Effect of the bulkiness of the end functional amide groups on the optical, gelation, and morphological properties of oligo(p-phenylenevinylene) π-gelators

Article abstract of DOI:10.1002/asia.201402235

Herein, we describe the role of end functional groups in the self-assembly of amide-functionalized oligo(p-phenylenevinylene) (OPV) gelators with different end-groups. The interplay between hydrogen-bonding and π-stacking interactions was controlled by the bulkiness of the end functional groups, thereby resulting in aggregates of different types, which led to the gelation of a wide range of solvents. The variable-temperature UV/Vis absorption and fluorescence spectroscopic features of gelators with small end-groups revealed the formation of 1D H-type aggregates in CHCl₃. However, under fast cooling in toluene, 1D H-type aggregates were formed, whereas slow cooling resulted in 2D H-type aggregates. OPV amide with bulky dendritic end-group formed hydrogen-bonded random aggregates in toluene and a morphology transition from vesicles into fibrous aggregates was observed in THF. Interestingly, the presence of bulky end-group enhanced fluorescence in the xerogel state and aggregation in polar solvents. The difference between the aggregation properties of OPV amides with small and bulky end-groups allowed the preparation of self-assembled structures with distinct morphological and optical features. Buying in bulk: OPV amides with small end-groups self-assemble into 2D/1D aggregates in toluene and 1D aggregates in CHCl₃. Bulky end-groups impede fluorescence quenching in the self-assembled state by blocking π-stacking and facilitate morphological transition in THF.

Full text of DOI:10.1002/asia.201402235

FULL PAPER
DOI: 10.1002/asia.201402235
Effect of the Bulkiness of the End Functional Amide Groups on the Optical,
Gelation, and Morphological Properties of Oligo(p-phenylenevinylene)
p-Gelators
Sukumaran Santhosh Babu, Vakayil K. Praveen, Kalathil K. Kartha,
Sankarapillai Mahesh, and Ayyappanpillai Ajayaghosh*[a]
Abstract: Herein, we describe the role
of end functional groups in the self-as-
troscopic features of gelators with
small end-groups revealed the forma-
tion of 1D H-type aggregates in CHCl3.
However, under fast cooling in toluene,
1D H-type aggregates were formed,
whereas slow cooling resulted in 2D H-
type aggregates. OPV amide with bulky
dendritic end-group formed hydrogen-
bonded random aggregates in toluene
and a morphology transition from vesi-
cles into fibrous aggregates was ob-
served in THF. Interestingly, the pres-
ence of bulky end-group enhanced
fluorescence in the xerogel state and
aggregation in polar solvents. The dif-
ference between the aggregation prop-
erties of OPV amides with small and
bulky end-groups allowed the prepara-
tion of self-assembled structures with
distinct morphological and optical fea-
tures.
sembly
of
amide-functionalized
oligo(p-phenylenevinylene) (OPV) ge-
lators with different end-groups. The
interplay between hydrogen-bonding
and p-stacking interactions was con-
trolled by the bulkiness of the end
functional groups, thereby resulting in
aggregates of different types, which led
to the gelation of a wide range of sol-
vents. The variable-temperature UV/
Vis absorption and fluorescence spec-
Keywords: gels · hydrogen bonds ·
phenylenevinylenes
· pi interac-
tions · self-assembly
Introduction
properties. Towards this direction, Lewis and co-workers re-
ported that amide-functionalized small p-systems formed
1D tapes or 2D sheets in the crystalline state.[8] The choice
between tape and sheet motifs was found to be sensitive to
the size of the N-substituent and to the spacer length.
Amides with small end-groups formed tape-like structures,
whereas bulky end substituents directed p-conjugated mole-
cules to form sheet-like structures. Although amide-func-
tionalized small p-systems in the crystalline state formed 1D
tape or two 2D sheets and, consequently, modulated their
excited-state properties, the usefulness of such a design
strategy has not been tested in the hierarchical self-assembly
of gelators based on extended p-systems.[1g,4–7] Herein, we
have synthesized OPV-based gelators with different amide
end-groups and investigated the effect of the bulkiness of
the end functional amide group on the optical, gelation, and
morphological properties.
Oligo(p-phenylenevinylene)s (OPVs) functionalized with
various end functional groups have been shown to spontane-
ously self-assemble in nonpolar hydrocarbon solvents, there-
by leading to gelation.[9–11] Detailed morphological studies
have shown that the formation of twisted and entangled
supramolecular tapes and their network structures are re-
sponsible for the gelation. It has been shown that p-stacking
occurs parallel to the long axis of the tapes, whereas the di-
rection of non-covalent interactions imparted by the end
functional groups is perpendicular to the length of the
tape.[10] The multilayer packing is assisted by van der Waals
interactions. The balancing of these non-covalent interac-
Functionalized p-systems are known to form a variety of
supramolecular structures of different shapes and sizes with
tunable optoelectronic properties.[1–5] Among the various
functional motifs that direct self-assembly, amide hydrogen-
bonding units are widely used for the construction of molec-
ular assemblies, owing to their strength, directionality, and
ease of functionalization.[4] When incorporated into p-sys-
tems, amide groups facilitate p-stacking, assisted by hydro-
gen-bonding interactions, thereby resulting in the gelation of
solvents in many cases.[1g,4,5] In recent years, there has been
significant progress in the design of self-assembling p-gela-
tors by using amide functional groups, thereby leading to
various exciting supramolecular nanostructures with diverse
properties.[1g,4–7] However, an understanding of the role of
amide functional groups in self-assembly pathways is essen-
tial to the design of soft materials with optimal physical
[a] Dr. S. S. Babu, Dr. V. K. Praveen, K. K. Kartha, Dr. S. Mahesh,
Prof. Dr. A. Ajayaghosh
Photosciences and Photonics Group
Chemical Sciences and Technology Division
CSIR-National Institute for Interdisciplinary Science
and Technology (CSIR-NIIST)
Trivandrum-695 019, Kerala (India)
Fax : (+91)471-249-1712
E-mail: ajayaghosh@niist.res.in
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.201402235.
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tions is important for the formation of supramolecular struc-
tures with distinct properties and functions.
second- and third-generation (G2 and G3) Frꢁchet-type den-
dritic wedges[12] are used, respectively. For this purpose,
OPV amine 4 was synthesized according to the procedure
shown in Scheme 1. The Wittig–Horner reaction between
the phosphonate ester of para-nitrobenzylbromide 2 and
OPV bis-aldehyde 1, which was prepared in several steps by
using known chemical reactions (see the Supporting Infor-
mation, Scheme S1),[9b,13] afforded OPV nitro derivative 3 in
90% yield.[9h,14] OPV amine 4 was obtained in 83% yield
from the reduction of compound 3 with tin(II) chloride
under acidic conditions.[9h] OPVA1 was prepared by the
treatment of compound 4 with
Results and Discussion
Our synthesis of amide-functionalized OPV derivatives with
different end-groups (OPVA1–OPVA4) is shown in
Scheme 1. In the case of OPVA1, the end functional moiety
is a simple methyl group, whereas, in OPVA2, a slightly
bulky 4-tert-butylbenzene is used. In OPVA3 and OPVA4,
acetyl chloride in the presence
of triethylamine. The synthesis
of OPVA2–OPVA4 was ach-
ieved by the reactions of com-
pound 4 with 4-tert-butylbenzo-
ic acid and dendritic G1 and
G2 acids[12] (see the Supporting
Information, Scheme S2), re-
spectively, by using 1-[bis(dime-
thylamino)methylene]-1H-1,2,3-
triazoloACTHNUTRGNE[NUG 4,5-b]pyridinium 3-oxid
hexafluorophosphate (HATU)
as the amide-coupling agent[15]
(Scheme 1). All of the new
compounds were characterized
by using FTIR, 1H, and
13C NMR spectroscopy and by
MALDI-TOF mass spectrome-
try.
The absorption and emission
characteristics of OPVA1–
OPVA4 in THF, together with
their quantum yields (Ff) and
lifetimes (t), are shown in the
Supporting
Information,
Table S1. Solutions of OPVA1–
OPVA3 in THF showed an ab-
sorption maximum in the
region 445–450 nm, whereas
OPVA4 displayed a blue-shift-
ed absorption maximum at
424 nm. Except for OPVA4, all
of the other OPV amides exhib-
ited two emission maxima in
THF, which were characteristic
of the molecularly dissolved
OPV units.[9] OPVA4 showed
a broad emission, with an emis-
sion maximum at 540 nm. As
the size of the end substituent
increased (from OPVA1 to
OPVA4), the values of loge
and Ff marginally increased.
Scheme 1. Synthesis of gelators OPVA1–OPVA4: a) NaH, dry THF, reflux, 5 h, 90% yield; b) SnCl2·2H2O,
dry THF, HCl, reflux, 5 h, 83% yield; c) triethylamine, acetylchloride, dry CH2Cl2, 08C to RT, 16 h, 73% yield
(OPVA1); HATU, diisopropylethylamine, 4-tert-butylbenzoic acid (OPVA2); dry CH2Cl2, 08C to RT, 24 h, G1
acid (OPVA3) or G2 acid (OPVA4), 69%, 61%, and 62% yield, respectively.
To understand the aggrega-
tion behavior of the OPVs,
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their absorption and emission spectra at low (108C) and
high temperatures (708C) were compared. The absorption
spectra of OPVA1–OPVA3 in CHCl3 and toluene at low
temperatures showed absorption maxima at about 420 nm,
which were blue-shifted by 20–25 nm from the absorption
maxima at elevated temperature (Figure 1 and the Support-
ing Information, Figures S1 and S2). At low temperatures,
the emission spectra in CHCl3 were broad and less intense,
The absorption and emission properties of OPVA1 in
CHCl3 (1ꢂ10ꢀ4 m) were remarkably different to those in tol-
uene. Upon heating, the absorption spectrum exhibited
a red-shift, which could be ascribed to a similar phenomen-
on to the breakage of H-type aggregates.[6a,f,9h,16] At 508C,
the absorption spectrum matched with the p–p* transition
of the isotropic molecules, which had an absorption maxi-
mum at 442 nm. A plot of the absorbance at 442 nm versus
temperature (Figure 1c, inset) was significantly different to
the behavior in toluene (Figure 1a, inset). The broad emis-
sion spectrum at 108C showed an enhancement in intensity
and reached the monomeric emission at 508C. In accord-
ance with the absorption changes, a plot of the emission in-
tensity at 514 nm versus temperature showed a single-step
transition (Figure 1d, inset).
These observations pointed to the existence of different
types of aggregates in toluene and CHCl3. Further evidence
was obtained from a series of variable-temperature aggrega-
tion studies. Interestingly, the rate of cooling was found to
be important in the aggregation pathways of OPVA1–
OPVA3; for example, for a solution of OPVA1 in toluene,
in comparison to the heating experiment (Figure 1a), fast
cooling (58Cminꢀ1) from the isotropic state allowed the ab-
sorbance to follow the same pathway until it reached the
half-way (lowest absorbance) point (Figure 2a). Further-
more, over time, the absorbance increased slowly and
reached the initial absorbance after 5 h (Figure 2b). This ob-
servation was confirmed by repeated heating–cooling cycles.
Similar observations were also made in the case of fluores-
cence (Figure 2c,d). Interestingly, during slow cooling
(0.58Cminꢀ1), the absorbance and fluorescence did not
Figure 1. Variable-temperature a) absorption and b) emission spectra of
OPVA1 in toluene and the corresponding c) absorption and d) fluores-
cence changes in CHCl3 (l=1 mm, c=1ꢂ10ꢀ4 m, lex =415 nm). Insets
show the variation in absorbance at a) 440 nm and c) 442 nm and in emis-
sion intensity at b) 511 nm and d) 514 nm with temperature.
whereas, in toluene, more quenching and structural features
were observed (Figure 1 and the Supporting Information,
Figures S1 and S2). Detailed variable-temperature UV/Vis
absorption and fluorescence studies of OPVA1–OPVA3 in
toluene and CHCl3 enabled us to have a better understand-
ing of the mode of aggregation and self-assembly. At lower
temperature, a solution of OPVA1 in toluene (1ꢂ10ꢀ4 m)
showed a blue-shift of the p–p* absorption maximum (Fig-
ure 1a). An unusual two-step transition was observed when
the absorbance at 440 nm was plotted against temperature
(Figure 1a, inset). As the temperature increased from 10–
448C, the absorbance decreased without much shift in the
maximum and reached a stable lower value. A further in-
crease in temperature resulted in an increase in absorbance
and, finally, reached the monomeric state at 708C. Similar
observations were also made in other solvents, such as ben-
zene and xylene. At 108C, a solution of OPVA1 in toluene
exhibited a structured emission with decreased intensity
(Figure 1b). Upon heating to 708C, the emission intensity
was enhanced, thus indicating the breaking of the self-as-
sembly, thereby leading to monomeric emission. Figure 1b,
inset, shows the variation in the emission intensity at 511 nm
with temperature. Up to 458C, the emission intensity in-
creased slowly. Further increasing the temperature resulted
in a sudden increase in the emission intensity.
Figure 2. a) Variable-temperature absorption spectra of OPVA1 in tolu-
ene at a faster cooling rate (58Cminꢀ1) and b) time-dependent changes
(0–5 h) after reaching the lowest absorbance point in the fast-cooling ex-
periment. Insets show the variation in absorbance at 440 nm with a) tem-
perature and b) time. c) Variable-temperature fluorescence spectra of
OPVA1 in toluene at a faster cooling rate (58Cminꢀ1) and d) time-de-
pendent changes (0–5 h) after the fast-cooling experiment. Insets show
the variation in emission intensity at 511 nm with c) temperature and
d) time. l=1 mm, c=1ꢂ10ꢀ4 m, lex =415 nm.
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follow the same pathway as in the cases of heating or fast
cooling (see the Supporting Information, Figure S3). As
a result, a large hysteresis was observed in the temperature-
dependent absorption, whereas, in the case of fluorescence,
the hysteresis was small. The results of the variable-temper-
ature photophysical studies in toluene could be ascribed to
interlinked 2D self-assembly of the 1D H-type aggregates.[9h]
The cooling rate had a relatively smaller influence on the
self-assembly of OPVA1 in CHCl3. In this case, fast and
slow cooling followed almost-identical pathways without
much hysteresis (see the Supporting Information, Figure S4).
These changes in the absorption and emission spectra could
be an indication of face-to-face 1D assembly of the possible
H-type aggregates of OPVA1 in CHCl3.[6a,f,9h,16]
(Figure 3b) compared to 78% quenching of the emission of
OPVA1 (Figure 1b), thus revealing that the former com-
pound was more emissive in toluene (Figure 4c). This con-
clusion was supported by fluorescence quantum yields deter-
mined for dilute solutions in toluene (Ff =0.12 for OPVA1,
These experiments indicated that a two-stage self-assem-
bly process was operative in toluene, whereas a single-stage
transition from aggregate to monomer was operative in
CHCl3. OPVA2 and OPVA3 showed similar absorption and
emission properties (see the Supporting Information, Figur-
es S1 and S2) to OPVA1. Depending on the end substitution
pattern, slight variation was noted in the absorption, where-
as no noticeable change was observed in the emission. How-
ever, in the case of OPVA4, a significant difference between
the variable-temperature absorption and emission spectra
was noted (Figure 3). For example, in toluene, OPVA4
showed relatively weak absorption and emission changes
with temperature when compared to OPVA1. On heating
from 108C to 708C, a small red-shift of 3 nm was observed
in the absorption maximum. Notably, in this case, a plot of
absorbance at 449 nm versus temperature only showed one
transition (Figure 3a, inset). The emission spectrum also ex-
hibited a relatively small change compared to OPVA1. In
this case, only 22% quenching in the emission was noted
Figure 4. Polarizing optical micrographs of toluene gels of a) OPVA1
(0.32 wt%) and b) OPVA4 (0.87 wt%) at RT. Inset shows photographs
of the corresponding gels in daylight. c) Photographs of solutions of
OPVA1 and OPVA4 in toluene under daylight (left) and UV light
(365 nm, right). d) Emission spectra (lex =435 nm) of xerogels of OPVA1
(solid line) and OPVA4 (dotted line). Inset shows the corresponding
photographs of xerogel coatings illuminated with 365 nm UV light.
Ff =0.84 for OPVA4). This increase in the quantum yield of
OPVA4 revealed that the bulky end-groups prevented the
molecules from forming perfect p-stacked aggregates.[17,18]
The end G2 dendron group in OPVA4 not only served as
a solubilizing group, but also controlled its aggregation
properties.[17–19] Variable-temperature experiments of
OPVA4 in toluene exhibited no hysteresis during the heat-
ing and slow cooling (0.58Cminꢀ1) cycles (see the Support-
ing Information, Figure S5). Similarly, in CHCl3, OPVA4
did not show any considerable changes in its absorption and
emission properties, thus indicating the absence of aggrega-
tion (Figure 3c,d).
OPV amides OPVA1–OPVA4 were found to gelate
a wide variety of organic solvents (Table 1). Of the different
solvents that were used, toluene was found to be the best
for gelation. As the size of the end functional group in-
creased, the gelation ability was found to decrease. On
moving from OPVA1–OPVA3, the gelation ability steadily
decreased, whereas a dramatic increase in critical gelator
concentration (CGC) was observed for OPVA4. This obser-
vation could be attributed to the presence of bulky end-
groups, which impeded the facile formation of strong direc-
tional hydrogen-bonding and p-stacking interactions be-
tween the molecules.
Figure 3. Variable-temperature a) absorption and b) fluorescence spectra
of OPVA4 in toluene and the corresponding changes in c) absorption
and d) fluorescence in CHCl3 (l=1 mm, c=1ꢂ10ꢀ4 m, lex =430 nm).
Insets show the variation in absorbance at a) 449 nm and c) 446 nm and
in emission intensity at b) 525 nm and d) 530 nm with temperature.
Of the four OPV amide derivatives under investigation,
OPVA1, which contained methyl end-groups, was found to
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Table 1. Gelation characteristics of OPV amide gelators OPVA1–OPVA4.[a]
de II). These results indicated a stronger hydrogen-bonding
ability of OPVA1 compared to OPVA4.
Solvent
OPVA1
OPVA2
OPVA3
OPVA4
Rheology measurements of gels of OPVA1 and OPVA4
were performed to obtain further information on the me-
chanical response of the gel fibers upon exposure to stress
(see the Supporting Information, Figure S8).[20c,22] The differ-
ent rheological properties of these two derivatives under the
same fiber mass highlighted the difference between their
mechanical responses to the applied stress. In the case of
a toluene gel of OPVA1 (2 mm), the elastic modulus (G’)
and loss modulus (G’’) were almost-completely independent
of the oscillation frequency. The G’ value was significantly
higher than the corresponding G’’ value, thus indicating the
dominant elastic behavior of the system over their viscous
properties. The system behaved as a viscoelastic solid and
was robust against stress over the applied frequency range.
A toluene gel of OPVA4 (2 mm) showed a decrease in vis-
coelastic nature with increasing frequency. At higher fre-
quency, the loss modulus increased and showed a more-
liquid-like property, thus indicating the ineffective resistance
and fragile nature of the gel matrix against a mechanical
force at higher frequency. This observation supported the
weaker aggregation of OPVA4 in toluene compared to
OPVA1. CHCl3 gels of OPVA1 and OPVA4 (2 mm) were
weak and did not show strong viscoelastic character (see the
Supporting Information, Figure S8). Frequency-sweep rheol-
ogy experiments revealed a difference between the mechani-
cal responses of the gels to an external force, thus giving an
indication of the effect of end-substitution on aggregation
and gel stability.[22]
Polarizing optical microscopy (POM) of a toluene gel of
OPVA1 showed the presence of birefringent fibrous aggre-
gates (Figure 4a), which is an indication of the long-range
order of the anisotropic hydrogen-bonded OPV assemblies
in the gel fibers. The nature and size of the aggregates were
different for the gel of OPVA4 and no fibrous aggregates
were observed in this case (Figure 4b). On cooling from the
isotropic state, a xerogel of OPVA1 from toluene showed
a birefringent ribbon-like morphology at 1008C, whereas, in
the case of OPVA4, no such structure formation was ob-
served (see the Supporting Information, Figure S9). The X-
ray diffraction (XRD) pattern of OPVA1 in the xerogel
state showed peaks that corresponded to d-spacing values of
3.1, 3.6, 4.5, and 9.5 ꢃ, which were characteristic of long-
range ordering of the molecules (see the Supporting Infor-
mation, Figure S10).[9b,g,11a,23] The peak in the wide-angle
region at 3.6 ꢃ corresponded to the p–p-stacking distan-
ce,[9b,23] whereas peaks at 4.5 ꢃ corresponded to amide-hy-
drogen-bonding-assisted stacking of the aromatic units.[6b,c,f]
The absence of well-defined XRD peaks in the wide-angle
region indicated a low degree of ordering of aggregates in
the xerogel state of OPVA4.[6c,f]
n-hexane
methyl cyclohexane
benzene
styrene
toluene
CHCl3
CH2Cl2
CCl4
EtOAc
THF
I
PS
I
PS
I
PS
I
PS
0.57 (S, Tr)
0.52 (S, Tr)
0.32 (S, Tr)
0.41 (S, Tr)
0.43 (S, Tr)
0.70 (S, Tr)
0.52 (S, Tr)
0.87 (S, O)
0.59 (S, Tr)
0.52 (S, Tr)
0.38 (S, Tr)
0.52 (S, Tr)
0.45 (S, Tr)
0.71 (S, Tr)
0.57 (S, Tr)
0.87 (S, Tr)
0.68 (S, Tr)
0.67 (S, Tr)
0.64 (S, Tr)
0.58 (S, Tr)
0.64 (S, Tr)
0.74 (S, Tr)
0.74 (S, Tr)
0.87 (S, Tr)
0.95 (Th)
0.89 (S, Tr)
0.87 (S, Tr)
0.87 (S, Tr)
0.89 (S, Tr)
0.88 (S, Tr)
PS
0.94 (S, Tr)
[a] CGC is the minimum concentration (wt%) required for the formation of
a stable gel at RT. In parentheses, S=stable, Th=thixotropic, Tr=transpar-
ent, O=opaque, I=insoluble, and PS=partially soluble.
be the best gelator, with gels that were stable for months.
Small end-groups were sterically less-hindering for the hy-
drogen-bonding-assisted self-assembly of p-units. OPVA1
only required 0.32 wt% to form a stable gel in toluene,
whereas 0.87 wt% was required for OPVA4. A strong visi-
ble color difference could be seen between the transparent
toluene gels of OPVA1 and OPVA4. The toluene gel of
OPVA1 was orange–yellow, whereas the gel of OPVA4 was
reddish in color (Figure 4a,b, inset). The gelation and spec-
troscopic features (see below) of the gel of OPVA4 indicat-
ed that, in the bulk self-assembly, the OPV units were site-
isolated, owing to the presence of G2 dendritic end-groups.
The thermotropic behavior of toluene gels of OPVA1–
OPVA4 at various concentrations was studied by using the
dropping-ball method.[9,20] The Tgel values were found to in-
crease with increasing concentration and reached a plateau
at higher concentrations (see the Supporting Information,
Figure S6). Compared to the other derivatives, OPVA1
showed a maximum Tgel value of 608C at a concentration of
2.5 mm. On moving from OPVA1 to OPVA4, the Tgel values
decreased in the order OPVA1>OPVA2>OPVA3>
OPVA4. The Tgel values in the saturation region showed
a significant decrease from OPVA1 to OPVA4, thus indicat-
ing a lower stability of the gel of OPVA4 compared to that
of OPVA1.
FTIR data in solution, as well as in the gel state, can pro-
vide information about the extent of involvement of the
amide functional groups in the self-assembly process.[6f,21] To
compare the strengths of the hydrogen-bonding interactions
in the self-assembled state, a FTIR spectrum of a dilute so-
lution of OPVA4 in CDCl3 was recorded, which exhibited
peaks at 3439, 1700, 1516, and 1505 cmꢀ1; these peaks were
characteristic of non-hydrogen-bonded amide A, I, and II
bands, respectively (see the Supporting Information, Fig-
ure S7).[6f,21] In the xerogel state, OPVA1 and OPVA4
showed a shift in the amide A and I bands towards lower
frequency and a shift in the amide II bands towards higher
frequency (see the Supporting Information, Figure S7). IR
peaks of a xerogel sample of OPVA1 showed sharp bands
at 3290 (amide A), 1658 (amide I), and 1524, 1515 cmꢀ1
(amide II), whereas OPVA4 displayed broad bands at about
3382 (amide A), 1675 (amide I), 1516, and 1505 cmꢀ1 (ami-
To gain a better understanding of the self-assembly of
OPVA1 and OPVA4, the absorption and emission of their
toluene gels (0.8 mm) were recorded (see the Supporting In-
formation, Figure S11).[24] The absorption spectrum of
OPVA1 showed a maximum at 430 nm, which was blue-
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shifted by 20 nm compared to that of OPVA4. The intensity
of the p–p* transition in OPVA1 was significantly lower
compared to that in OPVA4. The emission of OPVA1 was
significantly quenched in the gel state compared to that of
OPVA4. The difference between the structural features and
emission intensity of OPVA1 and OPVA4 indicated the
presence of different modes of aggregation in the self-as-
sembled state. Because the chromophore unit was the same,
the enhanced emission of OPVA4 compared to OPVA1 in
the gel state was probably due to isolation of the OPV unit
by the dendritic end-substitution.[17,18]
Fluorescence-lifetime-decay profiles in toluene (0.8 mm)
revealed that, irrespective of the excitation wavelength,
OPVA1 and OPVA4 showed biexponential decay with
a long-lived component and a short-lived component (see
the Supporting Information, Figure S12). In toluene,
OPVA1 decayed with lifetimes of 1.19 (92%) and 0.32 ns
(8%), whereas OPVA4 showed lifetimes of 1.17 (93%) and
0.37 ns (7%). The lifetimes of the long-lived component of
OPVA1 and OPVA4 were higher than those of the molecu-
larly dissolved species. Time-resolved emission spectra
(TRES) of toluene gels of OPVA1 and OPVA4 at room
temperature are shown in the Supporting Information, Fig-
ure S13a,b. In the case of OPVA1, on monitoring the emis-
sion over time after excitation at 401 nm, a small red-shift in
the long-wavelength region was observed. After 336 ps, the
spectrum was almost identical to the steady-state emission
of the toluene gel of OPVA1. The TRES results could be at-
tributed to the presence of aggregates that differed slightly
in their energy levels and to the migration of excitation
energy within these aggregates.[25] They also indicated the
presence of long-range order within the aggregates of the
OPVA1 gel. In the case of a toluene gel of OPVA4, no
time-dependent red-shift of the emission over the entire
spectrum was observed after excitation at 401 nm. TRES
studies justified the observed difference between the aggre-
gation modes of OPVA1 and OPVA4 in toluene.
Comparison of the emission spectra of OPVA1 and
OPVA4 in the xerogel state also revealed different modes
of aggregation in these two cases. The emission spectrum of
OPVA1 was very weak, with a maximum at 550 nm, where-
as a relatively strong emission, with a maximum at 570 nm,
was observed for OPVA4 (Figure 4d). The emission
maxima of xerogels of OPVA1 and OPVA4 showed a red-
shift of 10 and 50 nm, respectively, from those of the toluene
gels. The enhancement in the emission for OPVA4 could be
due to isolation of the conjugated backbone by the flexible
poly(benzyl ether) dendritic envelope, which prevented the
extent of inter-chromophore interactions whilst retaining the
aggregation.[17,18]
Figure 5. SEM, TEM, and AFM images of assemblies of a,c,e) OPVA1
and b,d,f) OPVA4 in toluene. Concentrations of 1 mm (SEM) and
0.1 mm (TEM and AFM) were used in the analysis.
width and several micrometers in length. The gels of
OPVA4 did not show the formation of a fibrous network
structure of definite size and shape. SEM images of toluene
and CHCl3 gels of OPVA4 showed completely different ill-
defined clustered nanostructures. These structures of
OPVA4 may not be as efficient in holding the solvent mole-
cules as the fibrous network of OPVA1. TEM images of
OPVA1 and OPVA4 that were obtained from a dilute solu-
tion in toluene (0.1 mm) are shown in Figure 5c,d, respec-
tively. OPVA1 showed the presence of entangled supra-
molecular fibers of 100–500 nm in width and several micro-
meters in length, whereas OPVA4 formed short fibrous ag-
gregates. The SEM and TEM results were supported by
atomic force microscopy (AFM) analysis of the aggregates
in toluene (0.1 mm; Figure 5e,f). Supramolecular fibers of
several micrometers in length and widths of 100–250 nm
were obtained for OPVA1 (Figure 5e), whereas fibrous ag-
gregates of a few micrometers in length were observed for
OPVA4 (Figure 5 f). The superstructures of OPVA4 at
higher concentrations in toluene, as observed in the SEM
images (Figure 5b), could be the result of agglomeration of
these aggregates.
SEM images of toluene and CHCl3 gels of OPVA1
(1 mm) showed an entangled network of fibrous aggregates
(Figure 5a and the Supporting Information, Figure S14a),
whereas no such fibrous network structure was found in the
case of OPVA4 (Figure 5b and the Supporting Information,
Figure S14b). The fibers of OPVA1 that were obtained
from CHCl3 and toluene were approximately 100–200 nm in
The broad absorption and emission spectra of OPVA4 in
THF (see the Supporting Information, Figure S15) prompt-
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Ayyappanpillai Ajayaghosh et al.
ed us to perform a concentration-dependent TEM study of
OPVA4, which revealed that the dendritic wedge could con-
trol the self-assembly[19,26] of OPVs in polar solvents. TEM
studies at a lower concentration of OPVA4 (0.001 mm in
THF) showed the formation of spherical particles (diameter:
80–200 nm; Figure 6a), most of which were fused together
to form an extended assembly (Figure 6b). On increasing
Figure 6. TEM images of a,b) 0.001 mM, c) 0.005 mm, d) 0.01 mm,
e) 0.025 mm, and f) 0.05 mm OPVA4 in THF.
the concentration to 0.005 and 0.01 mm, fusion of the spheri-
cal particles occurred, thereby leading to an extended chain-
like morphology (Figure 6c,d). A further increase in con-
centration (0.025 mm) resulted in the formation of fibrous
assemblies, together with the spherical particles (Figure 6e).
At a concentration of 0.05 mm, a complete transition of
spheres into extended long fibers was observed (Fig-
ure 6 f).[27] No such morphology transition was found for
OPVA1 in THF; instead, an ill-defined morphology was ob-
served (see the Supporting Information, Figure S16).
Based on the absorption, emission, FTIR, rheological,
XRD, and morphological studies, it was clear that OPVA1-3
and OPVA4 showed significantly different self-assembly be-
haviors. Based on the obtained data, a plausible mode of ag-
gregation into different types of self-assembled nanostruc-
tures is proposed in Figure 7. Variable-temperature absorp-
tion and emission changes of OPVA1 in CHCl3 strongly sug-
gested the formation of face-to-face (H-type) aggregates,
which is a common phenomenon in amide-linked chromo-
phores (Figure 7a).[4–7] However, the observed variable-tem-
perature absorption and emission changes of OPVA1 in tol-
uene are unusual.[9h] In the case of OPVA4, the presence of
bulky end-substituents prevented 1D and 2D aggregation.
OPVA4 preferred to form a random self-assembly through
weak hydrogen-bonding interactions between the molecules
(Figure 7b). At a higher concentration in toluene, these
random aggregates may form large 2D assemblies, thereby
leading to gelation of the solvent. The presence of bulky
dendritic end-groups prevented OPVs from forming perfect
H-type aggregates through p-stacking and, therefore,
random network assemblies were preferentially formed.
Figure 7. Schematic representations of the molecular packing of
a) OPVA1 in CHCl3 (left) and toluene (right) and of OPVA4 in b) tolu-
ene and c) THF.
Hence, the chromophore–chromophore distance was larger
than the usual p-stacking distance. This “site isolation” of
the chromophores[17,18] could prevent self-quenching of the
fluorescence, even in the gel and xerogel states. As shown in
Figure 6, THF, which is a relatively polar solvent, facilitated
the transition of OPVA4 from a spherical structure into a fi-
brous structure with increasing concentration.
Conclusions
In conclusion, small substituents on amide groups direct the
organization of OPVs through the 2D self-assembly of 1D
H-type aggregates in toluene and 1D H-type aggregation in
CHCl3. This self-assembly pathway with different aggregates
was clear from the unusual UV/Vis variable-temperature
spectroscopic changes in toluene. The attachment of a bulky
G2 dendron amide group caused the OPV to preferentially
form a randomly hydrogen-bonded 2D network assembly, in
which the chromophore units were isolated, thereby result-
ing in molecular self-assemblies with a very good fluores-
cence quantum yield. The bulky dendritic groups imparted
aggregation in polar solvents and facilitated a concentra-
tion-dependent morphology transition from vesicles into
fibers. This study demonstrates that the optical, gelation,
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Ayyappanpillai Ajayaghosh et al.
sodium sulfate, and the solvent was removed under reduced pressure. Pu-
rification of the crude product by column chromatography (n-hexane/
CHCl3, 3:7) on silica gel (100–200 mesh) yielded OPVA1 as an orange–
red solid in 70% yield. M.p. 245–2478C; 1H NMR (300 MHz, CDCl3,
TMS, 258C): d=0.86–0.89 (t, 18H; CH3), 1.24–1.36 (m, 120H; CH2),
4.03–4.07 (t, 12H; OCH2), 7.02–7.15 (m, 6H; aromatic H), 7.32–7.37 (m,
6H; aromatic H), 7.44–7.5 (m, 10H; aromatic H), 8.3 ppm (br s, 2H;
NH); 13C NMR (75 MHz, CDCl3, 258C): d=14.12, 14.36, 22.69, 25.90,
29.38, 29.6, 29.72, 31.92, 69.20, 114.31, 117.86, 123.19, 124.93, 127.38,
130.52, 139.74, 145.62, 167.58 ppm; FTIR (KBr): n˜max =721, 850, 964,
1034, 1071, 1205, 1257, 1316, 1350, 1387, 1421, 1466, 1513, 1595, 1663,
2851, 2922, 3049, 3296, 3412 cmꢀ1; MS (MALDI-TOF): m/z calcd for
C114H180N2O8: 1706.37 [M]+; found: 1706.16.
and morphological properties of OPV-based p-gelators can
be considerably modified by varying the bulkiness of the
end substituents on the gelator molecule.
Experimental Section
General Methods
Unless otherwise stated, all of the starting materials and reagents were
purchased from commercial suppliers and used without further purifica-
tion. The solvents were purified and dried by using standard methods
prior to use. Melting points were determined on a Mel-Temp-II melting-
point apparatus. 1H and 13C NMR spectra were recorded on a 300 MHz
Bruker Avance DPX spectrometer. Chemical shifts are reported in ppm
by using tetramethylsilane (TMS, dH =0 ppm) or the residual solvent
signal (CDCl3, dC =77.00 ppm) as an internal reference. The resonance
multiplicity is described as s (singlet), d (doublet), t (triplet), m (multip-
let), or br s (broad singlet). FTIR spectra were recorded on a Shimadzu
IRPrestige-21 Fourier-transform infrared spectrophotometer. Matrix-as-
sisted laser-desorption ionization time-of-flight (MALDI-TOF) mass
spectra were recorded on a Perseptive Biosystems Voyager DE-Pro
MALDI-TOF mass spectrometer by using an a-cyano-4-hydroxy cinnam-
ic acid matrix.
Synthesis of OPVA2–OPVA4
Diisopropylethylamine (0.15 mmol) and HATU (0.15 mmol) were added
to a solution of OPV amine 4 (0.06 mmol) and 4-tert-butylbenzoic acid
(0.15 mmol) for OPVA2, the G1 acid (0.24 mmol) for OPVA3, or the G2
acid (0.24 mmol) for OPVA4 in dry CH2Cl2 at 08C. The reaction mixture
was stirred for 24 h at RT, filtered, and washed several times with water.
The filtrate was dried over anhydrous sodium sulfate and the solvent was
evaporated under reduced pressure. The purification of the crude product
by using column chromatography (n-hexane/CHCl3, 3:7) on silica gel
(100–200 mesh) afforded the pure product as an orange–dark-red solid.
OPVA2: Yield: 69%; M.p. 241–2438C; 1H NMR (300 MHz, CDCl3,
Synthesis of Compound 3
TMS, 258C): d=0.77–0.79 (t, 18H; CH3), 1.18–1.53 (m, 120H; CH2), 1.57
(s, 18H; CACTHNUGTRNE(UNG CH3)3) 3.96–4.02 (t, 12H; OCH2), 7.05–7.09 (m, 4H; aroma-
NaH (1.24 mmol) was carefully added to a solution of OPV bis-aldehyde
1 (0.20 mmol) and phosphonate ester 2 (0.46 mmol) in THF (35 mL)
under an argon atmosphere. The reaction mixture was heated at reflux
for 5 h and the solvent was removed under reduced pressure. The resul-
tant residue was extracted with CHCl3 and washed several times with sa-
turated brine and water. Evaporation of the organic layer under reduced
pressure, followed by column chromatography (n-hexane/CHCl3, 3:1) on
silica gel (100–200 mesh), gave pure compound 3 as a dark-red solid in
90% yield. M.p. 245–2468C; 1H NMR (300 MHz, CDCl3, TMS, 258C):
d=0.86–0.89 (t, 18H; CH3), 1.24–1.36 (m, 120H; CH2), 4.03–4.07 (t,
12H; OCH2), 7.12–7.21 (m, 8H; aromatic H), 7.46–7.51 (m, 4H; aroma-
tic H), 7.62–7.67 (m, 6H; aromatic H), 8.20–8.23 ppm (d, J=8.68 Hz, 4H;
aromatic H); 13C NMR (75 MHz, CDCl3, 258C): d=16.37, 22.97, 26. 68,
29.72, 32.21, 69.53, 110.58, 111.301, 114.86, 123.50, 124.71, 127.38, 130.39,
tic H), 7.16–7.21 (m, 6H; aromatic H), 7.32–7.37 (m, 8H; aromatic H),
7.57–7.60 (d, J=8.1 Hz, 4H, aromatic H), 7.74–7.77 (d, J=9.3 Hz, 8H; ar-
omatic H), 8.29 ppm (br s, 2H; NH); 13C NMR (75 MHz, CDCl3, 258C):
d=14.12, 22.69, 26.21, 29.38, 29.67, 29.72, 31.92, 34.33, 69.19, 114.34,
117.84, 121.89, 124.93, 127.38, 131.44, 137.94, 145.42, 154.39, 164.68 ppm;
FTIR (KBr): n˜max =721, 806, 845, 963, 1070, 1204, 1256, 1322, 1421, 1465,
1514, 1646, 2851, 2921, 3458 cmꢀ1; MS (MALDI-TOF): m/z calcd for
C132H200N2O8: 1942.53 [M]+; found: 1942.48.
OPVA3: Yield: 61%; M.p. 216–2188C; 1H NMR (300 MHz, CDCl3,
TMS, 258C): d=0.87–0.89 (t, 18H; CH3), 1.12–1.37 (m, 120H; CH2),
4.03–4.08 (t, 12H; OCH2), 3.46–3.49 (t, 12H; OCH2), 7.16–7.22 (d, J=
8.69 Hz, 4H; vinylic H), 7.16–7.22 (d, J=9.2 Hz, 2H; vinylic H), 7.15–
7.18 (t, J=6.66 Hz, 4H; vinylic H), 6.84 (t, 2H; aromatic H), 6.90 (m,
4H; aromatic H), 6.99 (m, 2H; aromatic H), 7.04 (m, 4H; aromatic H),
7.37–7.38 (m, 20H; aromatic H), 7.40–7.43 (m, 4H; aromatic H), 7.51–
7.33 (m, 4H; aromatic H), 7.55–7.58 (d, J=17.87 Hz, 4H; aromatic H),
7.64–7.61 (d, J=8.66 Hz, 4H; aromatic H), 9.5 ppm (s, 2H; NH);
13C NMR (75 MHz, CDCl3, 258C): d=14.12, 14.36, 22.69, 26.21, 26.30,
29.38, 29.47, 29.53, 29.67, 29.72,31.92, 60.28, 69.20, 69.39, 110.09, 110.60,
112.31, 117.86, 123.19, 124.93, 127.38, 130.52, 139.74, 150.62, 151.17,
152.49, 167.58 ppm; FTIR (KBr): n˜max =807, 847, 963, 1050,1163, 1206,
1308, 1347, 1423, 1465, 1517, 1659, 2851, 2922, 3457 cmꢀ1; MS (MALDI-
TOF): m/z calcd for C152H208N2O12: 2254.58 [M]+; found: 2254.51.
OPVA4: Yield: 62%; M.p. 210–2128C; 1H NMR (300 MHz, CDCl3,
TMS, 258C): d=0.80–0.84 (t, 18H; CH3), 1.13–1.33 (m, 12H; CH2), 3.95–
4.03 (t, 12H; OCH2), 4.98–5.04 (t, 24H; OCH2), 6.68 (t, 2H; aromatic H),
6.80 (m, 4H; aromatic H), 6.99 (m, 2H; aromatic H), 7.04 (m, 4H; aro-
matic H), 7.15–7.18 (t, J=6.66 Hz, 4H; vinylic H), 7.18–7.22 (d, J=
9.2 Hz, 2H; vinylic H), 7.37–7.38 (m, 24H; aromatic H), 7.40–7.43 (m,
16H; aromatic H), 7.31–7.33 (m, 4H; aromatic H), 7.55–7.58 (d, J=
17.87 Hz, 4H; aromatic H), 7.64–7.61 (d, J=8.66 Hz, 4H; aromatic H),
9.8 ppm (s, 2H; NH); 13C NMR (75 MHz, CDCl3, 258C): d=14.12, 14.36,
22.69, 26.21, 26.30, 29.38, 29.47, 29.53, 29.67, 29.72,31.92, 60.28, 69.20,
69.35, 110.06, 110.62, 112.32, 117.86, 123.17, 124.91, 127.35, 130.50, 139.54,
150.61, 151.25, 152.57, 167.49 ppm; FTIR (KBr): n˜max =688, 808, 846, 963,
1054,1161, 1204, 1309, 1348, 1424, 1465, 1517, 1659, 2855, 2924,
3458 cmꢀ1; MS (MALDI-TOF): m/z calcd for C208H256N2O20: 3103.91
[M]+; found: 3103.82.
132.55, 144.93, 146.82, 151.26, 151.48, 151.98 ppm; FTIR (KBr): n˜max
=
668, 860, 964, 1039, 1105, 1206, 1249, 1340, 1421, 1466, 1514, 1587, 1600,
1661, 2358, 2850, 2922, 2954 cmꢀ1; MS (MALDI-TOF): m/z calcd for
C
110H172N2O10: 1682.30 [M]+; found: 1682.58.
Synthesis of Compound 4
Compound 3 (0.18 mmol) and SnCl2·2H2O (6.75 mmol) were added to
THF (15 mL), followed by 4 drops of 37% HCl, and the mixture was
stirred at reflux for 5 h. The reaction mixture was diluted with CH2Cl2
(50 mL) and washed once with 0.1m sodium bicarbonate and twice with
water. The organic solvent was removed on a rotary evaporator and the
crude product was filtered through a pad of silica gel (CH2Cl2) to afford
compound 4 in 83% yield. M.p. 251–2538C; 1H NMR (300 MHz, CDCl3,
TMS, 258C): d=0.86–0.89 (t, 18H; CH3), 1.24–1.36 (m, 120H; CH2),
4.03–4.07 (t, 12H; OCH2), 6.3 (br s, 4H; NH2), 6.67–6.70 (d, J=8.38 Hz,
4H; aromatic H), 7.02–7.15 (m, 8H; aromatic H), 7.32–7.37 (m, 4H; aro-
matic H), 7.43–7.48 ppm (m, 6H; aromatic H); 13C NMR (75 MHz,
CDCl3, 258C): d=14.10, 22.68, 26.25, 26.32, 29.56, 31.92, 69.53, 110.59,
115.22, 119.97, 123.28, 127.38, 128.65, 128.82, 145.91, 150.85, 151.06 ppm;
FTIR (KBr): n˜max =668, 717, 804, 858, 963, 1072, 1205, 128, 1350, 1422,
1465, 1506, 1607, 1661, 2849, 2921, 2954, 3436 cmꢀ1; MS (MALDI-TOF):
m/z calcd for C110H176N2O6: 1622.36 [M]+; found: 1622.63.
Synthesis of OPVA1
Acetyl chloride (0.15 mmol) was added to a solution of OPV amine 4
(0.06 mmol) and triethylamine (0.15 mmol) in dry CH2Cl2 at 08C and the
mixture was stirred for 16 h at RT. The reaction mixture was extracted
with CH2Cl2 and washed several times with water, dried over anhydrous
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Ayyappanpillai Ajayaghosh et al.
Optical Spectroscopy
Samples for the imaging were prepared by drop-casting a solution of the
OPV onto freshly cleaved mica at the required concentrations. POM
Electronic absorption spectra were recorded on a Shimadzu UV-3101 PC
NIR scanning spectrophotometer; emission spectra were recorded on
studies were performed on
a Nikon HFX 35A Optichot that was
equipped with a Linkan THMS 600 heating and freezing stage connected
to Linkan TP 92 temperature programmer.
a
SPEX-Flourolog F112X spectrofluorimeter. Temperature-dependent
studies were performed by using a thermistor that was directly attached
onto the wall of the cuvette holder.
XRD Analysis
Fluorescence Quantum Yield in the Solution State
Samples for the XRD studies were prepared by transferring OPV gels
onto glass plates, dried slowly to evaporate the solvent, and finally dried
under vacuum. X-ray diffractograms of the dried films were recorded on
a Phillips Diffractometer by using Ni-filtered CuKa radiation.
Fluorescence quantum yields of solutions of the OPVs in THF (Fs) are
reported relative to 10-methylacridinium trifluoromethane sulfonate
(Fr =0.99 in water). The experiments were performed by using optically
matching solutions and the quantum yields were calculated by using
Equation (1),[28] where As and Ar are the absorbance of the sample and
reference solutions at the same excitation wavelength, respectively, Fs
and Fr are the corresponding relative integrated fluorescence intensities,
and h is the refractive index of the solvents used.
Rheological Analysis
Rheological measurements were performed on an Anton Paar modular
compact (MCR 150) stress-controlled rheometer (Physica) that was
equipped with a parallel-plate geometry (20 mm diameter), a striated
cone, and a rough plate to minimize errors owing to sliding of the gel
layers. Hot solutions of the OPVs (2 mm) in toluene and CHCl3 were
poured onto to the Peltier at 258C and was allowed to form a uniform
gel layer. To avoid evaporation of the solvent, the plate was properly cov-
ered. The gap between the cone and the plate was fixed at 0.25 mm.
2
Fs ¼ Fr ꢁ ðArFs=AsFrÞ ꢁ ðhs2=hr
Þ
ð1Þ
Fluorescence-Lifetime and Time-Resolved Emission Measurements
Fluorescence lifetime and time-resolved emission spectra (TRES) were
measured by using an IBH (FluoroCube) time-correlated picosecond
single-photon-counting (TCSPC) system. The solutions were excited with
a pulsed diode laser (pulse duration<100 ps) at a wavelength of 401 nm,
with a repetition rate of 1 MHz. The detection system consisted of a mi-
crochannel plate photomultiplier (5000U-09B, Hamamatsu) with a re-
sponse time of 38.6 ps that was coupled to a monochromator (5000m)
Acknowledgements
A.A. is grateful to the Department of Atomic Energy, Government of
India, for a DAE-SRC Outstanding Researcher Award. K.K.K. is thank-
ful to the Council of Scientific and Industrial Research (CSIR), Govern-
ment of India, for a research fellowship. We acknowledge Mr. R. Philip,
Mr. P. Chandran, Dr. J. D. Sudha, and Mr. J. S. Kiran (NIIST) for per-
forming the TEM, SEM, rheology measurements and artworks, respec-
tively.
and
a
TCSPC electronics DataStation Hub including Hub-NL,
a NanoLED controller with preinstalled Fluorescence Measurement and
Analysis Studio (FMAS) software. The fluorescence lifetimes were deter-
mined by deconvoluting the instrument-response function with biexpo-
nential decay by using DAS6 decay-analysis software. The quality of the
fit was judged by using fitting parameters, such as c2 = <1.2, as well as by
visual inspection of the residuals. The measurements in the gel state were
performed in a 0.1 mm demountable cuvette by using a front-facing
sample holder (5000U-04). For the TRES measurements, the decay
curves were measured at multiple emission wavelengths (450–700 nm) to
construct a 3D dataset of counts versus time versus wavelength. By using
the FMAS software, this 3D dataset was sliced orthogonally to the time
axis to produce 2D spectra of counts versus wavelength to visualize how
the emission spectrum evolved during the fluorescence-decay time.
[1] a) F. J. M. Hoeben, P. Jonkheijm, E. W. Meijer, A. P. H. J. Schenning,
Chem. Rev. 2005, 105, 1491–1546; b) T. Yamamoto, T. Fukushima,
T. Aida, Adv. Polym. Sci. 2008, 220, 1–27; c) V. K. Praveen, S. S.
Babu, C. Vijayakumar, R. Varghese, A. Ajayaghosh, Bull. Chem.
Soc. Jpn. 2008, 81, 1196–1211; d) Y. S. Zhao, H. Fu, A. Peng, Y. Ma,
Q. Liao, J. Yao, Acc. Chem. Res. 2010, 43, 409–418; e) W. Li, Y.
Kim, M. Lee, Nanoscale 2013, 5, 7711–7723; f) B. Dong, H. Maeda,
Chem. Commun. 2013, 49, 4085–4099; g) S. S. Babu, V. K. Praveen,
A. Ajayaghosh, Chem. Rev. 2014, 114, 1973–2129.
Gelation Studies
The gelation studies were performed according to a literature proce-
dure.[9] A weighed amount of the compound in an appropriate solvent
was sealed in a glass vial (diameter=1 cm) and heated until the com-
pound dissolved. The solution was allowed to cool and gel formation was
confirmed by the failure of the content to flow by inverting the glass vial.
Repeated heating and cooling confirmed the thermal reversibility of the
gelation. The CGC was determined from the minimum amount of gelator
that was required for the formation of a stable gel at RT. Tgel was deter-
mined by using the dropping-ball method.[9,20]
[2] a) A. Ajayaghosh, V. K. Praveen, C. Vijayakumar, Chem. Soc. Rev.
2008, 37, 109–122; b) S. S. Babu, K. K. Kartha, A. Ajayaghosh, J.
Phys. Chem. Lett. 2010, 1, 3413–3424; c) F. Wꢄrthner, T. E. Kaiser,
C. R. Saha-Mçller, Angew. Chem. Int. Ed. 2011, 50, 3376–3410;
Angew. Chem. 2011, 123, 3436–3473; d) L. Maggini, D. Bonifazi,
Chem. Soc. Rev. 2012, 41, 211–241; e) B.-K. An, J. Gierschner, S. Y.
Park, Acc. Chem. Res. 2012, 45, 544–554; f) Y. Hong, J. W. Y. Lam,
B. Z. Tang, Chem. Soc. Rev. 2011, 40, 5361–5388; g) M. J. Mayoral
MuÇoz, G. Fernꢅndez, Chem. Sci. 2012, 3, 1395–1398; h) V. K.
Praveen, C. Ranjith, N. Armaroli, Angew. Chem. Int. Ed. 2014, 53,
365–368; Angew. Chem. 2014, 126, 373–376.
Morphological Studies
SEM was performed on a JEOL 5600 LV scanning electron microscope
at an accelerating voltage of 10 kV. The samples were prepared by either
drop-casting a solution of the OPV or by transferring the gel onto a pol-
ished metal surface, followed by drying and sputtering with gold under
a vacuum. TEM was performed on a FEI, TECNAI 30 G2 S-TWIN mi-
croscope at an accelerating voltage of 100 kV. The samples were pre-
pared by drop-casting a solution of the OPV onto a carbon-coated
copper grid and the TEM pictures were taken without staining. AFM
was performed under ambient conditions by using a Digital Instrument
Multimode Nanoscope IV operating in tapping mode. Microfabricated
silicon cantilever tips (MPP-11100-10) with a resonance frequency of
299 kHz and a spring constant of 20–80 Nmꢀ1 were used. The scan rate
varied from 0.5 to 1.5 Hz. AFM section analysis was performed offline.
[3] a) S. S. Babu, S. Prasanthkumar, A. Ajayaghosh, Angew. Chem. Int.
Ed. 2012, 51, 1766–1776; Angew. Chem. 2012, 124, 1800–1810; b) E.
Moulin, J. J. Cid, N. Giuseppone, Adv. Mater. 2013, 25, 477–487;
c) H. Li, J. Choi, T. Nakanishi, Langmuir 2013, 29, 5394–5406;
d) M. Kumar, K. Venkata Rao, S. J. George, Phys. Chem. Chem.
Phys. 2014, 16, 1300–1313; e) A. Das, S. Ghosh, Angew. Chem. Int.
Ed. 2014, 53, 2038–2054; Angew. Chem. 2014, 126, 2068–2084; f) Q.
Yan, Z. Luo, K. Cai, Y. Ma, D. Zhao, Chem. Soc. Rev. 2014, DOI:
10.1039/c3cs60375j; g) V. K. Praveen, C. Ranjith, E. Bandini, A.
Ajayaghosh, N. Armaroli, Chem. Soc. Rev. 2014, DOI: 10.1039/
c3cs60406c.
ˇ
´
[4] a) F. Fages, F. Vçgtle, M. Zinic, Top. Curr. Chem. 2005, 256, 77–131;
b) T. Ishi-i, S. Shinkai, Top. Curr. Chem. 2005, 258, 119–160; c) D.
9
&
&
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ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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www.chemasianj.org
Ayyappanpillai Ajayaghosh et al.
Gonzꢅlez-Rodrꢆguez, A. P. H. J. Schenning, Chem. Mater. 2011, 23,
310–325; d) M. R. Rao, S.-S. Sun, Langmuir 2013, 29, 15146–15158.
[5] a) J.-L. Li, X.-Y. Liu, Adv. Funct. Mater. 2010, 20, 3196–3216; b) A.
Dawn, T. Shiraki, S. Haraguchi, S.-I. Tamaru, S. Shinkai, Chem.
Asian J. 2011, 6, 266–282; c) X. Yang, G. Zhang, D. Zhang, J. Mater.
Chem. 2012, 22, 38–50; d) K. K. Kartha, R. D. Mukhopadhyay, A.
Ajayaghosh, Chimia 2013, 67, 51–63; e) A. Y.-Y. Tam, V. W.-W.
Yam, Chem. Soc. Rev. 2013, 42, 1540–1567.
[6] a) S. Ghosh, X.-Q. Li, V. Stepanenko, F. Wꢄrthner, Chem. Eur. J.
2008, 14, 11343–11357; b) R. Abbel, R. van der Weegen, W. Pisula,
M. Surin, P. Leclꢇre, R. Lazzaroni, E. W. Meijer, A. P. H. J. Schen-
ning, Chem. Eur. J. 2009, 15, 9737–9746; c) S. Diring, F. Camerel, B.
Donnio, T. Dintzer, S. Toffanin, R. Capelli, M. Muccini, R. Ziessel,
J. Am. Chem. Soc. 2009, 131, 18177–18185; d) P. Iavicoli, H. Xu,
L. N. Feldborg, M. Linares, M. Paradinas, S. Stafstrçm, C. Ocal, B.
Nieto-Ortega, J. Casado, J. T. Lꢈpez Navarrete, R. Lazzaroni, S. De
Feyter, D. B. Amabilino, J. Am. Chem. Soc. 2010, 132, 9350–9362;
e) Y. Chen, F. Zhang, B. Zhu, Y. Han, Z. Bo, Chem. Asian J. 2011,
6, 226–233; f) J. M. Malicka, A. Sandeep, F. Monti, E. Bandini, M.
Gazzano, C. Ranjith, V. K. Praveen, A. Ajayaghosh, N. Armaroli,
Chem. Eur. J. 2013, 19, 12991–13001.
[7] a) K. Sugiyasu, S. Kawano, N. Fujita, S. Shinkai, Chem. Mater. 2008,
20, 2863–2865; b) Y. Chen, B. Zhu, F. Zhang, Y. Han, Z. Bo,
Angew. Chem. Int. Ed. 2008, 47, 6015–6018; Angew. Chem. 2008,
120, 6104–6107; c) Y. Tatewaki, T. Hatanaka, R. Tsunashima, T. Na-
kamura, M. Kimura, H. Shirai, Chem. Asian J. 2009, 4, 1474–1479;
d) D. A. Stone, A. S. Tayi, J. E. Goldberger, L. C. Palmer, S. I.
Stupp, Chem. Commun. 2011, 47, 5702–5704; e) G.-C. Kuang, M.-J.
Teng, X.-R. Jia, E.-Q. Chen, Y. Wei, Chem. Asian J. 2011, 6, 1163–
1170; f) D. K. Maiti, A. Banerjee, Chem. Asian J. 2013, 8, 113–120;
g) F. Garcꢆa, J. Buendꢆa, S. Ghosh, A. Ajayaghosh, L. Sꢅnchez,
Chem. Commun. 2013, 49, 9278–9280; h) X. Wang, P. Duan, M. Liu,
Chem. Asian J. 2014, 9, 770–778; i) S. Ogi, K. Sugiyasu, S. Manna, S.
Samitsu, M. Takeuchi, Nat. Chem. 2014, 6, 188–195; j) F. Aparicio,
B. Nieto-Ortega, F. Najera, F. J. Ramꢆrez, J. T. Lꢈpez Navarrete, J.
Casado, L. Sꢅnchez, Angew. Chem. Int. Ed. 2014, 53, 1373–1377;
Angew. Chem. 2014, 126, 1397–1401.
Mahesh, A. Ajayaghosh, Chem. Eur. J. 2010, 16, 8652–8661; e) J.
Hou, X. Wu, Y.-J. Li, Supramol. Chem. 2011, 23, 533–538; f) S.
Bhattacharya, S. K. Samanta, Chem. Eur. J. 2012, 18, 16632–16641;
g) J. Lin, Z. Guo, J. Plas, D. B. Amabilino, S. De Feyter, A. P. H. J.
Schenning, Chem. Commun. 2013, 49, 9320–9322; h) J. D. Tovar,
Acc. Chem. Res. 2013, 46, 1527–1537.
[12] a) C. J. Hawker, J. M. J. Frꢁchet, J. Am. Chem. Soc. 1990, 112, 7638–
7647; b) J. Apperloo, R. A. J. Janssen, P. R. L. Malenfant, J. M. J.
Frꢁchet, Macromolecules 2000, 33, 7038–7043; c) J. Jiang, H. Liu, Y.
Zhao, C. Chen, F. Xi, Synth. Met. 2002, 132, 1–4.
[13] B. Wang, M. R. Wasielewski, J. Am. Chem. Soc. 1997, 119, 12–21.
[14] a) H. Detert, E. Sugiono, J. Phys. Org. Chem. 2000, 13, 587–590;
b) H. Detert, V. J. Schmitt, J. Phys. Org. Chem. 2004, 17, 1051–1056.
[15] K. C. Nicolaou, B. Zou, D. H. Dethe, D. B. Li, D. Y.-K. Chen,
Angew. Chem. Int. Ed. 2006, 45, 7786–7792; Angew. Chem. 2006,
118, 7950–7956.
[16] a) U. Rçsch, S. Yao, R. Wortmann, F. Wꢄrthner, Angew. Chem. Int.
Ed. 2006, 45, 7026–7030; Angew. Chem. 2006, 118, 7184–7188;
b) N. S. S. Kumar, S. Varghese, G. Narayan, S. Das, Angew. Chem.
Int. Ed. 2006, 45, 6317–6321; Angew. Chem. 2006, 118, 6465–6469;
c) S. Yagai, T. Seki, T. Karatsu, A. Kitamura, F. Wꢄrthner, Angew.
Chem. Int. Ed. 2008, 47, 3367–3371; Angew. Chem. 2008, 120, 3415–
3419; d) F. C. Spano, Acc. Chem. Res. 2010, 43, 429–439; e) M.
Kumar, S. J. George, Chem. Eur. J. 2011, 17, 11102–11106.
[17] a) T. Sato, D.-L. Jiang, T. Aida, J. Am. Chem. Soc. 1999, 121, 10658–
10659; b) J. J. Apperloo, R. A. J. Janssen, P. R. L. Malenfant, J. M. J.
Frꢁchet, J. Am. Chem. Soc. 2001, 123, 6916–6924; c) W.-S. Li, D.-L.
Jiang, T. Aida, Angew. Chem. Int. Ed. 2004, 43, 2943–2947; Angew.
Chem. 2004, 116, 3003–3007; d) F. Wꢄrthner, V. Stepanenko, A.
Sautter, Angew. Chem. Int. Ed. 2006, 45, 1939–1942; Angew. Chem.
2006, 118, 1973–1976; e) Y. Chen, Y. Lv, Y. Han, B. Zhu, F. Zhang,
Z. Bo, C.-Y. Liu, Langmuir 2009, 25, 8548–8555.
[18] a) W. Stocker, B. Karakaya, B. L. Schꢄrmann, J. P. Rabe, A. D.
Schlꢄter, J. Am. Chem. Soc. 1998, 120, 7691–7695; b) Y. Sagara, S.
Yamane, T. Mutai, K. Araki, T. Kato, Adv. Funct. Mater. 2009, 19,
1869–1875; c) Q. Chen, Y. Feng, D. Zhang, G. Zhang, Q. Fan, S.
Sun, D. Zhu, Adv. Funct. Mater. 2010, 20, 36–42; d) Q. Chen, D.
Zhang, G. Zhang, X. Yang, Y. Feng, Q. Fan, D. Zhu, Adv. Funct.
Mater. 2010, 20, 3244–3251; e) Y. Sagara, T. Kato, Angew. Chem.
Int. Ed. 2011, 50, 9128–9132; Angew. Chem. 2011, 123, 9294–9298;
f) P. Rajamalli, E. Prasad, New J. Chem. 2011, 35, 1541–1548; g) P.
Rajamalli, E. Prasad, Langmuir 2013, 29, 1609–1617.
[19] a) C. Park, J. Lee, C. Kim, Chem. Commun. 2011, 47, 12042–12056;
b) Y. Feng, Y.-M. He, Q.-H. Fan, Chem. Asian J. 2014, DOI:
10.1002/asia.201400043.
[20] a) K. Murata, M. Aoki, T. Suzuki, T. Harada, H. Kawabata, T.
Komori, F. Ohseto, K. Ueda, S. Shinkai, J. Am. Chem. Soc. 1994,
116, 6664–6676; b) A. R. Hirst, I. A. Coates, T. R. Boucheteau, J. F.
Miravet, B. Escuder, V. Castelletto, I. W. Hamley, D. K. Smith, J.
Am. Chem. Soc. 2008, 130, 9113–9121; c) S. Srinivasan, V. K.
Praveen, R. Philip, A. Ajayaghosh, Angew. Chem. Int. Ed. 2008, 47,
5750–5754; Angew. Chem. 2008, 120, 5834–5838.
[8] a) F. D. Lewis, J.-S. Yang, C. L. Stern, J. Am. Chem. Soc. 1996, 118,
2772–2773; b) F. D. Lewis, J.-S. Yang, C. L. Stern, J. Am. Chem. Soc.
1996, 118, 12029–12037; c) F. D. Lewis, J.-S. Yang, J. Phys. Chem. B
1997, 101, 1775–1781.
[9] a) A. Ajayaghosh, S. George, J. Am. Chem. Soc. 2001, 123, 5148–
5149; b) S. J. George, A. Ajayaghosh, Chem. Eur. J. 2005, 11, 3217–
3227; c) A. Ajayaghosh, C. Vijayakumar, R. Varghese, S. J. George,
Angew. Chem. Int. Ed. 2006, 45, 456–460; Angew. Chem. 2006, 118,
470–474; d) V. K. Praveen, S. J. George, A. Ajayaghosh, Macromol.
Symp. 2006, 241, 1–8; e) A. Ajayaghosh, C. Vijayakumar, V. K.
Praveen, S. S. Babu, R. Varghese, J. Am. Chem. Soc. 2006, 128,
7174–7175; f) A. Ajayaghosh, V. K. Praveen, S. Srinivasan, R. Var-
ghese, Adv. Mater. 2007, 19, 411–415; g) S. S. Babu, V. K. Praveen,
S. Prasanthkumar, A. Ajayaghosh, Chem. Eur. J. 2008, 14, 9577–
9584; h) S. S. Babu, S. Mahesh, K. K. Kartha, A. Ajayaghosh, Chem.
Asian J. 2009, 4, 824–829; i) D. Dasgupta, S. Srinivasan, C. Rochas,
A. Thierry, A. Schrçder, A. Ajayaghosh, J. M. Guenet, Soft Matter
2011, 7, 2797–2804.
[10] a) A. Ajayaghosh, V. K. Praveen, Acc. Chem. Res. 2007, 40, 644–
656; b) J. van Herrikhuyzen, S. J. George, M. R. J. Vos, N. A. J. M.
Sommerdijk, A. Ajayaghosh, S. C. J. Meskers, A. P. H. J. Schenning,
Angew. Chem. Int. Ed. 2007, 46, 1825–1828; Angew. Chem. 2007,
119, 1857–1860; c) Y. Hirai, S. S. Babu, V. K. Praveen, T. Yasuda, A.
Ajayaghosh, T. Kato, Adv. Mater. 2009, 21, 4029–4033; d) V. R. R.
Kumar, V. Sajini, T. S. Sreeprasad, V. K. Praveen, A. Ajayaghosh, T.
Pradeep, Chem. Asian J. 2009, 4, 840–848.
[21] a) D. J. Skrovanek, S. E. Howe, P. C. Painter, M. M. Coleman, Mac-
romolecules 1985, 18, 1676–1683; b) W. Herrebout, K. Clou, H. O.
Desseyn, N. Blaton, Spectrochim. Acta Part A 2003, 59, 47–59; c) E.
Jahnke, J. Weiss, S. Neuhaus, T. N. Hoheisel, H. Frauenrath, Chem.
Eur. J. 2009, 15, 388–404.
[22] a) S. Yao, U. Beginn, T. Gress, M. Lysetska, F. Wꢄrthner, J. Am.
Chem. Soc. 2004, 126, 8336–8348; b) S. Yagai, M. Higashi, T. Karat-
su, A. Kitamura, Chem. Mater. 2005, 17, 4392–4398; c) W. Weng,
J. B. Beck, A. M. Jamieson, S. J. Rowan, J. Am. Chem. Soc. 2006,
128, 11663–11672; d) M.-O. M. Piepenbrock, N. Clarke, J. W. Steed,
Soft Matter 2010, 6, 3541–3547; e) K. V. Rao, S. J. George, Chem.
Eur. J. 2012, 18, 14286–14291.
[23] a) D. J. Abdallah, S. A. Sirchio, R. G. Weiss, Langmuir 2000, 16,
7558–7561; b) Y. Hirai, H. Monobe, N. Mizoshita, M. Moriyama, K.
Hanabusa, Y. Shimizu, T. Kato, Adv. Funct. Mater. 2008, 18, 1668–
1675; c) Y.-T. Shen, C.-H. Li, K.-C. Chang, S.-Y. Chin, H.-A. Lin, Y.-
M. Liu, C.-Y. Hung, H.-F. Hsu, S.-S. Sun, Langmuir 2009, 25, 8714–
[11] a) B. W. Messmore, J. F. Hulvat, E. D. Sone, S. I. Stupp, J. Am.
Chem. Soc. 2004, 126, 14452–14458; b) S. S. Babu, V. K. Praveen, A.
Ajayaghosh, Macromol. Symp. 2008, 273, 25–32; c) P. Xue, R. Lu,
X. Yang, L. Zhao, D. Xu, Y. Liu, H. Zhang, H. Nomoto, M. Takafu-
ji, H. Ihara, Chem. Eur. J. 2009, 15, 9824–9835; d) S. Yagai, H.
Aonuma, Y. Kikkawa, S. Kubota, T. Karatsu, A. Kitamura, S.
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Ayyappanpillai Ajayaghosh et al.
8722; d) H. Cao, Q. Yuan, X. Zhu, Y.-P. Zhao, M. Liu, Langmuir
2012, 28, 15410–15417.
2009, 109, 6047–6076; c) D. Astruc, E. Boisselier, C. Ornelas, Chem.
Rev. 2010, 110, 1857–1959.
[27] a) A. Ajayaghosh, R. Varghese, V. K. Praveen, S. Mahesh, Angew.
Chem. Int. Ed. 2006, 45, 3261–3264; Angew. Chem. 2006, 118, 3339–
3342; b) A. Ajayaghosh, R. Varghese, S. Mahesh, V. K. Praveen,
Angew. Chem. Int. Ed. 2006, 45, 7729–7732; Angew. Chem. 2006,
118, 7893–7896; c) S. Varghese, N. S. S. Kumar, A. Krishna, D. S. S.
Rao, S. K. Prasad, S. Das, Adv. Funct. Mater. 2009, 19, 2064–2073;
d) M. J. Mayoral, C. Rest, J. Schellheimer, V. Stepanenko, G.
Fernꢅndez, Chem. Eur. J. 2012, 18, 15607–15611; e) A. Gopal, R.
Varghese, A. Ajayaghosh, Chem. Asian J. 2012, 7, 2061–2067.
[28] a) J. R. Lakowicz, Principles of Fluorescence Spectroscopy, 3rd ed.,
Springer, New York, 2006; b) S. A. Jonker, F. Ariese, J. W. Verho-
even, Recl. Trav. Chim. Pays-Bas. 1989, 108, 109–115.
[24] A concentration of 0.8 mm was sufficient to form a stable gel in a de-
mountable cuvette having a path length of 0.1 mm.
[25] a) K.-Y. Peng, S.-A. Chen, W.-S. Fann, S.-H. Chen, A.-C. Su, J. Phys.
Chem. B 2005, 109, 9368–9373; b) A. Ajayaghosh, V. K. Praveen, C.
Vijayakumar, S. J. George, Angew. Chem. Int. Ed. 2007, 46, 6260–
6265; Angew. Chem. 2007, 119, 6376–6381; c) A. F. Grimes, S. E.
Call, E. J. Harbron, D. S. English, J. Phys. Chem. C 2007, 111,
14257–14265; d) C. Vijayakumar, V. K. Praveen, A. Ajayaghosh,
Adv. Mater. 2009, 21, 2059–2063; e) C. Vijayakumar, V. K. Praveen,
K. K. Kartha, A. Ajayaghosh, Phys. Chem. Chem. Phys. 2011, 13,
4942–4949; f) K. K. Kartha, S. S. Babu, S. Srinivasan, A. Ajaya-
ghosh, J. Am. Chem. Soc. 2012, 134, 4834–4841.
[26] a) B. Rosen, C. Wilson, D. Wilson, M. Peterca, M. Imam, V. Percec,
Chem. Rev. 2009, 109, 6275–6540; b) W.-S. Li, T. Aida, Chem. Rev.
Received: March 14, 2014
Published online: && &&, 0000
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These are not the final page numbers! ÞÞ

FULL PAPER
Self-Assembly
Sukumaran Santhosh Babu,
Vakayil K. Praveen, Kalathil K. Kartha,
Sankarapillai Mahesh,
Ayyappanpillai Ajayaghosh*
&& — &&
Effect of the Bulkiness of the End
Functional Amide Groups on the
Optical, Gelation, and Morphological
Properties of Oligo(p-phenyleneviny-
lene) p-Gelators
Buying in bulk: OPV amides with
small end-groups self-assemble into
2D/1D aggregates in toluene and 1D
aggregates in CHCl3. Bulky end-
groups impede fluorescence quenching
in the self-assembled state by blocking
p-stacking and facilitate morphological
transition in THF.
&
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Chem. Asian J. 2014, 00, 0 – 0
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ÝÝ These are not the final page numbers!