Conveniently Synthesized Butterfly-Shaped Bitriphenylenes and their Application in Solution-Processed Organic Field-Effect Transistor Devices

Article abstract of DOI:10.1002/ejoc.201901470

Various π-extended new bitriphenylene derivatives (both conformationally-free and conformation-locked) have been successfully synthesized by a facile Scholl oxidative cyclodehydrogenation method in good to excellent yields. Their optical properties in solution and film states reveal possibility for self-ordering. The molecular packing in solid-state demonstrates favorable π–π stacking as well as weak intermolecular interactions leading to face-to-face or slipped-stack arrangements. Besides, these butterfly-shaped large bitriphenylenes display near-UV absorption, excellent photochemical, thermal, and electrochemical stabilities. The all-organic anneal-free transparent FETs fabricated from solution-processable bitriphenylenes showcase significant improvement (ca. 4 orders of magnitude higher) in charge transporting abilities (μ_h: from ca. 10^–7 to 10^–3 cm²/(Vs)) when compared to model triphenylene. The fabricated FETs unveil excellent air stability (> 1 year under atmospheric conditions) highlighting the utility of these novel link-locked triphenylene skeletons in organic electronics.

Full text of DOI:10.1002/ejoc.201901470

A Journal of
Accepted Article
Title: Conveniently Synthesized Butterfly-Shaped Bitriphenylenes
and their Application in Solution-Processed Organic Field-Effect
Transistor Devices
Authors: Jagarapu Ramakrishna, Logesh Karunakaran, P. Shyam
Vinod Kumar, Ajith Mithun Chennamkulam, Venkatesan
Subramanian, Soumya Dutta, and Parthasarathy
Venkatakrishnan
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Eur. J. Org. Chem. 10.1002/ejoc.201901470
Link to VoR: http://dx.doi.org/10.1002/ejoc.201901470
Supported by

10.1002/ejoc.201901470
European Journal of Organic Chemistry
FULL PAPER
Conveniently Synthesized Butterfly-Shaped Bitriphenylenes and
their Application in Solution-Processed Organic Field-Effect
Transistor Devices
Jagarapu Ramakrishna,[a] Logesh Karunakaran,[b] P. Shyam Vinod Kumar,[c] Ajith Mithun
Chennamkulam,[b] Venkatesan Subramanian,*[c] Soumya Dutta*[b] and Parthasarathy
Venkatakrishnan*[a]
Dedication ((optional))
Abstract: Various π-extended new bitriphenylene derivatives (both
devices, such as, organic field-effect transistors (OFETs), organic
solar cells (OSCs), organic light emitting diodes (OLEDs).[1] Under
this category, soft and self-organizing large and rigid disc-like
aromatics[2] surrounded by long flexible chains have
demonstrated high promise due to their inherent capability to (i)
conformationally-free and conformation-locked) have been
successfully synthesized via
a
facile Scholl oxidative
cyclodehydrogenation method in good to excellent yields. Their
optical properties in solution and film states reveal possibility for self-
ordering. The molecular packing in solid-state demonstrates
favourable π-π stacking as well as weak intermolecular interactions
leading to face-to-face or slipped-stack arrangements. Besides, these
butterfly-shaped large bitriphenylenes display near-UV absorption,
excellent photochemical, thermal, and electrochemical stabilities. The
all-organic anneal-free transparent FETs fabricated from solution-
processable bitriphenylenes showcase significant improvement (ca. 4
orders of magnitude higher) in charge transporting abilities (μh: from
ca. 10-7 to 10-3 cm2/(Vs)) when compared to model triphenylene. The
fabricated FETs unveil excellent air stability (> 1 year under
atmospheric conditions) highlighting the utility of these novel link-
locked triphenylene skeletons in organic electronics.
promote
columnar
packing
behaviour
(columnar
mesophases/superstructures) by easily aligning themselves, (ii)
thereby favour a large area π-orbital overlap between the
adjacent molecules facilitating one dimensional (1D) migration of
charge carriers,[3] (iii) offer solution/melt-processability, and (iv) be
able to self-repair defects that act as charge carrier traps.
Ultimately, various large polycyclic aromatic cores, such as, hexa-
peri-hexabenzocoronene, coronene, porphyrin, phthalocyanine,
perylenebisimide, etc. have surfaced as high mobility liquid crystal
semiconductors in the literature.[4,5]
In relevance, triphenylene—a relatively small PAH—,despite its
great exploration in the field of liquid crystals due to its beneficial
1D columnar packing behaviour, chemical and photochemical
stability, tuneable optical, electronic and semiconducting
properties,[2,6,7] possesses high band gap energies (Eg  3.7 eV)
and is considered a poor (hole) semiconductor.[8] Consequently,
there exists scant reports on the applicability of simple
triphenylenes (for example, hexaalkoxytriphenylene HAT,
Introduction
Solution-processable π-conjugated organic semiconductors (for
example: polycyclic aromatic hydrocarbons, PAHs) are of
immense interest in recent days, especially, due to their profound
application in low-cost, large-area flexible organic electronic
hexaalkylthiotriphenylenes
HATT,
hexaphenyl/hexatrimethylsilylethynyltriphenylenes PETP/HTMT,
hexaphenyltriphenylenes PTP, etc., Figure 1)[9] or their π-
extended versions in electronic devices. For example, the
average mobilities of solution-processed FET devices fabricated
from π-extended hole semiconductors HHBT and HDBT are 1.4
× 10-4 and 2.8 × 10-5 cm2/(Vs),[9b,c] respectively (Figure 1).
However, the synthesis of HHBT/HDBT involve multiple steps
using expensive metal-based cross-coupling reactions, and
mobilities of such discotics seem to depend on annealing or
substrate temperatures. Such variation in mobility is reasoned to
the fluctuation of molecules within the stacks or intrastack
dynamism or self-healing behavior. One of the ways to improve
mobility in discotic systems is to impose intermolecular order and
interaction, within the stacks or between the stacks, creating
multiple charge transport pathways (e.g. 1D vs 2D). This
requirement could easily be met by connecting the discotics
(triphenylenes, C3h symmetric) covalently, locking them to provide
a large π-orbital area and peripherally incorporating groups
(polar) that induce intermolecular interactions. Thus, we
envisaged bitriphenylenes (C2v symmetric, link-locked, Figure 2)
[a]
[b]
[b]
Dr. J. Ramakrishna, Dr. P. Venkatakrishnan
Department of Chemistry
Indian Institute of Technology Madras, Chennai – 600 036
Tamil Nadu, India
E-mail: pvenkat@iitm.ac.in
http://chem.iitm.ac.in/faculty/venkat/
A. M. Chennamkulam, L. Karunakaran, Dr. Soumya Dutta
Department of Electrical Engineering
Indian Institute of Technology Madras, Chennai – 600 036
Tamil Nadu, India
E-mail: s.dutta@ee.iitm.ac.in
http://www.ee.iitm.ac.in/user/s.dutta/
P. Shyam Vinod Kumar, Dr. V. Subramanian
Inorganic and Physical Chemistry, Academy of Scientific and
Innovative Research (AcSIR), CSIR-CLRI Campus
Chennai - 600 020, Tamil Nadu, India
E-mail: subbu@clri.res.in
http://clri.res.in/subramanian/index.html
Supporting information for this article is given vi a a link at the end of
the document.((Please delete this text if not appropriate))
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201901470
European Journal of Organic Chemistry
FULL PAPER
analogous charge transport characteristics (p-type, 0.23 × 10-3
cm2/(V.s)) when compared to other solution-processed systems
based on hole-conducting triphenylenes.[9] Indeed, FETs based
on carbon-based large PAHs (p-type) are of huge interest at
present due to their notable structural stability.[11]
Figure 1. Structures of triphenylenes/π-extended triphenylenes explored in the
literature.
as hole-semiconductor candidates for function in FETs. To the
best of our knowledge, the candidature of covalently-connected
triphenylenes, i.e., bitriphenylenes (Figure 2), has not been
explored yet in organic electronics, while twinned triphenylenes
linked by a rigid or flexible spacer have been studied only for their
LC behavior.[10]
Figure 2. Construction of bitriphenylenes via a link-lock approach (top), and the
novel bitriphenylene (bottom) targets 1–4 for OFET applications.
Results and Discussion
To perk up the semiconducting nature and to capitalize on the
successful 1D self-assembling behaviour of discotic triphenylenes,
we designed and synthesized bitriphenylene 1 (triphenylenes are
directly-linked via a C–C bond along which free-rotation is
possible) and the conformationally-rigid methylene-locked (via
two C–C bonds) bitriphenylenes 2–4 (Figure 2). The designed
structures are aimed at the following benefits: (i) the planar π-
extended nature of the methylene-locked bitriphenylenes may
enhance π‒π stacking and molecular ordering thereby increase
transfer integrals, decrease reorganization energies leading to
improved charge transport properties, (ii) the incorporation of alkyl
(hexyl) chains may facilitate solution-processing of thin-film
devices, and (iii) the introduction of substituents of different
electronic nature onto the periphery may alter the energy gap,
HOMO/LUMO energy levels as well as tune intermolecular
interactions favorable for electronic applications. Herein, we have
demonstrated that methylene-bridged bitriphenylenes 2-4 reveal
improved optical (near-UV absorption, up to 400 nm), thermal
(high thermal stability > 340 °C), and electrochemical properties
(low Eg, i.e., 2.96–3.25 eV, with HOMOs lying as high as -5.32
eV), when compared to simple triphenylenes or bitriphenylene 1.
Powder XRD of spin-coated films or the X-ray crystal structure
analyses of 2–4 reveal significant overlap between the π-system.
The reported experimental observations are further supported by
theoretical calculations. The OFETs fabricated by a low-cost
solution-process led to stable devices and reveal improved or
Synthesis and Solubility
The general synthetic approach for the synthesis of
bitriphenylenes 1 and conformationally-locked bitriphenylenes 2-
4 is shown in Scheme 1. The detailed procedure for the synthesis
of bitriphenylene 1 and 3-4 is described in the Supporting
Information, pages S45-S50; the synthesis of 2 is reported
elsewhere.[12] We started our synthesis from the readily available
biphenylene (free-rotation is possible via C–C bonds connecting
the benzene rings), and fluorene (the biphenyl unit is
conformationally locked via a methylene bridge through its 2,2'-
positions arresting free-rotation). Initially, iodination of biphenyl
under I2/HIO4 in acidic conditions yielded 76% of 4,4'-
diiodobiphenyl.[13a] Dibromination of fluorene using liquid bromine,
afforded 2,7-dibromofluorene, in good yield (75%).[13b] The
precursor compound 2,7-dibromofluorene was then subjected to
dihexylation under phase transfer conditions to yield 2,7-dibromo-
9,9-dihexylfluorene in excellent yields.[13c] The hexyl groups were
purposefully introduced into the fluorene skeleton to improve the
solution-processability of the targets in FETs. The diiodo-
(5)/dibromo-(6)-derivatives were then subjected to nickel-
mediated Kumada-type C–C coupling[13d] or Pd(0)-mediated two-
fold Suzuki coupling[13e-i] (Step 1, Scheme 1) with excess of the
corresponding
2-biphenylmagnesium
bromide/2-
biarylpinacolboronate ester (12-13) derivatives to provide
compounds 4,4'-bis(biphenyl-2''-yl)biphenyl 8 and 2,7-bis(biaryl-
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201901470
European Journal of Organic Chemistry
FULL PAPER
Scheme 1. General scheme for the synthesis of bitriphenylenes 1 and conformation-locked bitriphenylenes 2-4. Step 1: 2-bromobiphenyl, Ni(dppp)Cl2, benzene, 0
C, 1 h, reflux, 3 h, 85% (for 8) or Pd(PPh3)4, aq. K2CO3, toluene:EtOH (3:1, v/v), 85 °C, 18 h, 50-78% (for 9-11); Step 2: FeCl3, DCM, 0 °C to rt, 15 min. 85% (for 1)
or DDQ/H+, DCM, 0 °C to rt, 15-150 min., 60-90% (for 2-4)..
2'-yl)fluorenes 9–10, respectively, in good to moderate yields. In
contrast, 2,7-fluorene-bis(boronate)ester 7[13j] was Suzuki-
coupled with bromotetramethoxybiphenyl 14 to offer 11. The
biphenyl/biaryl units in 8–11 are now appropriately positioned for
oxidative Scholl cyclization to provide the desired
conformationally-locked π-extended bitriphenylene analogs.
Realizing the potential of FeCl3 in producing the chlorinated side
products (especially with 9), we opted for Rathore's mild oxidative
cyclization procedure (DDQ/H+, Step 2, Scheme 1) for the
synthesis of 9-11 as reported by us earlier.[14] This method gave
us the desired dicyclized products 2-4 in excellent yields, without
Optical Properties in Solution and Film
The optical properties of 1-4 were examined in dilute chloroform
solutions (ca. 1 × 10-5 M) at room temperature (Table 1). The UV-
vis absorption spectral profiles of 2-4 (Figure 3) display typical
vibronic features similar to those observed for rigid coplanar
polycyclic aromatic hydrocarbons (PAHs), unlike 1.[16] All the
bitriphenylenes exhibit relatively sharper low-energy absorption
band corresponding to π-π* transition in the wavelength range
360‒410 nm, besides high-energy absorptions at ca. 285 (not
shown in Figure 3) and 335–345 nm. It is important to mention
that the expectedly-twisted bitriphenylene 1 (calculated twist
angle is ca. 40, vide-infra), similar to simple triphenylene (λmax in
CH3OH = 247, 310 nm),[17] possesses an absorption maximum at
ca. 320 nm besides a forbidden transition at ca. 370 nm; the latter
is found to be prominent in the conformation-locked new C2v-
symmetric bitriphenylene systems 2-4.[18] This near-UV
absorption probably arises due to the extended π-conjugation
(mixing of orbitals) established by the methylene bridge in 2-4, the
observation which is in excellent agreement with the near-planar
structure (tilt angle, ca. 1.95–3.82) derived by X-ray structural
analysis and DFT calculations (vide-infra). While the long
wavelength absorption band for 2 is seen at 373–375 nm, it is
slightly (ca. 10 nm) red-shifted to 383–385 nm in cases of 3-4.
Such a bathochromic shift in 3-4, upon introduction of electron
donating methoxy substituents (mesomeric effect) on to 2 is
evident here.[19]
any side products.[12] However, synthesis of
1 could be
accomplished by both FeCl3 and DDQ/H+ conditions. The
oxidative Scholl cyclization method used in the final step for the
synthesis of triphenylene derivatives is metal-free, very facile and
involves organic oxidants and reagents. All the intermediates and
the target bitriphenylenes 1-4 were thoroughly characterized by
their melting points, infra-red, 1H and 13C NMR spectroscopy, high
resolution mass spectrometry techniques (see Supporting
Information, pages S52-S58). All the synthesized compounds 2-
4, except 1 (<0.5 mg/mL) possess remarkable solubility in
common organic solvents at room temperature; for example:
~140 mg/mL (2), ~150 mg/mL (3) and ~220 mg/mL (4) in
chloroform. The attachment of hexyl chains into bitriphenylenes
definitely improves the solubility as expected, which may facilitate
solution process of FET devices.[15] Hence, only the methylene-
bridged bitriphenylenes 2-4 were opted for device studies.
To gain further insights into the structural and opto-electronic
properties of the synthesized bitriphenylenes 1-4, density
functional theory (DFT) and time dependent DFT (TD-DFT)
calculations (for computational details, see Supporting
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201901470
European Journal of Organic Chemistry
FULL PAPER
1.0
Solution
Film
Film (annealed
at 150 °C)
1
2
3
4
0.4
0.3
0.2
0.1
0.0
0.5
0.0
300
350
400
450
320
360
400
440
Wavelength (nm)
Wavelength, nm
Figure 3. Normalized UV-vis absorption spectra of compounds 1-4 in
chloroform solution (ca. 1 × 10-5 M).
Figure 4. Comparative UV-vis absorption spectra of chloroform solution, as-
cast film and of film annealed at 150 C, of 2.
Information, pages S2-S4) were carried out. The simulated optical
spectra of the molecules 1–4 in chloroform are depicted in Figure
S1 (page S2), and the corresponding molecular orbital
contributions along with the transition states and oscillator
strengths are presented in Table S1 (page S3). The theoretical
results show a similar trend as those of the experiments. The
absorption maximum of these bitriphenylenes range between
~280–400 nm. The low energy transitions of each molecule
display π→π* character with major contributions from
HOMO→LUMO transitions. The molecules 2–4 reveal a red-
shifted absorption, when compared to 1, suggesting excellent π-
conjugation in conformation-locked bitriphenylenes 2-4; the twist
angle calculated for 1 is ca. 40 (vide infra) which is similar to
biphenyls/2,2'-binaphthyls reported in the literature (Figure S2,
page S4).[20]
As expected, the absorption maximum of bitriphenylenes 1-4 is
red-shifted (ca. 4‒21 nm) in films when compared to those in
solution (Figure S3a,b, page S5). Besides, absorption spectrum
of films (spin-coated under optimized conditions), showed a
typical broadening with a residual tail-end absorption extending
up to ca. 430 nm (Figure S3, page S5).[21] This feature points to
the existence of increased intermolecular π-π stacking
interactions between the large π-extended, conformationally-
locked bitriphenylenes 2-4, and suggests increased planarity of 1
in the film state.[22] This proposal was further supported by the
concentration dependent studies (UV-vis and 1H NMR
spectroscopy) of 2 and 3 in solution (Figures S3-S4, page S5-S6).
When the films were annealed at 150 C, a mild increase in the
residual absorption at the tail-end (ca. 390‒430 nm) of the
absorption spectrum accompanied by a featureless broadening
(in the range 320-365 nm) and slight bathochromic shift (ca. 1‒5
nm) were noted against as-cast films. Such a characteristic
phenomenon is noticed during the annealing of other large PAH
films too.[23] This highlights the effect of annealing in promoting
intermolecular interactions, molecular organization and ordering
in thin films of 2-4.[23] This tendency of π-extended bitriphenylenes
2-4 to self-organize is noteworthy, and may be beneficial for
solution-processed application in organic electronics. The typical
absorption spectral profiles of 2 in solution and as films are
displayed in Figure 4 for comparison.
Photochemical and Thermal Stabilities
To check the photostability, the films/solutions of 2 were
photoirradiated (λexc = 250/350 nm) for extended hours (i.e., 36–
48 h) under atmospheric conditions. The UV-vis absorption
spectrum as well as the 1H NMR spectrum recorded after
photoirradiation revealed no photoreaction/photodecomposition
attesting to its excellent photostability (Figure S5, page S7). It
should be noted that very popular semiconductors, such as,
pentacene, tetracene, and fluorene, are known to undergo
photooxidation in air and(or) photodimerization in presence of
light limiting their application in electronics.[24]
In order to gauge the applicability in electronic devices, thermal
stabilities of compounds 1-4 were estimated by thermogravimetric
(TGA) and differential scanning calorimetric (DSC) analyses
under nitrogen gas (N2) atmosphere (Figure 5). All these
compounds 1-4 exhibited excellent thermal stabilities (Table 1);
thermal decomposition temperatures (Td at 5% weight loss) were
close to or greater than 340 °C. As may be noticed from Table 1,
the highest thermal stability is owned by 1 (409 °C). The thermal
stabilities are relatively higher in case of 2, when compared to 3
and 4. This may be due to the substituent methoxy groups (as
rotors) in 3 and 4. The thermal stability trend follows the order: 3
< 4 < 2 < 1. DSC studies of 1-4 display both the sharp endothermic
melting (Tm) and the crystallization transitions (Tc) upon several
heating and cooling cycles, respectively (Table 1). On heating, 1
exhibited a reversible endothermic transition at 344 °C with a
reversible Tc around 272 °C. The melting transition of compounds
2-4 show the following trend: 3 < 2 < 4. Notably, all of them
possessed crystallization temperature supporting their highly
crystalline nature. The above results on thermal studies reveal
that bitriphenylenes 2-4 are endowed with desired virtues, i.e.,
high thermal stability and crystallinity, for their exploration in FETs.
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201901470
European Journal of Organic Chemistry
FULL PAPER
bitriphenylene systems. Interestingly, introduction of electron
donating groups alters the Eg to an extent ~0.14–0.16 eV. On
comparing 3 and 4 with HMT, one observes a significant reduction
in Eg (up to 0.39 eV), which can be due to the link-lock effect in
the former. The electronic effects caused (by π-extension and –
OMe substituents) in the HOMO and LUMO energy levels of
bitriphenylenes 2-4 were extracted from cyclic voltammetry (CV)
experiments (Figure 6). Whereas bitriphenylene 2 displayed one
oxidation reversibly, 3 and 4 revealed two reversible oxidations
probably due to the presence of electron donating methoxy
groups. The HOMO energy levels were calculated from the
oxidation peak potentials (Eox) derived from the differential pulse
voltammograms (DPV) using the relation EHOMO = –(Eox – E(Fc+/Fc)
+ 4.8) eV against Fc/Fc+ (Figures S6 and S7, page S9). The
LUMO energy levels were derived from the optical energy-gap
values (Eg, solution) and the corresponding HOMO energy levels
(ELUMO = EHOMO + Eg eV).[27] The HOMO/LUMO values thus
deduced are provided in Table 1. As may be noted, the HOMO
energy levels of 3 and 4 are raised when compared to 2. This may
be attributed to the presence of electron donating methoxy groups
in the former. In contrast, the HOMO energy level of 2 is slightly
increased (ca. 0.08 eV) than that of 1, which in turn is deeper (0.61
eV) than triphenylene HMT, besides lowering of its LUMO energy
levels (ca. 0.12 eV).[9,28] The above result evidently indicates that
the extended π-conjugation via C–C link in 1 or the methylene-
bridge (lock) in 2-4 stabilizes both the HOMO/LUMO energy levels
of HMT offering air-stability to bitriphenylenes.[28]
4
3
100
80
1
60
40
20
0
2
3
4
2
0
200
400
600
800
Temperature, °C
50 100150200250300350
Temperature, °C
Figure 5. TGA traces of 1-4 (left) and DSC traces of 2-4 (right) under nitrogen
gas atmosphere at a heating rate of 20 C/min and 10 C/min, respectively.
Electrochemical Properties
In addition, semiconductors must possess appropriate molecular
orbital energy levels for efficient charge injection from the metal
electrodes. To estimate them, the optical energy gap (Eg) values
of conformationally flexible 1 and locked bitriphenylenes 2-4, were
determined from the onset of their absorption spectrum (λonset, SI,
page S9). The Eg values thus estimated for their solutions and
films lie in the range 3.09‒3.44 eV and 2.96‒3.25 eV (Table 1),
respectively. The Eg trend observed in both solution and film is
very similar, and the Eg values less than 3.4 eV suggest a
semiconducting nature for 2-4. A slight reduction in the energy
gap observed, in case of films, may be attributed to the
differences in intermolecular interaction or molecular organization
(or refractive index).[25]
The energy gap (Eg) obtained in these novel bitriphenylenes 2-4
are smaller than or comparable to those of twisted 1, π-expanded
fluorenes (Eg of DTF/DSF = ca. 3.6 eV;[26a] Eg of truxene = ca. 3.1
eV)[26b] and triphenylene derivatives (for example, Eg of
hexamethoxytriphenylene, HMT = ca. 3.4 eV)[9] reported earlier.
This indicates the role of methylene-bridge in extending the π-
conjugation or reducing the Eg (~0.13–0.20 eV) in these novel
For comparison, the frontier molecular orbitals (FMOs) and
energy gaps of 1-4 were calculated using DFT methods, and the
results are presented in Table 2. The corresponding electron
density maps of bitriphenylenes are shown in Figure 6. The
calculated HOMO energy levels of 1-4 are in the range -5.40 to -
6.02 eV. In all the cases, the experimental trend is observed. The
HOMO energy levels of 3 (-5.47 eV) and 4 (-5.40 eV) are more
destabilized than that of 2 (-5.85 eV) which again is more
destabilized than 1. This can be related to the substitution of
Table 1. Optical, electrochemical and thermal properties of compounds 1-4 and model HMT.
Molecule
λmax, nm
Eg,d eV
Eox/HOMO,e
LUMO,f
eV
Td/Tm/Tc,g
eV
°C
Solna/Filmc
Abs (soln)a
Abs (film)b
Abs (film)c
1
2
324
344, 370
347, 361, 379
353, 370, 393
349, 374, 398
387h
345, 374
347, 380
359, 398
353, 398
387h
3.44/3.25
3.24/3.12
3.09/2.98
3.09/2.96
3.35/na
1.62/-5.84
1.49/-5.76
1.21/-5.48
1.12/-5.40
-5.23
-2.40
-2.52
-2.39
-2.31
-1.88
409/344/272
396/287/184
340/262/215
358/294/249
na
321, 342, 357, 375
327, 346, 364, 385
337, 362, 370, 383
274h
3
4
HMT
a in CHCl3 solutions. b as-cast. c annealed at 150 °C for 20 min. d optical energy gap derived from the onset of absorption. e calculated from cyclic
voltammetry using DCM solutions (Bu4NPF6 was the supporting electrolyte) against Fc/Fc+. f calculated from the optical energy gap and HOMO
energy level. g Td-decomposition temperature at 5% weight loss, Tm-melting temperature, Tc-crystallization temperature. h in DCM solution. na: not
available.
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201901470
European Journal of Organic Chemistry
FULL PAPER
diagrams are shown in Figure 7. As may be seen, all of them are
nearly coplanar in nature; deviation from planarity calculated as
the dihedral angle between the mean planes of the triphenylenes
on either side of the central 5-membered ring varies from 1.95°
(2) to 3.82° (3) to 3.01° (4). Interestingly, the central fluorene ring
is mildly bent in all the cases (1.94° to 3.11°). The molecular
packing diagrams of 2-4 clearly confirm the π-π stacking
arrangement between the molecules (Figure 7). What is
noteworthy is, the expanded π-system of the discotics (i.e.
triphenylenes) present in bitriphenylenes 2-4 ensures strong π-π
stacking interactions.[29] The molecules of 2 (space group = P21/n,
Z = 4; Table S2, pages S11-S12) arrange in a face-to-face
manner (along a-axis) with a π-π stacking distance (measured
between the mean planes) of 3.563 Å (Figure 7); the long
molecular axis is along the crystallographic c-axis. Further, these
dimers of 2 are packed in a herringbone fashion, as reported
earlier.[30] Such face-to-face interactions in a 2D π-expanded
system and the sandwich herringbone-type arrangement are
known to enhance the charge transport characteristics (via edge-
face interactions as in pentacene/rubrene/thienoacenes), when
compared to linear π-conjugated systems.[6,30] The molecular
packing diagram of 3 (space group = P-1, Z = 2; Table S3, pages
S13-S14) exhibits a sandwich brick-layer arrangement with its
long molecular axis oriented along the crystallographic b-axis
(Figure 7). The π-π stacks of distance ca. 3.586 Å are found along
the crystallographic c-axis. In addition, the molecular packing of 3
4
3
2
0.0
0.5
1.0
1.5
2.0
4
1
2
3
Potential (V)
Figure 6. Left: Cyclic voltammogram of 2-4 (1.0 mM) recorded in
dichloromethane using tetrabutylammonium hexafluorophosphate as the
supporting electrolyte (0.1 M). Right: Ordering of HOMO and LUMO levels of 1-
4 and their respective electron density plots at B3PW91/6-31+G** level of theory.
electron donating methoxy groups in 3 and 4 as opposed to 2, and
absence of planarity in 1. The LUMO energy levels of 1-4 are in
the range -1.75 to -1.96 eV. Notably, the HOMO levels of 3 and 4
are destabilized to a greater extent than their corresponding
LUMO energy levels. A closer look at the electron density plots of
bitriphenylenes 1-4 reveals that the HOMOs are delocalized over
the entire molecule while the LUMOs are localized on the fused
central six-membered rings (Figure 6). The cyclic voltammetry
and DFT results suggest that bitriphenylenes (especially 3 and 4)
described here are electron-rich and can be readily oxidized (p-
type), and their HOMO energy levels can be conveniently fine-
tuned upto ca. -5.4 eV by attachment of –OMe groups. This
enables Au (gold) to be used as source-drain electrodes for FET
fabrication.
is benefited by weak C–H···O (dH···O = 2.678 Å and θC-H···O
=
149.05°) interactions supplied by the –OMe substituents.[31]
Theoretically, the observed cofacial lamellar packing is realized
as the most ideal arrangement for facilitating intermolecular
interactions and maximizing transfer integrals (as in 3) for an
efficient 2D network charge transport.[32] Similarly, the molecule 4
(space group = P-1, Z = 2; Table S4, pages S15-S16) exhibits
dimers in a slipped-π-stack arrangement (along a-axis).[30] This
displaced arrangement (along the molecular long as well as the
short axes, Figure 7) is probably promoted either because the
additional methoxy groups (when compared to 3) in 4 occupy the
available space in its curved arm-chair region preventing them to
stack in a face-to-face manner, or due to the electrostatic
repulsions between the cofacial electron-rich π-conjugated
X-ray Crystal Structure Analyses
Investigation of solid-state packing arrangement of organic
semiconductors is important as it can be correlated to the charge
transport property in films, reasonably. Single crystals of 2-4
suitable for X-ray diffraction studies were grown by slow
evaporation of their solutions of chloroform-hexane, chloroform-
toluene, etc. The ball-stick model of molecular structures of
bitriphenylenes 2-4, their dimensions and molecular packing
Table 2. DFT calculated FMO energies, energy gaps (Eg) and hole and electron reorganization energies of 1-4, and transfer integrals of 2-4.
Molecule
HOMOa (eV)
LUMOa (eV)
Ega (eV)
λholeb (eV)
λelectronb (eV)
ΔEb (eV)
Vholec (meV)
1
2
3
4
-6.02 (-5.84)
-5.85 (-5.76)
-5.47 (-5.48)
-5.40 (-5.40)
-1.86 (-2.40)
-1.96 (-2.52)
-1.76 (-2.39)
-1.75 (-2.31)
4.16 (3.44)
3.89 (3.24)
3.70 (3.09)
3.65 (3.09)
0.210
0.165
0.204
0.202
0.334
0.216
0.246
0.258
0.124
0.051
0.042
0.056
--
2.60
42.35
5.30
a FMOs (HOMO and LUMO) and energy gaps (Eg) were calculated in DCM medium with B3PW91/6-31+G** level of theory. The experimental
values are given in brackets for comparison. b The internal reorganization energies (ΔE = λelectron – λhole) were calculated using B3LYP/6-
31+G** level of theory. c The charge transfer integral values for holes (Vhole) were calculated using GGA-PW91 functional along with TZP
basis set.
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201901470
European Journal of Organic Chemistry
FULL PAPER
bitriphenylenes certainly alters the stacking behaviour thereby π-
orbital interactions, which consequently may influence molecular
ordering and charge transport.
1.70 nm
2
3.56 Å
P21/n
face-to-face
2
3
4
2.13 nm
3
4
3.605Å
3.495Å
P-1
3.559Å
3.59 Å
face-to-face
2.16 nm
E = -53.96 kcal/mol
E = -31.82 kcal/mol
E = -39.51 kcal/mol
P-1
3.42 Å
Figure 8. Geometries of optimized dimers of 2-4 and their binding energies at
M06L/6-31G** level of theory.
slipped-stack
Figure 7. Molecular structures (left), π-π stacks (middle) and unit-cell packing
diagrams of 2-4 describing dimeric herringbone, brick-layer and slipped-
stackarrangements (right, top to bottom) viewed along c-, a-, c-axes,
respectively.
Evaluation of Charge Transport Property by OFET Devices
After probing the optical/electrical properties and possible solid-
state arrangements of butterfly-shaped bitriphenylenes 2-4, their
charge transport properties were investigated by constructing
OFET devices by low-cost solution-process.[34] OFET devices
with bottom-gate/bottom-contact configuration were fabricated
using patterned gate structure to avoid gate leakage current and
parasitic effect that could lead to over-estimation of mobility.
Towards application in transparent, flexible electronics and
circuits,[35] polymer dielectric (cross-linked poly(4-vinylphenol), in
particular) was adopted as gate insulator. The compatibility of π-
expanded semiconductors with the insulator system was tested.
Aluminium was deposited and patterned using photolithography
on top of cleaned boro-float glass wafer as the gate electrode.
Commercially available poly(4-vinylphenol) (PVP) was cross-
linked using copolymer poly(melamine-co-formaldehyde)-
methylated, followed by spin-coating on the patterned gate metal
using our optimized recipe to provide pin-hole-free gate dielectric
of thickness about 500 nm. Photolithographically-patterned gold
electrodes atop cross-linked PVP layer were used as drain and
source. Finally, the organic semiconductor (OSC) layer was spin-
coated (2-4, ca. 5.0 mg/mL, chloroform solutions) on the
patterned Au (source-drain) substrates (for details, see Figure 9
and Supporting Information, pages S17-S19). Other than the as-
cast devices, few devices underwent a post thermal annealing at
150 °C for 20 min. The entire fabrication was carried out inside a
glove-box except sample cleaning and lithography processes.
Both the as-cast and annealed FETs were characterized inside a
probe station under vacuum using parameter analyser. Thus, 20
FET devices of molecule 4, and 5 devices of each of molecule 2
and 3 were fabricated, for calculating the mobility (μ) and Ion/Ioff
ratio. The extracted parameters of the best devices of 2-4 and
model compound HMT are compared in Table 3 (for average
values, see: Figure S13, page S19). The output and transfer
characteristics of the OFET using semiconductor 4 are shown in
Figure 9.
dimeric stacks. However, the π-π stacking distance in 4 is
measured as the shortest, i.e., 3.418 Å. Besides, its molecular
packing diagram highlights the presence of weak C–H···O (dH···O
=
2.560
Å
and θC-H···O
=
139.77°) interactions via
a
centrosymmetric dimeric motif favouring 2D network.[31] Here, the
molecular long axis is along the crystallographic b-axis, as in 3. A
tuneability in the molecular packing arrangement from
herringbone to face-to-face to slipped-stack by simple
introduction of –OMe substituents on bitriphenylenes is
remarkable. Indeed, the C–H···O interactions are popularly used
in the design of organic solids for device applications exploiting
crystal engineering strategies.[31,33] The near-planar large
molecular structure, short stacking distance, and dimeric face-to-
face or brick-layer or slipped-stack 2D arrangement of C2v-
symmetric bitriphenylenes (as against 1D columnar arrangement
of C3-symmetric triphenylenes) are the ideal characteristics
desired to activate multiple charge transport pathways (vide infra).
To comprehend the structure-property relationship of
bitriphenylenes, ground state geometry optimization was
performed using DFT-based calculations for 1–4 and their
optimized geometries are shown in Figure S2, page S4. As
expected, 1 shows a highly twisted conformation with a dihedral
angle ~40°, whereas 2–4 show high degree of planarity, in
agreement with the UV-vis and X-ray studies, due to the
conformation rigidification by the methylene bridge. Further, to
understand the packing pattern, the π-π stacking of dimers of 2–
4 were optimized using DFT. The geometries of these optimized
dimers, their stacking distances and binding energies are shown
in Figure 8. The calculated π-π stacking distances of 2, 3 and 4
are 3.559, 3.605 and 3.495 Å, respectively. The observed results
are in good agreement with the experimental data. It can be seen
that the substitution of methoxy groups in 3 increases the stacking
distance in the order of 0.05 Å, when compared to 2. Interestingly,
the octamethoxy derivative 4 exhibits the lowest π-stacking
distance between its monomers due to its slipped-stack
arrangement, which is in resemblance with the X-ray analyses.
The calculated binding energies of 2, 3 and 4 are -31.82, -39.51
and -53.96 kcal.mol-1, respectively (Figure 8). The above results
also illustrate that the incorporation of methoxy groups into large
The π-rich bitriphenylenes 2-4 exhibited
a typical p-type
accumulation characteristics, as observed by CV studies and
theoretical calculations. The as-cast films of 4 (purified once by
column-chromatography) showed the highest hole mobility (μ) of
0.56 × 10-4 cm2/(Vs) with a Ion/Ioff ratio greater than 104 at room
temperature, while compounds 2, 3 and 4 demonstrated hole
mobilities of 0.71 × 10-6, 0.26 × 10-4 cm2/(Vs) and 0.55 × 10-4
cm2/(Vs), respectively, after anneal treatment. Annealing certainly
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201901470
European Journal of Organic Chemistry
FULL PAPER
has improved the FET performance of 2 and 3. It is to be noted
that there is no appreciable change in the performance of the
device of 4 after annealing, which also reveals that the compound
may be quite ordered even as-cast film. This result corroborates
the effect of annealing (UV studies/AFM) in thin films. The
chromatography run twice) sample of 4, resulted in an appreciable
mobility of 0.23 × 10-3 cm2/Vs with Ion/Ioff ratio more than 105 (i.e.,
4-fold enhancement in mobility and one-order of magnitude
higher Ion/Ioff ratio as compared to that of a singly purified material
or 2-fold improvement in mobility when compared to that of its as-
cast film) (Figure S11, page S18). Moreover, the better
performance of FET devices of 3 and 4 when compared to 2 may
be attributed to the role of –OMe groups in improving the HOMO
and probably the molecular arrangement favourable for charge
transport. It is important to state that the OFET device fabricated
for the model compound HMT under the identical condition
revealed a hole mobility of only 0.19 × 10-7 cm2/(Vs), which is
three to four orders of magnitude lower than that observed for 3
and 4. Such an improved hole-transport characteristics of
bitriphenylenes 3 and 4 are essentially attributed to their large,
planar, extended π-conjugation, favourable π-π stacking
interactions, and apt HOMO energy levels. It is remarkable that
the un-encapsulated devices of 3 and 4 reveal nearly unaltered
performance (reduction of mobility only by half) even after keeping
the device under exposure to atmosphere for almost one year, as
shown in Figure S12, page S18. Some of the salient features of
the devices that project material 4 as a promising candidate are:
(i) statistical observation of mobility as a function of channel
lengths reveals that the change in average mobility of best-to-
worst device is within 15% (Figure S13, page S19), (ii) excellent
stability under atmospheric condition was achieved, (iii) almost
100% yield (ratio of number of fabricated devices to the working
devices) with reasonably small tolerance in mobility from device
to device and batch to batch was observed, (iv) untreated polymer
dielectric was used as insulator, which is compatible to flexible
electronics, unlike SiO2, and (iv) Ion/Ioff ratio more than 104 is good
enough for use in analog-circuit applications. These aspects
highlight the electronically-perturbed twinned-triphenylenes 2-4
(as against twisted 1 or discotic triphenylenes) as potential
organic semiconductors, and the fabrication method adapted
herein showcase the realization of low-cost flexible electronics
possible with these sytems. It is to be kept in mind that not only
the molecular property, but also several factors, such as,
crystallinity, molecular orientation, uniformity and connectivity
between the crystalline grains in thin films, device conditions and
configuration, etc., are known to influence the overall device
performance.
a)
c)
b)
OSC
Au
Au
Au
PVP Au
Al
Glass
d)
0.12
0.10
0.08
0.06
0.04
0.02
0.00
1E-8
1E-9
-70
-60
-50
-40
-30
-20
-10
0
0 V
-10 V
-20 V
-30 V
-40 V
-50 V
VDS = -100 V
1E-10
1E-11
1E-12
1E-13
0
-10 -20 -30 -40 -50 -60
-30 -40 -50 -60 -70 -80
V
(V)
VGdsS(V)
VGS (V)
Figure 9. OFET device characteristics of 4. (a) General device configuration,
(b) Photograph showing array of fabricated devices on transparent glass
substrate and polymer dielectric, (c) Output (VDS
characteristics of devices of singly purified 4 (L = 10 μm, W = 1000 μm) after
= -100 V) and (d) transfer
annealing.
Table 3. OFET device characteristics of 2–4 and the model compound
HMT.a
Molecule
At r.t. (as-cast film)
At 150 °C (annealed film)
µ (cm2/Vs)
Ion/Ioff
nr
µ (cm2/Vs)
0.71 × 10-6
0.26 × 10-4
0.55 × 10-4
0.25 × 10-4 b
0.23 × 10-3 c
0.19 × 10-7
Ion/Ioff
103
2
3
4
nr
0.78 × 10-6
0.56 × 10-4
102
104
>104
>104
>104 b
>104 c
27
0.89 × 10-4
nr
>105
nr
Thin-film Microstructural Characterization
HMT
To understand the performance results of OFETs, out-of-plane X-
ray diffraction measurements were conducted on spin-coated
thin-films (device conditions) of 2-4 at room temperature and after
annealing at 150 C. The X-ray diffractograms (XRD, Figure 10)
obtained for the room-temperature as-cast films of 2-4 exhibited
a broad and less intense peak between 2θ = 18 and 38; no sharp
features were observed between 2θ = 4 and 50 pointing to a poor
molecular ordering/crystallinity (Figure S14, page S20). The
above observation thus corroborates the no or poor performance
of the as-cast devices of 2 or 3, respectively. On the other hand,
annealed films (Figure 10) exhibited sharp and strong peaks at 2θ
= 6.62/6.38,7.72/6.97 besides a broad peak with maximum
intensity at 2θ around 24.31/24.62/24.29 for 2/3/4, respectively.
This definitely suggests an improved crystallinity of the films upon
annealing (AFM studies, vide-infra), probably due to better
molecular ordering. Therefore, it is no surprise that annealed
a
b
all the parameters are for devices with L = 10 μm, W = 1000 μm. after
c
one year under optimal conditions. after double purification by column
chromatography. r.t.: room temperature (25 C). nr: no response.
improved hole mobilities in the case of 4 (as-cast/annealed films)
can be readily understood from (i) the alignment of its HOMO (-
5.27 eV) close to the Fermi level of Au, (ii) slipped-π-stack
arrangement in crystal packing diagrams, and (iii) continuous
crystalline morphology and uniformity of their thin films (as
confirmed by AFM, vide infra). The above result of 4 coincides
with the observation from X-ray structural analyses, binding
energy calculations and thin-film microstructural characterization
studies (vide infra). Surprisingly, a doubly-purified (column-
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201901470
European Journal of Organic Chemistry
FULL PAPER
devices of 2-3 performed better than the as-cast devices. It
appears that the as-cast or annealed films of 4 display similar
crystalline behaviour leading to comparable FET performance.
The XRD pattern of the annealed thin films of 2-4, both at lower
and higher theta values, can be matched with the simulated
note that a minor variation in substitution leads to substantially
different morphologies and device performances.
4
3
2
Figure 11. AFM height images of thin films of OFET devices of 2-4 (left to right).
Top row: as-cast at room temperature; bottom row: annealed at 150 C.
0
0
10 20 30 40 50
2  (degrees)
Figure 10. Out-of-plane XRD of the thermally annealed (150 ºC) films of 2-4.
Reorganization Energies and Transfer Integrals
Further, to understand the carrier transport mechanism in
bitriphenylenes 1-4, the internal reorganization energies (λhole for
holes and λelectron for electrons) and their energy differences (ΔE)
were calculated using DFT (Supporting Information, pages S22-
S23). The results are displayed in Table 2. The λhole values of 1-4
range between 0.163–0.210 eV and the λelectron values range
between 0.212–0.334 eV. The fact that λhole values are lower than
λelectron values (shallow LUMO levels) suggests faster hole
transportation character.[37] This is in good alignment with the FET
device results which reveal p-type transport characteristics.
Interestingly, the energy difference (ΔE) between hole and
electron reorganization values of the conformation-locked
bitriphenylenes 2–4 are lower (0.05 eV) than the twisted
bitriphenylene 1 (0.124 eV). This result reiterates that the
structural modification by methylene-bridge provides large
extended π-conjugation and improves charge transport
characteristics in 2-4, as observed by experiments.
Intermolecular electronic coupling (Vhole) has also been computed
for bitriphenylenes 2-4. Vhole values for different charge transport
pathways (Figure S15, page S24) were calculated using the X-ray
structural data, and the results are consolidated in Table 4. From
the crystal packing of 2, three different charge transport pathways,
ie., face-to-face, edge-to-edge and face-to-edge orientations of
molecular dimers were considered. The Vhole of 2 in the face-to-
face direction was calculated to be 2.60 meV, which is lower than
the values of 3 and 4. Also, for the edge-to-edge and face-to-edge
direction of 2, the transfer integrals were calculated as 1.36 and
4.31 meV, respectively. These results indicate that in 2, the
charge transport occurs mainly along the face-to-edge direction
of the dimers, which is in line with its XRD and discouraging FET
results. For bitriphenylenes 3 and 4, due to their planar π-π
stacking arrangements in the crystal lattice, only two pathways
were evaluated, i.e, face-to-face and edge-to-edge orientations.
In the case of 3, the Vhole values along the face-to-face and edge-
to-edge directions were 42.35 and 2.31 meV, respectively, which
are the highest among the three bitriphenylenes considered. This
is in contrary to the device measurements where the as-cast 4
exhibits enhanced mobility in comparison to 3. The primary
powder pattern of the bulk single crystals (Figure S14, page S20).
Thus, upon comparison one may assign the broad peak observed
around 2θ = 24.3 to 24.6 (i.e., d = 3.61–3.66 Å), in both the
before- and after-annealed films of 2-4, to the distance between
the molecules that are involved in π-π stacking interaction. These
d values are very much close to the π-π stacking distance
calculated from the X-ray crystal structures and the calculated
geometry-optimized structures. Similarly, the sharp signal(s) at
lower theta values (corresponding to d = 11.45–13.8 Å), in case
of annealed films, may suggest
a
tilted edge-on
(vertical/horizontal) arrangement of molecules possible on the
substrate surface, retaining π-π stacking (for more discussion,
see Supporting Information, page S21).[36]
Another important factor that usually affects the charge transport
characteristics is the morphology of thin films. Hence, to
understand the morphological influence in device performance
thin film morphologies of the OFET devices of 2-4 were probed by
tapping-mode atomic force microscopy (AFM, Figure 11). The
AFM images obtained for the annealed thin films of devices 2 and
3 exhibited discontinuous larger grain sizes (ca. 50–69 nm) when
compared to their continuous film morphology (ca. 5–10 nm) at
room temperature. Generally, thin films of larger grain sizes
contribute to increased carrier mobility, and greater discontinuity
leads to poorer results. Clearly, this morphological behaviour falls
in line with the observed device results of 2 and 3. Indeed, the
mobilities as well as the Ion/Ioff ratios are observed to be higher in
the case of annealed devices of 2 and 3. In contrast, the FET
device of annealed thin films of 4 under AFM revealed only minor
differences in its morphology, as noticed in XRD. While films of 4
in both the conditions showcase uniform, continuous and
crystalline morphology, the annealed ones appear to have slightly
larger (ca. 12–19 nm) grain sizes than that in non-annealed films.
This supports the observation of near identical carrier mobility
values as well as high Ion/Ioff ratios for the FET devices of 4 under
both annealed and non-annealed conditions. It is surprising to
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201901470
European Journal of Organic Chemistry
FULL PAPER
charge transport pathway in 3 is along the face-to-face direction.
For 4, the Vhole values for the above two pathways were 5.30 and
0.68 meV, respectively, with face-to-face pathway having higher
probability of charge transport. The reason for higher electronic
coupling values for 3 than 4 may be due to the slipped-stack
packing nature of 4 which minimizes the HOMO overlap between
the dimers. However, we believe other factors/parameters that
control the morphology of thin-film in FET devices may also play
significant roles in the efficient charge transport of 4. As proposed
by Marcus theory, large transfer integrals and small
reorganization energies are expected to lead to high mobility.[38,39]
One must also keep in mind that transfer integrals are very
sensitive to the relative positions of the neighboring molecules.
That is, the intermolecular distance, shifting or tilting of the
molecules in films impact carrier transport considerably. Hence,
accurate theoretical predictions of charge transport properties of
organic semiconductors in the film-state remain quite challenging.
with appreciable Ion/Ioff ratios (greater than 105). Valuably, these
FET devices reveal excellent air-stability for more than a year
without much performance deterioration. Thin-film microstructural
characterization studies support that the films of annealed
devices are crystalline when compared to the as-cast devices.
The theoretical calculations reiterate that these bitriphenylenes
can be potential candidates for OFET applications. From the point
of view of advantages associated with discotic small molecules
such as triphenylenes, these large π-extended butterfly-shaped
bitriphenylenes can be excellent candidates for cost-efficient,
stable, light-weight, solution-processable and plastic/transparent
electronic devices and circuits.
Experimental Section
Materials. All the reagents and solvents described in the manuscript were
of high purity (Analytical Grade) and were purchased from commercial
sources. They were used as received without further purification unless
mentioned. The key starting materials, 4,4'-diiodobiphenyl (5),[13a] 2,7-
dibromofluorene,[13b] 9,9-dihexyl-2,7-dibromofluorene 6,[13c] 2-bromo-3',5-
dimethoxy-1,1'-biphenyl,[40] 2-bromo-3',4,4′,5-tetramethoxy-1,1'-biphenyl
Table 4. Charge transfer integrals (Vhole) for the molecular dimers 2-4 in
different orientations obtained from X-ray crystal structure.
(14),[41]
2,2’(9,9’-dihexyl-9H-fluorene-2,7-diyl)bis(4,4,5,5-tetramethyl-
Molecule
Charge-transfer integrals (Vhole) in meV
1,3,2-dioxaborolane (7),[13j] 4,4'-bis(biphenyl)biphenyl (8),[13d] 9,9-dihexyl-
2,7-bis(biphenyl-2'-yl)fluorene 9[12] and 2,[12] were synthesized according
to the literature reported procedures and the spectra were verified. The
complete experimental procedures including general aspects, analytical
and characterization data of the compounds 1, 3, 4, 10, 11 and 13, their
spectral traces are provided in the supporting information.
Face-to-face
2.60
Edge-to-edge
1.36
Face-to-edge
2
3
4
4.31
42.35
2.31
-
-
5.30
0.68
Acknowledgements
Otherwise, the trends seen here with the theoretical results are
comparable with the OFET device mobility measurements. It is
obvious that further optimization on this skeleton and the device
conditions may enroute to stable, efficient solution-processable
bitriphenylenes for organic electronics. This aspect of research is
presently ongoing in our laboratory.
P.V.K. is grateful to DST-SERB (SB/S1/OC-47/2014) and CSIR
(02(0185)/13/EMRII), New Delhi, India for a generous support,
and Department of Chemistry, IIT Madras for the infrastructural
facilities. J.R. is thankful to CSIR for a SRF. Mr. V. Ramkumar,
Department of Chemistry, IIT Madras and the CeNSE facility at
IISc Bangalore, India are acknowledged for the X-ray structural
solution and for the AFM images, respectively.
Conclusions
Keywords: Triphenylenes
•
π-Extension
•
Optical and
Electrochemical • Charge Transport • Field-Effect Transistors
The
conformationally-free
and
methylene-bridged
conformationally-rigid bitriphenylenes are synthesized using a
facile and efficient Scholl oxidative cyclodehydrogenation strategy.
Methylene-bridged bitriphenylenes are nearly planar, and their
optical characteristics reveal similarity to that of a typical PAH
system. Planarization via methylene-bridge has led to large
extended π-conjugation, lowering of HOMO/LUMO energy levels
and considerable reduction in optical band gap. Incorporation of
electron donating substituents raises the HOMO energy levels
considerably. The films of bitriphenylenes reveal excellent
thermal and photochemical stabilities and tendency for molecular
organization. Their solid-state structures display substituent-
dependent dimeric face-to-face or slipped-stack or herringbone
2D arrangement indicating a promise for charge transport
behaviour. They possess good solubility in common organic
solvents, facilitating low-cost solution-process fabrication of
transparent organic FET devices. The average mobilities of FETs
achieved from bitriphenylenes can be as high as ca. 10-3 cm2/(Vs)
[1]
a) Organic Field-Effect Transistors, (Eds: Bao, Z.; Locklin, J.), CRC press,
Boca Raton, FL 2007; b) M. Caironi, Y.-Y. Noh, Large Area and Flexible
Electronics, John Wiley and Sons, 2015; c) H. T. Yi, M. M. Payne, J. E.
Anthony, V. Podzorov, Nature. Commun., 2012, 3, 1259 and references
cited therein.
[2]
[3]
a) S. Sergeyev, W. Pisula, Y. H. Geerts, Chem. Soc. Rev. 2007, 36,
1902-1929; b) S. Kumar, Chem. Soc. Rev. 2006, 35, 83-109.
T. Wohrle, I. Wurzbach, J. Kirres, A. Kostidou, N. Kapernaum, J.
Litterscheidt, J. C. Haenle, P. Staffeld, A. Baro, F. Giesselmann, S.
Lascht, Chem. Rev. 2016, 116, 1139-1241.
[4]
[5]
M. Funahashi, Polymer Journal 2009, 41, 459-469 and references cited
therein.
a) C. W. Struijk, A. B. Sieval, J. E. Dakhorst, M. Dijk, P. Kimkes, R. B. M.
Koehorst, H. Donker, T. J. Schaafsma, S. J. Picken, A. M. Van de Craats,
J. M. Warman, H. Zuilhof, E. J. R. Sudhölter, J. Am. Chem. Soc. 2000,
122, 11057-11066; b) B. Zhao, C.- Z. Li, S.- Q. Liu, J. J. Richards, C.-C.
Chueh, F. Ding, L. D. Pozzo, X. Li, A. K.- Y. Jen, J. Mater. Chem. A, 2015,
3, 6929-6934; c) R. Gupta, A. A. Sudhakar, Langmuir 2019, 35, 2455-
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201901470
European Journal of Organic Chemistry
FULL PAPER
2479; d) J. L. Segura, R. Juárez, M. Ramos, C. Seoane, Chem. Soc. Rev.
2015, 44, 6850-6885.
[24] a) A. Maliakal, K. Raghavachari, H. Katz, E. Chandross, T. Siegrist,
Chem. Mater. 2004, 16, 4980-4986; b) J. Reichwagen, H. Hopf, A. D.
Guerzo, J.-P. Desvergne, H. Bouas-Laurent, Org. Lett. 2004, 6, 1899-
1902; c) B. Kobin, S. Behren, B. Braun-Cula, S. Hecht, J. Phys. Chem.
A. 2016, 120, 5474-5480.
[6]
[7]
C. Wang, H. Dong, W. Hu, Y. Liu, D. Zhu, Chem. Rev. 2012, 112, 2208-
2267.
a) S. K. Pal, S. Setia, B. S. Avinash, S. Kumar, Liquid Crystals, 2013, 40,
1769-1816; b) N. Boden, R. J. Bushby, J. Clements, M. V. Jesudason, P.
F. Knowles, G. Williams, Chem. Phys. Lett. 1988, 152, 94-99.
Z. Sun, Q. Ye, C. Chi, J. Wu, Chem. Soc. Rev. 2012, 41, 7857-7889.
a) J. Simmerer, B. Glüsen, W. Paulus, A. Kettner, P. Schuhmacher, D.
Adam, K.-H.Etzbach, K. Siemensmeyer, J. H. Wendorff, H. Ringsdorf, D.
Haarer, Adv. Mater. 1996, 8, 815-819; b) M. H. Hoang, M. J. Cho, K. H.
Kim, M. Y. Cho, J.-s. Joo, D. H. Choi, Thin Solid Films 2009, 518, 501-
506; c) M. H. Hoang, D. N. Nguyen, D. H. Choi, Adv. Nat. Sci.: Nanosci.
Nanotechnol. 2011, 2, 035002, and references cited therein.
[25] P.-Y. Gu, Z. Wang, G. Liu, H. Yao, Z. Wang, Y. Li, J. Zhu, S. Li, Q. Zhang,
Chem. Mater. 2017, 29, 4172-4175.
[8]
[9]
[26] a) C.-H. Lee, Y.-Y. Lai, S.-W. Cheng, Y.-J. Cheng, Org. Lett. 2014, 16,
936-939; b) J. Luo, Y. Zhou, Z.-Q. Niu, Q.-F. Zhou, Y. Ma, J. Pei, J. Am.
Chem. Soc. 2007, 129, 11314-11315.
[27] I. Seguy, P. Jolinat, P. Destruel, J. Farenc, R. Mamy, H. J. Ip. Bock, T.
P. Nguyen, J. Appl. Phys. 2001, 89, 5442.
[28] F. Valiyev, W.-S. Hu, H.-Y. Chen, M.-Y. Kuo, I. Chao, Y. T. Tao, Chem.
Mater. 2007, 19, 3018-3026.
[10] a) J. Li, Z. He, H. Gopee, A. N. Cammidge, Org. Lett. 2010, 12, 472-475;
b) X. Kong, Z. He, Y. Zhang, L. Mu, C. Liang, B. Chen, X. Jing, A. N.
Cammidge, Org. Lett. 2011, 13, 764-767; c) L. Zhang, D. L. Huges, A. N.
Cammidge, J. Org. Chem. 2012, 77, 4288-4297; d) H. Gopee, X. Kong,
Z. He, I. Chambrier, D. L. Hughes, G. J. Tizzard, S. J. Coles, A. N.
Cammidge, J. Org. Chem. 2013, 78, 9505-9511.
[29] a) Z.-F. Yao, J.-Y. Wang, J. Pei, Cryst. Growth Des. 2018, 18, 7-15; b)
M. Mas-Torrent, C. Rovira, Chem. Rev. 2011, 111, 4833-4856; c) T.
Wöhrle, I. Wurzbach, J. Kirres, A. Kostidou, N. Kapernaum, J.
Litterscheidt, J. C. Haenle, P. Staffeld, A. Baro, F. Giesselmann, S.
Laschat, Chem. Rev. 2016, 116, 1139-1241.
[30] a) T. Yamamoto, S. Shinamura, E. Miyazaki, K. Tamkimiya, Bull. Chem.
Soc. Jpn. 2010, 83, 120-130; b) T. Izawa, E. Miyazaki, K. Takimiya, Adv.
Mater. 2008, 20, 3388-3392; c) J. G. Laquindanum, H. E. Katz, A. J. J.
Am. Chem. Soc. 1998, 120, 664-672; d) C. C. Mattheus, G. A. de Wijs,
R. A. de Groot, T. T. M. Palstra, J. Am. Chem. Soc. 2003, 125, 6323-
6330; e) V. C. Sundar, J. Zaumseil, V. Podzorov, E. Menard, R. L. Willett,
T. Someya, M. E. Gerhenson, J. A. Rogers, Science, 2004, 303, 1644-
1646.
[11] a) S. Pola, C.- H. Kuo, Kuo, W.-T. Peng, Md. M. Islam, I. Chao, Y. T. Tao,
Chem. Mater. 2012, 24, 2566-2571; b) J. Hu, Current Organic Chemistry
2007, 11, 1220-1240; c) A. Bayn, X. Feng, K. Müllen, H. Haick, ACS Appl.
Mater. Interfaces. 2013, 5, 3431-3440; d) X. Pisula, X. Feng, K. Müllen,
Chem. Mater. 2011, 23, 554-567.
[12] J. Ramakrishna, P. Venkatakrishnan, Chem. Asian J. 2017, 12, 181-189.
[13] a) A. Moroda, H. Togo, Tetrahedron, 2006, 62, 12408-12414; b) J. Hai,
B. Zho, F. Zhang, C.-X. Sheng, L. Yin, Y. Li, E. Zhu, L. Bian, H. Wu, W.
Tang, Polymer 2013, 54, 4930; c) G. Xu, L. Ping, Y. Ma, Polymer 2014,
55, 3083; d) E. Ibuki, S. Ozasa, Y. Fujioka, M. Okada, Y. Yanagihara,
Chem. Pharm. Bull. 1982, 30, 2369-2379; e) N. Miyaura, A. Suzuki.
Chem. Rev. 1995, 95, 2457-2483; f) Z. Peng, S. Tao, X. Zhang, J. Tang,
C. S. Lee, S.-T. Lee, J. Phys. Chem. C, 2008, 112, 2165-2169; g) A. F.
Littke, C. Dai, G. C. Fu, J. Am. Chem. Soc. 2000, 122, 4020-4028; h) J.
P. Wolfe, R. A. Singer, B. H. Yang, S. L. Buchwald, J. Am. Chem. Soc.
1999, 121, 9550-9561; i) W. Tang, A. G. Capacci, X. Wei, W. Li, A. White,
N. Patel, J. Savoie, J. J. Gao, S. Rodriguez, B. Qu, N. Haddad, B. Z. Lu,
D. Krishnamurthy, N. K. Yee, C. A. Senanayake, Angew. Chem. Int. Ed.
2010, 49, 5879-5883; j) M. V. Ivanov, M. R. Talipov, A. Boddeda, S. H.
Abdelwahed, R. Rathore, J. Phys. Chem. C 2017, 121, 1552-1561.
[14] a) L. Zhai, R. Shukla, R. Rathore, Org. Lett. 2009, 11, 3474-3477; b) L.
Zhai, R. Shukla, S. H. Wadumethrige, R. Rathore, J. Org. Chem. 2010,
75, 4748-4760; c) S. Maddala, S. Mallick, P. Venkatakrishnan, J. Org.
Chem. 2017, 82, 8958-8972.
[31] a) G. R. Desiraju, Acc. Chem. Res., 1991, 24, 290-296; b) C. Shao, M.
Grüne, M. Stolte, F. Würthner, Chem. Eur. J., 2012, 18, 13665-13677; c)
F.- P. Wu, H.- L. Un, Y. Li, H. Hu, Yi. Yuan, B. Yang, K. Xiao, W. Chen,
J. -Y. Wang, Z.- Q. Jiang, J. Pei, L.- S. Liao, Chem. Eur. J. 2017, 23,
14723-14727.
[32] C. Wang, H. Dong, H. Li, H. Zhao, Q. Meng, W. Hu, Cryst. Growth Des.
2010, 10, 4155-4160.
[33] a) J. Reichwagen, H. Hopf, A. D. Guerzo, C. Belin, H. B-. Laurent, J.-P.
Desvergne, Org. Lett. 2005, 7, 971-974; b) S. Salman, M. C. R. Delgado,
V. Coropceanu, J. L. Brédas, Chem. Mater. 2009, 21, 3593-3601; c) A.
Sakalyte, J. Simokaitiene, A. Tomkeviciene, J. Keruckas, G. Buika, J. V.
Grazulevicius, V. Jankauskas, C.-P. Hsu, C.-H. Yang, J. Phys. Chem. C
2011, 115, 4856-4862.
[34] I. Temiño, F. G. D. Pozo, M. R. Ajayakumar, S. Galindo, J. Puigdollers,
M. M-Torrent, Adv. Mater. Technol. 2016, 1, 1600090-1600099 and
references cited therein.
[35] Y. Zhao, C. -A. Di, X. Gao, Y. Hu, Y. Guo, L. Zhang, Y. Liu, J. Wang, W.
Hu, D. Zhu, Adv. Mater. 2011, 23, 2448-2453.
[15] T. Lei, J.-Y. Wang, J. Pei, Chem. Mater. 2014, 26, 594.
[16] a) J. B. Birks, Photophysics of Aromatic Molecules, Wiley, New York,
1970; b) Y. Zhou, W. J. Liu, W. Zhang, X. Y. Cao, Q. F. Zhou, Y. Ma, J.
Pei, J. Org. Chem. 2006, 71, 6822-6828.
[36] a) D. H. Kim, J. T. Han, Y. D. Park, Y. Jang, J. H. Cho, M. Hwang, K.
Cho, Adv. Mater. 2006, 18, 719-723; b) A. Salleo, Mater. Today. 2007,
10, 38-45; c) W. Hu, C. Wang, H. Dong, Chem. Commun. 2010, 46,
5211-5222; d) C. R. Swartz, S. R. Parkin, J. E. Bullock, J. E. Anthony,
Org. Lett. 2005, 7, 3163-3166.
[17] R. Dabestani, I. N. A. Ivanov, Photochem. Photobiol. 1999, 70, 10-34.
[18] I. B. Berlman, Handbook of Fluorescence Spectra of Aromatic
Molecules; Academic Press: New York, 1965; p 173.
[37] For example: a) M. L. Tang, A. D. Reichardt, T. Okamoto, N. Miyaki, Z.
Bao, Adv. Funct. Mater. 2011, 23, 2448-2453; b) Y. Ogawa, C.
Yamamoto, Miura, S. Tamura, M. Saito, M. Mamada, D. Kumaki, S.
Tokito, H. Katagiri, ACS. Appl. Mater. Interfaces. 2017, 9, 9902-9909.
[38] a) M.-Y. Kuo, and C.-C. Liu, J. Phys. Chem. C, 2009, 113, 16303-16308;
b) H. Dong, X. Fu, J. Liu, Z. Wang, W. Hu, Adv. Mater.2013, 25, 6158-
6183.
[19] R. Nandy, S. Sankararaman, Beilstein J. Org. Chem. 2010, 6, 992-1001.
[20] a) H. Huang, D. G. Drueckhammer, Chem. Commun. 2006, 2995-2997;
b) T. Sun, L. Shen, H. Liu, X. Sun, X. Li, J. Mol. Struct. 2016, 1116, 200-
206; c) H.-D. Becker, V. Langer, J. Sieler, H.-C. Becker, J. Org. Chem.
1992, 57, 1883-1887.
[21] L. Ding, H.-B. Li, T. Lei, H.-Z. Ying, R.-B. Wang, Y. Zhou, Z.-M. Su, J.
Pei, Chem. Mater. 2012, 24, 1944-1949.
[39] R. A. Marcus, Rev. Mod. Phys.1993, 65, 599-610.
[22] a) L. Zhang, Y. Che, J. S. Moore, Acc. Chem. Res. 2008, 41, 1596-1608;
b) S. Chen, P. Slattum, C. Wang, L. Zang, Chem. Rev. 2015, 115, 11967-
11988.
[40] S. Tang, M. Liu, C. Gu, Y. Zhao, P. Lu, D. Lu, L. Liu, F. Shen, B. Yang,
Y. Ma, J. Org. Chem. 2008, 73, 4212-4218.
[41] Y. Wu, W. Zhang, Q. Peng, C.-K. Ran, B.-Q. Wang, P. Hu, K.-Q. Zhao,
C. Feng, S.-K. Xiang, Org. Lett. 2018, 20, 2278-2281.
[23] a) F. Würthner, V. Stepanenko, Z. Chen, C. R. Saha-Moller, N. Kocher,
D. Stalke, J. Org. Chem. 2004, 69, 7933-7939; b) W. W. H. Wong, T. B.
Singh, D. Vak, W. Pisula, C. Yan, X. Feng, E. L. Williams, K. L. Chan, Q.
Mao, D. J. Jones, C.-Q. Ma, K. Müllen, P. Bäuerle, A. B. Holmes, Adv.
Funct. Mater. 2010, 20, 927-938.
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201901470
European Journal of Organic Chemistry
FULL PAPER
Entry for the Table of Contents (Please choose one layout)
Layout 1:
FULL PAPER
Link-Lock Synthesis
Butterfly-shaped methylene-bridged
Jagarapu Ramakrishna, Logesh
R R
bitriphenylenes are synthesized via
Karunakaran, P. ShyamVinod Kumar,
Ajith Mithun Chennamkulam,Venkatesan
Subramanian,* Soumya Dutta* and
Parthasarathy Venkatakrishnan*
Link
Lock
C–C
2 × C–C
Scholl cyclization, and they are shown
to be promising solution-processable
candidates for stable, transparent
OFET device application.
R R
Triphenylene
Conformationally-free
Bitriphenylene
Conformationally-locked
Bitriphenylene
Extended large π-conjugation
Solution-processable
Highly crystalline, Strong π-π stacking
Transparent and stable OFETs
Page No. – Page No.
Organic Electronics
Layout 2:
FULL PAPER
Author(s), Corresponding Author(s)*
Page No. – Page No.
Title
Text for Table of Contents
This article is protected by copyright. All rights reserved.