Fully sp2-Carbon-Linked Crystalline Two-Dimensional Conjugated Polymers: Insight into 2D Poly(phenylenecyanovinylene) Formation and its Optoelectronic Properties

Article abstract of DOI:10.1002/chem.201806385

Cyano-substituted polyphenylene vinylenes (PPVs) have been the focus of research for several decades owing to their interesting optoelectronic properties and potential applications in organic electronics. With the advent of organic two-dimensional (2D) cr

Full text of DOI:10.1002/chem.201806385

A Journal of
Accepted Article
Title: Fully sp²-Carbon-Linked Crystalline Two-Dimensional Conjugated
Polymers: Insight into 2D Poly(Phenylenecyanovinylene)
Formation and their Optoelectronic Properties
Authors: Daniel Becker, Bishnu Prasad Biswal, Paula Kaleńczuk,
Naisa Chandrasekhar, Lars Giebeler, Matthew Addicoat,
Silvia Paasch, Eike Brunner, Karl Leo, Arezoo Dianat,
Gianaurelio Cuniberti, Reinhard Berger, and Xinliang Feng
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To be cited as: Chem. Eur. J. 10.1002/chem.201806385
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Fully sp2-Carbon-Linked Crystalline Two-Dimensional Conjugated
Polymers: Insight into 2D Poly(Phenylenecyanovinylene)
Formation and Their Optoelectronic Properties
Daniel Becker,[a],‡ Bishnu P. Biswal,[a],‡ Paula Kaleńczuk,[a] Naisa Chandrasekhar,[a] Lars Giebeler,[b]
Matthew Addicoat,[c] Silvia Paasch,[d] Eike Brunner,[d] Karl Leo,[e] Arezoo Dianat,[f] Gianaurelio
Cuniberti,[f] Reinhard Berger,*[a] Xinliang Feng*[a]
Abstract: Cyano-substituted polyphenylene vinylenes (PPVs) have been in the focus of research for several decades due to their interesting
optoelectronic properties and potential applications in organic electronics. With the advent of organic two-dimensional (2D) crystals, the
question arose how the chemical and optoelectronic advantages of PPVs evolve in 2D compared to their linear counterparts. In this work, we
present the efficent synthesis of two novel 2D fully sp²-carbon-linked crystalline PPVs and investigate the essentiality of inorganic bases for
their catalytic formation. Notably, among all bases screened, cesium carbonate (Cs2CO3) plays a crucial role and enables reversibility in the
first step with subsequent structure locking by formation of a C=C double bond to maintain crystallinity, which is supported by density
functional theory (DFT) calculation. We propose a quantifiable energy diagram of a “quasi-reversible reaction” which allows to identify further
suitable C-C bond formation reactions for 2D polymerizations. Moreover, we delineate the narrowing of the HOMO-LUMO gap by expanding
conjugation into two dimensions. To enable environmentally benign processing, we further perform the post-modification of 2D PPVs, which
renders stable dispersions in the aqueous phase.
130 GPa, e.g.[4] Conjugation in 2D directions can offer multiple
conjugation pathways and thus can overcome the problem of
Introduction
limited conjugation lengths and possible point defects. On a
Since the discovery of electrical conductivity in polyacetylene
fundamental level, extending the conjugation significantly alters
through doping in 1977,[1] linear conjugated polymers are an
the electronic structure of conjugated polymers compared to their
important materials class for applications in organic light-emitting
linear cases. It has been theoretically predicted that the energy
diodes, organic photovoltaics and organic field-effect
gap between highest occupied molecular orbital (HOMO) and
transistors.[2] In contrast to linear conjugated polymers, extension
lowest unoccupied molecular orbital (LUMO) evolves faster in the
of conjugation in two dimension (2D) has fascinated theoreticians
2D structure, whereas the experimental proof is still missing.[5]
for several decades.[3] However, it was only until the discovery of
Towards the synthesis of 2D conjugated polymers, several
graphene in 2004 that 2D conjugated polymer frameworks
become emerging synthetic targets for experimental chemists
strategies have been attempted so far. For instance, a meta-
connected 2D polyphenylene as the “porous graphene” and
because graphene has demonstrated outstanding physical
covalent assemblies of porphyrin monomers have been reported
properties, including high room temperature mobility of µ = 2.5 ×
via the on-surface synthesis under ultra-high vacuum
105 cm2 V−1 s−1, Young modulus of 1 TPa and intrinsic strength of
conditions.[6] However, a transfer of such metal surface-binding
2D conjugated polymers is a difficult issue. Recently, a solid-state
polymerization approach was presented, which nonetheless
required the monomers pre-arranged in bulk crystals, thus limiting
the kind of monomers and type of reactions.[7] 2D π-conjugated
covalent organic frameworks (COFs), which are also considered
as stacked, crystalline 2D conjugated polymers, are typically
formed by employing reversible condensation reactions in
solution synthesis approach. They mostly contain C=N linkages,
which lack efficient conjugation.[8] In contrast, 2D conjugated
polymer backbones consisting of entirely C=C linkages which
would provide superior conjugation as well as chemical and
electrochemical stabilities, remain an enormous synthetic
challenge.[9,10] Despite of the recent progress in the synthesis of
sp²-carbon-linked 2D conjugated polymers by Knoevenagel
polycondensation reaction, the formation mechanism is still
unknown which hampers the establishment of a robust synthetic
methodology for the further development of related materials and
[a]
[b]
D. Becker,‡ Dr. B. P. Biswal,‡ P. Kaleńczuk, Dr. N. Chandrasekhar,
Dr. R. Berger, Prof. Dr. X. Feng
Faculty of Chemistry and Food Chemistry, Center for Advancing
Electronics Dresden, Technische Universitat Dresden, 01062,
Dresden, Germany.
E-mail: xinliang.feng@tu-dresden.de;
reinhard.berger@tu-dresden.de
Dr. L. Giebeler
Department Chemistry of Functional Materials, Leibniz Institute for
Solid State and Materials Research Dresden, Helmholtzstr. 20,
01069 Dresden, Germany
[c]
[d]
[e]
[f]
Dr. M. Addicoat
School of Science and Technology, Nottingham Trent University,
Clifton Lane, Nottingham, NG11 8NS, UK
Dr. S. Paasch, Prof. Dr. E. Brunner
Chair of Bioanalytical Chemistry, Technische Universität Dresden,
01069, Dresden, Germany.
Prof. Dr. Karl Leo
Dresden Integrated Center for Applied Physics and Photonic
Materials (IAPP), Nöthnitzer Str. 61, 01187 Dresden
Dr. A. Dianat, Prof. Dr. G. Cuniberti
applications.[11]
.
Herein, we demonstrate the efficient synthesis of two novel
2D cyano-substituted poly(phenylene vinylene)s (CN-PPVs),
namely 2D-CN-PPV-1 and -2 (Scheme 1a) by controlling the
Knoevenagel polycondensation reaction between 1,3,5-tris(4-
cyanomethylphenyl)benzene (TCPB) with 1,3,5-tris(4-formyl-
Institute for Materials Science, Technische Universität Dresden,
01062, Dresden, Germany.
[‡]
These authors contributed equally to this work.
Supporting Information and the ORCID number(s) for the author(s)
of this article can be found under https://doi.org/xxxxxxxxxxxxxx.
1
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phenyl)benzene (TFPB) and 4,4'-biphenyldicarboxaldehyde
(BPDA), respectively.
Scheme 1. Schematic illustration of Knoevenagel polycondensation reaction employed in a) formation of crystalline 2D-CN-PPVs and demonstration of the
conjugation degree, i) Cs2CO3; o-DCB, 120 ºC, 3 days; b) model reactions resembling solvothermal conditions with inorganic Lewis bases optimization; c) Proposed
Cs2CO3 mediated reaction pathway for the formation of 2D-CN-PPVs.
The chemical structure and long range ordering of the targeted
2D-CN-PPVs have been unambiguously confirmed by Fourier
transformed Infrared Spectroscopy (FT-IR), 13C cross-polarization
magic-angle spinning (CP-MAS) NMR and powder X-ray
Result and Discussion
diffraction (P-XRD). In order to gain insight into the propagation
mechanism of the polymerization step, we examined the
essentiality of inorganic bases by means of DFT-NEB theoretical
modelling. Importantly, we observed that Cs2CO3 inherits the
unique ability to facilitate reversible C-C bond formation and lower
activation energy in the first step in contrast to all other applied
bases, which are crucial for the final crystalline 2D polymer
formation. Furthermore, we explored the optoelectronic
characterizations of these 2D PPVs employing Ultraviolet/Visible
(UV/Vis), photoluminescence (PL) spectroscopy and cyclic
voltammetry (CV). Moreover, the evolution of band gaps by
improved conjugation of three different 2D-CN-PPVs was clearly
demonstrated. Finally, a post-modification has been developed
on 2D-CN-PPVs to improve the dispersibility in aqueous phase
for better solution processability, which can be essential for the
application of such new polymeric materials for thin-film based
devices.
The polymerizations toward targeted 2D-CN-PPVs (Scheme 1a)
were achieved by employing Knoevenagel condensation
reactions of aromatic aldehydes such as TFPB, BPDA and TCPB,
respectively. For comparison, we also synthesized the earlier
reported polymer, namely 2D-CN-PPV-0, starting from TFPB and
1,4-bis(cyanomethyl)benzene (phenylenediacetonitrile, PDAN).[9]
In addition, we investigated the effect of polymerization efficiency
by examining the homologous row of alkali metal carbonates
(from Na to Cs), CsF, BaCO3 and NaOH in model reactions
resembling the solvothermal conditions (o-DCB, 120 °C, 3 days)
between TCPB and benzaldehyde (Scheme 1b). It has been
noticed that, from all applied Lewis bases, only Cs2CO3 (84%
yield) and BaCO3 (53%) yielded the model compound. In
agreement, targeted crystalline 2D conjugated polymers resulted
only from using Cs2CO3, while no other bases worked at all. This
result strongly suggests that Cs2CO3 plays an important and
particular role. To understand the role of Cs2CO3 in the
Knoevenagel condensation reaction (Scheme 1c), we examined
2
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the reaction mechanism by means of DFT – nudged elastic band
(NEB) calculations by considering one condensation step
between TFPB and TCPB (Figure 1). We observed that among all
bases studied (see Figure S10-1, Electronic Supplementary
Information), Cs2CO3 is able to reduce the energy barrier on the
way towards the initial C-C single bond from stage 1 (STG1) to
STG3 most effectively as shown in Figure 1. Through bridging
oxygen and nitrogen, forming a five-membered transition state
(Figure 1, STG3), Cs+ can well stabilize the intermediate state.
neighbouring the nitrile group at 110 ppm, and the nitrile-C at 119
ppm. No residual aldehyde peak was observed, which would be
expected at 191 ppm compared with the CP-MAS NMR spectra
of the monomer (Figure S3-6, ESI) which supports the
polymerization efficiency. Thermogravimetric analyses (TGA)
disclose that all three 2D-CN-PPVs have excellent thermal
stabilities up to 400°C (Figure S6-3, ESI).
Scanning electron microscopy (SEM) and transmission
electron microscope (TEM) imaging were performed to unravel
the morphology of these 2D-CN-PPVs. Toward this end, 2D-CN-
PPVs were exfoliated by mechanical grinding for 15 min. and
followed by sonication in ethanol. The as-prepared dispersions
were filtered through a syringe filter and drop-casted on the
substrate. In all cases they show layered morphologies with sizes
up to 10 µm (Figure 2c-e and Figure S7-1, ESI). In order to prove
the regioregular crystalline 2D structure in each 2D-CN-PPVs, (P-
XRD) measurements were conducted. The first intense reflection
for 2D-CN-PPV-1 was observed at 3.91° 2θ corresponding to the
(100) plane along with other minor reflections at 6.91°, 7.94° and
8.30° 2θ. Similarly for 2D-CN-PPV-0 and 2D-CN-PPV-2 the first
reflection appeared at 2.74° and 2.27° 2θ, respectively, which are
attributed to the (100) plane. 2D-CN-PPV-2 with the BPDA
spacer only shows two major reflections in the P-XRD pattern,
indicating moderate crystallinity (Figure 2b). This observation
could be explained by the lower shape persistency of the starting
monomers leading to weaker interlayer π-π stacking and
therefore worse alignment in the plane.[13] The structures of all the
2D-CN-PPVs were optimized in typical eclipsed (AA), staggered
(AB) and slipped eclipsed (slip-AA) π-π stacking arrangements
using the Density Functional Tight Binding method. It has been
found that the experimental P-XRD of all 2D-CN-PPVs are
matched well with the simulated one derived from the eclipsed
(AA) π-π stacking arrangement (Figure S4-1 – S4-3, ESI).
Figure 1. Energy profiles at different stages (STG1-6) calculated in eV using
DFT-NEB method describing the proposed reaction mechanism.
However, its energy is slightly higher than the comparable
intermediates employing Li+ and Na+ ions (see Figure S10-1, ESI).
Therefore, the energetic position of STG3 seems to promote
bond cleavage and thus the back reaction: On the one hand from
intermediate STG3 C-C-bond cleavage back into STG2 is
possible as well as on the other hand continuation of the reaction
path via protonation of STG3 and the release of Cs2CO3 into
STG4. After a subsequent elimination of water in STG5, the
formation of the targeted C=C double bond in the final STG6 is
possible. The energy barrier for the condensation step (Figure 1,
STG5) can be overcome easily by thermal fluctuations with all
alkali metal carbonates. Taken these results into account Cs2CO3
seems to play a specific role due to its size,[12] which has the
ability to bridge oxygen and nitrogen, to stabilize the carbanion in
STG2 and to slightly but importantly destabilize the intermediate
STG3. As the result, it enables a polymer growth with a “quasi-
reversible” C-C bond formation. Such error correcting process is
assumed to play the key role in achieving crystalline 2D
conjugated polymer structures. We propose, that DFT – NEB
calculation allows to draw a quantifiable energy diagram of a
“quasi-reversible” reaction and may identify suitable C-C bond
formation reaction for 2D polymerization during or even before
experimental “try and error” screening. The chemical composition
and functional groups of all 2D-CN-PPVs are confirmed by FT-IR
and CP-MAS NMR characterizations. In the FT-IR spectra (Figure
S3-1 – S3-4, ESI), the C=C stretch signal is identified at 3050 cm-
Further, the Pawley refinement was carried out for 2D-CN-
PPV-1 and -2 to calculate the lattice parameter using the same
AA model (Figure S4-5 and S4-6, ESI). In their stacked form, the
permanent porosity and pore size distribution of 2D-CN-PPV
powders
were
determined
through
N2
physisorption
measurements at 77 K (Figure S6-1 and S6-2).[14] Reversible type
I adsorption-desorption isotherms with specific surface areas of
301 m² g-1 for 2D-CN-PPV-1 and 638 m² g-1 for 2D-CN-PPV-2,
respectively, according to the Brunauer-Emmett-Teller model in
the relative pressure range 0.01 to 0.2, were found. From the N2
adsorption data the pore size distributions were calculated using
the Non-Local Density Functional Theory (NLDFT) model, which
shows the primary peak positioned at 1.45 nm for 2D-CN-PPV-1
and 3.24 nm for 2D-CN-PPV-2, respectively. The experimentally
determined pore sizes are slightly smaller than the predicted
values from the structural models (2.1 nm for 2D-CN-PPV-1 and
4.0 nm for 2D-CN-PPV-2), which are attributed to the eclipsed
stacking arrangements.
To gain insight into the fundamental optoelectronic
properties of the 2D-CN-PPVs, we performed UV-Vis (Figure 3a)
and photoluminescence (PL) spectroscopic experiments (Figure
3b). Measurements were carried out with as-prepared dispersions
(~1 mg mL-1) in isopropanol in the center of an Ulbricht sphere to
avoid the contribution of reflectance.[15] 2D-CN-PPV-1 shows an
absorption band centered at 368 nm, 2D-CN-PPV-0 at 372 nm
and 2D-CN-PPV-2 at 384 nm with corresponding absorption
edges of 460, 501 and 488 nm, respectively. These values
correspond to optical band gaps of 2.70, 2.47 and 2.54 eV for 2D-
CN-PPV-1, 2D-CN-PPV-0 and 2D-CN-PPV-2, respectively.[16] The
visual appearance of all 2D-CN-PPV dispersions under UV light
exposure is shown in Figure 3d. For comparison, we carried out
1
for all 2D-CN-PPVs. Further, the appearance of a peak at 2250
cm-1 from the nitrile groups and the negligible peak at 1667 cm-1
corresponding to the aldehyde group of the starting monomers
suggest high polymerization efficiency. The CP-MAS NMR
spectra of all the 2D-CN-PPVs (Figure 2a) show a similar pattern
with clear peak resolution, which refers to a high degree of
structural ordering. The chemical shift of quaternary benzene
ring-C atoms appears at 141 ppm along with the tertiary benzene
C-atoms at 127 ppm. The chemical shift of the C-atom attached
to the nitrile group is assigned to 132 ppm, the quaternary C-atom
3
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the UV-Vis measurement in solid state and observed a good
agreement with the absorption from dispersion with only a slight
bathochromic shift of the maximum absorption for all three
polymers in the range of 11 to 26 nm.[17] PL measurements were
performed in dispersions in isopropanol (5 mg mL-1). All 2D-CN-
PPV materials showed strong and distinct fluorescence at 498,
550 and 511 nm with PL quantum yields of 5%, 3.5% and 8.1%
for 2D-CN-PPV-1, -0, and -2, respectively.[18]
Figure 2. Evaluation of chemical structure, morphology and crystallinity of 2D-CN-PPVs. a) CP-MAS NMR spectra; b) experimental and simulated P-XRD patterns of
2D-CN-PPV-2 (blue), 2D-CN-PPV-0 (red) and 2D-CN-PPV-1 (black); c), d) and e) TEM images of mechanochemically exfoliated 2D-CN-PPV-2 , 2D-CN-PPV-0 and
2D-CN-PPV-1, respectively, after sonication in ethanol. Scale bar 500 nm. f) and g) show the spacefill models of the two new synthesized 2D-CN-PPV-1 and -2,
respectively.
Additionally, cyclic voltammetry (CV, Figure 3c) was performed on
the drop-casted samples of 2D-CN-PPVs. In all systems, a quasi-
limited. This result strongly suggests that the 2D-CN-PPVs own
significant cross-conjugation along the meta-direction. The
experimental energy band gaps of reported linear meta-
connected CN-PPV polymers are found to be at 2.7 eV and
generally higher than the para-connected counterparts and herein
the achieved 2D-CN-PPVs.[17,18] With this series of 2D-CN-PPVs
in our hand, our results for the first time experimentally
demonstrate the declining effect of the HOMO-LUMO gap for 2D
conjugated polymers with increasing conjugation. As similar to
many other 2D layered materials, one major drawback of 2D
conjugated polymers can be their poor solution processability.
Therefore, to increase the dispersibility and processability of 2D-
CN-PPVs from environmentally friendly solvents, we further
hydrolysed 2D-CN-PPV-1 in basic conditions, which produced
2D-COOH-PPV-1 (Figure 4a, experimental procedure can be
found in Supplementary Information). The carboxylic acid
moieties of 2D-COOH-PPV-1 increase the water affinity and the
water vapor uptake in comparison to the parent 2D-CN-PPV-1
bearing nitrile groups. This behavior is shown by the water vapor
sorption isotherms in the low pressure region, which is indicative
of high-water-surface interactions (Figure 4b).[19] The measured
Zeta potential of 2D-COOH-PPV-1 in neutral water (-73.6 mV) is
much lower than the well-known graphene oxide (-43 mV),
reversible
reduction
step
at
-0.76,
-0.85 and 0.78 V was observed, corresponding to LUMO values
of -3.41, -3.44 and -3.42 eV and irreversible oxidation at 1.30,
1.21 and 1.26 eV for 2D-CN-PPV-1, -0, and -2, respectively. All
optoelectronic data are summarized and compared to the linear
PPV counterparts (Table S9-1, ESI). Apparently, the band gap
decreases from 2.70 eV for 2D-CN-PPV-1 to 2.47 eV for 2D-CN-
PPV-0 by 0.23 eV. This behaviour is explained by the longer
conjugation length of the linear linkage contribution (Scheme 1a).
Although, for 2D-CN-PPV-2 lateral extension by one additional
phenylene is introduced, the increase of the optical band gap is
likely due to the higher twisting degree of biphenylene unit and,
therefore, affected conjugation degree (see Scheme 1a). The
same trend is found for the UV-Vis absorption maxima and is
supported by theoretical modelling on the single layer 2D
conjugated polymers. Interestingly, the optical band gaps of
2D-CN-PPV-0 and 2D-CN-PPV-2 are in the same range as the
para-connected 1D-CN-PPV. Only the band gap of 2D-CN-PPV-1
is slightly higher (2.7 eV). It should be emphasized that in the
linear 1D-CN-PPV only para-connection is employed, whereas,
the percentage of strictly para-linkage in the 2D-CN-PPVs is very
4
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indicating a stable dispersion in aqueous phase. A Zeta potential
of -30 mV is considered as threshold for stable dispersions in
water (Figure 4c).[20] The SEM image of drop-casted 2D-COOH-
PPV-1 in water shows a homogeneous polymer film formation,
which further supports good solution processability of the
hydrolysed polymer than the parent 2D-CN-PPV-1 (Figure S7-2,
ESI).
Figure 3. UV/Vis absorption and b) PL spectra (λex = 420 nm at 25 °C) of 2D-CN-PPVs from dispersions in isopropanol; c) CV (in acetonitrile with
0.1 M [nBu4N][PF6] as electrolyte, measured at a scan rate of 0.1 V s-1) from 2D-CN-PPV-1 (black), 2D-CN-PPV-0 (red) and 2D-CN-PPV-2 (blue), respectively. d)
Photo of 2D-CN-PPVs dispersed in Ethanol under 365 nm UV-light irradiation.
(Figure S4-4, ESI). Solid state UV/Vis measurements showed an
absorption edge of 467 nm for 2D-COOH-PPV-1, which is
consistent to the absorption edge of 465 nm for 2D-CN-PPV-1
(Figure S5-1, ESI).
Conclusions
In summary, we demonstrate two novel 2D cyano- substituted
polyphenylene vinylene polymers
by controlling the
Knoevenagel condensation reaction, and conduct a deep study
on the crystalline 2D conjugated polymer formation as a function
of inorganic Lewis bases and explore their optoelectronic
properties. Our experimental and theoretical results disclose the
crucial and unique role of the base in the formation mechanism
for polymerizations in 2D. We propose a quantifiable energy
diagram of a “quasi-reversible reaction” which allows to identify
further suitable C-C bond formation reactions for new 2D
conjugated polymers. Furthermore, we delineate the narrowing
of the HOMO-LUMO band gaps of 2D conjugated polymers with
increasing conjugation and reveal the significant cross-
conjugation over meta-linkages. A post-modification of 2D-CN-
PPVs was developed through hydrolysis, which results into high
surface polarity and better solution processability from aqueous
solution. We believe that our work will provide novel insight into
the synthetic development of emerging crystalline 2D conjugated
polymers with low band gaps for applications in organic
electronics.
Figure 4. a) Schematic illustration of post-synthetic modification of 2D-CN-
PPV-1 to 2D-COOH-PPV-1; b) water absorption isotherms; c) Zeta Potential of
2D-COOH-PPV-1 (0.05 mg/mL) in water of 2D-COOH-PPV-1 (green) and 2D-
CN-PPV-1 (black), respectively.
Remarkably enough, the hydrolyzed polymer 2D-COOH-PPV-1
well maintained its crystallinity and, thus structural integrity
5
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Conflict of Interest
There are no conflicts to declare.
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Acknowledgements
This research was supported financially by the EC under Graphene
Flagship (No. CNECT-ICT-604391), the Center for Advancing Electronics
Dresden (cfaed), the European Union/European Social Fund and the
Free State of Saxony (ESF project “GRAPHD”, TU Dresden). We thank
Dr. Philipp Schlender for P-XRD, Dr. Tilo Lübken for NMR in solution,
M.Sc. Felix Fries and Prof. Dr. Sebastian Reineke for PLQY
measurements, M.Sc. Sven Grätz and Dr. Lars Borchardt for
vaporsorption measurements and Dresden Center for Nanoanalysis
(DCN) and Mr. SangWook Park for SEM, Mr. Hafesudeen Sahabudeen
and Mr. Kejun Liu for TEM measurements. We also acknowledge Dr.
Renhao Dong, Dr. Junzhi Liu for helpful discussions and Ms. Verena
Müller for practical support as student research assistant. Computational
resources were provided by the Center for Information Services and High
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Keywords: 2D Conjugated Polymers • Polyphenylene Vinylene
• Density Functional Calculations • Optoelectronics • Post-
synthetic Modification
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This article is protected by copyright. All rights reserved.

10.1002/chem.201806385
Chemistry - A European Journal
FULL PAPER
FULL PAPER
In this work, we present the efficent
synthesis of two novel 2D fully sp²-
carbon-linked crystalline PPVs and
investigate the essentiality of
inorganic bases for their catalytic
formation. Notably, among all bases
screened, cesium carbonate (Cs2CO3)
plays a crucial role and enables
reversibility in the first step with
subsequent structure locking by
formation of a C=C double bond to
maintain crystallinity, which is
Daniel Becker, Bishnu P. Biswal, Paula
Kaleńczuk, Naisa Chandrasekhar, Lars
Giebeler, Matthew Addicoat, Silvia
Paasch, Eike Brunner, Karl Leo, Arezoo
Dianat, Gianaurelio Cuniberti, Reinhard
Berger,* Xinliang Feng*
Page No. 1 – Page No. 7
Title
Fully sp2-Carbon-Linked Crystalline
Two-Dimensional Conjugated
Polymers: Insight into 2D
Poly(Phenylenecyanovinylene)
Formation and Their Optoelectronic
Properties
supported by density functional theory
(DFT) calculation.
7
This article is protected by copyright. All rights reserved.