Effects of chalcogen atom variation in chalcogenadiazole fused indolo[2,3-: A] carbazoles

Article abstract of DOI:10.1039/c7nj04661h

A series of chalcogenadiazole fused indolo[2,3-a]carbazoles 1-3 were prepared, wherein a chalcogen atom was varied from oxygen (O) to sulphur (S) to selenium (Se) in the chalcogenadiazole unit. A Cadogan ring closing reaction was used as the key synthetic step for the preparation of 1-3. The chalcogen alteration (O, S and Se) led to a significant change in the structural, optical and electrochemical properties of 1-3, indicating a subsequent change in their HOMO-LUMO energy levels. Density functional theory (DFT) calculations were performed to further support the experimentally observed trend.

Full text of DOI:10.1039/c7nj04661h

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Effect of chalcogen atom variation in chalcogenadiazole
fused indolo[2,3-a]carbazoles
Sirina Ghosh, Neha Rani Kumar and Sanjio S. Zade*
Department of Chemical Sciences and Centre for Advanced Functional Materials, Indian
Institute of Science Education and Research (IISER) Kolkata, Mohanpur 741246, Nadia, West
Bengal, India
email: sanjiozade@iiserkol.ac.in
Abstract: A series of chalcogenadiazole fused indolo[2,3ꢀa]carbazoles 1ꢀ3 was prepared,
wherein chalcogen atom was varied from oxygen (O) to sulphur (S) to selenium (Se) in the
chalcogenadiazole unit. Cadogan ring closing reaction was used as the key synthetic step for the
preparation of 1ꢀ3. Chalcogen alteration (O, S and Se) led to a significant change in structural,
optical and electrochemical properties of 1ꢀ3 indicating a subsequent change in their HOMOꢀ
LUMO energy levels. Density functional theory (DFT) calculations were performed to further
support the experimentally observed trend.
1

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Introduction
In recent years organic πꢀconjugated small molecules have engrossed significant attention for
their widespread applicability in organic solar cells (OSCs),1,2,3 organic field effect transistors
(OFETs),4,5,6 organic light emitting diodes (OLEDs),7,8,9 sensors10,11 and memory devices.12
Small molecules find an edge over polymeric materials owing to their wellꢀdefined structure,
easy synthesis, high purity and excellent solution processability.
The performance of the organic electronic devices can be tuned by incorporating different
kinds of electronꢀrich donor (D) and electronꢀdeficient acceptor (A) units into the molecular
backbone. The structure and properties of active organic materials can be modulated by changing
the position, types, numbers and ratios of the donor and acceptors. However, many structural
modifications in the same molecule can lead to difficulty in correlating the minute structural
effect with the performance in devices. On this note, the structureꢀproperty relationship13,14 can
be best studied by following the atomistic approach. A single atom variation in the specific
donor/acceptor unit of the molecule appears to be more straightforward and effective in this
regard. Moreover, if the study includes the heteroatom alternation within the same group in the
periodic table then it will be rather more interesting.15,16,17
Benzoxadiazole (BOD), benzothiadiazole (BTD), and benzoselenadiazole (BSeD) are
popular conjugated building blocks with single heteroatom variation for the construction of DꢀA
type small molecules and polymers.18,19,20 Incorporation of heavier elements with larger
polarizability in the conjugated system such as selenium in BSeD is of potential interest for
effectively regulating the structural and optoelectronic properties.21 Several studies on the
conjugated system having BOD in the molecular backbone showed that BOD is stronger
acceptor than BTD and BSeD, due to the presence of oxygen with large electron affinity.22
Moreover oxygen based materials are biodegradable23,24 and biocompatible which makes them
desirable in the field of organic electronics.
The fusion of DꢀAꢀD unit creates a structural framework featuring high planarity,
rigidity, extended πꢀconjugation and compact molecular packing. Many compounds based on
Indolo[2,3ꢀa]carbazole unit found applications in biology, sensing25 and material sciences. Balaji
et al.26 have discussed the synthesis and electrochemical polymerization of Indolo[2,3ꢀ
2

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a]carbazole fused with benzothiadiazole acceptor. Biniek et al. have investigated the scope of
functionalization for indolocarbazole fused with benzothiadiazolo unit.27 Polymers involving
benzothiadiazolo fused indolocarbazole have been reported28 and applied in organic solar cells.29
Thiadiazole (acceptor moiety) fused indolo[2,3ꢀa]carbazole (donor moiety) based heteroacenes
motivated us to synthesize compounds 1ꢀ3 wherein indolo[2,3ꢀa]carbazole (donor moiety) is
fused with different chalcogenadiazole30,31,32 (acceptor moiety). In this context we are presenting
the synthesis, structural and optoelectronic properties of 1ꢀ3.
Results and discussion
Synthesis
The synthetic routes toward the synthesis of 1ꢀ3 are depicted in Scheme 1. 4,7ꢀ
dibromobenzoxadiazole (4a)33 and 4,7ꢀdibromobenzoselenadiazole (4b)34 were subjected to
Suzuki coupling reaction with 2ꢀnitrophenylboronic acid to give compounds 6a and 6b in 47%
and 40% yields, respectively. Stille coupling reaction of 4,7ꢀdibromo,5,6ꢀdinitrobenzothiadiazole
(5)35 with tributylphenyltin36 afforded compound 7 in 70% yield. Cadogan37 ring closing reaction
was carried out on 6a, 6b and 7 in the presence of PPh3 in oꢀdichlorobenzene (oꢀDCB) solvent
under refluxing condition to obtain 8a, 8b and 8c in 48%, 80% and 36% yields, respectively. A
common alkylation method was used with DMF/NaOH and nꢀbutyl bromide to obtain the
desired compounds 1, 2 and 3 in 44%, 58% and 49% yields, respectively. Furthermore all the
1
newly synthesized compounds were characterized by H, 13C NMR spectroscopy and high
resolution mass spectrometry (HRMS).
NO2
B(OH)2
NO2
O2N
Pd(PPh3)4
Br
Br
THF/water, reflux
E=O/Se
C4H9 C4H9
N
N
H
H
N
N
E
N
N
E
N
N
n-BuBr, NaOH
DMF
PPh3
4a, E=O;
4b, E=Se
6a, E=O;
6b, E=Se
o-DCB, reflux
SnBu3
O2N
Br
NO2
Br
O2N
NO2
N
N
N
N
E
E
Pd(PPh3)4
8a, E=O;
8b, E=S;
8c, E=Se
1, E=O;
2, E=S;
3, E=Se
toluene, reflux
N
N
N
N
S
5
S
7
Scheme 1 Synthetic routes of 1ꢀ3.
3

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Structural properties:
The structures of compounds 1 and 2 were examined by singleꢀcrystal Xꢀray diffraction
(SCXRD) technique. Single crystals were obtained by the slow evaporation of their
hexane/dichloromethane (1/1) solution. Crystallographic data along with structure refinement
parameters are listed in Table 1 of supporting information. The crystallization of compound 3
has been attempted using different solvent systems and conditions. However, all attempts were
unsuccessful to afford crystalline 3 suitable for single crystal Xꢀray diffraction. In most of
the attempts, compound 3 was precipitated as amorphous solid. The ORTEP diagrams of
compounds 1 and 2 are shown in Fig. 1. Compound 1 crystallizes in the monoclinic space group
whereas 2 crystallizes in the triclinic space group. SCXRD structures revealed that the molecules
adapted wavy fused ring structures to minimize the steric repulsion between Nꢀalkyl substituents.
The dihedral angles between the central BOD/BTD and outer phenyl rings (C23, C18, C17 and
C16; C26, C13, C14 and C15) are found to be 167° and 175° in 1 and 173° and175° in 2,
respectively, which implies a nearly planar framework due to the presence of nitrogen bridges in
the fused system.
In the crystal structure of compound 1, the molecules form 1ꢀD chains via weak C‒H···O (2.592
Å, 149°) interaction (Fig. 2) and butyl chain interdigitation. Molecular 1ꢀD chain are slippedꢀ
stacked by π···π interactions (3.326 Å and 3.355 Å) and CꢀH···π interactions (Fig. S1). The
crystal structure of compound 2 possesses solvent accessible voids filled up with
dichloromethane molecules along c‒axis (Fig. S2). The dichlromethane molecule stitches
together two molecules of compound 2 via C‒H···Cl (2.947 Å, 149°) interaction (Fig. S3).
Molecules in crystal structures of compound 2 forms molecular sheets which are stacked
together by π···π and CꢀH···π interactions (3.376 Å). The packing of compound 2 creates a
slipped columnar pattern.
4

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Fig. 1 ORTEP representation (Thermal ellipsoids are drawn at 50% probability level) of (a) 1
and (b) 2 (dichloromethane molecule is omitted for clarity).
Fig. 2 C‒H···O (2.592 Å, 134.52°) interaction in compound 1.
Photophysical properties
To examine the optical properties, the UVꢀvis absorption spectra of compounds 1ꢀ3 in 10ꢀ
5
M toluene solutions were recorded (Fig. 3a). Compound 1 showed dual band absorption. The
higher energy band at ~300 nm is due to πꢀπ* transition and the lower energy band at ~340 nm
originates from intramolecular charge transfer (ICT) between indole units and BOD. Instead of
showing two distinctive peaks, compounds 2 and 3 displayed a peak and a shoulder peak. The
absorption maxima of both peaks exhibited a red shift when heavier chalcogens are incorporated
5

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into the chalcogenadiazole skeleton. It can be ascribed to the increasing polarizibility of the
heteroatom (from O to Se) resulting in a better intramolecular charge transfer. The relative
intensity of low energy peak/shoulder peak decreases upon moving from compound 1 to 3,
which can be attributed to the decrease in electronegativity of the heteroatom and diminishing
ability to stabilize a charge separated state. The optical properties in thin films were also studied
for 1ꢀ3. A significant bathochromic shift was observed in the thin film absorption spectra of 1ꢀ3
compared to that of solution state (Fig. 4a). It indicates the presence of strong intermolecular
interactions such as πꢀstacking interaction in the solid state. The emission spectra in thin films
(Fig. 4b) for 1ꢀ2 also shifted bathochromically than that of the solution state (Fig. 3b). However,
compound 3 turned out to be nonꢀemissive in solution as well as in solid state.
Solvatochromic experiments were performed on 1ꢀ3 to study the solvent dependent
spectral changes. Solvents with increasing dielectric constants [toluene (2.3), THF (7.5), DCM
(8.9) and DMSO (46.7)] were chosen to record the absorption and emission spectra of 1ꢀ3. Fig. 5
depicts the colour change in emission of compound 2 with the change in solvent polarity from
toluene to DMSO. The UVꢀvis absorption spectra of 1ꢀ3 remained almost unaffected upon
changing the solvent polarity (Fig. S4). Compound 1 and 2 showed clear emission maxima,
whereas 3 emitted via nonꢀradiative processes. By changing solvent from nonpolar toluene to
polar DMSO the emission maxima shifted bathochromically by 36 (460 to 496 nm) and 38 nm
(474 to 512 nm) for compound 1 and 2, respectively (Fig. 6) It indicates the presence of positive
solvatochromism in emission which also supports the existence of more polar excited states.38
(a)
1
2
3
1
2
(b) 1.0
1.0
0.8
0.6
0.4
0.2
0.0
0.8
0.6
0.4
0.2
300
350
400
450
400
450
500
550
600
650
700
Wavelength (nm)
Wavelength (nm)
Fig. 3 Normalized absorption (a) spectra of 1ꢀ3 and emission (b) spectra of 1ꢀ2 in 10ꢀ5 M toluene
solution.
6

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(a)
(b) 1.0
1
2
1
2
3
1.0
0.8
0.6
0.4
0.2
0.0
0.8
0.6
0.4
0.2
0.0
550
600
650
700
750
800
400
500
600
700
800
Wavelength (nm)
Wavelength (nm)
Fig. 4 Normalized absorption (a) spectra of 1ꢀ3 and emission (b) spectra of 1ꢀ2 in thin film.
Fig. 5 Colour change in emission of compound 2 from toluene to DMSO.
(a) 1.0
Toluene
(b) 1.0
Toluene
THF
THF
DCM
DMSO
DCM
DMSO
0.8
0.6
0.4
0.2
0.0
0.8
0.6
0.4
0.2
0.0
400
450
500
550
600
650
700
450
500
550
600
650
700
Wavelength (nm)
Wavelength (nm)
Fig. 6 Normalized emission spectra of (a) 1and (b) 2in different solvents (10ꢀ5 M).
7

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Table 1 Optical and Electrochemical Properties of Fused systems 1ꢀ3.
λꢀꢁ.
Thinfilm
(nm)
λ
(
Thinfilm
(nm)
a
b
c
Compound
Solution
(nm)
Solution
(nm)
(eV)
(eV)
(eV)
306, 342 357, 377,
418
461
634
−5.61
−2.45
3.16
1
328,
366
473
ꢀ
−5.53
−5.46
−2.48
−2.61
3.05
2.85
2
3
412
598
ꢀ
344, 391
419, 460
aThe HOMO energy levels were obtained from the equation
= − (4.8 −
=
+
)
b
c
eV. LUMO energy levels were calculated from the equation
+
. calculated
from
= hc/
.
Electrochemical properties
The electrochemical properties of compounds 1ꢀ3 were measured in dry acetonitrile (ACN)
using 0.1 M tetrabutylammonium perchlorate (TBAPC) as electrolyte by cyclic voltammetry
with Ptꢀdisk as working electrode, Ag/Ag+ as reference electrode and Pt wire as counter
electrode. Compounds 1ꢀ3 showed oxidation potentials (
) of 1.28, 1.20, and 1.30 V with
onset values 1.18, 1.10 and 1.03 V, respectively (Fig. 7). From the oxidation potential onset
values the HOMO levels for 1, 2 and 3 were evaluated as −5.61, −5.53 and −5.46 eV,
respectively. The onset oxidation potential of 1 is higher than those of 2 and 3 due to the
significantly strong electron accepting nature of BOD unit. Whereas the oxidation potential of
compound 3 is lower than that of 2 due to presence of Se atom. The LUMO energy levels were
estimated by subtraction of the optical band gap values from the HOMO energy level values and
found to be −2.45, −2.48 and −2.61 eV for 1ꢀ3, respectively. Thus systematic change of a single
atom in the chalcogenadiazole can vary the electrochemical behavior of the resulting compounds
in an efficient manner.
8

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6
5
4
3
2
1
0
1
2
3
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
Voltage (V)
Fig. 7 CV of (a) 1, (b) 2 and (c) 3 in ACN and 0.1 M TBAPC on a Pt electrode at a scan rate of
50 mV/s vs Ag/Ag+wire.
Theoretical Calculations
DFT calculations were performed on compounds 1-3 using Gaussian 09 program39 with B3LYP
functional and 6ꢀ31G(d) basis set. DFT calculated trend in HOMOꢀLUMO energy gap (1>2>3)
is in well agreement with the experimental results. Electron density of HOMOs of compounds 1-
3 are located over indolo[2,3ꢀa]carbazole backbone, whereas LUMOs are mostly located on
benzochalcogenadiazole unit resulting in an ICT interactions (Table 2). These interactions are
majorly responsible for low energy absorption bands in absorption spectra. Moving along the
series from compounds 1 to 3, LUMO electron density becomes prominent on
benzochalcogenadiazole unit resulting redꢀshift in higher energy band from compounds 1 to 3.
Table 2. Frontier molecular orbital diagrams of 1, 2 and 3.
Compound
HOMO (eV)
LUMO (eV)
HOMOꢀLUMO
gap (eV)
3.51
1
ꢀ1.83
ꢀ5.34
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3.38
2
ꢀ5.21
ꢀ1.84
3.23
3
ꢀ5.14
ꢀ1.91
Conclusion
In conclusion, a series of chalcogenadiazole acceptors fused indolo[2,3ꢀa]carbazole based
molecules (1-3) have been designed and synthesized. These homologous DꢀAꢀD fused
compounds clearly show the effect of single heteroatom substitution on the structural, optical and
electrochemical properties. We have found that BOD is stronger electron acceptor than BTD and
BSeD. Trends obtained from experimental findings were in good agreement with DFT
calculations.
Experimental details
General Measurement and Characterization
All reactions were carried out under nitrogen atmosphere to maintain the inert condition. Dry
toluene and tetrahydrofuran (THF) were distilled from sodium/benzophenone before use. Other
reagents were purchased from commercial sources and used without further purification.1H
13
NMR and C NMR spectra of the compounds were taken on Jeol ECS 400 MHz spectrometer
with CDCl3 or DMSOꢀd6 as the solvent, and chemical shifts (δ) are reported in parts per million
(ppm) relative to tetramethylsilane as the internal standard values. The coupling constants (J) are
10

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given in Hz. The apparent resonance multiplicity is described as s (singlet), brs (broad singlet), d
(doublet), t (triplet), q (quartet), and m (multiplet). Electrochemical studies were carried out with
a Princeton Applied Research 263A potentiostat using platinum (Pt) disk electrode as the
working electrode, a platinum wire as counter electrode and an AgClꢀcoated Ag wire as the
reference electrode. Nonaqueous Ag/Ag+ wire was prepared by dipping silver wire in a solution
of FeCl3 and HCl. Pt disk electrodes were polished with alumina and washed with water, and
acetone and were dried with nitrogen gas before use to remove any incipient oxygen. UV–vis–
near infrared (NIR) spectra were recorded on a HITACHI Uꢀ4100 UV–vis–NIR
spectrophotometer. All electrochemical potentials were reported against Ag/Ag+taking ferrocene
as external standard; the Eferrocene1/2 is +0.37 V.
Synthesis
The synthesis of compounds 4a,24 4b,40 5,41 740and 8b40were followed from the reported
procedure.
Synthesis of compound 6aand 6b
In a 100 ml three neck round bottomed flask under nitrogen atmosphere were added compound
4a/4b (0.35 mmol) and 2ꢀ nitrophenyl boronic acid (174.19 mg, 1.04 mmol) in THF:H2O (1:1).
The reaction mixture was purged with nitrogen for 15 min, then Pd(PPh3)4 (5 mol%) was added
and the reaction mixture was refluxed overnight. Then the solvent was evaporated and the
desired compound was isolated by silica gel column chromatography with hexane/ethyl acetate
(1/1) for compound 6a and (4/1) for 6b.
Compound6a: Pale yellow solid (yield: 47%). Mp. 135 °C. 1H NMR (400 MHz, CDCl3, δ/ppm):
8.20ꢀ8.18 (m, 2H), 7.81ꢀ7.79 (m, 2H), 7.77ꢀ7.66 (m, 4H), 7.45 (s, 2H).13C NMR (100 MHz,
CDCl3, δ/ppm): 148.6, 148.4, 133.5, 132.2, 130.4, 130.2, 129.7, 127.7, 125.2. HRMS (M+H)+:
+
calculated for C18H11N4O5 363.0685, found 363.0630.
Compound 6b: White solid (yield: 40%). Mp. 153°C.1H NMR (400 MHz, CDCl3, δ/ppm): 8.17ꢀ
8.15 (m, 2H), 7.76ꢀ7.75 (m, 2H), 7.65ꢀ7.63 (m, 4H), 7.38 (s, 2H). 13 C NMR (100 MHz, CDCl3,
δ/ppm): 158.1, 149.3, 133.4, 133.2, 132.6, 132.5, 129.4, 128.0, 124.7. HRMS (M+H)+:
calculated for C18H11N4O4Se+426.9901, found 426.9830.
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Synthesis of compound 8a and 8b
In a 100 ml three necked round bottomed flask under nitrogen atmosphere oꢀdichlorobenzene (2
ml), compound 6a/6b (0.27 mmol) and PPh3 (362mg, 2.76 mmol) were added and heated at 180
°C overnight. Then the solvent was evaporated under reduced pressure and the reaction mixture
was subjected to column chromatography (silica gel, 60ꢀ120 mesh) using hexane/ethyl acetate
(4/1) to yield 8a/8c.
Compound 8a: Light yellow solid (yield: 48%). Mp 130°C.1H NMR (400 MHz, DMSOꢀd6,
δ/ppm): 12.12 (br s, 2H), 8.17 (d, J = 4 Hz, 2H), 7.88 (d, J = 4 Hz, 2H), 7.47ꢀ7.41 (m, 4H). 13
C
NMR (100 MHz, DMSOꢀd6, δ/ppm): 144.2, 137.6, 130.0, 124.5, 123.1, 121.8, 120.2, 113.1,
100.7. HRMS (M + H)+: calculated for C18H11N4O+299.0888, found 299.0801.
Compound 8c: Yellow solid (yield: 36%). Mp 145°C.1H NMR (400 MHz, DMSOꢀd6, δ/ppm):
11.77 (br s, 2H), 8.50 (d, J = 4.3 Hz, 2H), 7.83 (d, J = 4.3 Hz, 2H), 7.43ꢀ7.35 (m, 4H). 13 C NMR
(100 MHz, DMSOꢀd6, δ/ppm): 154.8, 137.6, 129.4, 124.3, 123.9, 121.4, 120.7, 112.6,
109.6.HRMS (M + H)+: calculated for C18H11N4Se+ 363.0104, found 363.0120.
Synthesis of compound 1
A mixture of compound 8a/8b (0.16 mmol), butylbromide (0.12 ml, 1.08mmol), and sodium
hydroxide (66.8 mg, 1.67 mmol) in DMF was stirred at rt for 6 h. Then the reaction mixture was
poured into water and the resulting suspension was extracted with ethyl acetate. The ethyl acetate
layer was collected and dried over Na2SO4. The solvent was removed by rotary evaporation, and
the residue was purified by silica gel column chromatography with hexane/ethyl acetate (4/1) to
yield 1/2.
Compound 1: Yellow solid (44%). Mp180 °C.1H NMR (400 MHz, CDCl3, δ/ppm): 8.44ꢀ8.42
(m, 2H), 7.64ꢀ7.62 (m, 2H), 7.51ꢀ7.46 (m, 4H), 4.68 (t, J = 7.2 Hz, 4H), 1.69ꢀ1.65 (m, 4H), 1.01ꢀ
13
0.97 (m, 4H), 0.76ꢀ0.72 (t, 6H).
C NMR (100 MHz, CDCl3, δ/ppm): 144.8, 141.1, 133.4,
125.3, 124.9, 122.5, 122.0, 112.1, 106.0, 48.4, 31.2, 19.8, 13.4.HRMS (M + H)+: calculated for
C26H27N4O+ 411.2173, found 411.2081.
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Compound 2: Yellow solid (58%). Mp190 °C.1H NMR (400 MHz, CDCl3, δ/ppm): 8.78ꢀ8.76
(m, 2H), 7.64 (m, 2H), 7.51ꢀ7.47 (m, 4H), 4.71 (t, J = 7.2 Hz, 4H), 1.65ꢀ1.63 (m, 4H), 1.00ꢀ0.96
13
(m, 4H), 0.74ꢀ0.70 (t, 6H). C NMR (100 MHz, CDCl3, δ/ppm): 149.4, 141.7, 132.7, 125.9,
124.7, 122.2, 112.6, 112.0, 48.5, 31.2, 19.9, 13.5.HRMS (M + H)+: calculated for C26H27N4S+
427.1973, found 427.1754.
Synthesis of compound 3
A mixture of compound 8c (50 mg, 0.13 mmol), butylbromide (0.09 ml, 0.85 mmol), and sodium
hydroxide (51.9 mg, 1.3 mmol) in DMF was stirred at rt for 6 h. Then the reaction mixture was
poured into water and the resulting suspension was extracted with ethyl acetate. The ethyl acetate
layer was collected and dried over Na2SO4. The solvent was removed by rotary evaporation, and
the residue was purified by silica gel column chromatography with hexane/ethyl acetate (4/1) to
yield 3 as yellow solid (30 mg, 49%). Mpꢀ188°C, 1H NMR (400 MHz, CDCl3, δ/ppm): 8.78 (m,
2H), 7.61 (m, 2H), 7.47ꢀ7.45 (m, 4H), 4.67 (t, J = 7.2 Hz, 4H), 1.68ꢀ1.64 (m, 4H), 1.01ꢀ0.97 (m,
4H), 0.74ꢀ0.70 (t, 6H). 13 C NMR (100 MHz, CDCl3, δ/ppm): 155.7, 141.3, 133.1, 126.5, 124.3,
122.4, 122.3, 113.7, 111.9, 48.3, 31.2, 19.8, 13.5.HRMS (M + H)+: calculated for C26H27N4Se+
475.1473, found 475.1261.
Supporting Information:
1H and 13C NMR spectra of all new compounds and optimized structures, absolute energies,
absorption spectra, picture of HOMO and LUMO, and coordinates for optimized structure of 1,2
and 3.
Acknowledgements
We acknowledge SERB, India for financial support (project no. EMR/2015/000241). SG thanks
CSIR for research fellowship. NRK thanks DST for INSPIRE fellowship.
There are no conflicts of interest to declare.
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Effect of chalcogen atom variation in chalcogenadiazole
fused indolo[2,3-a]carbazoles
Sirina Ghosh, Neha Rani Kumar and Sanjio S. Zade*
Department of Chemical Sciences and Centre for Advanced Functional Materials, Indian
Institute of Science Education and Research (IISER) Kolkata, Mohanpur 741246, Nadia,
West Bengal, India
TOC
Chalcogen (O/S/Se) induced intriguing variation of structural and optoelectronic properties
for a series of chalcogenadiazole fused Indolo[2,3-a]carbazole donor-acceptor (D-A)
molecules.