Crystal Structure, Hydrogen-Bonding Properties, and DFT Studies of 2-((2-(2-Hydroxyphenyl)benzo[ d ]thiazol-6-yl)methylene)malononitrile

Article abstract of DOI:10.1080/15421406.2015.1011460

The title compound, 2-((2-(2-hydroxyphenyl)benzo[d]thiazol-6-yl)methylene)malono-nitrile (1), was synthesized and characterized by single-crystal X-ray diffraction. The crystal belongs to monoclinic, space group P21/c, with a = 7.4351(8), b = 7.6568(10),

Full text of DOI:10.1080/15421406.2015.1011460

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: http://www.tandfonline.com/loi/gmcl20
Crystal Structure, Hydrogen-Bonding
Properties, and DFT Studies of 2-((2-
(2-Hydroxyphenyl)benzo[d]thiazol-6-
yl)methylene)malononitrile
Kew-yu Chen
To cite this article: Kew-yu Chen (2015) Crystal Structure, Hydrogen-Bonding Properties, and
DFT Studies of 2-((2-(2-Hydroxyphenyl)benzo[d]thiazol-6-yl)methylene)malononitrile, Molecular
Crystals and Liquid Crystals, 623:1, 285-296, DOI: 10.1080/15421406.2015.1011460
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Date: 05 January 2016, At: 09:55

Mol. Cryst. Liq. Cryst., Vol. 623: pp. 285–296, 2015
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2015.1011460
Crystal Structure, Hydrogen-Bonding Properties,
and DFT Studies of
2-((2-(2-Hydroxyphenyl)benzo[d]thiazol-6-
yl)methylene)malononitrile
KEW-YU CHEN∗
Department of Chemical Engineering, Feng Chia University, Taichung,
Taiwan, ROC
The title compound, 2-((2-(2-hydroxyphenyl)benzo[d]thiazol-6-yl)methylene)malono-
nitrile (1), was synthesized and characterized by single-crystal X-ray diffraction. The
crystal belongs to monoclinic, space group P21/c, with a = 7.4351(8), b = 7.6568(10),
c = 24.542(2) Å, α = 90◦, β = 96.680(9)◦, ανδ γ = 90◦. Compound 1 possesses
a strong intramolecular six-membered-ring hydrogen bond, from which excited-state
intramolecular proton transfer takes place, resulting in a proton-transfer tautomer
emission of 658 nm in ethyl acetate. In the crystal structure, intermolecular C–H···N
hydrogen bonds lead to the formation of columns along the [010] direction that are
connected to one another via intermolecular π···π interactions, so linking the molecules
into a continuous three-dimensional framework. Furthermore, the geometric structures,
frontier molecular orbitals and the potential energy curves for 1 in the ground and the
first singlet excited state were fully rationalized by density functional theory (DFT) and
time-dependent DFT calculations.
Keywords DFT calculations; ESIPT; X-ray diffraction; 2-((2-(2-hydroxyphenyl)
benzo[d]thiazol-6-yl)methylene)malononitrile
1. Introduction
Organic compounds with excited-state intramolecular proton transfer (ESIPT) character-
istics have been drawing great attention due to their unique optical properties [1–3]. An
ESIPT reaction usually involves the transfer of a hydroxyl proton to an acceptor such as
imine nitrogen through a preexisting hydrogen bonding configuration [4–8], as depicted in
Fig. 1. The resulting proton-transfer tautomer (keto-form) possesses significant differences
in structure and electronic configuration from its corresponding ground state (enol-form),
i.e., a large Stokes shifted K∗→K emission. This peculiar photophysical property has found
many important applications such as probes for solvation dynamics [9–11] and biological
environments [12,13], chemosensors [14–18], fluorescence microscopy imaging [19], pho-
tochromic materials [20], nonlinear optical materials [21], organic light-emitting diodes
∗Address correspondence to Kew-Yu Chen, Department of Chemical Engineering, Feng Chia
University 40724, Taichung, Taiwan, ROC. E-mail: kyuchen@fcu.edu.tw
Color versions of one or more of the figures in the article can be found online at
www.tandfonline.com/gmcl.
285

286
Kew-Yu Chen
Figure 1. Characteristic four-level photocycle scheme of the ESIPT process.
[22–26], and near-infrared fluorescent dyes [27]. To expand the scope of the benzothiazol-
based chromophores available for designing systems for excited-state PT-induced
charge-transfer reaction, we have recently [28] synthesized a benzothiazol derivative, 2-((2-
(2-hydroxyphenyl)benzo[d]thiazol-6-yl)methylene)malononitrile (1). Herein, we report its
X-ray structure, as well as hydrogen-bonding properties and complementary density func-
tional theory (DFT) calculations. The results offer the potential to synthesize benzothiazol
derivatives with extended molecular architectures and optical properties.
2. Experimental
2.1. Chemicals and Instruments
The starting materials such as salicylaldehyde, 2-amino-5-methylbenzenethiol, lead(IV)
acetate, and acetic acid were purchased from Merck, ACROS and Sigma–Aldrich. Column
chromatography was performed using silica gel Merck Kieselgel si 60 (40–63 mesh).
1H and 13C NMR spectra were recorded in CDCl3 on a Bruker 400 MHz. Mass
spectra were recorded on a VG70-250S mass spectrometer. The absorption and emission
spectra were measured using a Jasco V-570 UV–Vis spectrophotometer and a Hitachi
F-4500 fluorescence spectrophotometer, respectively. The single-crystal X-ray diffraction
data were collected on a Bruker Smart 1000CCD area-detector diffractometer.
2.2. Synthesis and Characterization
2.2a. Synthesis of 1. Compound 2 (0.15 g, 0.59 mmol) was dissolved in a mixture of
20 mL of THF and 20 mL of MeOH. Then malononitrile (0.19 g, 2.88 mmol) and two
drops of piperidine were added to the mixture and stirred for 2 hr at 45◦C. After solvent
was removed under vacuum, the mixture was extracted with CH2Cl2 and washed with

Crystal Structure, Hydrogen-Bonding Properties, and DFT Studies
287
Scheme 1. The synthetic route and the structure for 1.
water. The organic layer was dried with anhydrous MgSO4 and evaporated. The product
was purified by silica gel column chromatography with eluent ethyl acetate/n-hexane (1/4)
to afford 1 (0.13 g, 73%). 1H NMR (400 MHz, CDCl3, ppm) 12.13 (s, 1H), 8.54 (s, 1H),
8.12 (d, J = 8.6 Hz, 1H), 8.05 (d, J = 8.6 Hz, 1H), 7.92 (s, 1H), 7.77 (d, J = 7.4 Hz,
1H), 7.48 (t, J = 8.1 Hz, 1H), 7.12 (d, J = 8.3 Hz, 1H), 7.03 (t, J = 7.4 Hz, 1H); 13C
NMR (100 MHz, CDCl3, ppm) 158.75, 158.32, 155.54, 148.59, 134.13, 133.89, 129.18,
128.90, 128.10, 124.57, 122.73, 119.89, 118.02. 116.20, 113.82, 112.81, 82.41; MS (EI,
70eV): m/z (relative intensity) 303 (M+, 100); HRMS calcd. for C17H9N3OS 303.0466,
found 303.0469. Yellow parallelepiped-shaped crystals suitable for the crystallographic
studies reported here were isolated over a period of 7 weeks by slow evaporation from a
dichloromethane solution.
2.2b. Crystal Structural Determination. A single crystal of the title compound with di-
mensions of 0.68 mm × 0.12 mm × 0.06 mm was selected. The lattice constants and
diffraction intensities were measured with a Bruker Smart 1000CCD area detector radi-
ation (λ = 0.71073 Å) at 297.0(2) K. An ω-2θ scan mode was used for data collection
in the range of 2.79 ꢀ θ ꢀ 29.14◦. A total of 6454 reflections were collected and 3170
were independent (Rint = 0.0418), of which 2068 were considered to be observed with
I > 2σ(I) and used in the succeeding refinement. The structure was solved by direct
methods with SHELXS-97 [29] and refined on F2 by full-matrix least-squares proce-
dure with Bruker SHELXL-97 packing [30]. All nonhydrogen atoms were refined with
anisotropic thermal parameters. The hydrogen atoms were refined with riding model, ex-
cept for hydroxyl hydrogen, which was located from the difference Fourier map. At the

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Kew-Yu Chen
Figure 2. Calculated energies of different conformers of 1 and 2 (DFT/B3LYP/6-31G∗∗).
final cycle of refinement, R = 0.1184 and wR = 0.2984 (w = 1/[σ2(Fo ) + (0.1039P)2 +
2
2
2
6.4727P], where P = (Fo + 2Fc )/3). S = 1.152, (ꢀ/σ)max = 0.001, (ꢀ/ρ)max = 0.762 and
(ꢀ/ρ)min = −0.350 e/Å3 were observed. Crystallographic data for compound 1 have been
deposited in the Cambridge Crystallographic Data Center with a supplementary publication
number of CCDC 1026966. Copies of these information can be obtained free of charge
from the Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: +44 1223 336
033; e-mail: deposit@ccdc.cam.ac.uk).
2.3. Computational Methods
The Gaussian 03 program was used to perform the ab initio calculation on the molec-
ular structure [31]. Geometry optimization for compound 1 was carried out with the 6-
31G∗∗ basis set to the B3LYP functional. After obtaining the converged geometries, the
TD-B3LYP/6-31G∗∗ was used to calculate the vertical excitation energy, and the emis-
sion energy was obtained from TDDFT/B3LYP/6-31G∗∗ calculations performed on S1
optimized geometries. The phenomenon of photo-induced PT reaction in 1 can be most
critically addressed and assessed by evaluating the potential energy curve (PEC) for the PT
reaction. For the S0 state all of the other degrees of freedom are relaxed without imposing
any symmetry constraints. The excited-state (S1) PEC for the ESIPT reaction in 1 has been
constructed on the basis of TDDFT optimization method. The energy shown in the curves
are relative values, with the lowest point on the curve as zero.
3. Results and Discussion
Scheme 1 shows the chemical structure and the synthetic route of 1 [28]. In brief, the synthe-
sis of 1 started from a condensation of salicylaldehyde and 2-amino-5-methylbenzenethiol
in the presence of lead(IV) acetate catalyst, followed by the acetylation of benzothiazole
(6), giving an ester compound 5. The bromination of 5 allowed for efficient synthesis of

Crystal Structure, Hydrogen-Bonding Properties, and DFT Studies
289
Table 1. Crystallographic data for compounds 1 and 2
Compound
1
2
Chemical formula
Formula weight
Crystal system
Space group
a (Å)
C17H19N3OS
303.33
Monoclinic
P21/c
7.4351(8)
7.6568(10)
24.542(2)
90
96.680(9)
90
C14H9NO2S
255.28
Monoclinic
P21/c
8.2645(3)
5.6449(2)
23.8341(9)
90
98.147(2)
90
1100.69(7)
4
b (Å)
c (Å)
α (◦)
β (◦)
γ (◦)
Volume (Å3)
Z
1387.7(3)
4
1.452
Dcalc (g cm−3
)
1.541
0.285
μ (mm−1
)
0.238
F000
624
528
Crystal size (mm3)
0.68 × 0.12 × 0.06
2.79–29.14
−9 ꢀ h ꢀ 8
−8 ꢀ k ꢀ 10
−24 ꢀ l ꢀ 33
6454
3170 (0.0418)
Full-matrix least-squares
1.152
0.38 × 0.14 × 0.04
1.73–25.02
−9 ꢀ h ꢀ 9
−6 ꢀ k ꢀ 3
−28 ꢀ l ꢀ 28
8427
1943 (0.0417)
Full-matrix least-squares
0.895
θ range (◦)
Index ranges
Reflections collected
Independent reflections (Rint)
Refinement method on F2
GOF on F2
R1 [I > 2σ (I)]
0.1184
0.0291
wR2 [I > 2σ (I)]
R1 (all data)
0.2984
0.1649
0.0558
0.0454
wR2 (all data)
Residual (e Å−3
0.3227
0.762 and −0.350
0.0575
0.223 and −0.265
)
benzyl bromide 4. Next, the oxidation of the bromo compound (4), followed by the hy-
drolysis of the ester adduct (3), gave compound 2. Finally, the Knoevenagel condensation
was catalyzed by piperidine to give the target molecule 1. To confirm its structure, a single
crystal of 1 was obtained from a dichloromethane solution, and the molecular structure was
determined by X-ray diffraction analysis. In addition, its X-ray structure is compared with
that of its precursor 2 [32].
1
The dominance of an enol-form for 1 and 2 is supported by a combination of H
NMR and X-ray single-crystal analyses. In the 1H NMR studies, the existence of a strong
hydrogen bond between O–H and N is evidenced by the observation of a large downfield
shift of the proton peak at δ > 12 ppm (in dry CDCl3) for both compounds 1 (12.13 ppm)
and 2 (12.26 ppm). The hydrogen bonding energy (ꢀE in kcal/mol) of 1 and 2 can be
calculated by introducing Schaefer’s correlation [33], expressed as ꢀδ = (−0.4 0.2) +
ꢀE, where ꢀδ is given in parts per million for the difference between chemical shift in
the O–H peak of 1 and 2 and that in phenol (δ 4.29). Accordingly, the hydrogen-bonding

290
Kew-Yu Chen
Figure 3. The molecular structure of 1, showing the atom-labeling scheme. Displacement ellipsoids
are drawn at the 50% probability level. Red and blue dashed lines denote the intramolecular O–H···N
and C–H···S hydrogen bonds, respectively.
energy is calculated to be 2 (8.37 0.2 kcal/mol) > 1 (8.24 0.2 kcal/mol), which is
consistent with the theoretical calculations (Fig. 2). Note that the substitution of the formyl
group in 2 by the strong electron-withdrawing dicyanovinyl moiety, forming 1, seems to
decrease the basicity of imine through an inductive effect. As a result, 1 shows an upfield
shift of the O–H proton, and hence, a weaker hydrogen bond relative to 2.
Compound 1, as well as compound 2, crystallizes in the monoclinic space group P21/c,
with a = 7.4351(8), b = 7.6568(10), c = 24.542(2) Å, α = 90◦, β = 96.680(9)◦, γ = 90◦,
and Z = 4 (Table 1). Figure 3 shows the molecular structure of 1. The complete molecule
is nearly planar, as indicated by the key torsion angles (Table 2). The maximum deviations
from the mean plane through the non-H atoms are 0.075(2) Å for atom O and 0.049(2) Å
for atom N(3). The dihedral angle between the two phenyl ring planes is 1.7(2)o, which is
slightly smaller than that in 2 (4.0(2)o). Compound 1 possesses an intramolecular O–H···N
hydrogen bond [34–38], which generates an S(6) ring motif. The dihedral angle between the
mean plane of the S(6) ring and the mean plane of the phenyl ring (C1–C6) is 1.3(2)o. This,
together with 2.661(7) Å of O···N(1) distance and 143(8)o of O–H(0A)···N(1), strongly
supports the S(6) ring formation (Table 3). The hydrogen bond O···N(1) distance of 1 is
slightly larger than that of 2 (2.623(2) Å), consistent with the hydrogen-bonding strength
estimated from 1H NMR measurements and theoretical calculations (vide supra). Moreover,
there is a weak intramolecular C–H···S hydrogen bond in 1 (3.107(8) Å of C(5)···S distance
and 109◦ of C(5)–H(5A)–S, Table 3), which generates another S(5) motif. As a result, the
intramolecular O–H···N and C–H···S hydrogen bonds stabilize compound 1 and make the
phenyl ring (C1–C6) roughly coplanar with respect to the benzothiazole ring.
Figure 4 shows the molecular packing of 1. The crystal structure is stabilized
by intermolecular π–π interactions (Fig. 4a), which links a pair of molecules into a
cyclic centrosymmetric dimer. Pertinent measurements for these π···π interactions are:
centroid–centroid distances of 3.640(3) (black dashed lines, symmetry code: 1–X, 1–Y, –Z),
3.889(3) (green dashed lines, symmetry code: 2–X, 1–Y, –Z), and 3.872(3) Å (blue dashed
line, symmetry code: 2–X, 1–Y, –Z). The crystal packing is further stabilized by intermolec-
ular C–H···N hydrogen bonds (Table 3). These C–H···N hydrogen bonds [39,40] lead to the
formation of columns along the [010] direction that are connected to one another via inter-
molecular π···π interactions, so linking the molecules into a continuous three-dimensional
framework (Fig. 4b).

Crystal Structure, Hydrogen-Bonding Properties, and DFT Studies
291
Table 2. Comparison of the experimental and optimized geometric parameters of 1
(Å and ◦)
X-ray
DFT
Bond lengths (Å)
O-C(1)
S-C(7)
S-C(8)
C(1)-C(6)
C(2)-C(3)
C(4)-C(5)
N(1)-C(7)
N(1)-C(9)
C(8)-C(9)
C(11)-C(12)
C(12)-C(14)
C(14)-C(15)
1.343(9)
1.754(6)
1.723(7)
1.416(9)
1.374(12)
1.371(10)
1.310(8)
1.378(8)
1.409(8)
1.411(9)
1.454(9)
1.350(10)
1.448(9)
1.148(10)
1.341
1.783
1.753
1.426
1.385
1.383
1.315
1.374
1.416
1.421
1.449
1.368
1.434
1.164
C(15)-C(16)
N(3)-C(17)
Bond angles (◦)
O-C(1)-C(6)
123.1(6)
120.6(8)
121.7(7)
120.0(6)
89.2(3)
123.3
120.6
121.6
119.9
88.9
C(1)-C(2)-C(3)
C(4)-C(5)-C(6)
C(1)-C(6)-C(7)
C(7)-S-C(8)
C(7)-N(1)-C(9)
N(1)-C(9)-C(8)
C(8)-C(9)-C(10)
C(11)-C(12)-C(14)
C(14)-C(15)-C(16)
C(15)-C(16)-N(2)
C(15)-C(17)-N(3)
Torsion angles (◦)
O-C(1)-C(6)-C(7)
C(6)-C(7)-N(1)-C(9)
C(6)-C(7)-S-C(8)
C(7)-N(1)-C(9)-C(8)
N(1)-C(9)-C(10)-C(11)
C(10)-C(11)-C(12)-C(14)
C(11)-C(12)-C(14)-C(15)
C(12)-C(14)-C(15)-C(16)
111.6(5)
114.3(6)
119.7(6)
125.3(6)
119.3(6)
177.7(8)
178.1(8)
112.6
114.8
119.4
124.8
119.0
179.6
178.9
−1.8(11)
180.0(6)
180.0(5)
0.0(8)
−179.7(6)
180.0(6)
−0.6(12)
−179.1(7)
−0.1
179.9
180.0
0.0
−179.9
180.0
0.1
−179.9
Figure 5 shows the steady state absorption and emission spectra of 1 in ethyl acetate.
The lowest energy absorption band of 1 appears at about 390 nm, which is assigned to the
π−π∗ transition. Another higher energy absorption band is also observed at 260 nm. As for
the steady-state emission, compound 1 exhibits remarkable dual emission at 448 and 658 nm
in ethyl acetate. The 658 nm band with a remarkably large Stokes shift (11,118 cm−1) can

292
Kew-Yu Chen
Table 3. Hydrogen-bond geometry (Å, o)
D–H···Cg
d(D–H)
d(H···Cg)
d(D···Cg)
∠DHCg
O–H(0A)···N(1)
0.91(9)
0.93
0.93
1.87(10)
2.68
2.46
2.661(7)
3.107(8)
3.377(10)
143(8)
109
169
C(5)–H(5A)···S
C(14)–H(14A)···N(2)a
a Symmetry code: –x+3/2, y+1/2, –z+1/2.
be assigned to the keto emission resulting from ESIPT, while the 448 nm band that is a
mirror image of the lowest-energy absorption band is ascribed to the fluorescence of the
enol species. This viewpoint can be further supported by a theoretical approach based on
DFT (vide infra).
To gain more insight into the molecular structure and electronic properties of 1,
quantum chemical calculations were performed using DFT at the B3LYP/6-31G∗∗ level.
The calculated geometric parameters (bond lengths, bond angles, and torsion angles) were
compared to the corresponding X-ray determination results of the compound (Table 2).
There are no obvious differences between the experimental and DFT/B3LYP calculated
geometric parameters. Therefore, we can conclude that basis set 6-31G∗∗ is suited in its
approach to the experimental results.
The optimized geometric structures and the corresponding hydrogen bond lengths of
enol and keto forms for 1 in the ground (S0) and the first singlet excited state (S1) are
Figure 4. (a) Part of the crystal structure in the unit cell of 1, showing the formation of the dimmer
built from π···π interactions. (b) A section of the crystal packing of 1, viewed along the b-axis.
Cg1 (red circles) and Cg2 (blue circles) are the centroids of the N1/C7/S/C8/C9 and C8–C13
rings, respectively. Black, blue, and green dashed lines denote three different intermolecular π···π
interactions, respectively. Pink dashed lines denote intermolecular C–H···N hydrogen bonds.

Crystal Structure, Hydrogen-Bonding Properties, and DFT Studies
293
Figure 5. Normalized absorption (blue line) and emission (red line) spectra of 1 in ethyl acetate.
Figure 6. The optimized geometric structures of enol (E) and keto (K) forms for 1 in the ground (S0)
and the first singlet excited state (S1) together with the intramolecular hydrogen bond lengths. Red
dashed lines denote the intromolecular O–H···N hydrogen bonds.
Figure 7. Selected frontier molecular orbitals involved in the excitation and emission of 1. GSIPT
stands for ground-state intramolecular proton transfer.

294
Kew-Yu Chen
Figure 8. Potential energy curves from enol-form to keto-form of 1 at the ground state and excited
state.
shown in Fig. 6. From E (K∗) to E∗ (K), one can see that the intramolecular hydrogen bond
length (red dashed lines) decreases from 1.767 (1.725) Å to 1.510 (1.574) Å. The results
clearly provide the evidence for the strengthening of the intramolecular hydrogen bond from
S0 → S1 (S1 → S0), which is consistent with our previous study [34,35]. Consequently, the
decrease of intramolecular hydrogen bond lengths from E to E∗ is a very important positive
factor for the ESIPT reaction.
Figure 7 shows the HOMO and LUMO of enol and keto form of 1. It can be clearly
observed that the first excited states for both enol and keto forms are a dominant π → π∗
transition from the HOMO to the LUMO. Figure 7 also displays that the electron density
around the intramolecular hydrogen binding site is chiefly populated at phenolic oxygen
and benzothiazol nitrogen at HOMO and LUMO, respectively. The results demonstrate
that upon electronic excitation of 1, the hydroxyl proton (O–H) is expected to be more
acidic, whereas the benzothiazol nitrogen is more basic with respect to their ground state,
driving the PT reaction. Additionally, the absorption and emission spectra of 1 were cal-
culated by time-dependent DFT (TDDFT) calculations (Franck–Condon principle). The
calculated excitation (fluorescence) wavelength for the S0 → S1 (S1 → S0) transition is
425 (468 and 663) nm, which is slightly overestimated with respect to the experimental
value.
To explain the ESIPT properties of compound 1, the PECs of the intramolecular PT
(i.e., the transformation from the enol-form to the keto-form) at both the ground state
and the excited state were investigated (Fig. 8). The full geometry optimization based on
the B3LYP/6-31G∗∗ theoretical level reveals that the enol-form of 1 in the ground state
is more stable than the tautomeric keto-form of 1 by 11.1 kcal/mol. However, further
calculations show that the corresponding proton-transfer tautomer is lower in energy than
the respective 1 by 7.7 kcal/mol in the excited state. The result clearly shows that ESIPT
for compound 1 is thermodynamically favorable, which is consistent with the experimental
conclusion.

Crystal Structure, Hydrogen-Bonding Properties, and DFT Studies
295
4. Conclusions
benzothiazol derivative, namely, 2-((2-(2-hydroxyphenyl)benzo[d]thiazol-6-
A
yl)methylene)malononitrile (1) was synthesized and characterized by single-crystal
X-ray diffraction. Compound 1 shows remarkable dual emission originated from the
locally excited state and the intramolecular PT state. The geometric structures, frontier
molecular orbitals and the PECs for 1 in the ground and the first singlet excited state were
fully rationalized by DFT and TDDFT calculations, and were in good agreement with
the experimental results. Furthermore, the single-crystal X-ray structure determinations
described here have brought to light a number of interesting properties between 1 and 2 in
the solid phase, including π···π stacking and intra- and intermolecular hydrogen bonds.
This offers the potential for synthesizing benzothiazol derivatives with extended molecular
architectures and photophysical properties.
Acknowledgments
The project was supported by the Ministry of Science and Technology (MOST 103-2113-
M-035-001) in Taiwan. The authors appreciate the Precision Instrument Support Center of
Feng Chia University for providing the fabrication and measurement facilities.
References
[1] Paul, B. K., & Guchhait, N. (2012). J. Lumin., 132, 2194.
[2] Guo, Z. Q., Chen, W. Q., & Duan, X. M. (2011). Dyes Pigm., 92, 619.
[3] Xu, S., et al. (2013). J. Lumin., 136, 291.
[4] Chen, K. Y., et al. (2006). Chem. Commun., 42, 4395.
[5] Luo, M. H., et al. (2012). Chin. Chem. Lett., 23, 1279.
[6] Satam, M. A., Raut, R. K., Telore, R. D., & Sekar, N. (2013). Dyes Pigm., 97, 32.
[7] Fang, T. C., Tsai, H. Y., Luo, M. H., Chang, C. W., & Chen, K. Y. (2013). Chin. Chem. Lett.,
24, 145.
[8] Satam, M. A., Raut, R. K., & Sekar, N. (2013). Dyes Pigm., 96, 92.
[9] Chen, W. H., & Pang, Y. (2010). Tetrahedron Lett., 51, 1914.
[10] Mahapatra, A. K., Mait, i K., Sahoo, P., & Nandi, P. K. (2013). J. Lumin., 143, 349.
[11] Xie, L., et al. (2012). Dyes Pigm., 92, 1361.
[12] Maupin, C. M., et al. (2011). J. Am. Chem. Soc., 133, 6223.
[13] Lim, C. K., et al. (2011). Dyes Pigm., 90, 284.
[14] Hong, W. H., Lin, C. C., Hsieh, T. S., & Chang, C. C. (2012). Dyes Pigm., 94, 371.
[15] Lin, W. C., Fang, S. K., Hu, J. W., Tsai, H. Y., & Chen, K. Y. (2014). Anal. Chem., 86, 4648.
[16] Huang, Q., Yang, X. F., & Li, H. (2013). Dyes Pigm., 99, 871.
[17] Prabhu, S., Saravanamoorthy, S., Ashok, M., & Velmathi, S. (2012). J. Lumin., 132, 979.
[18] Patil, V. S., Padalkar, V. S., Tathe, A. B., & Sekar, N. (2013). Dyes Pigm., 98, 507.
[19] Santos, R. C., et al. (2011). Tetrahedron Lett., 52, 3048.
[20] Ito, Y., Amimoto, K., & Kawato, T. (2011). Dyes Pigm., 89, 319.
[21] Ashraf, M., et al. (2012). Dyes Pigm., 95, 455.
[22] Li, Y., et al. (2012). J. Lumin., 132, 1010.
[23] Chuang, W. T., et al. (2011). J. Org. Chem., 76, 8189.
[24] Tang, K. C., et al. (2011). J. Am. Chem. Soc., 133, 17738.
[25] Xu, H., et al. (2012). J. Lumin., 132, 919.
[26] Fang, S. K., Tsai, H. Y., Hu, J. W., & Chen, K. Y. (2014). Int. J. Photoenergy,
doi:10.1155/2014/124753.
[27] Ikeda, S., et al. (2010). J. Org. Chem., 75, 8637.

296
Kew-Yu Chen
[28] Hsieh, C. C., Cheng, Y. M., Hsu, C. J., Chen, K. Y., & Chou, P. T. (2008). J. Phys. Chem. A.,
112, 8323.
[29] Sheldrick, G. M. (1997). SHELXS97, A Program for Automatic Solution of Crystal Structure,
University of Go¨ttingen: Germany.
[30] Sheldrick, G. M. (1997). SHELX97, A Program for Crystal Structure Refinement, University of
Go¨ttingen: Germany.
[31] Frisch, M. J., et al. (2003). Gaussian 03, Gaussian, Inc., Pittsburgh PA.
[32] Chen, K. Y., Fang, T. C., Chang, M. J., Tsai, H. Y., & Luo, M. H. (2011). Acta Cryst., E67,
o2862.
[33] Schaefer, T. (1975). J. Phys. Chem. 79, 1888.
[34] Chen, K. Y., et al. (2014). J. Lumin., 154, 168.
[35] Chen, K. Y., et al. (2014). J. Chem. Sci., 124, 955.
[36] Paul, P., & Bhattacharya, S. (2012). J. Chem. Sci., 124, 1265.
[37] Phatangare, K., et al. (2013). J. Chem. Sci., 125, 141.
[38] Sharma, S., Kaur, A., Hundal, M. S., & Hundal, G. (2013). Mol. Cryst. Liquid Cryst., 577, 73.
[39] Chen, K. Y., Chang, M. J., Fang, T. C., Luo, M. H., & Tsai, H. Y. (2011). Acta Cryst., E67,
o3312.
[40] Tsai, H. Y., Chang, M. J., Fang, T. C., Luo, M. H., & Chen, K. Y. (2012). Acta Cryst., E68,
o867.