Effects of Donor and Acceptor Units Attached with Benzoselenadiazole: Optoelectronic and Self-Assembling Patterns

Article abstract of DOI:10.1021/acs.cgd.5b01179

Here, we report the effects of electron donor and acceptor units attached with benzoselenadiazole for the change in optoelectronic and packing patterns in solid states. We have synthesized 4-methoxybenzene, naphthalene, and 4-nitrobenzene capped benzoselenadiazoles (compounds 1-3 respectively) and studied their photophysical as well as electrochemical properties. All three molecules show two absorption bands (π-π transition band and CT-band). Three molecules (1-3) show orange, yellow-green, and green colors in dichloromethane solutions upon irradiation of UV light at 365 nm. Benzoselenadiazole-based compounds 1-2 form head to head dimers via Se···N interactions in the solid states. Compounds 1 and 2 show interlock type packing via Se···N interaction in their solid state structures. Se···π interaction takes a major role to form interlocked sheet type structures in crystal packing of compound 1, whereas Se···N, N···N, and CH···π interactions help to form a supramolecular sheet type of structure in the crystal packing of compound 2. Band gaps of these compounds were tuned by changing the electron donating to electron withdrawing units attached with a benzoselenadiazole core.

Full text of DOI:10.1021/acs.cgd.5b01179

Article
pubs.acs.org/crystal
Effects of Donor and Acceptor Units Attached with
Benzoselenadiazole: Optoelectronic and Self-Assembling Patterns
†
†
‡
†
,†
Sahidul Mondal, Maruthi Konda, Brice Kauffmann, Manoj K. Manna, and Apurba K. Das*
†
Department of Chemistry, Indian Institute of Technology Indore, Indore 452017, India
‡
CNRS UMS3033, INSERM US001, Institut Europee
́
n de Chimie et Biologie (IECB), Universite
́
de Bordeaux, , 2 rue Escarpit,
3
3600 Pessac, France
*
S Supporting Information
ABSTRACT: Here, we report the effects of electron donor
and acceptor units attached with benzoselenadiazole for the
change in optoelectronic and packing patterns in solid states.
We have synthesized 4-methoxybenzene, naphthalene, and 4-
nitrobenzene capped benzoselenadiazoles (compounds 1−3
respectively) and studied their photophysical as well as
electrochemical properties. All three molecules show two
absorption bands (π−π transition band and CT-band). Three
molecules (1−3) show orange, yellow-green, and green colors
in dichloromethane solutions upon irradiation of UV light at
365 nm. Benzoselenadiazole-based compounds 1−2 form head
to head dimers via Se···N interactions in the solid states. Compounds 1 and 2 show interlock type packing via Se···N interaction
in their solid state structures. Se···π interaction takes a major role to form interlocked sheet type structures in crystal packing of
compound 1, whereas Se···N, N···N, and CH···π interactions help to form a supramolecular sheet type of structure in the crystal
packing of compound 2. Band gaps of these compounds were tuned by changing the electron donating to electron withdrawing
units attached with a benzoselenadiazole core.
wide range of π-conjugated systems are investigated for
exploitation in device applications. Aromatic π-conjugated
were described by Zade et al. to understand the substitution
pattern of donor aromatic units attached with acceptor
A
22
optoelectronic materials are important because they provide
optical, electronic, and optoelectronic behavior. Aromatic π-
conjugated molecules serve as active materials for the
development of devices, in particular, for field-effect transistors,
benzoselenadiazole unit. Mikroyannidis et al. investigated
the incorporation of low band gap Se-based small organic
molecules in copolymer solar cells which show improved
photovoltaic properties due to the increase in crystalline
1
−3
23
light-emitting diodes, and photovoltaics.
Small π-conjugated
nature. Recently, Patil et al. investigated in detail the change
donor−acceptor−donor (D-A-D) systems as optoelectronic
materials have been well developed. The optical and electronic
properties of small conjugated molecules can be tuned by a
in electrical and optical properties by comparing two DAD
24
molecules differing only by a chalcogen atom. The band gap
of D-A systems can be tuned by replacing with a heteroatom in
an acceptor unit as well as by changing the donor unit.
However, the number of reported examples with A-A units is
very limited.
4
−6
small change in their molecular architectures.
π-Conjugated
DAD systems are also used in conjugated polymers for the
development of field effect transistors and solar cells. Donor−
acceptor (D-A) based conjugated compounds have a low band
In this paper, we report synthesis, optical, packing patterns,
electrochemical, and theoretical studies of BDS containing
molecules 1, 2, and 3 (Scheme 1). To study the effect of donor
and acceptor units attached with BDS, we have synthesized 4-
methoxybenzene (compound 1), naphthalene (compound 2),
and 4-nitro benzene (compound 3) capped benzoselenadia-
zoles. The optical properties of compounds 1−3 were studied
in an organic solvent dichloromethane. Compounds 1 and 2
show strong Se···N interaction, which facilitates the formation
of a head to head pairwise dimer structure. In higher order self-
7
gap and wide light absorption spectra. Especially for the D−A
systems, intramolecular charge transfer occurs from the
electron-rich donor to electron-deficient acceptor units.
8
−11
12−15
Benzooxadiazole (BDO),
benzothiadiazole (BDT),
1
6−18
and benzoselenadiazole (BDS)
based acceptor units
were used in conjugated molecules for the development of
several electronic devices. Nevertheless, benzoselenadiazole-
19
based molecules have also been used as probes for enzymes
and anions sensing.
20
Wong et al. reported benzochalocogenodiazole-based D-A-A
configured molecular donors for the development of organic
solar cells. Structural and optoelectronic properties of
benzoselenadiazole containing DAD-based small molecules
Received: August 17, 2015
Revised: September 27, 2015
2
1
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.cgd.5b01179
Cryst. Growth Des. XXXX, XXX, XXX−XXX

Crystal Growth & Design
Article
a
spectrophotometer (Horiba Jobin Yvon) with a 1 cm path length
quartz cell at room temperature. HRMS spectra were recorded on a
Bruker micrOTOF-Q II mass spectrometer. The density functional
theory (DFT) calculations were carried out at the B3LYP/6-31G**
level for C, N, Se, H, O in the Gaussian 09 program. Cyclic
voltammograms were recorded on an electrochemical analyzer (CH
Instruments, model no: 600 E Series) using glassy carbon as the
working electrode, Pt wire as the counter electrode, and saturated Ag/
AgCl as the reference electrode. The scan rate was 100 mV s− for CV
measurements. A solution of tetrabutylammonium hexafluorophos-
Scheme 1. Synthesis of Compounds 1, 2, and 3
1
phate (TBAPF ) in DCM (0.1 M) was employed as the supporting
6
electrolyte.
a
Synthesis. Here, we have synthesized compounds 1, 2, and 3 by
the Suzuki coupling reaction between 4,7-dibromo-2,1,3-benzoselena-
diazole and boronic acid of corresponding donor and acceptor units at
different reaction conditions.
Reagents and conditions: (i) SeO , EtOH, 1 h reflux; (ii) Ag SO ,
2
2
4
H SO , Br ; (iii) naphthaleneboronic acid, K CO , Pd(PPh ) , THF/
water, 85 °C, 12 h, yield = 72% (compound 2); (iv) para substituted
benzeneboronic acid, K CO , Pd(PPh ) ,THF/water, 80 °C,12 h,
yield = 81% (compound 1), 66% (compound 3).
2
4
2
2
3
3 4
2
3
3 4
Synthesis of 2,1,3-Benzoselenadiazole 5. 2,1,3-Benzoselenadiazole
5
was prepared from o-phenylenediamine 4 according to a previously
25
reported method and obtained as a faint pink colored solid (54.9
assembly, compounds 1 and 2 stack to form an interlocked
structure using hydrogen bonding, C−H···π and π−π stacking
interactions. Compounds 1 and 2 showed strong orange and
yellow-green emissions in dichloromethane solution respec-
tively, whereas compound 3 shows green emission due to the
presence of a strong electron withdrawing 4-nitrobenzene
group with a central BDS unit (Figure 1).
1
mmol, 98.9%). H NMR (400 MHz, CDCl ) δ 7.83 (d, J = 9.5 Hz,
3
2H), 7.45 (d, J = 9.8 Hz, 2H). 13C NMR (100 MHz, CDCl ) δ 160.50,
3
129.44, 123.43.
Synthesis of 4,7-Dibromo-2,1,3-benzoselenadiazole 6. 4,7-
Dibromo-2,1,3-benzoselenadiazole 6 was prepared from 5 according
2
6
to previously reported method and obtained as golden yellow
1
needles (4.06 mmol, 74.6%). H NMR (400 MHz, CDCl ) δ 7.64 (s,
3
2
H). 13C NMR (100 MHz, CDCl ) δ 157.21, 132.14, 116.51.
3
Synthesis of Compound 2. In a 100 mL two neck round-bottom
flask, 4,7-dibromo-2,1,3-benzoselenadiazole (300 mg, 0.882 mmol)
and naphthalene-1-boronic acid (379 mg, 2.205 mmol) were dissolved
in THF (30 mL). Potassium carbonate (1.22 g, 8.82 mmol) was
dissolved in 10 mL of water and added to the previous mixture. The
reaction mixture was purged with nitrogen gas for 20 min. Pd(PPh3)4
(55 mg, 0.05 mmol) was added to the reaction mixture. The reaction
mixture was stirred overnight at 85 °C. The solvent was removed
under reduced pressure. The product was extracted using dichloro-
methane and washed with Milli-Q water followed by brine solution (3
×
30 mL). The organic part was dried over sodium sulfate, and the
solvent was evaporated using rotary evaporator. Purified compound 2
1
was obtained as a yellow solid powder (0.632 mmol, 72%). H NMR
(
400 MHz, CDCl ) δ 7.96−8.01 (m, 4H), 7.63−7.70 (m, 8H), 7.53 (t,
3
13
J = 7.4 Hz, 2H), 7.43 (m, 2H); C NMR (100 MHz, CDCl ) δ
3
1
1
60.25, 135.94, 135.01, 133.75, 132.01, 130.26, 128.84, 128.51, 127.84+,
26.12, 126.01, 125.96, 125.34. HRMS (ESI-TOF) m/z: (M + Na)
calcd for C H N SeNa 459.0376, found 459.0372.
26
16
2
Synthesis of Compounds 1 and 3. In a 100 mL two neck round-
bottom flask, 4,7-dibromo-2,1,3-benzoselenadiazole (300 mg, 0.882
mmol), potassium carbonate (1.22 g, 8.82 mmol), and para-substituted
boronic acid (2.205 mmol) were mixed in water (5 mL) and THF (20
mL). The reaction mixture was purged with nitrogen gas for 20 min.
Pd(PPh ) (55 mg, 0.05 mmol) was added to the reaction mixture.
Figure 1. Photographs of compounds 1, 2, and 3 in dichloromethane
solutions under a 365 nm UV lamp.
3
4
The reaction mixture was stirred overnight at 80 °C. The solvent was
removed under reduced pressure. The product was extracted using
dichloromethane and washed with Milli-Q water followed by brine
solution. The organic part was dried over sodium sulfate, and the
solvent was evaporated using a rotary evaporator.
EXPERIMENTAL SECTION
General Methods. All reagents and chemicals were obtained
commercially. All the reactions were performed under nitrogen
atmosphere using a standard method. Toluene and tetrahydrofuran
THF) were distilled from sodium/benzophenone prior to use.
Dichloromethane and hexane were also distilled from calcium chloride
for purification purposes. DCM was freshly distilled from CaH prior
to use for optical and electrochemical studies. Final compounds were
purified by using silica gel column (60−120 mesh). The hexane/DCM
9:1) system for compound 2 and the toluene/ethyl acetate (9:1)
■
Purified compound 1 was obtained as an orange solid powder
1
(
(0.712 mmol, 81%). H NMR (400 MHz, CDCl
3
) δ 7.83 (d, J = 7.8
1
3
Hz, 4H), 7.56 (s, 2H), 7.06 (d, J = 7.8 Hz, 2H), 3.81 (s, 6H).
NMR (100 MHz, CDCl ) δ 159.93, 159.65, 134.17, 130.61, 127.81,
113.95, 55.38. HRMS (ESI-TOF) m/z: (M + Na) calcd for
SeNa 419.0270, found 419.0279.
Purified compound 3 was obtained as a yellow solid powder (0.58
mmol, 66%). H NMR (400 MHz, CDCl ) δ 8.40 (d, J = 8.2 Hz, 4H),
8.10 (d, J = 8.2 Hz, 4H), 7.77 (s, 2H). C NMR (100 MHz, CDCl ) δ
C
2
3
+
C H N O
20 16 2 2
(
1
1
system for compounds 1 and 3 were used for purification purposes. H
NMR (400 MHz) and 13C NMR (100 MHz) spectra were recorded
on a Bruker AV 400 MHz spectrometer at 300 K. Compound
3
13
3
+
143.48, 130.08, 128.76, 123.43. HRMS (ESI-TOF) m/z: (M + Na)
−1
concentrations were in the range 5−10 mmol L in CDCl . UV−vis
calcd for C H N O SeK 464.9504, found 464.9504.
3
18 10
4
4
absorption spectra of all compounds were recorded using a Varian
Cary100 Bio UV−vis spectrophotometer. Fluorescence spectra of all
compounds were recorded on Horiba Scientific Fluoromax-4
Crystal Structure Solution and Refinement. Crystallographic
data for compounds 1 and 2 were collected on a Rigaku FRX
microfocus rotating anode (3 kW) and a Rigaku MM007 HF (1.2 kW)
B
DOI: 10.1021/acs.cgd.5b01179
Cryst. Growth Des. XXXX, XXX, XXX−XXX

Crystal Growth & Design
Article
at the copper Kα edge equipped with a Dectris Pilatus 200 K hybrid
detector and R-AXIS SPIDER image plate (IP) respectively. The
diffraction intensities were integrated and scaled with the CrystalClear
suite version 2.1b25 and 2.1b43. Both structures were solved using
SHELXT and refined with SHELXL 2015 version. Full-matrix least-
absorption spectra of compounds 1−3 possess a characteristic
dual-band nature. The higher-energy bands (333−337 nm) are
attributed due to the π → π* transition of the conjugated
backbones. The lower-energy bands (390−432 nm) are
assigned to charge transfer transitions (CT). The λmax of the
higher-energy band remains relatively constant for all three
compounds 1−3. The lower-energy charge transfer band is
blue-shifted upon moving from compound 1 to compound 3.
Compound 1 shows an internal charge transfer (ICT) band at a
significantly higher wavelength as 4-methoxybenzene is a
stronger donor unit. The charge transfer band for compound
2
squares refinement were performed on F for all unique reflections,
minimizing w(Fo2 − F ) , with anisotropic displacement parameters
2 3
c
for non-hydrogen atoms. All H atoms found in difference electron-
density maps were refined freely, and all the others were treated as
riding on their parent C or N atoms. Data statistics are reported in the
27
Table S1 and CIF files.
RESULTS AND DISCUSSION
3
is blue-shifted due to the presence of strong electron
■
To elucidate the role of electron donating and accepting units
attached with benzoselenadiazole (BDS), we synthesized 4-
methoxybenzene (compound 1), naphthalene (compound 2),
and 4-nitrobenzene (compound 3) capped benzoselenadia-
zoles. Syntheses of compounds 1, 2, and 3 were achieved by
Suzuki coupling reaction shown in Scheme 1. To synthesize
these three compounds, first we synthesized benzoselenadiazole
with the reaction between o-phenylenediamine and selenium
dioxide. Four and seven positions of benzoselenadiazole were
brominated in the presence of bromine, silver sulfate, and
concentrated sulfuric acid. The 4,7-dibromo benzoselenadiazole
was treated with corresponding boronic acids in the presence of
potassium carbonate and tetrakis triphenylphosphene palla-
dium (0) as a catalyst at 80 °C to synthesize compounds 1, 2,
and 3 respectively. All three compounds were well charac-
withdrawing group.
Emission spectra of compounds 1−3 were recorded in
dichloromethane (DCM) via excitation at the corresponding
λ
max of lower energy bands. Compounds 1−3 exhibit emission
maxima at 675, 546, and 483 nm with Stokes shifts of 8334,
−1
7130, and 4937 cm , respectively. A small Stokes shift is
observed upon attachment of electron withdrawing units (4-
nitrobenzene) with benzoselenadiazole (compound 3) unit. A
larger Stokes shift is found when electron donating units are
attached with benezoselenadiazole moiety (compound 2). The
most dramatic Stokes shift is observed for compound 1 when
stronger donor units (4-methoxybenzene) are attached with an
electron accepting unit benzoselenadiazole. The absorption
peak at lower energy band is shifted to visible wavelength at
432 nm, and the emission is shifted to 675 nm. The long
wavelength emission is attributed to an internal charge transfer
1
13
terized by H NMR, C NMR, and mass spectral studies.
Optical Properties. The absorption and emission spectra
of all three compounds in dichloromethane solutions are shown
in Figure 2, and all data are summarized in Table 1. The
28
(ICT) state.
Electrochemical Properties. The role of electron
donating as well as electron withdrawing units on the redox
behavior of 2,1,3-benzoselenadiazole based systems 1−3 was
investigated by cyclic voltammetry studies (Figure S2).
Compounds 1−3 show the oxidation potentials at 1.23, 1.46,
and 1.56 V respectively and the corresponding reduction peaks
in the region of −1.005 to −1.108 V. Corresponding band gaps
of compounds 1−3 were calculated as 2.34, 2.55, and 2.58 eV
29
respectively. The lowest and highest band gaps were observed
for compounds 1 and 3 respectively, due to the presence of
strong donating and withdrawing groups at the para position of
the benzene ring which was capped with 2,1,3-benzoselenadia-
zole.
Thermogravimetric Analysis. To examine the thermal
−1
stability, compounds 1−3 were heated at 10 °C min under
the nitrogen atmosphere (Figure 3). The decomposition
temperatures at 5% weight loss of compounds 1−3 were
calculated as 237, 306, and 184 °C respectively. So the thermal
stability of compound 2 is higher up to 5% weight loss of the
compound. Again the decomposition temperature at 40%
weight loss of compounds 1−3 was 344, 371, and 383 °C
Figure 2. Absorption and emission spectra of compounds 1−3 in
dichloromethane solutions.
Table 1. Photophysical and Electrochemical Properties of Compounds 1−3
photophysical properties
electrochemical properties
a
compound
absorption (λmax,abs (nm))
emission (λmax,em (nm))
Stokes shift (cm−1)
8334
Eox (V)
HOMO (eV)
LUMO (eV)
energy gap (eV)
2.34
1
337
675
1.23
−5.69
−5.92
−6.02
−3.35
4
32
335
93
333
90
2
3
546
483
7130
4937
1.46
1.56
−3.37
−3.44
2.55
2.58
3
3
a
The values in parentheses corresponds to oxidation potential of small molecules.
C
DOI: 10.1021/acs.cgd.5b01179
Cryst. Growth Des. XXXX, XXX, XXX−XXX

Crystal Growth & Design
Article
of compound 2. Strong Se···N and N···N interactions are
observed in compound 2 due to its more twisted nature (Figure
4
).
Two molecules are present in the asymmetric unit of the
solid state structure of compound 1. Two molecules form head
to head dimers via Se···N interaction with distances of 3.070
and 3.071 Å (Figures 4a and S3). N···N (3.169 Å) interaction is
very large which does not participate in crystal packing. Strong
Se01···π (3.375 Å) and Se02···π (3.552 Å) interactions are
present, which lead to form a twisted structure and interlock
type packing along the a axis, whereas compound 2 contains
only one molecule in the asymmetric unit. It also shows head to
head dimerization via Se···N and N···N interactions with
intermolecular distances of 2.950 and 2.890 Å, respectively (the
van der Waals radii of Se and N is 3.450 Å; and N and N is 3.10
Å) (Figure 4b and S3). Also Se···π (3.434 Å) and CH···π
(
2.901 Å) inteactions (Figure 4b and S4) are present in the
Figure 3. TGA thermograms of compounds 1−3 at a heating rate of
crystal packing of compound 2. The presence of strong Se···N,
N···N, and CH···π interactions lead to interlock-type crystal
packing for compound 2. Two BDS planes in the dimer of
compound 1 deviate with a angle of 14.80 Å, whereas the
planes of two BDS units in the dimer of compound 2 are
almost parallel to each other with Se···N and N···N
interactions. The close parallel overlapping of BDS units help
to form strong Se···N and N···N interactions in compound 2
compared to compound 1. D−A−D type benzoselenadiazole-
based molecules have a strong tendency to form dimer and
interlock-type packing, which also depends on the nature of
aromatic rings and the twisted behavior of capped aromatic
10 °C/min under nitrogen gas.
respectively. So, the thermal stability of compound 3 is higher
as the decomposition temperature is higher for compound 3
(
Table S3).
Molecular Packing of Compounds 1 and 2. Single
crystal analysis of molecules is important to understand the
packing patterns in the solid state. Single crystals suitable for X-
ray diffraction for compounds 1 and 2 were obtained by slow
evaporation from dichloromethane at room temperature.
Crystallographic data and structure refinement parameters are
listed in Table S1. Compounds 1 and 2 were crystallized in the
22,30
rings.
Overall Se···N, π-interaction, D−A interaction, and
monoclinic P2 /n and triclinic P1
̅
space groups, respectively. In
the nature of capped aromatic rings play an important role in its
1
crystal structure of compound 1, two p-methoxy phenyl rings
are twisted by ∼34° from the central BDS unit, whereas two
naphthalene rings are twisted by ∼64° for the crystal structure
solid state crystal packing.
Various noncovalent interactions play an important role to
form supramolecular assemblies of benzoselenadiazole contain-
Figure 4. Crystal structure of (a) compound 1 and (b) compound 2. Intermolecular interactions are responsible for head-to-head dimer formation
(
interactions are indicated as dotted lines with distance parameters in Å).
D
DOI: 10.1021/acs.cgd.5b01179
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Crystal Growth & Design
Article
Figure 5. Crystal packing of compound 1 shows various noncovalent interactions (indicated as dotted lines).
Figure 6. Crystal packing of compound 2 shows a columnar type supramolecular sheet with various noncovalent interactions (indicated as dotted
lines). The central dimerized BDS units organized in a face to face manner and hydrophobic naphthyl shoulders are projecting toward columnar rays
by interacting with other columnar molecules.
ing compounds which are well characterized by crystallog-
diazole and other interacting donor methoxy phenylene
residue. Because of strong Se···π interactions between the
molecules, other considerable CH···π interactions are also
observed between donor methoxy phenylene residues of
individual molecules with distances of 2.884 and 2.925 Å
(Figures 5 and S5−S6). As a result of these major
supramolecular interactions, an interlocked sheet type packing
is observed in the crystal structure of compound 1 along the b
axis.
Similarly compound 2 also forms an interlock-type dimer
using strong intermolecular Se···N (2.950 Å), N···N (2.890 Å),
Se···π (3.434 Å) and CH···π (2.901 Å) interactions. In the
process of a supramolecular arrangement, the dimerized units
grow further to form a columnar type of packing pattern by
using repeated CH···π (3.132 Å) interactions along the
crystallographic a axis. There are repeated CH···π (3.132 Å,
2.901 Å) interactions which are observed in between the
2
1,22,24,30
raphy.
In crystal structure, compounds 1 and 2 show
well order supramolecular arrangements at the molecular level
using noncovalent interactions including Se···π and CH···π
interactions (Figures 5 and 6). From the asymmetric unit, it is
observed that compound 1 forms dimers to give an interlock-
type twisted structure. However, in the process supramolecular
assembly in crystal packing, one molecule of the dimer interacts
with other neighboring molecules. Se(02) of acceptor
benzoselenadiazole and the C(010) atom of donor methoxy
phenylene of the neighboring molecule form an Se···π
interaction with a distance of 3.463 Å. Additional Se···π
interaction is observed in between Se(02) of the acceptor of the
neighboring molecule and the C(010) atom of donor methoxy
phenylene of the same molecule in the asymmetric unit with a
distance of 3.463 Å. Similarly Se01···π (C00S) with a distance
of 3.423 Å is observed in between the acceptor benzoselena-
E
DOI: 10.1021/acs.cgd.5b01179
Cryst. Growth Des. XXXX, XXX, XXX−XXX

Crystal Growth & Design
Article
naphthyl rings of different molecules. As a result of these
interactions, a columnar type of supramolecular sheet is formed
along the crystallographic b axis (Figures 6 and S7).
strong Se···N, N···N, and CH···π interactions lead to form
interlock type crystal packing. Strong Se01···π (3.375 Å) and
Se02···π (3.552 Å, 3.425 Å) interactions present in the crystal
structure of compound 1 lead to form a twisted structure and
interlock-type packing along the crystallographic a axis. Here
we tuned the band gap of compounds from 2.34 to 2.58 eV by
changing the donor unit 4-methoxybenzene- to acceptor unit 4-
nitrobenzene attached with benzoselenadiazole. Theoretical
study also supports the change in the band gap by changing the
electron donating units to electron withdrawing units attached
with benzoselenadiazole.
THEORETICAL STUDY
■
The density functional theory (DFT) calculations were carried
out at the B3LYP/6-31G** level in the Gaussian 09 program.
From DFT calculations, we calculated the optimized energy
structure, HOMO and LUMO wave functions for all the
compounds 1−3 (Figure 7). Later, we also calculated the band
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the
■
*
S
.
ACS Publications website at DOI: 10.1021/acs.cgd.5b01179.
The X-ray crystallographic files (CIF) have been deposited in
the Cambridge Structural Database with CCDC numbers
1
418400 (compound 2) and 1418401 (compound 1).
Several experimental results and characterization of
compounds 1−3 (PDF)
Crystallographic information files (CIF1 and CIF2)
AUTHOR INFORMATION
Corresponding Author
*E-mail: apurba.das@iiti.ac.in.
■
Figure 7. HOMO and LUMO frontier orbitals of compounds 1−3 at
the B3LYP/6-31G** level for C, N, O, H, and Se.
Notes
gap energy of the corresponding molecules. Band gap energy
for the compounds 1−3 are 2.82, 3.08, and 3.20 eV
respectively. HOMO, LUMO, and energy gap of the frontier
orbitals of all three compounds are listed in Table S4. The
theoretical values show similar trends with the experimental
values calculated from cyclic voltametry. The highest and
lowest energy gaps for compounds 3 and 1 are exhibited due to
the presence of electron withdrawing and donating groups
attached with the BDS capped benzene moieties. The LUMO
orbitals for compounds 1 and 2 are localized in the central BDS
unit, whereas the LUMO orbital in compound 3 is delocalized
on the BDS unit to the p-nitrobenzene ring.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
A.K.D. is thankful to Council of Scientific and Industrial
Research (CSIR), New Delhi, India (Grant No. 02(0056)/12/
EMR-II) for financial support. M.K. acknowledges CSIR, New
Delhi, for his fellowship for this work.
REFERENCES
■
(
1) Li, C.; Liu, M.; Pschirer, N. G.; Baumgarten, M.; Mullen, K.
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(
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CONCLUSION
■
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