181 g of 3

after crystallisation from CH2Cl2/hexane (90 %).1H NMR (300 MHz, CDCl3, d): 7.90 (s, 1H), 7.79 (dd, 2H,

3J¼ 8.5 Hz, 4J¼ 1.7 Hz), 7.29 (dd, 2H, 3J¼ 8.7 Hz, 4J¼ 1.9 Hz),

7.11 (s, 2H), 3.94 (s, 6H), 3.92 (s, 3H), 2.53 (s, 6H), 2.30 (q, 4H,3J¼ 7.5 Hz), 1.36 (s, 6H), 0.98 (t, 6H, 3J¼ 7.5Hz); 13CNMR (75

MHz, CDCl3, d): 165.7, 153.6, 141.6, 139.7, 138.7, 138.4, 133.0,

131.9, 131.1, 130.3, 129.3, 120.5, 104.7, 61.1, 56.6, 17.2, 14.8, 12.7,

12.1; 11B NMR (128 MHz, CDCl3, d): 3.87 (t, 1J¼ 32 Hz); IR

(KBr): n¼ 2960, 2932, 2870, 2839, 1675, 1648, 1583, 1539, 1497,

1474, 1413, 1399, 1373, 1363, 1334, 1318, 1295, 1273, 1235, 1184,

1124, 1072, 1045, 1007, 977 cm�1; UV-vis (CH2Cl2): l (e)¼525 (60 000), 492 (sh, 19 000), 367 (9400), 276 nm

(24 000M�1 cm�1); FABþ-MS (m/z (%)): 590.2 (100) [MþH]þ,

þ, 570.2 (15) [M-F]þ; Anal. calcd for C33H38BF2N3O4: C 67.24,

H 6.50; N 7.13; found: C 67.01, H 6.27, N 6.86.


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3,4,5-tris-octyloxy-benzoic acid (0.23 mmol), 3 mL of SOCl2,

0.090 g of 2 (0.23 mmol), 0.06 mL of distilled triethylamine

(0.46 mmol) and 20 mL of distilled CH2Cl2 to give 0.122 g of 4

after precipitation from CH2Cl2/CH3CN (61 %).1H NMR (400 MHz, CDCl3, d): 7.84 (s, 1H), 7.78 (dd, 2H,

3J¼ 8.3 Hz, 4J¼ 1.6 Hz), 7.28 (dd, 2H, 3J¼ 8.7 Hz, 4J¼ 2.1 Hz),

7.08 (s, 2H), 4.07–4.02 (m, 6H, OCH2), 2.53 (s, 6H), 2.31 (q, 4H,3J¼ 7.5 Hz), 1.90–1.72 (m, 6H, CH2), 1.53–1.44 (m, 6H, CH2),

1.41-1.20 (m, 30H, CH3þCH2), 0.99 (t, 6H, 3J¼ 7.4 Hz),

0.92-0.85 (m, 9H, CH3);13C NMR (75 MHz, CDCl3, d): 165.9,

153.9, 153.5, 142.0, 139.8, 138.8, 138.5, 133.0, 131.8, 131.1, 129.8,

129.3, 120.4, 106.1, 73.7, 69.7, 32.04, 32.0, 31.0, 30.5, 29.7, 29.53,

29.51, 29.4, 26.2, 22.84, 22.81, 17.2, 14.7, 14.2, 12.6, 12.1;11B NMR (128 MHz, CDCl3, d): 3.87 (t, 1J¼ 32 Hz); IR

(KBr): n¼ 2971, 2926, 2856, 1649, 1582, 1547, 1512, 1495, 1398,

1337, 1264, 1238, 1114, 1084, 983 cm�1; UV-vis (CH2Cl2): l(e)¼ 525 (73 000), 493 (sh, 24 000), 367 (12 000), 278 nm


864.2 (20) [M-F]þ; Anal. calcd for C54H80BF2N3O4: C 73.37, H

9.12, N 4.75; found: C 73.17, H 8.75, N 4.42.

Compound 5 : The compound was prepared from 0.128 g of

3,4,5-tris-dodecyloxy-benzoic acid (0.19 mmol), 3 mL of

SOCl2, 0.075 g of 2 (0.19 mmol), 0.05 mL of distilled triethyl-

amine (0.38 mmol) and 20 mL of distilled CH2Cl2 to give 0.109

g of 5 after precipitation from CH2Cl2/CH3CN (55 %).1H NMR (300 MHz, CDCl3, d): 7.82–7.76 (m, 3H), 7.28 (d,

2H, 3J¼ 8.7 Hz), 7.08 (s, 2H), 4.1–4.0 (m, 6H, OCH2), 2.53 (s,

6H), 2.31 (q, 4H, 3J¼ 7.5Hz), 1.88-1.72 (m, 6H, CH2), 1.51–1.27

(m, 60H, CH2þCH3), 0.98 (t, 6H, 3J¼ 7.5 Hz), 0.88 (m,

9H, CH3);13C NMR (75 MHz, CDCl3, d): 165.8, 157.9, 153.4,

141.9, 136.2, 132.9, 131.1, 129.3, 120.4, 113.7, 107.8, 106.0, 31.9,

29.74, 29.71, 29.6, 29.41, 29.37, 26.1, 22.7, 17.1, 14.8, 14.6, 14.1,

12.5, 11.9; 11B NMR (128 MHz, CDCl3, d): 3.86 (t,1J¼ 32 Hz);

IR (KBr): n¼ 2918, 2849, 1644, 1579, 1541, 1497, 1470, 1390,

1335, 1315, 1263, 1236, 1189, 1114, 1075, 976 cm�1; UV-vis

(CH2Cl2): l (e)¼ 525 (72 000), 492 (sh, 24 000), 370 (13 000),

278 nm (32 000 M�1 cm�1); FABþ-MS (m/z (%)): 1052.1

(100) [MþH]þ, 1032.1 (10) [M-F]þ; Anal. calcd for

C66H104BF2N3O4: C 75.33, H 9.96, N 3.99; found: C 75.18,

H 9.64, N 3.64.


3,4,5-tris-hexadecyloxy-benzoic acid (0.16 mmol), 3 mL of

SOCl2, 0.065 g of 2 (0.16 mmol), 0.05 mL of distilled

triethylamine (0.32 mmol) and 20 mL of distilled CH2Cl2to give 0.135 g of 6 after precipitation from CH2Cl2/

CH3CN (89%).1H NMR (300 MHz, CDCl3, d): 7.84–7.76 (m, 3H), 7.28 (d,

2H, 3J¼ 8.5 Hz), 7.08 (s, 2H), 4.1–4.0 (m, 6H, OCH2), 2.53 (s,

6H), 2.31 (q, 4H, 3J¼ 7.5 Hz), 1.88–1.71 (m, 6H, CH2),

1.49–1.26 (m, 84H, CH2þCH3), 0.99 (t, 6H, 3J¼ 7.5 Hz), 0.88

(m, 9H, CH3);13C NMR (75 MHz, CDCl3, d):¼ 165.9, 153.9,

153.5, 145.2, 143.2, 142.0, 139.7, 138.8, 138.4, 132.9, 131.8, 131.1,

129.8, 129.3, 120.3, 106.0, 73.7, 69.7, 32.1, 30.5, 29.9, 29.8, 29.7,


29.6, 29.5, 26.2, 22.8, 17.2, 14.8, 14.2, 12.7, 12.1; 11B NMR

(128 MHz, CDCl3, d): 3.87 (t, 1J¼ 32 Hz); IR (KBr): n¼ 3285,

2951, 2916, 2849, 1673, 1648, 1584, 1540, 1524, 1497, 1467, 1423,

1403, 1383, 1337, 1313, 1276, 1264, 1179, 1158, 1115, 1082, 1057,

969 cm�1; UV-vis (CH2Cl2): l (e)¼ 525 (77 000), 493

(sh, 30 000), 362 (20 000), 276 nm (40 000 M�1 cm�1);

FABþ-MS (m/z (%)): 1220.2 (100) [MþH]þ, 1200.1 (25)

[M-F]þ; Anal. calcd for C78H128BF2N3O4: C 76.75, H 10.57, N

3.44; found: C 76.39, H 10.27, N 3.21.

Compound 7: This compound was prepared from 0.146 g of

3,4,5-tris-(3,7,11,15-tetramethyl-hexadecyloxy)-benzoic acid

(0.14 mmol), 3 mL of SOCl2, 0.057 g of 2 (0.14 mmol),

0.04 mL of distilled triethylamine (0.28 mmol) and 20 mL of

distilled CH2Cl2 to give 0.102 g of 7 after precipitation

from CH2Cl2/CH3CN (51%).1H NMR (300 MHz, CDCl3, d): 7.84 (s, br, 1H), 7.78 (d, 2H,

3J¼ 8.7 Hz), 7.28 (d, 2H, 3J¼ 8.4 Hz), 7.1 (s, 2H), 4.12–4.03 (m,

6H,OCH2), 2.53 (s, 6H), 2.31 (q, 4H, 3J¼ 7.5 Hz), 1.93–0.83 (m,

129H); 13C NMR (75 MHz, CDCl3, d): 165.9, 153.9, 153.5,

142.0, 139.8, 138.8, 138.4, 133.0, 131.8, 131.1, 129.8, 129.3, 120.4,

106.0, 72.0, 68.1, 39.5, 37.7, 37.63, 37.59, 37.5, 37.4, 36.6, 36.5,

32.96, 30.07, 29.9, 28.1, 24.9, 24.6, 22.9, 22.8, 19.9, 19.83, 19.78,

19.7, 17.2, 14.7, 12.6, 12.1; IR (KBr): n¼ 2954, 2925, 2868, 1651,

1582, 1543, 1498, 1476, 1426, 1399, 1374, 1337, 1318,

1272, 1236, 1196, 1113, 1080, 1050, 982 cm�1; UV-vis

(CH2Cl2) l (e)¼ 525 (95 000), 492 (sh, 35 000), 363 (23 000),

276 nm (50 000 M�1 cm�1); FABþ-MS (m/z (%)): 1388.2

(100) [MþH]þ, 1368.2 (50) [M-F]þ; Anal. calcd for

C90H152BF2N3O4: C 77.82, H 11.03, N 3.03; found: C 77.44,

H 10.64, N 2.67.


3,4,5-tris-(3,7-dimethyl-octyloxy)-benzoic acid (0.17 mmol),

3 mL of SOCl2, 0.067 g of 2 (0.17 mmol), 0.05 mL of distilled

triethylamine (0.34 mmol) and 20 mL of distilled CH2Cl2 to

give 0.106 g of 8 after precipitation from CH2Cl2/CH3CN

(63 %).1H NMR (300 MHz, CDCl3, d): 7.85 (s, br, 1H), 7.78 (d, 2H,

3J¼ 8.5 Hz), 7.28 (d, 2H, 3J¼ 8.5 Hz), 7.09 (s, 2H), 4.15–4.0

(m, 6H, OCH2), 2.53 (s, 6H), 2.31 (q, 4H, 3J¼ 7.5 Hz), 2.0–1.47

(m, 12H, CHþCH2), 1.36–1.15 (m, 24H, CH2þCH3), 1.02–0.86

(m, 33H, CH3);13C NMR (75 MHz, CDCl3, d): 165.9, 153.9,

153.5, 142.0, 139.8, 138.8, 138.4, 133.0, 131.8, 131.1, 129.8, 129.3,

120.4, 106.0, 72.0, 68.0, 39.5, 39.4, 37.7, 37.5, 36.5, 30.0, 29.8,

28.1, 24.9, 22.85, 22.76, 22.7, 19.7, 17.2, 14.7, 14.2, 12.6, 12.1; IR

(KBr): n¼ 3288, 2990, 2922, 3695, 1650, 1579, 1539, 1519, 1493,

1473, 1462, 1423, 1392, 1364, 1335, 1315, 1274, 1261, 1232, 1194,

1109, 1075, 1044, 980 cm�1; UV-vis (CH2Cl2): l (e)¼525 (100 000), 490 (sh, 33 000), 364 (20 000), 278 nm


þ, 948.0 (15) [M-F]þ; Anal. calcd for C60H92BF2N3O4: C 74.43,

H 9.58, N 4.34; found: C 74.20, H 9.35, N 4.53.

Received: June 28, 2007

Revised: September 12, 2007


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412

L. Bonardi et al. / E

[1] a) U. Mitschke, P. Bauerle, J. Mater. Chem. 2000, 10, 1471. b) A. P.

Kulkarni, C. J. Tonzola, A. Babel, S. A. Jenekhe, Chem. Mater. 2004,

16, 4556.

[2] Special Issue on Organic Electronics and Optoelectronics (Eds: S. R.

Forrest, M. E. Thompson, Chem. Rev. 2007, 107, pp. 923–1386.

[3] a)M. Hissler, A. El-ghayoury, A. Harriman, R. Ziessel,Angew. Chem.

Int. Ed. 1998, 37, 1717. b) M. Hissler, A. Harriman, P. Jost, G. Wipff,

R. Ziessel, Angew. Chem. Int. Ed. 1998, 37, 3249. c) A. Harriman,

M. Hissler, P. Jost, G. Wipff, R. Ziessel, J. Am. Chem. Soc. 1999, 121,

14. d) H.Miyaji, W. Sato, J. L. Sessler,Angew. Chem. Int. Ed. 2000, 39,

1777. e) P. Anzenbacher, Jr., K. Jursikova, J. L. Sessler, J. Am. Chem.

Soc. 2000, 122, 9350. f) P. Zhang, T. Beck, W. Tan, Angew. Chem. Int.

Ed. 2001, 40, 402. g) T. D. James, S. Shinkai, Top. Curr. Chem. 2002,

218, 159. h) L. Charbonniere, R. Ziessel, M. Montalti, L. Prodi, N.

Zaccheroni, C. Boehme, G. Wipff, J. Am. Chem. Soc. 2002, 124, 7779.

i) F. Sancenon, R. Martinez-Manez, J. Soto, Angew. Chem. Int. Ed.

2002, 41, 1416.

[4] A. Hepp, H. Heil, W.Weise, M. Ahles, R. Schmechel, H. von Seggern,

Phys. Rev. Lett, 2003, 91, 157406.

[5] a) B. Prasad, P. K. Mishra, Indian J. Pure Appl. Phys. 1994, 32, 328.

b) M. Shengwei, A. Dongge, Semicond. Sci. Technol. 2005, 20, 1213.

[6] M. Muccini, M. Murgia, F. Biscarini, C. Taliani, Adv. Mater. 2001, 13,

355.

[7] The literature survey being too large we refer to this excellent review:

L. Akcelrud, Prog. Polym. Sci. 2003, 28, 875.

[8] a) S.-C. Chan, M. C. W. Chan, Y. Wang, C.-M. Che, K.-K. Cheung, N.

Zhu, Chem. Eur. J. 2001, 7, 4180. b) W. Lu, B.-X. Mi, M. C. W. Chan,

Z. Hui, C.-M. Che, N. Zhu, S.-T. Lee, J. Am. Chem. Soc. 2004, 126,

4958. c) W. Lu, M. C. W. Chan, N. Zhu, C.-M. Che, C. Li, Z. Hui,

J. Am. Chem. Soc. 2004, 126, 7639.

[9] J.-J. Shen, X.-L. Yang, T.-H. Huang, J. T. Lin, T.-H. Ke, L.-Y. Chen,

C.-C. Wu, M.-C. P. Yeh, Adv. Funct. Mater. 2007, 17, 983.

[10] Q.-D. Liu, J. Lu, J. Ding, M. Day, Y. Tao, P. Barrios, J. Stupak, K. C. J.

Li, Y. Chi, Adv. Funct. Mater. 2007, 17, 1028.

[11] R. P. Haugland, The Handbook: A Guide to Fluorescent Probes and

Labelling Technologies, 10th Ed., Invitrogen Molecular Probes Inc.,

2005.

[12] a) K. Yamada, T. Toyota, K. Takakura, M. Ishimaru, T. Sugawara,

New J. Chem. 2001, 25, 667. b) R. Reents, M.Wagner, J. Kuhlmann, H.

Waldmann, Angew. Chem. Int. Ed. 2004, 43, 2711.

[13] a) N. R. Cha, S. Y. Moon, S.-K. Chang, Tet. Lett. 2003, 44, 8265. (b) N.

Basaric, M. Baruah, W. Qin, B. Metten, M. Smet, W. Dehaen, N.

Boens, Org. Biomol. Chem. 2005, 3, 2755. (c) H. J. Kim, J. S. Kim,

Tetrahedron Lett. 2006, 47, 7051.

[14] a) Y. Gabe, Y. Urano, K. Kikuchi, H. Kojima, T. Nagano, J. Am.

Chem. Soc. 2004, 126, 3357. (b) T. Ueno, Y. Urano, H. Kojima, T.

Nagano, J. Am. Chem. Soc. 2006, 128, 10640.

[15] T. Gareis, C. Huber, O. S. Wolfbeis, J. Daub, Chem. Commun. 1997,

1717.

[16] M. Kollmannsberger, K. Rurack, U. Resch-Genger, J. Daub, J. Phys.

Chem. A 1998, 102, 10211.

[17] a) K. Rurack, M. Kollmannsberger, U. Resch-Genger, J. Daub, J. Am.

Chem. Soc. 2000, 122, 968. b) S. Y. Moon, N. R. Cha, Y. H. Kim, S.-K.

Chang, J. Org. Chem. 2004, 69, 181.

[18] a) R. P. Haugland, H. C. Kang, US 4, 774, 339, 1998. b) L. H. Thoresen,

H. Kim, M. B. Welch, A. Burghart, K. Burgess, Synlett 1998,

1276.

[19] C. Goze, G. Ulrich, L. Charbonniere, R. Ziessel,Chem. Eur. J. 2003, 9,

3748.

[20] W. Qin, M. Baruah, M. van der Auweraer, F. C. DeSchryver, N.

Boens, J. Phys. Chem. A 2005, 109, 7371.

[21] G. Ulrich, C. Goze, M. Guardigli, A. Roda, R. Ziessel, Angew. Chem.

Int. Ed. 2005, 44, 3694.


[22] a) R.W.Wagner, J. S. Lindsey, Pure Appl. Chem. 1996, 68, 1373. b) G.

Beer, K. Rurack, J. Daub, Chem. Commun. 2001, 1138. c) G. Beer, C.

Niederalt, S. Grimme, J. Daub, Angew. Chem. Int. Ed. 2000, 39,

3252. d) M. Kollmannsberger, K. Rurack, U. Resch-Genger, W.

Rettig, J. Daub, Chem. Phys. Lett. 2000, 329, 363. e) Y. Gabe, Y.

Urano, K. Kikuchi, H. Kojima, T. Nagano, J. Am. Chem. Soc. 2004,

126, 3357.

[23] T. A. Golovkova, D. V. Kozlov, D. C. Neckers, J. Org. Chem. 2005, 70,

5545.

[24] a) M. Kollmannsberger, T. Gareis, S. Heinl, J. Breu, J. Daub, Angew.

Chem. Int. Ed. 1997, 36, 1333. b) R. Y. Lai, A. J. Bard, J. Phys. Chem. B

2003, 107, 5036. c) C. Trieflinger, H. Rohr, K. Rurack, J. Daub,Angew.

Chem. Int. Ed. 2005, 44, 6943.

[25] a) J. M. Brom, Jr., J. L. Langer, J. Alloys Compd 2002, 338, 112. b) A.

Hepp, G. Ulrich, R. Schmechel, H. von Seggern, R. Ziessel, Synth.

Met. 2004, 146, 11.

[26] a) T. Chen, J. H. Boyer, M. L. Trudell,Heteroat. Chem. 1997, 8, 51. b)

G. Sathyamoorthi, L. T. Wolford, A. M. Haag, J. H. Boyer, Heteroat.

Chem. 1994, 5, 245.

[27] S. Hattori, K. Ohkubo, Y. Urano, H. Sunahara, T. Nagano, Y. Wada,

N. V. Tkchanko, H. Lemmetyinen, S. Fukuzumi, J. Phys. Chem. B

2005, 109, 15368.

[28] C. McCusker, J. B. Carroll, V. M. Rotello, Chem. Commun. 2005, 996.

[29] M. P. Debreczeny, W. A. Svec, M. R. Wasielewski, Science 1996, 274,

584.

[30] P. G. Van Patten, A. P. Sheve, J. S. Lindsey, R. J. Donohoe, J. Phys.

Chem. B 1998, 102, 4209.

[31] a) F. Li, S. I. Yang, Y. Ciringh, J. Seth, C. H. Martin III, D. L. Singh,

D. Kim, R. R. Birge, D. F. Bocian, D. Holten, J. S. Lindsey, J. Am.

Chem. Soc. 1998, 120, 10001. b) R. K. Lammi, R. W. Wagner, A.

Ambroise, J. R. Diers, D. F. Bocian, D. Holten, J. S. Lindsey, J. Phys.

Chem. B 2001, 105, 5341.

[32] a) R. W. Wagner, J. S. Lindey, J. Am. Chem. Soc. 1994, 116, 9759.

b) R. W. Wagner, J. S. Lindsey, J. Seth, V. Palaniappan, D. F. Bocian,

J. Am. Chem. Soc. 1996, 118, 3996. c) R.W.Wagner, J. S. Lindsey,Pure

Appl. Chem. 1996, 68, 1373.

[33] M. D. Yilmaz, O. A. Bozdemir, E. U. Akkaya, Org. Lett. 2006, 8,

2871.

[34] H. Imahori, H. Norieda, H. Yamada, Y. Nishimura, I. Yamazaki,

Y. Sakata, S. Fukuzumi, J. Am. Chem. Soc. 2001, 123, 100.

[35] F. D’Souza, P. M. Smith, M. E. Zandler, A. L. McCarty, M. Itou,

Y. Araki, O. Ito, J. Am. Chem. Soc. 2004, 126, 7898.

[36] a) B. Turfan, E. U. Akkaya, Org. Lett. 2002, 4, 2857. b) J. Wang,

X. Qian, Org. Lett. 2006, 8, 3721.

[37] a) L. Zeng, E. W. Miller, A. Pralle, E. Y. Isacoff, C. J. Chang, J. Am.

Chem. Soc. 2006, 128, 10. b) X. Qi, E. Jin Jun, L. Xu, S.-J. Kim, J. S. J.

Hong, Y. J. Yoon, J. Yoon, J. Org. Chem. 2006, 71, 2881.

[38] F. Camerel, L. Bonardi, M. Schmutz, R. Ziessel, J. Am. Chem. Soc.

2006, 128, 4548.

[39] F. Camerel, L. Bonardi, G. Ulrich, L. Charbonniere, B. Donnio, C.

Bourgogne, D. Guillon, P. Retailleau, R. Ziessel, Chem. Mater. 2006,

18, 5009.

[40] F. Camerel, G. Ulrich, J. Barbera, R. Ziessel, Chem. Eur. J. 2007, 13,

2189.

[41] H. Zhang, C. Huo, K. Ye, P. Zhang, W. Tian, Y. Wang, Inorg. Chem.

2006, 45, 2788.

[42] S. Laschat, A. Baro, N. Steinke, F. Giesselmann, C. Hagele, G. Scalia,

R. Judele, E. Kapatsina, S. Sauer, A. Schreivogel, M. Tosoni, Angew.

Chem. Int. Ed. 2007, 46, 4832.

[43] R. Ziessel, L. Bonardi, P. Retailleau, G. Ulrich, J. Org. Chem. 2006, 71,

3093.

[44] V. A. Azov, F. Diederich, Y. Lill, B. Hecht,Helv. Chim. Acta 2003, 86,

2149.

[45] F. Camerel, G. Ulrich, R. Ziessel, Org. Lett. 2004, 6, 4171.


FULLPAPER


[46] a) C.-W.Wan, A. Burghart, J. Chen, F. Bergstrom, L. B.-A. Johanson,

M. F. Wolford, T. G. Kim, M. R. Topp, R. M. Hochstrasser, K.

Burgess, Chem. Eur. J. 2003, 9, 4430. b) Z. Shen, H. Rohr, K. Rurack,

H. Uno, M. Spieles, B. Schulz, G. Reck, N. Ono, Chem. Eur. J. 2004,

10, 4853.

[47] a) T. Kato, T. Kutsuna, K. Hanabusa, M. Ukon, Adv. Mater. 1998, 10,

606. b) K. Hanabusa, C. Koto,M. Kimura, H. Shirai, A. Kakehi,Chem.

Lett. 1997, 429.

[48] R. M. Silverstein, G. C. Bassler, T. C. Morrill, Spectrometric Identi-

fication of Organic Compounds, 3rd ed., Wiley, New York 1976.

[49] a) A. Burghart, H. Kim, M. B. Wech, L. H. Thorensen, J. Reibenspies,

K. Burgess, J. Org. Chem. 1999, 64, 7813. b) H. Kim, A. Burghart,

M. B. Welch, J. Reibenspies, K. Burgess, Chem. Commun. 1999,

1889. c) J. Chen, J. Reibenspies, A. Derecskei-Kovacs, K. Burgess,

Chem. Commun. 1999, 2501. d) K. Rurack, M. Kollmannsberger, J.

Daub,New J. Chem. 2001, 25, 289. e) K. Rurack, M. Kollmannsberger,

J. Daub, Angew. Chem. Int. Ed. 2001, 40, 385.

[50] J. Karolin, L. B.-A. Johansson, L. Strandberg, T. Ny, J. Am. Chem.

Soc. 1994, 116, 7801.


[51] a)M.K.DeArmond, C.M. Carlin,Coord. Chem. Rev. 1981, 36, 325. b)

M. Klessinger, J. Michl, Excited States and Photochemistry of Organic

Molecules, VCH, Weinheim, Germany 1994.

[52] J. Olmsted, J. Phys. Chem. 1979, 83, 2581.

[53] G. Ulrich, R. Ziessel, J. Org. Chem. 2004, 69, 2070.

[54] F.Wurthner, C. Thalacker, S. Diele, C. Tschierske,Chem. Eur. J. 2001,

7, 2245.

[55] E. H. A. Beckers, S. C. J. Meskers, A. P. H. J. Schenning, Z. Chen,

F. Wurthner, R. A. J. Janssen, J. Phys. Chem. A 2004, 108, 6933.

[56] Y. Hamada, IEEE Trans. Electron. Devices 1997, 44, 1208.

[57] J. Pommerehne, H. Vestweber, W. Guss, R. Mahrt, H. Bassler, M.

Porsch, J. Daub, Adv. Mater. 1995, 7, 551.

[58] A. Bard, R. Faulkner, Electrochemical Methods-Fundamentals and

Applications, Wiley, New York 1980, Ch. 14, pp 634.

[59] J. Kido, K. Hongawa, K. Okuyama, K. Nagai, Appl. Phys. Lett. 1993,

63, 2627.

[60] P. Toele, H. Zhang, C. Trieflinger, J. Daub, M. Glasbeek, Chem. Phys.

Lett. 2003, 368, 66.

[61] C. Goze, G. Ulrich, R. Ziessel, J. Org. Chem. 2007, 72, 313.


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