Herringbone and helical self-assembly of π-conjugated molecules in the solid state through CH/π hydrogen bonds

Article abstract of DOI:10.1002/chem.201200705

Self-organization of organic molecules through weak noncovalent forces such as CH/π interactions and creation of large hierarchical supramolecular structures in the solid state are at the very early stage of research. The present study reports direct evid

Full text of DOI:10.1002/chem.201200705

FULL PAPER
DOI: 10.1002/chem.201200705
Herringbone and Helical Self-Assembly of p-Conjugated Molecules in the
Solid State through CH/p Hydrogen Bonds
Mahima Goel and Manickam Jayakannan*[a]
Abstract: Self-organization of organic
molecules through weak noncovalent
forces such as CH/p interactions and
creation of large hierarchical supramo-
lecular structures in the solid state are
at the very early stage of research. The
present study reports direct evidence
for CH/p interaction driven hierarchi-
cal self-assembly in p-conjugated mole-
cules based on custom-designed oligo-
phenylenevinylenes (OPVs) whose
structures differ only in the number of
carbon atoms in the tails. Single-crystal
X-ray structures were resolved for
these OPV synthons and the existence
of long-range multiple-arm CH/p inter-
actions was revealed in the crystal latti-
ces. Alignment of these p-conjugated
OPVs in the solid state was found to
be crucial in producing either right-
handed herringbone packing in the
crystal or left-handed helices in the
liquid-crystalline mesophase. Pitch- and
roll-angle displacements of OPV chro-
mophores were determined to trace
the effect of the molecular inclination
on the ordering of hierarchical struc-
tures. Furthermore, circular dichroism
studies on the OPVs were carried out
in the aligned helical structures to
prove the existence of molecular self-
assembly. Thus, the present strategy
opens up new approaches in supramo-
lecular chemistry based on weak CH/p
hydrogen bonding, more specifically in
p-conjugated materials.
Keywords: helical
structures
·
hydrogen bonds · liquid crystals ·
self-assembly
chemistry
·
supramolecular
Introduction
be lacking macroscopic self-organization such as liquid crys-
tallinity in the solid state.[10] Furthermore, packing of the
chromophores in the crystal lattices was found to be highly
sensitive to the structure of the p-conjugated backbone; as a
result, diverse self-organization in an identical p-conjugated
backbone was found to be very rare.[11] Herringbone motifs
were restricted only to planar p-conjugated molecules
whose structures were devoid of any substituent at the cen-
tral aromatic core.[12] Unfortunately, such structural restric-
tions in the p-conjugated systems result in poor solubility
and nonprocessability. As a consequence, solid-state order-
ing of the p-conjugated molecules beyond the herringbone
motif was not studied. Unlike synthetic molecules, bio-
Solid-state self-assembly of p-conjugated organic molecules
into hierarchical architectures and mapping out the origin of
their secondary interactions are emerging as challenging
tasks in the area of supramolecular chemistry.[1,2] The optical
and electronic features of devices made up of these p-conju-
gated materials could directly be correlated to the precise
arrangements of molecules in the solid state.[3,4] Though a
sizeable amount of research has already been done on sol-
vent-assisted self-assemblies of p-conjugated materials in
solution,[5–7] their packing in the solid state is understood
only at a premature level. This is partially associated with
the scarcity of single-crystal structures for large p-conjugat-
ed synthons which produce higher order supramolecular as-
semblies in the solid state. Recently, a few efforts have been
made to resolve the single-crystal structures of thin-film
transistor materials such as pentacene and thiophene deriva-
tives.[8] Contrary to expectations, it was found that these
molecules arrange with edge-to-face orientation in herring-
bone motifs rather than face-to-face p stacks.[9] Most of the
p-conjugated oligomers did not form single-crystal struc-
tures, and those which produce good crystals were found to
AHCTUNGTREGmNNNU acromolecules like proteins have been shown to cleverly
make use of weak noncovalent forces such as CH/p hydro-
gen-bond interactions to produce well-defined secondary or
tertiary structures.[13] The CH/p interactions have been pro-
jected as one of the main driving force in the complex for-
mation of proteins with cofactors and stabilization of water
molecules in the hydrophobic cavity, for example, for photo-
synthesis.[14] The CH/p interactions were also observed in
chemical research[15] in organic molecules and inorganic
crystals;[16] however, their full potential has not been exploit-
ed to obtain any types of hierarchical supramolecular assem-
blies.[11a] p-Conjugated oligomers (or polymers) are one of
the most promising chemical motifs for studying CH/p inter-
actions in the self-assembly approach because they have
1) rigid aromatic p-conjugated backbones (or extended p
systems) which can serve as H-bond acceptors and 2) flexi-
ble alkyl chains anchored on the periphery for solubility
purposes, which can behave as H-bond donors (CH groups).
[a] M. Goel, Dr. M. Jayakannan
Department of Chemistry
Indian Institute of Science Education and Research
Dr. Homi Bhabha Road, Pune 411008, Maharashtra (India)
Fax : (+91)20-2590 8186
E-mail: jayakannan@iiserpune.ac.in
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201200705.
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Recently we showed that the viability of CH/p interactions
in p-conjugated species is highly dependent on appropriate
design of the chromophore structure in hydrocarbon- and
fluorocarbon-tailed oligophenylenevinylenes (OPVs).[17]
The present approach demonstrates the potential of CH/p
interaction in making hierarchical supramolecular structures
like three-dimensional helical assemblies and herringbone
motifs of p conjugates in the solid state. The structures of
the OPV synthons were very carefully chosen with three im-
portant components: 1) a distyrylbenzene core as p accept-
or, 2) tricyclodecanemethylene (TCD) bulky units in the
middle as CH donors, and 3) alkyl tails of different lengths
as self-assembly directors (see Figure 1). The OPVs reported
assembly of organic solids, more specifically in p-conjugated
organic molecules.
Results and Discussion
Synthetic details, structural characterization, thermal analy-
sis, and polarizing microscopy studies are provided in the
Supporting Information. The TCD-OPVs with short tails
(n=0–4 C atoms) were found to be crystalline solids, where-
as increasing the tail length (n=5–9) resulted in thermo-
tropic cholesteric liquid crystals.[18] The long-tailed OPVs
(n=10-15) produced hierarchical helical, ring-banded supra-
molecular assemblies (see Figure 1). In the absence of crys-
tallographic evidence, based on photophysical characteriza-
tion and other analysis, the mechanism for this diverse self-
organization in TCD-OPVs was proposed on the basis of ar-
omatic
p
stacking and van der Waals interactions.[18a]
Herein, single-crystal structures of OPVs belonging to each
category of mesophases were successfully obtained: OPV-4
(crystalline solid), OPV-8 (short-pitch cholesteric), and
OPV-12 (helical bands) to trace the noncovalent interactions
behind these diverse LC mesophase organization in the
solid state. The crystal structures of the OPVs are shown in
Figure 2, and their unit-cell parameters are provided in the
Supporting Information (SF1 to SF-3 and ST1). All three
Figure 1. Diverse self-organization of OPVs in the solid state.
here are so simple as their structures differ only in the
number of carbon atoms in the alkyl tails. The uniqueness of
the TCD-OPV design is that it is devoid of strong intermo-
lecular interactions and only can self-organize via weak non-
covalent forces such as aromatic p stacking, CH/p interac-
tions, and van der Waals interactions, the energy terms of
which are less than 1–4 kcalmolꢀ1. Single-crystal structures
of OPV molecules were resolved to establish the role of
CH/p interactions and the origin of self-assembly at the mo-
lecular level. Further, crystallographic parameters such as
pitch and roll angles and their displacements were deter-
mined to establish the correlation between crystal structures
and liquid-crystalline (LC) mesophase morphology. The
findings revealed that the self-organization of p-conjugated
species underwent transformation from 2D herringbone
layer to 3D helical twist in the liquid crystalline mesophases.
Circular dichroism studies on the OPVs revealed that the
helical structures were produced only on aligning the chro-
mophores in the LC mesophase, and they were completely
lost in solution. Thus, the CH/p interaction has been proven
to be an important noncovalent force in the molecular self-
Figure 2. Single-crystal structures of OPV-4, OPV-8, and OPV-12.
benzene rings in the OPVs are in the same plane and consti-
tuted the molecular axis. OPV-4 has symmetric structure
and crystallizes in monoclinic space group P21/n, whereas
OPV-8 and OPV-12 crystallize in noncentrosymmetric tri-
clinic space groups. The TCD units attached at the center
occupy either side of the plane perpendicular to the aromat-
ic backbone. The two alkyl tails on the terminal aryl rings
are on the same plane constituted by the aromatic rings.
The crystal of OPV-8 contains one solvent molecule per
structure, but the solvent molecules are not involved in any
type of secondary interactions. The butyloxy tail in OPV-4
has one cis conformation, whereas the octyl and dodecyl
tails are aligned in all-trans conformations in OPV-8 and
OPV-12. The torsion angles from the central aromatic ring
to either side are 9.93 and 6.298 in OPV-12, 10.95 and 11.948
in OPV-8, and symmetric 6.888 in OPV-4. These values indi-
cate that the OPV backbone is indeed planar in all three
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Self-Assembly of p-Conjugated Molecules
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cases, but they differ in the orientation of alkyl tails along
the molecular axis.
The three-dimensional packing of all three OPVs is
shown in Figure 3. The bulky TCD units protrude from the
The packing of the planar organic molecules in the solid
state could be described in terms of two different angles,
termed pitch and roll inclinations, as reported by Curtis
et al.[9] A schematic diagram of pitch and roll displacements
Figure 3. Three-dimensional crystal packing of OPV-4, OPV-8, and OPV-
12.
p cores along the direction perpendicular to the molecular
axis. The packing of these three compounds differs widely
depending on the number of carbon atoms in the alkyl tails.
The rigid planar aromatic core and the absence of long lat-
eral side chains led OPV-4 to arrange in herringbone-type
packing. The herringbone arrangement is one of the most
stable packings for molecules in the solid state when adja-
cent stacks of molecules are arranged in opposite directions
in the unit cell.[9] The molecular planes in the adjacent
stacks are inclined with respect to each other, and the incli-
nation is known as the herring bone (HB) angle x,[12] which
is measured between molecules in adjacent stacks that are
diagonally oriented to each other. The HB angle x for OPV-
4 of 81.408 (see Supporting Information SF4) is very close to
perfect alignment of perpendicular herringbone sheets (x=
908). In herringbone-type packing so far observed for p-con-
jugated molecules, the absence of substituents in the central
aromatic core was considered to be an important structural
parameter for the existence of these patterns. Interestingly,
OPV-4 is the first example of a p-conjugated system which
contradicts the above assumption, since a herringbone pat-
tern was observed despite its having large bulky TCD sub-
stituents at the central aromatic core. Increasing tail length
facilitates interdigitation of tails along the molecular axis,
and as a result, the molecules in OPV-8 are closely packed
as bundles. The long dodecyloxy tails in OPV-12 resulted in
higher-ordered structures in which the molecules are packed
as columns along the b axis and pushed apart in the c axis
direction. The large difference in packing of OPVs revealed
that the custom designed OPV-TCD skeletons are unique in
producing diverse self-assembled structures in the solid
state.
Figure 4. a) Pitch and roll displacements of OPVs and their angles (b)
and distances (c) versus number of carbon atoms in the tail.
is shown in Figure 4. The planar aromatic core constitutes
the xy molecular plane. The x and y axes are perpendicular
to each other and represent the short and long axes of the
molecule, respectively (see Figure 4a). The shortest distance
between two adjacent molecules is defined by a vector d
and their stacking direction along the molecular packing as
a vector z. The pitch angle P and its distance dP correspond
to the molecular slip along the zL direction and the vector d.
The roll angle R and its distance dR are represented between
the projection of molecules on the short molecular axis
Zs and the
d
vector. The total slip distance
and the crystallographic repeat distance
ꢀ
ꢁ
1=2
dtot ¼ꢀ
d2p þ d2r
ꢁ
z ¼ dp2 þ dr2 þ d2 1=2were obtained from the pitch and roll
parameters.[9] The determination of dP, dR, P, R, dtot, and z
are given in the Supporting Information (SF-5 to SF-8). The
plot of the pitch and roll angles versus the number of
carbon atoms in OPV molecules (see Figure 4b) revealed
that the molecules underwent a pitch-angle distortion from
46.6 to 50.48 with increasing number of C atoms in the tail.
On the other hand, the roll-angle distortion was found to be
much stronger, and R varied from 55.8 to 67.28 (ꢁ128). In
Figure 4c, the shift distances are plotted against the number
of C atoms in the tail. Among the three molecules, the pitch
distance dP varied only by 0.56 ꢁ, but the variation in the
roll distance dR of 0.90 ꢁ was almost twice the difference in
pitch distances. This suggested that the effect of roll inclina-
tion in the OPV molecules is much stronger than that of dis-
placement in the pitch direction. The increase in tail length
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M. Jayakannan and M. Goel
increases the roll angle; as a result, the OPV-12 molecules
inclined more towards the x axis to attain layerlike self-as-
sembly. This suggests that OPV-12 molecules have a greater
tendency to pack the chromophores in parallel layers. This
is further evident from the OPV-12 molecular arrangements
in the crystal lattices (see Figure 3), in which each stack of
molecules appears as isolated pillars along the z axis (direc-
tion towards d vector in Figure 4a). In Figure 4c, the total
slip distance dtot and crystallographic repeat distance z in-
crease with increasing number of carbon atoms in the tail.
The values of dtot and z in all cases were found to be more
than 5.50 ꢁ, which is much greater than the typical aromatic
p-stacking distances observed in graphite (<3.50 ꢁ).[19]
Thus, it can be concluded that these OPV molecules do not
have any aromatic p-stacking interaction in the solid state.
Therefore, the diversity in the self-assembly of OPV chro-
mophores in the solid state is driven by secondary forces
other than aromatic p-stacking interactions.
OPV-12 molecule has close contact with four neighboring
molecules. Two of the molecules (green) lie on the same
plane along the a axis at a distance of 6.51 ꢁ, and other two
(orange) above and below the plane of the central molecule
along the b axis at 13.23 ꢁ. A total of eight CH/p interac-
tions per molecule (2ꢂ4 different types) was observed be-
tween the alkyl CH groups of TCD units and the aryl rings
or vinylene C=C bonds. These interactions involve CH55A
and a terminal aryl ring, CH62A or CH51A and the central
aryl ring (above and below), and CH64A and the vinyl C=C
bond. These multiple CH/p interactions extend along the b
axis throughout the crystal lattice. Four important crystallo-
graphic parameters describe the CH/p interactions: dCꢀX, q,
f, and dHpꢀX, where dCꢀX is the distance between the donor
carbon atom and the center of the acceptor p ring, q the
angle between the ring normal and a vector connecting the
donor carbon atom to the center of the aryl ring, f the
angle between the CH group and the vector connecting the
H atom to the ring center, and dHpꢀX the projection of the H
atom on the p ring.[13a]
To trace the intermolecular interactions responsible for
self-assembly in the OPVs, the close contacts between adja-
cent molecules were established. The close-contact interac-
tions in the OPV-12 molecule are shown in Figure 5. Each
Determination of these CH/p crystallographic parameters
is explained in the Supporting Information (SF-9). The CH/
p parameters (Table 1) are in accordance with literature re-
ports[13a] and confirm the existence of multiple-arm strong
Table 1. CH/p parameters for OPV-12.
CH
p
dCꢀX [ꢁ]
q [8]
f [8]
dHp X [ꢁ]
ꢀ
CH55A
CH51A
CH62A
CH64A
aryl
aryl
aryl
C20=C21
3.73
3.61
3.46
3.64
13.89
10.63
5.68
161.99
138.16
140.05
160.04
0.65
1.01
0.40
0.37
8.50
CH/p interaction in the OPV-12 molecules. The close con-
tacts in OPV-8 were also determined as described for OPV-
12 (see Supporting Information, SF-10). OPV-8 shows two
identical CH/p interactions per molecule between CH40A
and the C=C bond. However, OPV-4 did not show any
CH/p interactions exhibiting the required crystallographic
geometric parameters. The CH/p interactions observed in
OPV-8 are completely different from those of OPV-12:
1) the H acceptor (i.e., vinyl C=C bond) in OPV-8 is rela-
tively weak[16g] compared to the strong aryl-ring acceptor in
OPV-12 and 2) the existence of multiple-arm CH/p interac-
tion locks the 3D movement of the central aromatic core in
OPV-12, which is completely absent in OPV-8. Thus, the
strong multiple-arm CH/p interactions are essential for pro-
ducing the hierarchical structures seen in OPV-12. Though
OPV-8 has CH/p interactions, it does not show strong inter-
molecular locking (as seen in OPV-12) and turns out to be
simple liquid-crystalline material. In the absence of CH/p
interactions, OPV-4 packed in the herringbone motif. Sur-
prisingly, the long alkyl chains did not show any type of in-
teractions among themselves or with the aryl (or TCD)
units, and therefore it can be assumed that van der Waals
forces of attraction among the alkyl units are weak or
Figure 5. CH/p interactions in OPV-12 in the three-dimensional crystal
lattice. In the orange and green molecules part of one of the TCD groups
was omitted for clarity.
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Self-Assembly of p-Conjugated Molecules
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absent in the OPV molecules. Hence, it could be concluded
that the multiple-arm CH/p hydrogen-bonding interactions
are the prominent stabilizing force in OPVs that form
higher ordered structures in the solid state (OPV-12).
The mesophase morphology of the samples in single-crys-
tals and powder form was analyzed under a polarizing light
microscope (PLM) equipped with a hot stage (see Support-
ing Information, SF-11 to SF-14). Single crystals of OPV-4
and OPV-8 exhibited patterns of crystalline and cholesteric
mesophase, respectively (see Supporting Information, SF-
11). OPV-12 showed a birefringence pattern consisting of
fected by cooling from the isotropic state under either non-
isothermal (Supporting Information, SF-13) or isothermal
(Supporting Information, SF-14) conditions. Further, the
role of the number of carbon atoms in the tail in the forma-
tion of helical assemblies was also tested for OPVs with n=
10–16 (Supporting Information, SF-12). The pitch lengths of
helical rings gradually increased with increasing number of
carbon atoms in the tail up to n=15 and lost this tendency
at n=16 in OPV-16 (Supporting Information, SF-16 and
SF-17). Hence, the ring-banded self-assemblies in the TCD-
OPVs are a molecular property which is driven by both the
number of carbon atoms in the alkyl chain and CH/p inter-
actions.
Circular dichroism (CD) spectra of the OPVs were re-
corded to gain more insight into their LC mesophase helical
morphology. CD spectra of OPV samples were recorded in
both solution (in toluene and other solvents) as well as in
the solid state (fine powder and also in aligned films). All
three OPVs showed no CD signal in solution, which con-
firmed that they have no helical self-organization in the sol-
ution state (Supporting Information, SF-18). Therefore, the
presence of a weak chiral center in the TCD units (at the
bridging carbon atom ArOCH2C*H) did not provide any
additional advantages for molecular self-assembly in solu-
tion. In the powder state, the samples showed very weak
CD signals (Supporting Information, SF-18 and SF-19). On
aligning the molecules in the thin layer (OPV-4) or LC
mesoACTHNUTRGNEpNUG hase (OPV-8 and OV-12; samples were made as per
the method described for PLM studies), self-organization
became predominant and strong CD signals emerged from
the samples. Hence, alignment of the organic molecules pro-
moted self-organization of OPVs in the solid state. The CD
spectra and absorption spectra of OPVs are shown in Fig-
ure 6b. All three OPVs showed broad absorption spectra
from 300 to 500 nm and their CD spectra were observed in
the same region as their absorption spectra. OPV-4 showed
a strong positive Cotton effect with maximum at 345 nm
and zero crossing at 295 nm. This indicated that the OPV-4
molecules are arranged as right-handed sheetlike structures
(as seen in the herringbone layers in Figure 2). In contrast,
OPV-8 and OPV-12 showed intense negative CD signals cor-
responding to absorption of left circularly polarized light
(negative Cotton effect). The CD spectrum of OPV-12
showed two strong negative bands at 357 and 408 nm and a
weak positive band at 275 nm (OPV-8 also showed a similar
trend). The features of these negative signals in OPV-12
(and also in OPV-8 and OPV-11) confirmed that the mole-
cules were arranged in the left-handed helical assembly.
Hence, the helical lines observed under the plane-polarized
illumination in OPV-12 molecules (see Figure 6a) are noth-
ing but helical self-assemblies of the lamella in the solid
state. Thus, for the first time, a perfect correlation between
the LC helical mesophase (observed under PLM) with the
helical supramolecular structures (in CD signals) was estab-
lished in solid-state self-assembly.
Figure 6. a) Formation of helical assemblies in OPV-12 and b) solid-state
CD spectra of aligned OPV samples in the LC state (absorption spectra
are shown as inset). A schematic of chain length driven self-assembly is
shown bottom right.
concentric dark and bright rings (Figure 6). The mesophase
morphology was identical irrespective of the sample source
(single crystals or powder samples; Supporting Information,
SF-11). The existence of CH/p interactions in the LC meso-
phase morphology, similar to the single-crystal structures,
was confirmed by variable-temperature powder X-ray dif-
fraction studies (Supporting Information, SF-15). The con-
centric dark and bright rings in OPV-12 are simply the
Grandjean lines that are typically observed in chiral nematic
N* liquid-crystalline mesophase.[20] The appearance of dark
and bright lines under plane-polarized light is schematically
illustrated in Figure 6a.[20] The dark lines are observed when
the helical twist changes by p. From the distance l between
the two lines, the pitch length p of the helix could be calcu-
lated as l=p/2. The pitch length is typically constituted by
hundreds and thousands of molecules in lamellae which sub-
sequently twist to give helical superstructure.[20] The pitch
length can vary from as small as 100 nm to many microme-
ters. The pitch length in OPV-12 was determined to be
44.7ꢂ2.9 mm. Formation of the helical assembly was not af-
The photophysical characterization of OPV chromophores
showed that the emission spectra of OPV-4, OPV-8, and
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M. Jayakannan and M. Goel
OPV-12 in both LC phase and single crystals are almost
identical, with maxima at 490 nm. Furthermore, time-de-
pendent fluorescence time decay measurements by the time-
correlated single-photon counting technique (details are
provided in Supporting Information, SF-20) revealed that
the OPV chromophores show almost identical lifetimes irre-
spective of their occupancy either in herringbone sheets
(OPV-4) or in helical self-assembly (OPV-12 and OPV-8).
The absence of aromatic p-stacking interactions (responsible
for photophysical variation) among the chromophores ac-
counts for this similarity in PL characteristics. In our previ-
ous work, we noticed that the p-stacking interaction was
completely absent in undecyl-substituted OPV, which is
completely different from the TCD-OPVs.[17] Currently, we
are studying the role of p-stacking in the OPVs having sub-
stituents other than TCD (e.g., branched ethylhexyl or
linear octyl chains). A preliminary crystal structure analysis
(see Supporting Information, SF-21) revealed that the p-
stacking interaction is also not present in other OPV mole-
cules. Therefore, the lack of p-stacking interaction found in
the present investigation is not restricted to TCD-OPVs,
and it is also generally applicable to other OPVs. Thus, with-
out altering luminescent characteristics of the p-conjugated
chromophores, diverse self-assembly was achieved by only
varying the number of carbon atoms in the tails (see
Figure 6). Increasing the number of carbon atoms in the tail
transformed the chromophore packing from herringbone to
left-handed helical twist in the chiral nematic mesophase.
On the other hand, on decreasing the tail length, the chro-
mophores organized in highly packed herringbone patterns.
For longer alkyl chains (nꢃ14), the packing of the chromo-
phores is no longer controlled by the tails and the molecular
self-assemblies are lost. The CH/p interactions were found
to be a crucial stabilizing factor in aligning the chromo-
phores in the long-tailed OPVs (OPV-10 to OPV-15); a
result, the chromophores transformed into helical supramo-
lecular assemblies.
OPV-12 was further proved by a CD investigation in the
solid state. OPV-4 adopts a herringbone layer pattern and
forms right-handed sheetlike structures. The uniqueness of
the present approach is that both herringbone and helical
assemblies could be simply varied by means of the number
of carbon atoms in the tails. Though the approach demon-
strated here describes in detail the role of CH/p interactions
in OPVs, it is not restricted to any particular type of p-con-
jugated oligomers. The overall findings revealed that the
CH/p interaction is a very powerful noncovalent interaction
in supramolecular chemistry. This finding is just the tip of
the iceberg in the ocean of molecular self-organization and
has great potential for breakthrough discoveries in p-conju-
gated materials.
Experimental Section
Syntheses and characterization of compounds, crystallographic images,
unit cells, calculation of pitch and roll parameters, CH/p interaction pa-
rameters, DSC traces, temperature-dependent PLM textures, WXRD
plots, emission spectra and TCSPC life time plots and data, CD signals
for solution and powder samples, and 1H NMR, 13C NMR, MALDI mass
spectra are provided in the Supporting Information. CCDC 846783,
846784 and 846785 contain the supplementary crystallographic data for
this paper. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_re-
quest/cif.
Acknowledgements
Research grant from Department of Science and Technology (DST),
New Delhi, India under nanomission initiative project SR/NM/NS-42/
2009 is acknowledged. M.G. thanks CSIR, India for SRF fellowship.
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signed with suitable bulky TCD units as C H bond donor
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Received: March 2, 2012
Revised: June 11, 2012
Published online: && &&, 0000
Chem. Eur. J. 2012, 00, 0 – 0
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www.chemeurj.org
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These are not the final page numbers!

M. Jayakannan and M. Goel
Multiple CH/p interactions drive self-
organization of custom-designed oligo-
phenylenevinylenes with a distyrylben-
zene core as p acceptor, bulky tricyclo-
decanemethylene groups as CH
donors, and alkyl tails as self-assembly
directors. Both herringbone and helical
supramolecular structures could be
obtained in the solid state simply by
varying the number of carbon atoms in
the tails (see figure).&&original text
was too long, ok?&&
Supramolecular Chemistry
M. Goel, M. Jayakannan* . . &&&& — &&&&
Herringbone and Helical Self-
Assembly of p-Conjugated Molecules
in the Solid State through CH/p
Hydrogen Bonds
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Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!