Control of the aggregation of a phenylenevinylenediimide chromophore by use of supramolecular chemistry: Enhanced electroluminescence in supramolecular organic devices

Article abstract of DOI:10.1021/cm101343j

A new approach toward the tuning of the supramolecular organization of π-conjugated substructures containing imide functional groups has been investigated using the concept of supramolecular chemistry. This approach, which allows enhanced emission properties of the active material, was evaluated in the fabrication of optoelectronic devices. A linear ditopic chromophore H-ImPV was synthesized. This N-H imide constitutes a recognizing unit with an acceptor-donor-acceptor (ADA) hydrogen bond motif. End-capping of this new chromophore with a monotopic structuring unit allowed control of the supramolecular aggregation of the π-conjugated chromophore. The studies of the absorption and emission properties of the H-ImPV, in solution or in the solid state (thin films, powders), clearly revealed different aggregation behaviors, depending on the presence of the monotopic structuring unit: hindered unit (Cy-DAT) led to the formation of J-aggregates. In all cases, evidence for the heteromolecular association H-ImPV...Cy-DAT was obtained from an infrared absorption band located at 2715 cm^-1, which was typical of the hydrogen bonding present in the ADA...DAD triplet. This has been illustrated by the fabrication of light-emitting devices based on films of H-ImPV and [H-ImPV.(Cy-DAT)₂]. H-ImPV presents a poor ability to emit light, because of its aggregation, which induces quenching of luminescence. The high efficiencies exhibited by the devices based on a single layer of [H-ImPV.(Cy-DAT)₂] are the result of the J-aggregation of chromophores, because of the bulky cyclohexyl fragments of the Cy-DAT. Tuning of the supramolecular organization of the H-ImPV by the addition of two equivalents of Cy-DAT in the active layer allowed recovery of the performances exhibited by the organic light-emitting devices (OLEDs) of the isolated chromophore. Therefore, the use of Cy-DAT is an interesting alternative to avoid aggregation and to significantly increase luminance. As a consequence, the luminous efficiencies of the devices are much better for the coassembled active layer.

Full text of DOI:10.1021/cm101343j

5258 Chem. Mater. 2010, 22, 5258–5270
DOI:10.1021/cm101343j
Control of the Aggregation of a Phenylenevinylenediimide Chromophore
by Use of Supramolecular Chemistry: Enhanced Electroluminescence in
Supramolecular Organic Devices
Nicolas Delbosc,† Mathias Reynes,† Olivier J. Dautel,*,† Guillaume Wantz,‡
†
Jean-Pierre Lere-Porte, and Joel J. E. Moreau*
,†
ꢀ
€
†
ꢁ
Architecture Moleculaire et Materiaux Nanostructures, Instituts Charles Gerhardt Montpellier, Umr Cnrs
5253, Ecole Nationale Superieure de Chimie de Montpellier, 8 rue de l’Ecole Normale 34296 Montpellier
ꢁ
ꢁ
ꢁ
‡
ꢁ
Cedex 05, France, and Laboratory IMS, Umr Cnrs 5218, Ecole Nationale Superieure de Chimie et de
Physique de Bordeaux, 16 Av. Pey Berland, 33607 Pessac Cedex, France
Received May 12, 2010. Revised Manuscript Received July 13, 2010
A new approach toward the tuning of the supramolecular organization of π-conjugated sub-
structures containing imide functional groups has been investigated using the concept of supra-
molecular chemistry. This approach, which allows enhanced emission properties of the active material,
was evaluated in the fabrication of optoelectronic devices. A linear ditopic chromophore H-ImPV
was synthesized. This N-H imide constitutes a recognizing unit with an acceptor-donor-acceptor
(ADA) hydrogen bond motif. End-capping of this new chromophore with a monotopic structuring
unit allowed control of the supramolecular aggregation of the π-conjugated chromophore. The
studies of the absorption and emission properties of the H-ImPV, in solution or in the solid state (thin
films, powders), clearly revealed different aggregation behaviors, depending on the presence of the
monotopic structuring unit: hindered unit (Cy-DAT) led to the formation of J-aggregates. In all
cases, evidence for the heteromolecular association H-ImPV
Cy-DAT was obtained from an
3 3 3
infrared absorption band located at 2715 cm-1, which was typical of the hydrogen bonding present in
the ADA DAD triplet. This has been illustrated by the fabrication of light-emitting devices based
3 3 3
on films of H-ImPV and [H-ImPV.(Cy-DAT)2]. H-ImPV presents a poor ability to emit light, because
of its aggregation, which induces quenching of luminescence. The high efficiencies exhibited by the
devices based on a single layer of [H-ImPV.(Cy-DAT)2] are the result of the J-aggregation of
chromophores, because of the bulky cyclohexyl fragments of the Cy-DAT. Tuning of the supra-
molecular organization of the H-ImPV by the addition of two equivalents of Cy-DAT in the active layer
allowed recovery of the performances exhibited by the organic light-emitting devices (OLEDs) of the
isolated chromophore. Therefore, the use of Cy-DAT is an interesting alternative to avoid aggrega-
tion and to significantly increase luminance. As a consequence, the luminous efficiencies of the
devices are much better for the coassembled active layer.
Introduction
encountered phenomenon in dye chemistry, because of
strong intermolecular van der Waals-like attractive forces
between molecules. The aggregates in the solid state exhi-
bit distinct changes in the absorption band, compared to
the monomeric species.4 Thus, the aggregation pattern of
π-conjugated oligomers will determine the device perfor-
mance and/or goal, i.e., OLED or solar cells. In other
words, it should be possible, using the same electroactive
molecule, to tune its optoelectronic properties by simply
playing on the modulation of its aggregation.
The tendency of molecules to aggregate and the nature
of the supramolecular arrangement depend on the struc-
ture of the chromophore and also on its environment.
However, the rational control of a dye aggregation is still
difficult, because molecules tend to spontaneously align
themselves into a one-dimensional infinite aggregate in a
The detailed understanding of the supramolecular inter-
actions between the individual π-conjugated molecules
has become a challenging scientific research area.1 Recent
strategies based on self-assembly and supramolecular
chemistry are interesting alternatives for the bottom-up
design of organic devices.2,3 Controlled aggregation of
π-conjugated systems offers interesting electronic and
photonic functional materials that are different from their
monomeric state. The self-association of chromophores
in the solid or at the solid/liquid interface is a frequently
*Author to whom correspondence should be addressed. E-mail addresses:
joel.moreau@enscm.fr (J.J.E.M.), olivier.dautel@enscm.fr (O.J.D.).
(1) (a) Klaerner, G.; Mueller, M.; Morgenroth, F.; Wehmeier, M.;
Soczka-Guth, T.; Muellen, K. Synth. Met. 1997, 84, 297.
(b) Salzner, U. Curr. Org. Chem. 2004, 8, 569.
(2) Hoeben, F. J. M.; Jonkheijm, P.; Meijer, E. W.; Schenning, A. P. H.
J. Chem. Rev. 2005, 105, 1491.
(3) Huang, C. H.; McClenaghan, N. D.; Kuhn, A.; Hofstraat, J. W.;
Bassani, D. M. Org. Lett. 2005, 7, 3409.
(4) Mishra, A.; Behera, R. K.; Behera, P. K.; Mishra, B. K.; Behera,
G. B. Chem. Rev. 2000, 100, 1973.
r
pubs.acs.org/cm
Published on Web 08/17/2010
2010 American Chemical Society

Article
Chem. Mater., Vol. 22, No. 18, 2010 5259
Scheme 1. Cyclohexyle and Propyltriethoxysilyle End-Capped Bisimide Phenylenevinylene (Cy-ImPV and (EtO)3Si-ImPV)
face-to-face manner by means of π-stacking and/or van
der Waals interactions. The development of a method to
control their aggregation behavior and orientations is a
challenge.
As a result, we developed a new family of oligo-
phenylenevinylene derivatives incorporating a conju-
gated imide phenylene vinylene (ImPV) substructure
(Cy-ImPV and (EtO)3Si-ImPV; see Scheme 1).
electronics”, as defined by Meijer and Schenning.7-9 The
term “supramolecular electronics” refers to the formation
of semiconducting networks of single or multicompo-
nents, using the concept of supramolecular chemistry.
The ImPV moiety represents an interesting building block
to develop a new approach for controlling the supra-
molecular organization, using hydrogen bonding. Indeed,
the presence of an imide function in H-ImPV gives, to this
chromophore, the ability to act as both an hydrogen-bond
donor and acceptor (see Scheme 2). In that case, N-H
imides constitute a recognizing unit with the acceptor-
donor-acceptor (ADA) hydrogen-bond sequence. As
the complementary counterpart of this ADA sequence,
a donor-acceptor-donor (DAD) unit is required. DAD
subsequences are easily found in 2,4-diamino-1,3,5-
triazine moiety (DAT). Therefore, the end-capping of the
H-ImPV with DAT derivatives can bring different steric
effects and should allow the control of its supramolecular
aggregation. Here, we report the tuning of the aggrega-
tion properties of the H-ImPV, based on self-recognition
with complementary units with different steric hindrance
properties. Two derivatives of 2,4-diamino-1,3,5-triazine
were selected: (i) the 6-cyclohexyl derivative Cy-DAT,
which has a nonplanar aliphatic ring with a chair con-
formation, and (ii) the 6-phenyl planar derivative Ph-
DAT,10 which is of similar size to Cy-DAT but a different
shape. Because of the different steric properties, J- or H-
aggregation might be observed for Cy-DAT and Ph-DAT,
respectively.
The imide functions are thermally and chemically
stable. Their electron affinity confers to the entire mole-
cule the electron injection properties that are lacking to
the phenylenevinylene moiety. The study of the relation-
ship between the supramolecular organization of this
novel bis-imido-phenylene vinylene (Cy-ImPV) and its
optoelectronic properties revealed that the good efficien-
cies exhibited by the devices based on a layer of Cy-ImPV
were the result of the J-aggregation of chromophores in
the material. It arose from the presence of bulky cyclo-
hexyl fragments, which prevent card packing of the
π-conjugated units.5 Modifications of the aggregation
state can allow a tuning of the optical properties. (Since
the supramolecular organization of Cy-ImPV was the
result of combined steric effects with π-stacking and van
der Waals interactions, the only way to control it resides
in the chemical modification of ImPV. This could be
envisaged via the imide function. Indeed, any amine could
be condensed to the 4-bromophthalic anhydride to fur-
nish the reactive halogenated imide.) In a first approach,
we explored the incorporation of the ImPV substructure
in organosilica matrices, using the triethoxysilane func-
tion (Si(OEt)3) (see Scheme 1: (EtO)3Si-ImPV) as a modi-
fiable bulky fragment.6 After sol-gel hydrolysis, a change
in the aggregation of the chromophore is observed, from
J-aggregation to H-aggregation. The resulting material
exhibited no more fluorescence but higher photoconduc-
tivity. However, chemical modification of the ImPV sub-
structure is required to tune the molecular organization
and control the properties for future applications.
Sol-gel processing may lead to the same problems arising
from the exposure of the devices to HCl vapors or from a
premature hydrolysis/polycondensation of the sol con-
taining the sol-gel precursor and a catalyst (Hþ, OH-, F-).
We thought that a more interesting approach would
result from the use of the concept of “supramolecular
Results and Discussion
Synthesis. Linear ditopic chromophore H-ImPV was
prepared in two steps, starting from 4-bromophthalic
anhydride (1)11 (see Scheme 3). Imidification of 1 in melt
urea afforded 4-bromophthalimide (2). Finally, 2 readily
underwent a coupling reaction with 1,4-divinyl-2,5-
bis(octyloxy)benzene in the presence of a palladium
catalyst to obtain the ditopic chromophore H-ImPV.
(7) Meijer, E. W.; Schenning, A. P. H. J. Nature 2002, 419, 353.
(8) (a) Schenning, A. P. H. J.; Meijer, E. W. Chem. Commun. 2005,
3245. (b) Hoeben, F. J. M.; Jonkheijm, P.; Meijer, E. W.; Schenning,
A. P. H. J. Chem. Rev. 2005, 105, 1491.
ꢀ
(9) (a) Dautel, O. J.; Robitzer, M.; Lere-Porte, J.-P.; Serein-Spirau, F.;
Moreau, J. J. E. J. Am. Chem. Soc. 2006, 128, 16213. (b) Dautel,
O. J.; Robitzer, M.; Flores, J.-C.; Tondelier, D.; Serein-Spirau, F.;
ꢀ
ꢁ
Lere-Porte, J.-P.; Guerin, D.; Lenfant, S.; Tillard, M.; Vuillaume,
D.; Moreau, J. J. E. Chem.;Eur. J. 2008, 14, 4201.
(5) Wantz, G.; Hirsch, L.; Vignau, L.; Parneix, J.-P.; Dautel, O. J.;
ꢀ
(10) Diaz-Ortiz, A.; Elguero, J.; Foces-Foces, C.; de la Hoz, A.;
Moreno, A.; del Carmen Mateo, M.; Sanchez-Migallon, A.;
Valiente, G. New J. Chem. 2004, 28, 952–958.
Serein-Spirau, F.; Lere-Porte, J.-P.; Moreau, J. J. E.; Almairac, R.
Org. Electron. 2005, 7, 38.
(6) Dautel, O. J.; Wantz, G.; Almairac, R.; Flot, D.; Hirsch, L.; Lere-
ꢀ
Porte, J.-P.; Parneix, J. P.; Serein-Spirau, F.; Vignau, L.; Moreau,
ꢀ
(11) Dautel, O. J.; Wantz, G.; Flot, D.; Lere-Porte, J.-P.; Moreau,
J. J. E.; Parneix, J.-P.; Serein-Spirau, F.; Vignau, L. J. Mater.
Chem. 2005, 15, 4446.
J. J. E. J. Am. Chem. Soc. 2006, 128, 4892.

5260 Chem. Mater., Vol. 22, No. 18, 2010
Delbosc et al.
Scheme 2. Molecular Model of (a) H-ImPV, (b) Supramolecule of H-ImPV End-Capped with Cy-DAT, and (c) Supramolecule of
H-ImPV End-Capped with Ph-DAT and Expected Aggregation Type in the Solid State
The Heck reaction was conducted in dry N,N-dimethyl-
formamide at 90 °C in the presence of Pd(OAc)2 and
P(o-C6H4Me)3.
Monotopic structuring modules Cy-DAT and Ph-DAT
were synthesized from commercially available related cyano
derivatives.12 Cyclohexylcarbonitrile and benzonitrile react

Article
Chem. Mater., Vol. 22, No. 18, 2010 5261
Scheme 3. Steps for the Preparation of H-ImPV: (a) Urea, 160 °C, 2 h; (b) 1,4-Divinyl-2,5-bis(octyloxy)benzene, Pd(OAc)2,
P(o-C6H4Me)3, NEt3, DMF, 90 °C, 10 h
Chart 1. Structures of the Monotopic Structuring Modules,
Cy-Dat, Ph-Dat, and Cy-DATHex4
self-association constants. Based on those constants, the
formation of heterotrimers such as [H-ImPV.(Cy-DAT)2]
and [H-ImPV.(Ph-DAT)2] must be favored in nonpolar
solvents.
H-ImPV exhibits intense absorption bands in the UV
region (λabs-max = 430 nm) and is a strong luminophores
(λem-max = 510 nm) in polar solvents avoiding hydrogen
bonds such as tetrahydrofuran (THF) with a fluore-
scence quantum yield of 46% using perylene as standard
(Figure 1). The addition of 2 equiv of a monotopic struc-
turing module (Cy-DAT or Ph-DAT) to a THF solution
of H-ImPV (3 ꢀ 10-5 mol L-1) exhibited no spectral
changes, confirming that those monotopic modules have
no influence on the optoelectronic properties of the di-
topic chromophore. They will only play a role of structure
directing agent without any electronic interaction with
H-ImPV, such as charge transfer.
with dicyandiamide, under basic conditions at 150 °C, to
afford phenyl-diaminotriazine (Ph-DAT) and cyclohexyl-
diaminotriazine (Cy-DAT), respectively, in high yields.
(Chart 1 shows their chemical structures.) Reference com-
pound Cy-DATHex4, which displays a structure similar
to that of Cy-DAT but is incapable of establishing
H-bond donating interactions, was obtained upon alkyl-
ation of the amine functions of Cy-DAT with an excess
(5 equiv) of 1-bromohexane in the presence of 5 equiv of
potassium tert-butoxide.
The absorption and fluorescence bands of H-ImPV
in nonpolar solvents such as toluene or tetrachloro-
ethylene (TCE) (5.9 ꢀ 10-5 M) exhibit fully reversible
temperature-dependent profiles in the range of 25-
60 °C (see Figure 2). The lower energy absorption band
at 502 nm (not observed in THF) points to the presence
of π-π stacking interactions, most likely promoted by
preliminary double H-bonds between ditopic chomo-
phores.15,16 Parallel to the changes in the absorption
spectra, substantial variations of the fluorescence pro-
files occur when going from a polar solvent to the
nonpolar solvent. The strong green fluorescence signal
observed in THF (∼500 nm) decreases by 90%, with a
new maximum peak that appears at ∼530 nm (see
Figure 2b). These novel absorption and emission fea-
tures of H-ImPV in nonpolar solvents are progressively
lost upon increasing the temperature to 60 °C and are
reversibly recovered by cooling the sample to 25 °C, also
with the observation of a clean isosbestic point. These
findings suggest that H-ImPV undergoes self-aggrega-
tion, which might be driven by a combination of weak
homolecular hydrogen bonding, dipolar interactions,
and π-π stacking. We can reasonably assume that the
terminal units of the linear ditopic module H-ImPV
initially foster aggregation that further induces π-π
stacking.
Control of the Aggregation of H-ImPV in Solution.
While homodimers formed by AD
DA hydrogen
3 3 3
bonding interactions may exist for H-ImPV molecules,
heterotrimers (Scheme 2) will only be formed when the
respective partners are mixed. Heterotrimers, resulting
from self-assembly through triple hydrogen bonding,
should be more stable than homodimers self-assembled
through double hydrogen bonding.13 Because of its low
solubility in nonpolar solvents, attempts to determine the
1
equilibrium self-association constant of H-ImPV by H
NMR were unsuccessful. However, using phthalimide
(IM) as a model compound, self-association and inter-
association constants with Cy-DAT or Ph-DAT could be
measured in CDCl3 (see Figures S11-S26 in the Support-
ing Information). The value of the equilibrium self-
association constant for phthalimide (IM) was found to
be very low (8.8 mol-1 L). In a same way, self-association
constants of monotopic diaminotriazines are in the same
order (8.9 mol-1 L and 23.8 mol-1 L for Cy-DAT and Ph-
DAT, respectively), as reported by Beijer et al.14 for the
2,4-diamino-6-n-dodecyl-s-triazine. Values of the inter-
association constants of phthalimide with Cy-DAT or Ph-
DAT (42 mol-1 L and 33.5 mol-1 L, respectively), were
found to be higher in magnitude than the values of the
(12) Iwakura, Y.; Uno, K.; Shiraishi, S. Bull. Chem. Soc. Jpn. 1965, 38,
1820.
€
(15) Kaiser, T. E.; Stepanenko, V.; Wurthner, F. J. Am. Chem. Soc.
€
(13) Wurthner, F. Chem. Commun. 2004, 1564.
2009, 131, 6719.
(14) (a) Beijer, F. H.; Sijbesma, R. P.; Vekemans, J. A. J. M.; Meijer,
E. W.; Kooijman, H.; Spek, A. L. J. Org. Chem. 1996, 61, 6371.
(b) Krakovsky, I.; Lokaj, J.; Sedlakova, Z.; Ikeda, Y.; Nishida, K.
J. Appl. Polym. Sci. 2006, 101, 2338.
(16) (a) Yoosaf, K.; Belbakra, A.; Armaroli, N.; Llanes-Pallas, A.;
Bonifazi, D. Chem. Commun. 2009, 2830. (b) Lanes-Pallas, A.;
Palma, C.-A.; Piot, L.; Belbakra, A.; Listorti, A.; Prato, M.; Samori,
P.; Armaroli, N.; Bonifazi, D. J. Am. Chem. Soc. 2009, 131, 509.

5262 Chem. Mater., Vol. 22, No. 18, 2010
Delbosc et al.
Figure 1. (a) UV-vis absorption spectra and (b) emission spectra (λex = 430 nm) of H-ImPV (solid line), [H-ImPV.(Cy-DAT)2] in a 1:2 ratio (dotted line),
and [H-ImPV.(Ph-DAT)2] (dashed line) in a 1:2 ratio in THF (3ꢀ10-5 mol L-1).
Figure 2. (a) UV-vis absorption spectra and (b) emission (spectra excitation at the isosbestic point λex = 450 nm) of H-ImPV (5.9 ꢀ 10-5 mol L-1
)
in toluene, as a function of the temperature.
Figure 3. (a) UV-vis absorption spectra and (b) emission spectra (excitation at the isosbestic point, λex = 455 nm) of H-ImPV (5.9 ꢀ 10-5 mol L-1
in toluene at 25 °C with an increasing amount of Cy-DAT.
)

Article
Chem. Mater., Vol. 22, No. 18, 2010 5263
Figure 4. (a) UV-vis absorption spectra and (b) emission spectra (excitation at the isosbestic point λex = 455 nm) of [H-ImPV.(Cy-DAT)10] (blue lines),
[H-ImPV.(Cy-DATHex4)10] (green lines), and [H-ImPV.(Ph-DAT)10] (red lines) in toluene (5.9 ꢀ 10-5 mol L-1), as a function of the temperature.
The aggregation behavior of a mixture [H-ImPV.(Cy-
DAT)x] in toluene turns out to be rather different from
that obtained with H-ImPV itself (see Figure 3). The
addition of an increasing amount of 6-cyclohexyl deriva-
tive Cy-DAT, which has a nonplanar ring, to the initial
solution of H-ImPV in toluene allowed the formation of
the aggregates to be controlled. Upon increasing the
amount of Cy-DAT, the absorption band characteristic
of the aggregated state of the H-ImPV progressively
decreased (Figure 3a) while the strong green fluorescence
signal of the free chromophore is also recovered (Figure 3b)
with the observation of clean isosbestic and isoemissive
points. Finally, the addition of 10 equiv was sufficient to
avoid the aggregation of H-ImPV.
Once again, the supramolecular association of the two
components is stable and reversible, as attested by the
temperature-dependent experiments which evidence neg-
ligible spectral changes (see blue curves in Figures 4a and
4b). Using noncovalently bonded assemblies, we succeed
in recovering the optical behavior of the ImPV covalently
linked to a cyclohexyl fragment in Cy-ImPV (see Figure
S27 in the Supporting Information). The rationale is
supported by a control experiment carried out with Cy-
DATHex4 (incapable of establishing hydrogen bonding
interactions) and H-ImPV, where the experimental spec-
tra exhibited the aggregation of H-ImPV (see green curves
in Figure 4). This suggested that the suppression of the
aggregation of the chromophore in the supramolecule [H-
ImPV.(Cy-DAT)10] is most likely promoted by the pre-
liminary formation of the triple H-bonds between com-
plementary diaminotriazine and imide and not simply the
result of the intercalation of the bulky fragment between
the chromophores. In the same way, the nonplanar
structure of the Cy-DAT proves to be essential to avoid
aggregation through π-stacking interactions of the H-
ImPV. End-capping of the H-ImPV with 10 equiv of the
Ph-DAT, which is a planar monotopic module (see red
curves in Figure 4) results in the self-aggregation of the
trimolecule through π-π stacking interactions. As antici-
pated from the molecular modelization, the phenyl substi-
tuent of the Ph-DAT, being in the plane of the π-conjugated
chromophore (see Scheme 2), is not sufficient to avoid
aggregation of the supramolecule resulting from its asso-
ciation with H-ImPV.
Even if we demonstrated that the aggregation behavior
of the H-ImPV in solution could be tuned, in view of the
fabrication of optoelectronic devices, this approach had
to be transferred to the solid state. In solution, the
addition of 10 equiv of a sterically hindered end-capper
results in the formation of an isolated trimolecule. In
this case, the issue involves solubilization of the chromo-
phore through the formation of a soluble supramolecule.
No specific interaction could be observed between the
[H-ImPV.(Cy-DAT)x] supramolecules in the solution.
However, while going from the solution to the solid,
those supramolecules should interact between each other.
In this case, the Cy-DAT should drive the supramole-
cular organization of the trimolecules toward a J-aggre-
gation. This organization usually results in modification
of the spectroscopic behavior of the material (red shift
of the absorption maximum and strong fluorescence
emission).
Control of the Optoelectronic Properties of H-ImPV in
the Solid State. In a first approach, study of the aggrega-
tion behavior of H-ImPV was realized on thin films
(Figure 5). Surprisingly, the UV-vis absorption spectra
of thin films obtained from the spin coating of THF
solutions (3ꢀ10-3 mol L-1) of H-ImPV, [H-ImPV.(Ph-
DAT)2] or [H-ImPV.(Cy-DAT)2] exhibited the same spec-
tral modifications. In all cases, the strong absorption of
the chromophore observed at 430 nm in THF is dra-
matically red-shifted by ∼50 nm to be located at 489,
485, and 493 nm, respectively (see Figure 5a). However,
study of the emission properties of the different films
revealed different aggregation behaviors. Interestingly,
spin coating of those solutions on glass substrates re-
vealed that the emission properties were extremely en-
hanced by the addition of the cyclohexyl function (see

5264 Chem. Mater., Vol. 22, No. 18, 2010
Delbosc et al.
Figure 5. (a) UV-vis absorption spectra and (b) emission spectra of thin films obtained from the spin coating of THF solutions (3 ꢀ 10-3 mol L-1) of
H-ImPV (black curve), [H-ImPV.(Ph-DAT)2] (red curve), and [H-ImPV.(Cy-DAT)2] (blue curve) on glass plates. The absorption spectrum of the H-ImPV
in THF is added as a dotted line.
Figure 6. Pictures ofH-ImPV (left) and [H-ImPV.(Cy-DAT)2] (right) powders obtained from the recrystallization of the H-ImPV in dioxanein the absence
(or presence) of 4 equiv of Cy-DAT: (a) observed in the daylight, (b) observed under a 365-nm excitation, and (c) diluted in KBr under a 365-nm irradiation.
Figure 5b). A film of [H-ImPV.(Cy-DAT)2] is 1 order of
magnitude more fluorescent than a film composed of
H-ImPV. One could consider that it is simply a dilution
of the H-ImPV in the Cy-DAT. However, using Ph-DAT
instead of Cy-DAT, the Ph-DAT, being less hindered,
shows no improvement in the fluorescence properties of
the films. Two equivalents of Cy-DAT were sufficient to
optimize the fluorescence properties of the films. Increas-
ing the amount of Cy-DAT results in a decrease in the
fluorescence intensity of the thin film (see Figure S28 in
the Supporting Information). Again, this suggested that
the suppression of the aggregation of the chromophore in
the supramolecule [H-ImPV.(Cy-DAT)2] is most likely
promoted by the preliminary formation of the triple
H-bonds between complementary diaminotriazine and
imide and not simply the result of the intercalation of the
bulky fragment between the chromophores. These studies
of the absorption and emission properties of the different
films clearly revealed different aggregation behaviors. In-
deed, in the case of a Foster aggregation16 that further
induces π-π stacking, as in the case of a J-aggregation,
one can observe a red-shift of the absorption spectra;
however, the dipole configuration of a J-aggregates pre-
vents fluorescence quenching, unlike that observed for
Foster aggregates.
In a related approach, heteromolecular microcrystal-
line powders could be fabricated through the recrystalli-
zation of the H-ImPV in dioxane in the absence (or pre-
sence) of 4 equiv of Cy-DAT. The powders were obtained
from the slow cooling (0.2 °C/h) of dioxane solutions
preheated at 70 °C. Filtration of the resulting material
yielded a red powder in the case of the H-ImPV and a
yellow powder in the case of the heteromolecular material
(H-ImPV þ Cy-DAT) (see Figure 6).
The ratio between the H-ImPV and the Cy-DAT hosted
in the material could be determined by 1H NMR analysis
(see Figure S30 in the Supporting Information) and TGA
(see Figure S31 in the Supporting Information) analysis
of the powders. In good agreement with the conclusions
reached from the study of the emission properties of thin
films giving a 2:1 optimum ratio, both analyses resulted in
the same formulation.
Again, the [H-ImPV.(Cy-DAT)2] powder exhibited
much higher emitting properties than that of H-ImPV
(see Figures 6b and 6c). As an example, the fluorescence
intensity of KBr disks containing 2 wt % of [H-ImPV.(Cy-
DAT)2] powder is 1 order of magnitude more intense than
that of H-ImPV. (See Figure S29 in the Supporting In-
formation.) The better emitting properties of the [H-
ImPV.(Cy-DAT)2] powder could be quantified by the

Article
Chem. Mater., Vol. 22, No. 18, 2010 5265
Figure 7. Fourier transform infrared (FT-IR) spectra of a 10 mM solution of phthalimide (IM) in tetrachloroethylene (TCE), as a function of the
temperature in the region of (a) N-Himide stretching and (b) CdO stretching.
Figure 8. FT-IR spectra of a 10 mM solution of Cy-DAT in TCE, as a function of the temperature in the region of (a) NHamine stretching and (b) NHamine
bending and triazine ring.
determination of its absolute emission quantum yield (φ).
The quantum yields (φ) were measured at room temperature
using a quantum yield measurement system (Hamamatsu,
Model C9920-02) with a 150-W xenon lamp coupled to a
monochromator for wavelength discrimination, an inte-
grating sphere as the sample chamber, and a multichannel
analyzer for signal detection. In this case, the heteromole-
cular material exhibited a much higher absolute quantum
new types of hydrogen bonding not present in phthal-
imide or DAT themselves may be manifested in the spec-
tra of the mixture. However, to differentiate bands of
new N-Hamine
OdC, new N-Himide
OdC, new
Namine, re-
3 3 3
3 3 3
3 3 3
N-Himide
Namine and new N-Hamine
3 3 3
spectively, is a very difficult task. With this intention, our
strategy was to study first a simple model. In this case, it
will concern the association of phthalimide (IM) and Cy-
DAT (see Figures 7, 8, and 9). Moreover, the study was
carried out on solutions in TCE, as a function of the
temperature. It is easier to follow the evolution of a band
in terms of shape and wavenumber as a function of the
temperature than to compare steady state. At high tem-
perature, species appear as free molecules and with the
reduction in temperature, homomolecular or hetero-
molecular association will produce FTIR spectral mod-
ifications. As a consequence, experiments were performed
in a screw-sealed cell built from two slices of crystal-
line KBr (see Figure S32 in the Supporting Information).
yield (φ[H-ImPV.(Cy-DAT) ] = 37%) than that of the homo-
molecular material (φH-ImPV = 14%).
2
FTIR Evaluation of the Hydrogen Bonding. Results
from the optical properties of the films or the powders
do not give information about H-ImPV
Cy-DAT
3 3 3
interaction, i.e., if the role of DATs consists only in
breaking H-ImPV H-ImPV hydrogen bonds (inert
3 3 3
plasticizer) or new hydrogen bonds between H-ImPV
and Cy-DAT are formed in an ADA DAD triplet.
3 3 3
Such information may be provided by infrared spectros-
copy. In the case of H-ImPV Cy-DAT interaction,
3 3 3

5266 Chem. Mater., Vol. 22, No. 18, 2010
Delbosc et al.
Figure 9. FT-IR spectra of a 10 mM solution of IM:Cy-DAT in 1:1 ratio in TCE, as a function of the temperature in the region of (a) N-Himide stretching
and N-Hamine stretching and (b) CdO stretching, N-Hamine bending and triazine ring.
The control of the temperature was ensured by the
application of a bias on a resistance enveloping the cell.
In a first step, both modules have been studied sepa-
rately, to identify the modification of the IR absorption
resulting from their homoassociations. Finally, the study
of the mixture in a 1:1 ratio pointed out spectral modi-
fications resulting from the heteroassociations. A parti-
cular attention has been paid to the N-Himide and CdO
stretching of IM and N-Hamine stretching of Cy-DAT.
Two regions important for the investigation of hydrogen
bonding, N-Himide stretching (3600-2400 cm-1) and
CdO stretching (1800-1650 cm-1) in spectra obtained
from the phthalimide IM used in our study are shown in
Figure S33 in the Supporting Information. In accordance
with interpretation given by Krakovsky et al.,17 a broad
band centered at ∼3200 cm-1 (see Figure 7a) was assigned
to a wide distribution of hydrogen bonded structures
(multimers) resulting from the homoassociation of IM.
The sharp band at 3438 cm-1 was attributed to free IM
units. Similarly, two bands shown in Figure 7b;a smaller
band centered at 1775 cm-1 and the bigger one at ca. 1748
cm-1, respectively;can be attributed to the CdO
stretching which is either in-phase (νs(CdO)) or out-of-
phase (νas(CdO)) vibrations with the IM ring. Those two
bands are almost unchanged upon cooling.
and the in-plane vibration of the triazine ring is shifted to
lower wavenumbers (1510 cm-1). In the same way, the
second region (Figure 8a) contains two absorptions bands
of asymmetric νas(NHamine) and symmetric νs(NHamine
)
stretching at ca. 3551 and 3432 cm-1, corresponding to
the free DAT. Upon cooling, both sharp peaks are broad-
ened and shifted to lower frequencies and could be attri-
buted to the homoassociated DAT.
Spectra obtained from the 1:1 IM:Cy-DAT mixture are
more complex; nevertheless, a few conclusions can be
made (see Figure 9). At high temperature, both compo-
nents are free and the spectrum of the mixture results
from the addition of the spectra of the individual mod-
ules. The two broad bands at 1640 cm-1 and 1510 cm-1
assigned to bending of the NH2 (δ(NHamine)) and the in-
plane vibration of the triazine ring of the homoassociated
triazine (observed in Figure 8b), are in the mixture con-
verted to two sharp peaks, at 1652 cm-1 and 1550 cm-1
(see Figure 9b). This observation can be interpreted as an
indication of the participation of NH2 from DAT in a new
type of well-defined hydrogen-bonding pattern occurring
in the heteroassociated triplet. In a same way, the two
absorptions bands of asymmetric νas(NHamine) and sym-
metric νs(NHamine) stretching at ca. 3551 and 3432 cm-1
corresponding to the free DAT, are in the mixture con-
verted to a sharp doublet at 3385 cm-1 and 3338 cm-1
,
Spectra of Cy-DAT in TCE, as a function of the
temperature, were measured and reported in Figure 8.18
Two main regions of the infrared absorption were found:
1450-1800 cm-1 and 2550-3600 cm-1. The first region
contains, at high temperature, two sharp peaks, at 1591
cm-1 and 1555 cm-1, which were respectively assigned to
bending of the NH2 (δ(NHamine)) and the in-plane vibra-
tion of the triazine ring of the free triazine (see Figure 8b).
Upon cooling, both bands are broadened. The NH2
.
Similarly, the position of the asymmetric stretching of the
free imide (νas(CdO)), which was almost unchanged
upon cooling (recall Figure 7b), is shifted to lower fre-
quencies at 1720 cm-1 by the presence of the DAT.19 The
signature of the heteromolecular association is given by
the band at 2700 cm-1 in Figure 9a, which is typical of the
hydrogen bonding present in the ADA
DAD triplet.
3 3 3
This broad infrared absorption must be attributed the
central N-H N hydrogen bond involving the NH
bending is shifted to higher wavenumbers (1640 cm-1
)
3 3 3
group of the imide and the ring nitrogen in position 3 of
(17) Krakovsky, I.; Lokaj, J.; Sedlakova, Z.; Ikeda, Y.; Nishida, K.
J. Appl. Polym. Sci. 2006, 101, 2338.
(18) Padgett, W. M., II; Hammer, W. F. J. Am. Chem. Soc. 1958, 80,
803.
(19) Musto, P.; Karasz, F. E.; MacKnight, W. J. Macromolecules 1991,
24, 4762.

Article
Chem. Mater., Vol. 22, No. 18, 2010 5267
Figure 10. FTIR spectra realized on KBr pellets containing 2 wt % of Cy-DAT (green line), H-ImPV (black line) and [H-ImPV.(Cy-DAT)2] powder
(blue line) in the region of (a) N-Himide stretching and N-Hamine stretching and (b) CdO stretching, N-Hamine bending and triazine ring.
Figure 11. (a) Cyclic voltammograms of drop-cast films from THF solution of H-ImPV (black line) and [H-ImPV.(Cy-DAT)2] (blue line) on platinum
wires in CH3CN containing 0.1 mol L-1 of Bu4NPF6 as a supporting electrolyte at a scan rate of 100 mV s-1, referenced vs SCE. (b) Energy level diagram of
the organic light-emitting diodes (OLEDs) fabricated with evaporated films of H-ImPV or [H-ImPV.(Cy-DAT)2] (before contact).
the triazine.20 This type of N-H
N interaction is
3 3 3
O interaction, which
Cy-DAT and H-ImPV units, is again clearly seen in the
spectrum of the [H-ImPV.(Cy-DAT)2] powder shown in
Figure 10a.
Enhanced Electroluminescence in Hydrogen-Bonded
All-Organic Devices Based on H-ImPV. To gain informa-
tion on the charge injection, electrochemical measure-
ments were performed. Figure 11a shows full scan cyclic
voltammograms for thin films of H-ImPV and [H-ImPV.(Cy-
DAT)2] drop-cast on a platinum wire. Both compounds
exhibit two irreversible waves under cathodic sweep and
much stronger than the N-H
3 3 3
implies that the equilibrium constant describing inter-
association has greater value than that describing self-
association.21
In view of the above conclusions and observations
given by the study of the model, we were able to evidence
the heteroassociation of the H-ImPV and Cy-DAT in the
powder and in the films (see Figure 10).
FT-IR measurements realized on KBr pellets contain-
ing 2 wt % Cy-DAT (green line), H-ImPV (black line) and
[H-ImPV.(Cy-DAT)2] (blue line) confirmed the contribu-
tion of the imide group to the formation of heteromole-
cular association. The infrared spectrum of [H-ImPV.(Cy-
DAT)2], relative to H-ImPV, exhibited both shifting of
the symmetric νs(CdO) stretching to lower wavenumber
(Δν = -9 cm-1) and shifting of the asymmetric νas(CdO)
and (Δν = 19 cm-1) (see Figure 10b). Those shifts are
indicative of a more-effective hydrogen bond in the
the reduction occurred, respectively, at -1.37 V (ELUMO
=
-3.03 eV) and -1.31 V (ELUMO = -3.09 eV) versus satu-
rated calomel electrode (vs SCE).
The oxidation process exhibits an irreversible wave
when swept anodically, and the onset potential of oxida-
tion for H-ImPV is located at 1.05 V (EHOMO = -5.45
eV) vs SCE. [H-ImPV.(Cy-DAT)2] exhibits a higher
oxidation potential at 1.15 V (EHOMO = -5.55 eV). It
is easier to inject holes in the HOMO of H-ImPV than
that of [H-ImPV.(Cy-DAT)2]. The supramolecular aggre-
gation of H-ImPV optimizes the π-orbital overlap be-
tween chromophores and thus should improve its charge-
transport ability. These values of the oxidation potential
showed that the J-type aggregation of [H-ImPV.(Cy-
DAT)2] is more effective than that of Cy-ImPV. Indeed,
triplet ADA
DAD. The band at ca. 2715 cm-1
,
3 3 3
which is assigned to the N-H
N interassociation of
3 3 3
(20) Bishop, M. M.; Lindoy, L. F.; Skelton, B. W.; White, A. H.
J. Chem. Soc., Dalton Trans. 2002, 377.
(21) Vermeesch, I. M.; Groeninckx, G.; Coleman, M. M. Macro-
molecules 1993, 26, 6643.

5268 Chem. Mater., Vol. 22, No. 18, 2010
Delbosc et al.
the oxidation potential of Cy-ImPV (1.07 V, see ref 6)
resides between that of H-ImPV (1.05V) and[H-ImPV.(Cy-
DAT)2] (1.15 V) values. Similarly, good correlation could be
achieved with the study that we recently reported,5 regard-
ing the influence of the sol-gel process on the optoelec-
tronic properties of (EtO)3Si-ImPV. (OEt)3Si-ImPV, in a
J-aggregation before the sol-gel process, exhibits a higher
oxidation potential at 1.18 V (lower hole injection ability)
than the chromophore embedded in the sol-gel material
(O)1.5Si-ImPV with an oxidation potential of 1.0 V. The
supramolecular reorganization optimizes the overlap be-
tween chromophores during the sol-gel process and im-
proves the hole transport ability of the material. Finally,
the supramolecular organization of the supramolecule
[H-ImPV.(Cy-DAT)2], Eox = 1.15 V vs SCE) is closely
related to the J-aggregation of the sol-gel precursor
[(EtO)3Si-ImPV, Eox = 1.18 V vs SCE] and H-ImPV
(Eox = 1.05 V vs SCE) behaves as the sol-gel material in
an H-aggregation [(O)1.5Si-ImPV, Eox = 1.0 V vs SCE].
The electrochemical bandgaps (EEg C), calculated from
of the different modules in commonly used solvents for
device fabrication prohibited spin-coating deposition. An
alternative was found in the coevaporation of the chro-
mophore and the structuring module under vacuum (ca.
10-6 mbar). This approach has recently been exploited by
€
Fasel and Mullen for the deposition of heteromolecular
assemblies of PTCDI (perylene tetracarboxylicdiimide)
and 1,4-bisdiaminotriazinebenzene on a gold substrate.23
Using scanning tunneling microscopy, they nicely de-
monstrated that heteromolecular supramolecular struc-
tures could result from the coevaporation of comple-
mentary building blocks through one-dimensional (1D)
multitopic hydrogen-bonding interactions. In this con-
text, H-ImPV and Cy-DAT were disposed in individual
Al2O3 crucibles, and the flow rates were controlled by
slowly increasing the temperature of each oven to reach
the desired 1:2 H-ImPV:Cy-DAT stoichiometry. Experi-
mentally, the flow rate of the structuring unit (Cy-DAT)
was first tuned before closing the corresponding oven by a
shutter. The flow rate of the fluorophore was subse-
quently calibrated before opening both ovens. Finally,
after checking that the total flow was the sum of the two
contributions, the shutter of the substrate holder was
opened. The deposited thicknesses (50 nm) were moni-
tored using a piezoelectric balance setup inside the va-
cuum chamber close to the substrate holder. A cathode
composed of calcium (∼100 nm thick) was then sublimed
on the devices.
Figure 12a shows the measured intensity-luminance-
voltage (IVL) characteristics of devices based on H-ImPV
and on [H-ImPV.(Cy-DAT)2]. OLEDs based on [H-
ImPV.(Cy-DAT)2] exhibited good luminance levels for
voltages of <15 V (190 Cd/m2 at 14.5 V) and the onset
voltage is 8.5 V. An onset voltage of 12 V is recorded with
devices based on H-ImPV and much smaller luminances
for the same current density. Values of only 2.5 Cd/m2 are
observed at 15 V. Such very high applied voltages are
consistent with poor performances of H-ImPV-based
devices. As a consequence, the injection-related data re-
ported above are not sufficient to predict the performance
of OLEDs. We believe that H-ImPV presents a poor
ability to emit light, because of its aggregation, which
induces quenching of luminescence. Therefore, the use of
Cy-DAT is an interesting alternative to avoid aggregation
and to significantly increase luminance. As a conse-
quence, the luminous efficiencies of the devices are much
better for the coassembled active layer (see Figure 12b).
Finally, tuning of the supramolecular organization of the
H-ImPV by the addition of two equivalents of Cy-DAT in
the active layer allowed to recover the performances
exhibited by OLEDs of the chromophore covalently link
to steric hindered groups, such as a triethoxysilane ((EtO)3-
Si-ImPV) or a cyclohexyl (Cy-ImPV).6 The good efficien-
cies exhibited by the devices based on a single layer of /[H-
ImPV.(Cy-DAT)2] are the result of the J-aggregation of
ox
red
cyclic voltammetry data (E - E ), are ∼2.42 eV for
on
on
H-ImPV and 2.46 eV for [H-ImPV.(Cy-DAT)2], in some-
what good accordance with the optical bandgap (Egopt
)
estimated from the onset absorption of thin film of H-
ImPV (2.25 eV, λonset = 551 nm) and [H-ImPV.(Cy-
DAT)2] (2.25 eV, λonset = 549 nm).
According to the experimental data given by UV-
visible spectroscopies (absorption and emission) and elec-
trochemical measurements, H-ImPV and [H-ImPV.(Cy-
DAT)2], should exhibit two different optoelectronic be-
haviors. The J-aggregation of [H-ImPV.(Cy-DAT)2] fa-
vors its emission properties (solid-state fluorescence
quantum yield) and the Foster aggregation of H-ImPV
supports its charge transport abilities (intermolecular
overlaps). This has been illustrated by the fabrication of
light-emitting devices based on films of H-ImPV and [H-
ImPV.(Cy-DAT)2] sandwiched between two electrodes
(see Figure 11b). Taking into account HOMO (-5.45
eV) and LUMO (-3.03 eV) level positions, electrolumi-
nescent diodes based on H-ImPV were fabricated using a
system ITO/PEDOT-PSS (-5 eV) as an anode and
calcium (-2.9 eV) as a cathode. From such electronic
structures, it is believed that charge carrier injection may
differ. The energetic barrier at the anodic interface is
higher in OLEDs based on [H-ImPV.(Cy-DAT)2] than in
those based on H-ImPV. Hole injection is then easier in
H-ImPV. At the cathodic interface, electron injection
from calcium is not limited by any energetic barrier in
both cases. As a consequence, charge balance may be
better in H-ImPV than in [H-ImPV.(Cy-DAT)2]. On this
energetic basis, higher performances are expected from
H-ImPV. The structure of the device included a 50-nm-
thick layer of poly(styrene sulfonate)-doped poly(3,4-
ethylene dioxythiophene) (PEDOT-PSS) spun on indium
tin oxide (ITO).22 Then, the active layers of H-ImPV or
[H-ImPV.(Cy-DAT)2] were deposited. The low solubility
€
(23) Canas-Ventura, M. E.; Xiao, W.; Wasserfallen, D.; Mullen, K.;
(22) Wantz, G.; Hirsch, L.; Huby, N.; Vignau, L.; Silvain, J. F.;
ꢀ
Brune, H.; Barth, J. V.; Fasel, R. Angew. Chem., Int. Ed. 2007, 46,
1814.
Barriere, A.-S.; Parneix, J.-P. Thin Solid Films 2005, 485, 247.

Article
Chem. Mater., Vol. 22, No. 18, 2010 5269
Figure 12. Performance of ITO/PEDOT-PSS/H-ImPV (50 nm thick)/Ca (black curve) and ITO/PEDOT-PSS/[H-ImPV.(Cy-DAT)2] (50 nm thick)/Ca
(blue curve) devices: (a) intensity-luminance-voltage (IVL) curves and (b) luminous efficiencies.
Figure 13. Electroluminescence (EL) spectra of ITO/PEDOT-PSS/H-ImPV (50 nm thick)/Ca/Al (black curve) and ITO/PEDOT-PSS/[H-ImPV.(Cy-
DAT)2] (50 nm thick)/Ca/Al (blue curve) devices.
chromophores directed by the bulky cyclohexyl frag-
ments of the Cy-DAT.
The electroluminescence (EL) spectra have been mea-
compared to the photoluminescence spectrum of the
chromophore. Such an effect related to built-in electric
fields has already been observed.24
sured and found centered at 575 nm with an onset at λonset
495 nm for H-ImPV and at 570 nm with a onset at λonset
=
=
Fourier transform infrared spectroscopy-attenuated
total reflectance (FT-IR-ATR) measurements realized
on coevaporated films confirmed the contribution of the
imide group to the formation of heteromolecular associa-
tion. The infrared spectrum of [H-ImPV.(Cy-DAT)2],
relative to H-ImPV, exhibited both shifting of the sym-
metric stretching band (νs(CdO)) to lower wavenumber
(Δν = -5 cm-1) and shifting of the asymmetric stretching
503 nm for [H-ImPV.(Cy-DAT)2]. (See Figure 13.) Those
EL spectra are in good agreement with the HOMO and
LUMO level positions deduced by cyclic voltammetry,
since it provides bandgap widths of 2.50 and 2.46 eV.
As in the case of the photoluminescence of the films or
powders, the observed light is yellow in the case of [H-
ImPV.(Cy-DAT)2]-based OLEDs and red for H-ImPV-
based OLEDs. Even if the chromatic coordinates, respec-
tively calculated at x = 0.47/y = 0.51 and x = 0.48/y =
0.50 are quite similar, the H-ImPV device appeared red-
der than the two-component diode, because of its higher
full width at half-maximum (fwhm). A red-shift is also
observed on the EL spectra (see Figure 10, Δλ = 20 nm),
band (νas(CdO)) to higher wavenumber (Δν = 5 cm-1
(see Figure 14b). Those shifts are indicative of a more
effective hydrogen bond in the triplet ADA DAD.
)
3 3 3
(24) (a) Campbell, I. H.; Hagler, T. W.; Smith, D. L.; Ferraris, J. P.
Phys. Rev. Lett. 1996, 76, 1900. (b) Bolognesi, A.; Bajo, G.;
€
€
Paloheimo, J.; Ostergard, T.; Stubb, H. Adv. Mater. 1997, 9, 121.

5270 Chem. Mater., Vol. 22, No. 18, 2010
Delbosc et al.
Figure 14. Fourier transform infrared spectroscopy-attenuated total reflectance (FT-IR-ATR) spectra of H-ImPV (50 nm thick) and [H-ImPV.(Cy-
DAT)2] (50 nm thick) films evaporated on quartz substrates: (a) the N-H and C-H stretching mode region, and (b) the CdO stretching, the NH2 bending,
and in-plane triazine ring mode regions.
The band at ca. 2715 cm-1 assigned to N-H
association of Cy-DAT and H-ImPV units is again clearly
seen in the spectrum of the [H-ImPV.(Cy-DAT)2] film
shown in Figure 14a.
N inter-
the active layer allowed recovery of the performances
exhibited by OLEDs of the chromophore covalently link
to steric hindered group such as a triethoxysilane or a cyclo-
hexyl. The use of Cy-DAT seems to be a more interesting
alternative to avoid aggregation and significantly in-
crease luminance. We believe that this approach of the
control of electro-optical properties by the control of
aggregation properties could be generalized to many
labile and versatile structure-directing groups. As a con-
sequence, the luminous efficiencies of the devices are
much better for the coassembled active layer. Such a strat-
egy applied on multilayer and highly efficient OLEDs
should allow new display solutions to be developed.
We are currently working on the transfer of this plug-
and-play strategy to wet processes. In particular, spin-
coating-processed light-emitting diodes are under inves-
tigation and will be reported in due course.
3 3 3
Conclusion
In summary, we have developed a new strategy to tune
the aggregation of a chromophore without any covalent
modifications. For that purpose, a linear ditopic chro-
mophore H-ImPV was synthesized. This N-H imide
constitutes a recognizing unit with the acceptor-donor-
acceptor (ADA) hydrogen bond motif. End-capping of
this new chromophore with a monotopic structuring
module (Cy-DAT) bringing a steric hindrance allowed
the control of its supramolecular aggregation. The studies
of the absorption and emission properties of the H-ImPV,
in solution or in the solid state (thin films, powders),
clearly revealed different aggregation behaviors, depend-
ing on the presence of the monotopic structuring module
(Cy-DAT). In all cases, the signature of the heteromole-
Acknowledgment. The authors gratefully acknowledge
ꢀ
financial support from the “Ministere de la Recherche”
and the CNRS. This work was supported by the ANR-07-
JCJC-0022 grant/NANOTECTUM and the TRIMATEC
competitiveness cluster. We are grateful to Prof. Rute Sa
Ferreira (University of Aveiro, Departmente of Physics and
CICECO, Portugal) for the quantum yield measurements.
cular association H-ImPV
Cy-DAT was evidenced by
3 3 3
an infrared absorption band located at 2715 cm-1, typical
of the hydrogen bonding present in the ADA DAD
3 3 3
triplet. This has been illustrated by the fabrication of
light-emitting devices based on films of H-ImPV and [H-
ImPV.(Cy-DAT)2]. H-ImPV presents a poor ability to
emit light, because of its aggregation, which induces quench-
ing of luminescence. The good efficiencies exhibited by
the devices based on a single layer of [H-ImPV.(Cy-
DAT)2] are the result of the J-aggregation of chro-
mophores directed by the bulky cyclohexyl fragments of
the Cy-DAT. Tuning of the supramolecular organization
of the H-ImPV via the addition of 2 equiv of Cy-DAT in
Supporting Information Available: Experimental procedure
for the synthesis of H-ImPV, Cy-DAT, Cy-DATHex4, and Ph-
DAT. Spectral data sets (NMR, UV-vis, fluorescence and
FTIR spectra, HRMS, elemental analyses) and 1H and 13C
NMR spectra for H-ImPV, Cy-DAT, Cy-DATHex4, and Ph-
DAT. Determination protocol for association constants. Thin-
films and device fabrication methods. This material is available
free of charge via the Internet at http://pubs.acs.org.