Supramolecular Nanowires from an Acceptor–Donor–Acceptor Conjugated Chromophore

Article abstract of DOI:10.1002/chem.201904463

Oligothiophene derivatives have been extensively studied as p-type semiconducting materials in organic electronics applications. This work reports the synthesis, self-assembly and photophysical properties of acceptor–donor–acceptor (A–D–A)-type oligothiop

Full text of DOI:10.1002/chem.201904463

A Journal of
Accepted Article
Title: Supramolecular Nanowire from an Acceptor-Donor-Acceptor
Conjugated Chromophore
Authors: Suhrit Ghosh, Saptarshi Chakraborty, and Shinto Varghese
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Supramolecular Nanowire from an Acceptor-Donor-Acceptor
Conjugated Chromophore
Saptarshi Chakraborty, [a] Shinto Varghese,*[b] and Suhrit Ghosh*[a, b]
Abstract: Oligothiophene-derivatives have been extensively studied
as p-type semiconducting materials in organic electronics
applications. This manuscript reports the synthesis, self-assembly
and photophysical properties of a new acceptor-donor-acceptor (A-
D-A) type oligothiophene-derivative by end-group engineering of
quaterthiophene (QT) with naphthalene monoimide (NMI)
chromophores which are further connected to a tri-alkoxy benzamide
wedge. Conjugation to the NMI units reduces the HOMO-LUMO gap
significantly and consequently the absorption spectrum exhibits a
bathochromic shift of ~ 50 nm compared to QT. Furthermore,
extended H-bonding interaction among the amide groups of the
peripheral wedge produces entangled fibrillar nanostructure and
gelation in hydrocarbon solvent such as methylcyclohexane wherein
the A-D-A chromophore exhibits a typical H-aggregation. In contrary,
the same chromophore, lacking only the amide units, does not
produce gel or H-aggregation indicating strong impact of H-bonding
on the self-assembly. Computational studies reveal electronic
properties of the chromophore and predict the geometry of a dimer
in the H-aggregation which reasonably matches with the
experimental results. Bulk electrical conductivity measurements
estimate excellent conductivity value of 2.3 x 10-2 S cm-1 for the H-
aggregated system (OT-1) which is two orders of magnitude higher
than the same chromophore lacking the amide groups (OT-2).
small molecule conjugated donor chromophores. Oligothiophene
(OT) derivatives have been studied extensively as small
molecule donors for optoelectronic applications because of their
tunable band gap depending on the oligomeric length and/ or
nature of the ring substitution and high charge carrier mobility.[7]
End-group engineering of OTs by electron withdrawing
[8]
substituent’s have been attempted in few earlier examples
which showed promising results in charge transport and device
performance by inherently altering the electronic properties of
the conjugated chromophore. H-bonding driven supramolecular
assembly of such π-conjugated chromophores,[9] including OT-
[10]
derivatives
have been studied with great interest which
significantly improves electrical conductivity as it generates
percolation pathway for high charge carrier mobility. Such
supramolecular assembly approach enables control over internal
order as well as nanostructure morphology depending on the H-
bonding group, flexibility of linker, nature of the peripheral alkyl
chains etc all of which influence the packing of the
chromophores in self-assembled state. We wanted to explore
such supramolecular assembly approach for end-group
engineered OT-derivatives to realize dual effect of inherent
tuning of the electronic property of the chromophore and well-
defined self-assembly on their photophysical properties. To test
these possibilities we have synthesized oligothiophene
derivative OT-1 (Scheme 1) in which
a tetra-thiophene
chromophore is conjugated with acceptor type naphthalene-
monoimide chromophores in both terminals. The resulting
acceptor-donor-acceptor chromophore is connected with two
benzamide groups so that its supramolecular assembly could be
realized in non-polar solvents by H-bonding.
Introduction
Over the past two decades, significant efforts have been made
to study supramolecular assembly of wide ranging π-conjugated
[1]
molecules
which provides an effective strategy to fine tune
their optoelectronic properties. Subtle change in the π-orbital
overlap results in considerable modifications in the charge
[2-3]
transport and photophysical properties
and consequently
makes significant impact on device application.[4] Recent reports
indicate superb performance by nonfullerene acceptors
[5]
in
high performance organic solar cells which further motivate
research activities in this area. Although these reports indicate
that many small molecule acceptor type conjugated
chromophores are already at par with n-type conjugated
polymers in device performance, such examples are limited [6] for
Scheme 1. Structures of A-D-A type oligothiophene derivatives OT-1 and OT-
2.
[a]
[b]
Mr. S. Chakraborty and Professor Dr. S. Ghosh
School of Applied and Interdisciplinary Sciences
E-mail: psusg2@iacs.res.in
Dr. S. Varghese and Professor Dr. S. Ghosh
Technical Research Center
It is noteworthy that naphthalimide based donor-acceptor type
organic π-conjugated materials also found application in the very
recent past as small molecular acceptors in the organic
photovoltaics in an effort to replace the bench mark fullerene
derivatives as well as active materials in the field effect
Indian Association for the Cultivation of Science
2A and 2B Raja S. C. Mullick Road, Kolkata, India-700032
transistors and memory devices.[11] In the recent past we have
[12]
studied
such bisamide functionalized naphthalene-diimide
Supporting information for this article is given via a link at the end of
the document.
chromophores extensively and thus we felt the presence of the
two naphthalene-monoimide units would not only enhance the
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conjugation length and shift the electronic properties but also will
assist self-assembly by π-stacking interaction in addition to the
H-bonding among the amide groups. To specifically recognize
the impact of the H-bonding on the photophysical properties OT-
2 was synthesized which is similar to OT-1 except that the
amide groups are replaced by ester groups.
influence of H-bonding among the amide groups on gelation. To
directly probe H-bonding, solvent dependent FT-IR spectra of
OT-1 and OT-2 were compared (Figure 2a). In a good solvent
CHCl3, OT-1 exhibits few sharp peaks in the region of 1600-1800
cm-1 which can be assigned to symmetric (1700 cm-1) and
asymmetric (1657 cm-1) stretching of the imide carbonyl. In all
likelihood, the amide carbonyl stretching peak merged with the
imide asymmetric stretching peak.
Scheme 2. Synthesis of OT-1
In this manuscript we demonstrate synthesis, self-assembly,
photophysical
properties,
electrical
conductivity
and
computational studies to understand the electronic properties of
these new conjugated chromophores.
Results and Discussion
Figure 1. AFM image a) OT-1 and b) OT-2 in MCH (c = 0.05 mM) along with
Synthesis: Synthesis of OT-1 is shown in Scheme 2. The chiral
wedge (compound 3, Scheme S1) was synthesized from
commercially available methyl ester of gallic acid using few
standard synthetic steps. Tri-butyl tin substituted thiophene and
bi-thiophene derivatives (4 and 5) were synthesized from
commercially available thiophene and bi-thiophene, respectively,
using reported procedure. Boc-protected ethylene diamine was
reacted with commercially available 4-Bromo-1,8-naphthalic
anhydride to obtain compound 6 as a yellow solid. Compound 7
was prepared by the Stille Coupling between compound 6 and
thiophene derivative 4 using Pd(PPh3)4 as catalyst. Then, the
thiophene ring was brominated using N-bromosuccinimide to
obtain compound 8 which was treated with acid for deprotection
of the Boc group. The free amine (9) was coupled with the
wedge (3) to produce compound 10. Finally, Stille Coupling
between compound 5 and 10 produced the desired compound
OT-1 as a red solid. OT-2 was synthesized following similar
strategy which is described in the supporting information
(Scheme S2).
pictures of gel/ sol (in MCH; c = 10 mM). Insets show the height profile across
x-y.
For OT-2, similar spectral pattern was noticed except an
additional shoulder band at 1726 cm-1 corresponding to the ester
carbonyl. In MCH, for OT-1, a new band appeared at 1627 cm-1
which indicates that the peak for the amide carbonyl stretching
now shifted to lower wave number and thus was decoupled from
the imide carbonyl asymmetric stretching peak. H-bonding which
was also evident from the N-H bending peak that shifted from
3401 cm-1 (in CHCl3) to 3285 cm-1 (in MCH).
Solvent dependent UV/Vis spectra show (Figure 2b) identical
features for OT-1 and OT-2 in a good solvent CHCl3 exhibiting
broad absorption bands between 300-550 nm with λmax ~ 450 nm.
It is noteworthy that absorption spectrum of quaterthiophene
chromophore exhibits λmax ~ 400 nm [7, 10] and thus the observed
bathochromic shift of approximately 50 nm for OT-1/ OT-2 is
clearly a consequence of extending the conjugation with the
naphthalene-monoimide chromophores. Now in MCH the major
absorption band of OT-1 shows a blue shift of 30 nm with
concomitant appearance of a tailing in the longer wavelength
Supramolecular assembly: Supramolecular assembly of OT-1
was tested in methylcyclohexane (MCH) in which it was
dissolved at elevated temperature. Upon cooling the solution to
rt, it produced a viscous liquid which subsequently formed a
stable gel (Figure 1). However the control molecule OT-2 under
identical condition did not produce any gel. Atomic force
microscopy (AFM) images (Figure 1) show contrasting
[10, 14]
upto 600 nm indicating H-aggregation.
In contrast the
spectral nature of OT-2 does not change except a blue shift that
can be attributed to a mere solvatochromic effect. Therefore it is
evident that H-bonding strongly influences the self-assembly of
OT-1. Furthermore in CHCl3 OT-1 does not exhibit any notable
CD band (Figure 2c). In MCH, OT-1 shows a bisignated CD
band but not the ester containing OT-2. The zero crossing point
of the CD couplets overlaps with the H-aggregated absorption
band possibly indicating that the CD signal originates from a
morphology. OT-1 exhibits fibrillar structure (height- 4 nm,
[13]
length- several micrometers) which is typical for a gelator.
In
contrast, OT-2 produces spherical particle with an average
diameter in range of 300-400 nm clearly indicating strong
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exciton coupled species although contribution from the linear
dichroism cannot be fully eliminated at this stage. [15]
oxidation and reduction potential,
respectively.
The
electrochemical bad gaps were calculated to be 2.53 eV and
2.63 eV for OT-1 and OT-2, respectively. (Table 1). It can be
noted that the band gap for OT-1 is slightly lower than that of
OT-2 which can be attributed to π- π staking interaction.[17]
However this effect could not be fully realized in the CV
experiment for technical reasons as we could not conduct the
CV experiments in hydrocarbon solvents where self-assembly
was most prominent. Nevertheless the optical band gap could
be calculated for OT-1 in self-assembled state from the UV/Vis
spectrum in MCH which indicates a significant reduction (Table
1) from the monomeric state of OT-2.
Figure 3. Cyclic voltamograms of the OT-1 and OT-2 (1 mM, measured in
dichloromethane using TBAPF6 (0.1 M) as supporting electrolyte. All scan
rates were 100 mV S-1, potentials are internally referenced to the
ferrocene/ferrocenium (Fc/Fc+) couple. Arrows indicate the flow of current.
Table 1: Redox properties of OT-1 and OT-2
opt a)
b)
b)
CV
System
Eg
[eV]
Eox1
[V]
ERed1
[V]
EHOMO
[eV]
ELUMO
[eV]
Eg
[eV]
OT-1
OT-2
2.10
2.28
1.43
1.67
-1.10
-0.96
-5.73
-5.97
-3.20
-3.34
2.53
2.63
a)Estimated using the onset of absorption in solution spectra in MCH;
b)Calculated from onset values of the first oxidation and reduction waves
setting the ferrocene HOMO energy to 0.5 eV vs Ag/AgCl electrode
Figure 2. a) Solvent dependent FT-IR spectra of OT-1 and OT-2, the arrow
indicates the carbonyl and N-H stretching peak of the amide group in OT-1; c
= 5.0 mM. b) UV-Vis spectra of OT-1 and OT-2 in MCH and comparison with
that in CHCl3;c = 0.1 mM. c) Comparison of CD spectra of OT-1 with that of
OT-2 in MCH; c = 0.1 mM.
Geometry Optimization and Electronic Transitions: Density
functional (DFT) and time dependent density functional theory
(TD-DFT) were employed to understand the molecular geometry,
energy levels and electronic transitions of the Acceptor-Donor-
Acceptor triad. For both OT-1 and OT-2 only the π-conjugated
backbone was considered for the quantum chemical calculations.
Peripheral groups although influences the organization of
molecules, but to a lesser extent affect the electronic properties
in a molecular level and therefore were omitted. The geometry
optimization on a planar (C2h) as well as a fully relaxed
geometry was carried out with DFT/B3LYP/6-311G (d,p) level
with dichloromethane as solvent (Polarizable Continuum Mode-
PCM). The vibrational analysis on a planar centrosymmetric
structure showed imaginary frequencies, which implies a saddle
point, while the non-planar optimised structure exhibited no
imaginary frequencies indicating true minima on the potential
energy surface.
Redox properties: Cyclic Voltammetry was performed to
investigate the redox properties of OT-1 and OT-2 in 1.0 mM
solution of tetrabutyl ammonium hexafluorophosphate (TBAPF6)
in dichloromethane (Figure 3). Both OT-1 and OT-2 showed
double reversible reduction wave within the tested
electrochemical window, representing first reduction of NMI unit
to NMI radical anion followed by formation of di-radical anion
localised on each acceptor groups.[16] The first reduction
potential shifted to lower value going from OT-1 (Ered1 = -1.10) to
OT-2 (Ered1 = - 0.96) and first oxidation potential appeared at
1.43 eV and 1.67 eV, respectively. The HOMO and LUMO
energy levels are calculated to be -5.73 eV and -3.20 eV for OT-
1 and -5.97 eV and -3.34 eV for OT-2 from the onset of the first
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agreement with the mean absolute error of 0.2-0.3eV observed
in many chromophores exhibiting ICT at a DFT/B3LYP level of
theoretical investigations. [18] The vertical electronic transitions of
the A-D-A triad were simulated by time-dependent density
functional theory (TDDFT) with CAM-B3LYP/6-311G(d,p) level in
chloroform and methylcyclohexane solutions by employing PCM
solvation model. The solvent polarity has less effect on the
absorption spectra with a strong band around 430 nm in the
visible region. The S0 → S1 vertical transition energy and
oscillator strength are reasonably well reproduced by TD-DFT
with a deviation of about ~20 nm from the experimental spectra.
The lowest energy electronic transition is dominated by the
HOMO to LUMO transition with an overall contribution of 56%.
However, the contributions other than the pure frontier orbitals
are also significant (HOMO→LUMO+2, 26%). The orbital
contributions of the first four electronic transitions and the
corresponding oscillator strengths are shown in Table 2. The
natural transition orbitals (NTOs) of the lowest energy electronic
transition showed a very weak intra-molecular charge transfer
character compared to that of the pure frontier orbitals (Figure
5a) and is directly reflected in the minimal effect of solvent
polarity on the absorption spectra. The orbital contributions of
the electron–hole wave functions manly localized on the oligo
thiophene unit (Figure 5a). The excited state geometry and the
vertical transition energies (S1→S0) in solution was determined
at the same level as in the ground state (TD-CAM-B3LYP/6-
311G(d,p)/PCM), which gives an reasonable estimation of the
vertical excitation energies and the solvent effects. The vertical
transition energies of the molecules in methylcyclohexane
solution is 2.23eV (560 nm) and that of the chloroform solution is
2.12eV (590nm). The calculated values for the vertical transition
energies are in a reasonable agreement with the emission
spectra observed in solution, 540 nm in methylcyclohexane and
594 nm in chloroform (Figure S6). The NTO analysis showed a
substantial intra-molecular charge transfer character from
thiophene core to the peripheral naphthalimide unit (Figure 5b).
This corroborates with the observed red shift in emission with
increase solvent polarity in the (S1→S0) transition.
Figure 4. Illustration of the frontier molecular orbitals calculated at B3LYP/6-
311G(d,p)/PCM(DCM) level (isovalue surface 0.03 a.u).
The torsional angle of about ~54° between the naphthalimide
(acceptor) to the thiophene oligomeric unit (donor) and an
average displacement of about ~18° between the thiophene
rings due to steric demand was observed (See supporting
information for details, Figure S5).
b)
590nm
(f = 2.59)
S1→S0
a)
Table 2. The vertical transition energies of A-D-A triad calculated at TD-DFT
433nm
(f = 2.50)
S0→S1
level of theory (CAM-B3LYP/6-311G(d,p)). Configuration interaction (CI) is
given for relative weights >10%. Singlet oscillator strength
contributions are given in parenthesis.
f and CI
E / nm
( f )
E / nm
( f )
Trans.
CI Description
CI Description
Chloroform
Methylcyclohexane
Figure 5. The natural transition orbitals of the A-D-A triad for a) S0→ S1 and b) of
S1→ S0 transitions in chloroform solution. Significant charge transfer character is
observed for S1→ S0 transition compared to S0→ S1 transition. (isovalue surface
0.03 a.u)
H→L (56%)
H→L+2 (29%)
433
(2.50)
H→L(56%)
H→L+2(29%)
428
(2.48)
S0→S1
S0→S2
H→L+1(53%)
H→1→L (31%)
375
(0.00)
H→L+1(54%)
H-1→L(31%)
370
(0.00)
The HOMO and LUMO orbitals of the chromophore showed an
effective intra-molecular charge transfer (ICT) between the
donor and acceptor moieties with the electron density of the
HOMO localized mainly on the thiophene unit, whereas the
LUMO is localised on the peripheral naphthalimide units (Figure
4). The calculated frontier orbitals HOMO, LUMO and the energy
gap of the chromophore in dichloromethane solution are -5.42eV,
-2.86eV, and 2.56eV, respectively. The simulated energy levels
deviate from the experimental values (Table 1) by 0.19 and 0.3
eV for OT-1 and OT-2, respectively. These discrepancies are in
H→L+2 (46%)
H-1→L+1(25%)
H-2 →L (12%)
H-2→L+1(29%)
H→L+2(47)
H-1→L+1(24%)
H-2→L(12%)
347
(0.09)
344
(0.11)
S0→S3
H-2→L+1(32%)
H-3→L(20%)
H→L+3(18%)
H→L+3(23%)
H-3→L(19%)
H-1→L+2(11%)
310
(0.00)
308
(0.00)
S0→S4
S1→S0
560
(2.55)
590
(2.59)
H→L(83%)
H→L(83%)
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Aggregate Structure and exciton energetics: To have a
qualitative picture of the nature of absorption band and exciton
splitting in the molecular aggregates, calculations were carried
out on a co-facial dimer separated by a distance of 3.5Å and
progressively rotate along the axis orthogonal to the long
molecular axis to 45° with an interval of 5°. The introduction of
the amide groups is known to induce such rotations to have the
lowest energy (most stable) hydrogen bonded structures. A
planar optimised geometry is used to construct the dimer
structure, in expectation of a more planar structure induced by
close packing compared to that in solution. TD-DFT/CAM-
B3LYP/6-31G(d,p) level of theory was employed to calculate the
vertical transition energies. The lowest energy transition bearing
oscillator strength in all the dimeric structures shifted to a lower
wavelength (2.73eV) similar to that expected for the H-type
aggregates according to the molecular exciton model compared
to that of a planar (C2h) structure.[19] The lowest energy
transition in a perfect co-facial structure showed zero oscillator
strength and move progressively to higher values as the angle of
rotation increases, as expected due to the perturbed uniaxial
arrangement of the transition dipole moment. This is very much
evident from the absorption spectra of the aggregates in the
methylcyclohexane solution as the major absorption band has
some oscillator strength in the lowest energy while the maximum
shifted towards the high energy region. However, a one to one
correlation was not attempted due to the lack of molecular
packing information in the aggregates due to its dynamic nature.
The exciton coupling strength represented as half the energy
difference between the lowest excited state and the state that
bears reasonable oscillator strength.[20] Table SI summarises the
vertical transitions energies and exciton splitting energies
corresponds to the angle of rotation orthogonal to the long
molecular axis. The exciton splitting energy varies an order of
magnitude (0.31 to 0.03eV) with an angle of rotation from 0 to
45°.
Electrical Conductivity: To examine the impact of self-
assembly, bulk electrical conductivity of OT-1 and OT-2 was
examined by current-voltage (I-V) measurements (Figure 6)
using two point probe configuration. The room temperature
electrical conductivities (σ) of the drop casted films (from MCH)
were measured from the I-V experiment. Data for OT-1 device
showed typical nonlinear curve indicating contact resistance due
to a charge injection barrier.[21] The average conductivity value of
the OT-1 device was estimated to be 2.3 x 10-2 S cm-1 which is
an impressive value, [22] particularly considering that the samples
were prepared without any kind of doping. For control
experiment, I-V measurement was done for thin film of OT-2
which also showed semiconducting nature and conductivity
value was calculated to be 4 x 10-4 S cm-1 which is two orders of
magnitude less compared to the self-assembling OT-1 although
in both cases the conducting chromophore and peripheral
chains were exactly identical. The observed enhanced
conductivity of OT-1 is therefore attributed to the supramolecular
self-assembly by H-bonding.
Conclusions
We have introduced a new π-conjugated chromophore in which
two electron withdrawing naphthalimide derivatives have been
symmetrically conjugated with quaterthiophene chromophore
resulting in an A-D-A type conjugated molecule attached with
two tri-alkoxy benzamide wedge. The chromophore exhibits
significantly red shifted absorption compared to the parent
quaterthiophene derivative and in hydrocarbon solvent it shows
H-bonding regulated facile H-aggregation by face-to-face π-
stacking producing micrometer long fibrillar morphology and
gelation. In contrast the control molecule that lacks the amide
groups in the peripheral wedge shows no signature of self-
assembly under similar condition. Computational studies have
been performed to predict the electronic transitions, aggregated
structure and exciton energies of this newly introduced
conjugated chromophore which corroborate with the
experimental results.
Therefore the conjugation of the
naphthalimide units provides dual advantage of inherently
lowering the HOMO-LUMO gap as well as self-assembly to
produce percolated pathway which results in remarkably high
electrical conductivity that can be ranked among the top values
reported in the literature. We believe it will boost the search for
new molecular systems and self-assembly guideline for
improved performance in organic electronics.
Experimental Section
Gelation study: Stock solutions of both compounds (OT-1 and OT-2)
were made in CHCl3 at 10.0 mM concentration. Measured volume of
aliquot was transferred to a screw capped vial and the solvent was
evaporated by air blowing. Measured amount of methylcyclohexane was
added to the vial to make the concentration of solute 10 mM and then the
solution was heated to make homogenous solution and allowed to rest at
rt. OT-1 produced viscous solution followed by gelation (after 7 days)
whereas OT-2 remained as free flowing solution.
Figure 6. Representative I-V measurement curves of a) OT-1 and b) OT-2
devices drop casted from methylcyclohexane solution
Spectroscopy studies: Stock solutions 0.1 mM of OT-1 and OT-2 were
prepared in both chloroform and methylcyclohexane by directly dissolving
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the sample in the solvent at elevated temperature. These samples were
equilibrated at rt for 2h before spectral measurements were carried out.
UV/Vis studies were carried out at 25 °C using the cuvette of 1.0 cm path
length. FT-IR studies were done with relatively concentrated samples
(5.0 mM) using Perkin Elmer Spectrum 100FT-IR spectrometer for OT-1
and OT-2 in CHCl3 and MCH.
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AFM studies: Sample solutions of OT-1 and OT-2 (C= 0.05 mM) were
prepared in methylcyclohexane by directly dissolving the solid in a given
solvent at elevated temperature and then these solutions were
equilibrated at rt for 2h. 10 µl of each sample was drop casted on mica
surface and spin coated at speed of 1000 rpm for 1 min and air dried for
overnight before capturing AFM images.
[2]
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Cyclic voltammetry: Cyclic voltammetry experiment was performed in
dichloromethane (10-3 M) at a scan rate of 100 mV s-1 using a three
electrode setup consisting of a glassy carbon working electrode, a
platinum wire auxiliary electrode, and a silver wire (as the pseudo-
reference electrode). Tetra-n-butylammonium hexafluorophosphate (0.1
M) was used as the supporting electrolyte. Reference electrode was
frrocene/ferrocenium couple (Fc/Fc+). The HOMO and LUMO energy
levels of OT-1 and OT-2 molecule was calculated from the onset
oxidation potential (EOx1 onset) and the onset reduction potential (ERed1
onset) using following equations.
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ELUMO= - (ERed1 onset - E Fc/Fc+ onset) - 4.80 eV
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Acknowledgements
SC thanks CSIR for a research fellowship. SG thanks DST for
funding through SwarnaJayanti Fellowship (DST/SJF/CSA-01/2-
14-15). SV acknowledges Technical Research Centre, IACS
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Keywords: Supramolecular Assembly • Oligothiophene
derivative • H-aggregate • H-bonding• Organogel • Conductivity
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Entry for the Table of Contents
FULL PAPER
H-bonding regulated H-aggregation of
newly introduced acceptor-donor-
acceptor type conjugated
chromophore produces fibrillar
nanostructures for realizing
remarkably high electrical
conductivity.
Saptarshi Chakraborty, Shinto
Varghese* and Suhrit Ghosh*
Page No. – Page No.
Supramolecular Nanowire from an
Acceptor-Donor-Acceptor Conjugated
Chromophore
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