Solvatochromism and pH effect on the emission of a triphenylimidazole-phenylacrylonitrile derivative: Experimental and DFT studies

Article abstract of DOI:10.1039/c9ra01275c

In this work, a study of the photophysical properties in different solvents and at different pH values of a luminogenic compound with a donor-π-acceptor (D-π-A) structure was carried out. The compound (Z)-3-(4-(4,5-diphenyl-1H-imidazol-2-yl)phenyl)-2-phen

Full text of DOI:10.1039/c9ra01275c

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Solvatochromism and pH effect on the emission of
a triphenylimidazole-phenylacrylonitrile derivative:
experimental and DFT studies†
Cite this: RSC Adv., 2019, 9, 12085
a
a
Karnambaram Anandhan,
Paulina Ceballos,a Paola Gordillo-Guerra,a Enrique Perez-Gutierrez,a
Margarita Ceron,a Venkatesan Perumal,
´
´
´
Armando E. Castillo,a Subbiah Thamotharanb and M. Judith Percino
a
*
In this work, a study of the photophysical properties in different solvents and at different pH values of a luminogenic
compound with a donor–p–acceptor (D–p–A) structure was carried out. The compound (Z)-3-(4-(4,5-diphenyl-
1H-imidazol-2-yl)phenyl)-2-phenylacrylonitrile (2) was synthesized and characterized by SCXRD, FT-IR, 1H NMR,
13C NMR, EIMS, UV-Vis absorption and fluorescence. The SCXRD characterization reveals a monoclinic system,
P21/c, with Z ¼ 4 and an imidazole core having hydrogen bonding with respect to water molecules present in
the asymmetric unit. It leads to a strong p–p-interaction in the solid state. The fluorescence lmax emission of
the powder and thin film was observed at 563 nm and 540 nm respectively. Several degrees of positive
solvatochromic fluorescence were observed due to different molecular conformations in various solvents.
When the pH of the compound was changed with HCl or NaOH, a shift in the wavelength of emission was
observed in a reversible manner. At pH 2, the lmax of emission was at 541 nm whereas at pH 14 there were
two emissions at 561 nm and 671 nm. Due to their good emission in the solid state, compound 2 was tested as
an emitting layer in OLEDs; the devices showed an acceptable performance with a luminance average of 450
cd mꢀ2. The band gap was analyzed by optical absorption, cyclic voltammetry measurement and DFT calculations.
Received 19th February 2019
Accepted 9th April 2019
DOI: 10.1039/c9ra01275c
rsc.li/rsc-advances
Among heteroaromatic compounds, the imidazole scaffold
exhibits electron attracting or mild donating nature which
1. Introduction
displayed unique optical, thermal, electronic and biological
properties.19 Especially, 2,4,5-triphenyl-1H-imidazole, (lophine,
Scheme 1), exhibited uorescence and chemiluminescence
properties when reacted with oxygen in the presence of strong
basic conditions.20–23 It has three phenyl groups in the C-2, C-4
and C-5 positions on the imidazole structure. Functionalized
lophine derivatives are promising candidates for the light
emitting applications, because it is possible to alter the struc-
ture (p-conjugation) through the phenyl ring with different
donor (D) and acceptor (A). Triphenyl imidazole derivatives as
well as 1H-imidazol-5-yl-vinyl-benz[e]indolium, and metal based
imidazole complex showed halochromism and a discrete colour
change (labs 360, 430 and 477 nm in acidic, neutral and basic
conditions respectively) on pH variation in the range of 2 to 11
and also can act as uorescent pH sensor.24–28 However, there
are only a few optical pH sensors for use at high or low pH.29,30
In recent years, the p-conjugated luminophores have been
extensively investigated as uorescent sensors,1–5 for biological
imaging,6 and for other optoelectronic applications7–10 due to
their optical properties, charge transport properties and structure
tunability.11–14 Most of the organic luminophore molecules have
limitation in the uorophore's applications, because of a strong
p–p stacking interaction in the extended p-conjugated systems
and dipole–dipole interaction that resulted in a weak emission or
absolute absence in the condensed phase.15,16 Also, some uo-
rescent compounds change their absorption wavelength and
intensity of emission upon various polarity environments, i.e.
solvatochromism phenomenon. This behaviour has attracted
considerable attention because of the charge transfer nature
(intra/inter molecular); it could be used as sensors of solvent
polarity as well as volatile organic compounds.17,18
aUnidad de Polımeros
´
´ ´ ´
y Electronica Organica, ICUAP, Benemerita Universidad
´
Autonoma de Puebla, Val 3-Ecocampus Valsequillo, Independencia O2 Sur 50, San
Pedro Zacachimalpa, Pue., Mexico 72960. E-mail: judith.percino@correo.buap.mx
bBiomolecular Crystallography Laboratory, Department of Bioinformatics, School of
Chemical and Biotechnology, SASTRA Deemed University, Thanjavur 613 401, India
† Electronic supplementary information (ESI) available. CCDC 1888014. For ESI
and crystallographic data in CIF or other electronic format see DOI:
10.1039/c9ra01275c
Scheme 1 (a) Numbering of the 2,4,5-triphenyl-1H-imidazole, (b)
imidazole fused with a-cyanostilbene.
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By means of pH variations, it is possible to delineate the effect
of donor (push) or electron-withdrawing (pull) groups attached
to C-2 of imidazole ring that decides by the electronic density of
structure as well as donor capacity of N atom.
2.2 Single crystal X-ray crystallography
Compound 2 crystallizes in the monoclinic space group P21/c
with Z ¼ 4. The crystal data and renement parameters are
summarized in Table S1.† Fig. 1 shows the ORTEP diagram of
the asymmetric unit of crystal 2. The molecular structure shows
the bond lengths and bond distances are also listed in Table 1.
The bond distance of C(15)–N(2) is shorter, meanwhile the C(7)–
N(1) and C(8)–N(2) distances are longer compared with the re-
ported double bond lengths.44 In addition to that, the bond
C(7)–C(8) is longer and displays the electron delocalization over
the atoms of C(8), C(7), N(1), C(15) of the imidazole ring. The
nitrile –C(24)^N(3) bond length is the longest N–C bond and
falls into the range of a triple bond –C^N reported for TCNQ.44
In the imidazole ring, the torsion angles [N(1)–C(7)–C(8)–
N(2); N(2)–C(15)–N(1)–C(7); C(8)–C(7)–N(1)C(15); N(1)–C(15)–
N(2)–C(8) and C(7)–C(8)–N(2)–C(15)] are smaller, indicating that
the ring is found to be planar. The substituents such as phenyl
groups and [2,3-diphenylprop-2-enenitrile] moiety are rotated
with respect to imidazole ring, that was expected due to steric
effect with dihedral angles between atoms C(5)–C(6)–C(7)–N(1)
of ꢀ41.3(3)ꢁ and C(1)–C(6)–C(7)–C(8) of ꢀ40.2(3)ꢁ, whereas
between [2,3-diphenylprop-2-enenitrile] attached to imidazole
group is a peri-planar conformation as evident from the dihe-
dral angles of N(2)–C(15)–C(16)–C(21) of 21.8(3)ꢁ, N(1)–C(15)–
C(16)–C(17) of 22.3(3)ꢁ and the atoms C(18)–C(19)–C(22)–C(23)
of ꢀ25.6(3)ꢁ; C(19)–C(22)–C(23)–C(24) of ꢀ9.3(3)ꢁ and C(22)–
C(23)–C(25)–C(30) of ꢀ21.3(3)ꢁ (selected dihedral angles, bond
length, bond angle and torsion angles values are in the Tables
S2 to S5 in the ESI†).
The electronic factor of the cyano group played an excellent
acceptor for such D–p–A uorescent materials which was
responsible for the optical properties.31–33 In the past decade, a-
cyanostilbene derivatives have drawn attention because of their
unique charge-transfer characteristics and their utility as
promising uorescent materials for use in biological, the AIE/
AIEE-activity,33 optical applications34 and multi-stimuli
responsive properties.35–37 Our group are working to explore
the photophysical and optoelectronic properties of the
phenylacrylonitrile/pyridylacrylonitrile containing derivative.
Based on our previously reported the strong electron with-
drawing feature of the phenylacrylonitrile/pyridylacrylonitrile
based chromophore that act as a good acceptor and to show
an enhancement of emission in the solid state but some case its
weak.38–40 Hence it exhibited an important effect on the optical
and electronic properties.41–43
Herein we report the synthesis of a novel imidazole deriva-
tives containing the phenylacrylonitrile (half of the a-cyanos-
tilbene) unit using a simple route. Even though imidazole unit
has electron withdrawing nature when it combined through to
the phenylacrylonitrile to examine the emission properties in
the solution and solid state whether it shows enhanced or
quenching. In order to nd the electron charge distribution in
the molecular structure (D–p–A or A0–p–A structure motif) by
explore absorption and emission with varying the pH (acidic or
basic conditions) and different solvents. So, the title compound
undergoes a deep study of their photophysical properties in
solution and solid state besides solvatochromic property, pH
studies, electrochemical analysis, DFT calculations were carried
out. In addition, it was evaluated as an emitting layer in OLEDs.
The most interesting feature in the structure of compound 2
is concerned with the presence of two molecules of water in the
asymmetric unit. The intermolecular motif formed by N–H/O
and O(2) H/O(1) interactions are shown in Fig. 2 with
hydrogen bonds distances and chain motifs a, b, c and e, and
the atoms involved in chain motif formation. The water mole-
cules in the lattice, act as H-bond donor which bridges between
molecules extending along the c axis.
2. Result and discussion
Table 2 provides a list of graph-set motif of hydrogen bonds
in the compound 2 and it can be seen the –C^N group [C(24)–
N(3)] is found anti in the formed dimer. The face-to-face
arrangement in Fig. 3, owing to the intermolecular interaction
of O–H(solvent)/N hydrogen bond. Two neighbouring mole-
cules stacked face-to-face manner with centroid–centroid
2.1 Synthesis and characterisation
We reported the design and synthesis of a novel compound (Z)-
3-(4-(4,5-diphenyl-1H-imidazol-2-yl)phenyl)-2-phenylacrylo
nitrile (2) as shown in Scheme 2. The 4-(4,5-diphenyl-1H-
imidazol-2-yl) benzaldehyde (1) was synthesized via condensa-
tion of benzil with 4-formyl benzaldehyde in the presence of
NH4OAc and acetic acid at reux for 5 hours. The compound 1
was reacted with phenyl acetonitrile with KOH as catalyst and
MeOH as solvent at reux conditions to get the compound 2
with 65% yield (Scheme 2). The principal signals in IR, 1H NMR
and EI for compounds 1 and 2 are summarized in experimental
section.
Scheme 2 Synthesis of compound 2 (a) NH4OAc/HOAc/4-formyl Fig. 1 ORTEP X-ray crystal structure of compound 2 and 50% of
benzaldehyde, reflux; (b) cat. KOH/MeOH, phenylacetonitrile, reflux.
thermal ellipsoids.
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Table 1 Selected bond lengths for compound 2 with reported value
Length54 (A)
Compound 2
Length (A)
˚
˚
Bond
Imidazole
C(sp2)–N
C4–N3
1.349
1.376
1.370
C(15)–N(1)
C(15)–N(2)
C(7)–N(1)
C(8)–N(2)
C(7)–C(8)
C(22)–C(23)
C(8)–C(9)
C(6)–C(7)
C(15)–C(16)
C(19)–C(22)
C(20)–C(21)
C(17)–C(18)
C(9)–C(10)
C(25)–C(30)
C(24)–N(3)
1.349(2)
1.329(2)
1.383(2)
1.380(2)
1.391(2)
1.358(2)
1.475(2)
1.469(3)
1.468(2)
1.456(3)
1.385(3)
1.379(3)
1.398(3)
1.398(3)
1.149(3)
C5–N1
Csp2]Csp2
1.339
(C]C–CAr)
Csp2–CAr
1.455, overall 1.460
1.470, overall 1.480
(conjugated)
Csp2–CAr C]C–CAr
(conjugated)
CArzCAr
CzC (overall)
1.380
1.384
Csp^N
1.136
45
˚
˚
centroid–centroid distances > 3.65 A and offsets of 1.6–1.8 A).
The presence of solvent molecules in the crystal packing of
compound 2 might indicate that crystal growth is optimized
with O–H(solvent)/N(compound). The packing of structure 2
showed that the hydrogen bond interactions, the position of the
nitrogen atom within the imidazole core, and the phenyl-,
acrylonitrile groups play important roles and they interact with
the solvent47,48 (Fig. 4).
2.3 Optical properties
The absorption properties of compound 2 were measured in
various solvents to evaluate; methanol (a protic solvent), 1,4-
dioxane, CHCl3, ethylacetate (EtOAc), tetrahydrofuran (THF) as
well as dichloromethane (DCM), dimethylformamide (DMF),
Fig. 2 Intermolecular hydrogen bond interactions between the lattice
solvent molecules and compound 2.
˚
between phenyl ring distances of 3.07 A and off-set distance of
˚
˚
1.05 A which is much shorter than reported values 1.6 – 1.8 A
(ref. 45) and this shortening causes distribution of electronic
density that minimizes the p-electrons repulsion.
Fig. 3 Perspective view of the structures showing the strong p/p
interactions of compound 2.
Fig. 4 shows the distances calculated using OLEX 246 and
the typical values for aromatic p/p interactions (i.e., the
Table 2 Hydrogen-bonds D/H/A (A˚) and D–HA angles (ꢁ) of compound 2
D–H/A
d(A–H)
d(D/A)
<DHA
Symmetry equivalent
O2W/O1W
N2/O1W
N1/O2W
N3/O2W
O2W–H2(W2)
O1W–H1(W1)
N1–N1N
0.86(2)
0.86(2)
0.88(18)
0.84(2)
2.761
2.842
2.971
2.936
174.76
173.70
170.81
171.83
x, 1/2 ꢀ y, 1/2 + z
x, y, z
x, y, z
1 ꢀ x, ꢀ1/2 + y, 1/2 ꢀ z
O2W–H2(W2)
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Fig. 5 Absorption spectrum of compound 2 with various solvents.
Fig. 4 Intermolecular motif formed interaction shown with a bond
distance (A˚). Chain motif and atoms involved in chain motif formation
are shown in ball stick form.
DCM) gave Egap value increased from 2.78 to 2.82 eV (371 nm to
381 nm). In the case of the polar aprotic solvents (DMF, DMSO)
the Egap values are 2.79 eV, 2.77 eV respectively, whereas protic
solvent (MeOH) was 2.73 eV. The difference could be an indi-
cation of the intermolecular hydrogen bond or interaction with
imidazole moiety. These results are agreed with the solid-state
intermolecular interactions to the solvent.
dimethyl sulfoxide (DMSO) (polar aprotic solvents). UV-Vis
absorption maxima (labs), extinction coefficients (3) and
optical band gap (Egap) are listed in Table 3. The absorption
spectra of compound 2 (Fig. 5), shows two maxima absorption,
one in the range of 370–385 nm due to the p–p* transition. The
mild band at 281–305 nm in the higher energy, (labs 300 nm)
was assigned to n–p* transition of the imidazole moiety.49–51
The absorption bands of compound 2 observed when the
solvent polarity increases from 1,4-dioxane to DMSO. With
increasing polarity of aprotic solvents such as 1,4-dioxane (378
nm) < THF (381 nm) < DMF (382 nm) < DMSO (385 nm).
However, there is a blue shi slightly (15 nm) observed for the
protic solvent (MeOH). Non-polar solvents (dioxane < THF <
DCM) showed higher molar extinction coefficient (3) value than
polar aprotic solvents (DMF, DMSO) and protic solvent (MeOH)
(Table 4).
2.4 Photoluminescence studies
The photoluminescence (PL) study of the compound 2 in the
selected solvents which are followed in the UV-Vis absorption
study. The emission lmax values are listed in Table 4 and the
graph shown in Fig. 6. The compound 2 showed a red-shi with
the increasing solvent polarity. Here we noticed that the solvent
effect was stronger in emission compared to the absorption
study, 503 nm to 568 nm as follow: dioxane (503 nm), CHCl3
(502 nm), EtOAc (515 nm), THF (520 nm), DCM (523 nm). But
there are longer shis towards to longer wavelength in the case
of polar protic solvents: MeOH (554 nm) and aprotic solvents
DMF (559 nm), and DMSO (568 nm). In the same solvents, the
quantum yield54 was calculated to evaluate the effect of solvent,
(solvatochromic effect). The calculated quantum yield54 of the
compound 2 is listed in Table 4.
The optical band gap (Egap) for compound 2 was estimated
from the absorption spectrum edge using the absorption on
set52,53 (see Fig. S3 in ESI†). The calculate of Egap values for the
absorption band in range of 370 to 385 nm are summarised in
Table 3. The non-polar aprotic solvents (dioxane, CHCl3 THF,
Table 3 The data of absorbance for the compound 2 in the different Table 4 The data of emission for the compound 2 in the different
solvents
solventsa
Dielectric labs1 labs2
constant
Dielectric
constant
lem
Stoke shi
Solvent
(nm) (nm) 3a (ꢂ10ꢀ4) (Mꢀ1 cmꢀ1
)
Egap
Solvent
(nm)
(cmꢀ1
)
FF
1,4-Dioxane
CHCl3
EtOAc
THF
DCM
MeOH
DMF
2.25
4.81
6.02
7.58
8.93
32.7
36.7
46.7
300
297
293
305
281
290
300
297
378
375
376
381
371
370
382
385
3.337
3.088
3.284
3.607
3.938
2.878
2.689
3.202
2.82 1,4-Dioxane
2.78 CHCl3
2.78 EtOAc
2.78 THF
2.82 DCM
2.73 MeOH
2.79 DMF
2.25
4.81
6.02
7.58
8.93
32.7
36.7
46.7
503
502
515
520
523
554
559
568
6574
6746
7178
7016
7833
8976
8289
8368
0.10
0.07
0.16
0.10
0.21
0.11
0.17
0.20
DMSO
2.77 DMSO
a
a
labs ¼ maximum absorption wavelength, c ¼ 2.5 ꢂ 10ꢀ5 mol Lꢀ1; 3 ¼
lem ¼ maximum emission wavelength, c ¼ 2.5 ꢂ 10ꢀ5 mol Lꢀ1; FF
¼
maximum molar absorption coefficient (Mꢀ1 cmꢀ1); Egap ¼ optical band quantum yield measured by using uorescein in 0.1 mol Lꢀ1 NaOH as
gap derived from onset wavelength of the UV-Vis absorption spectra.
standard.
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in the range of 6574–8368 cmꢀ1 (Table 4), accordingly, the
Stokes shi values are signicantly increased with increasing
the solvent polarity which indicated the presence of different
charge distribution in the excited state (S1) as compared to
ground state (S0). Here, phenylacrylonitrile part introduced in
the imidazole derivative was the responsible for the more Stokes
shi value when compare to the simple lophine (6513 cmꢀ1
)
20
By plotting the Stokes shis (Dn) against the solvent polarity
parameter Df (3, n), show approximately a linear relationship
according to the Lippert–Mataga plot for the compound 2
(Fig. S2, ESI†). The change of the solvent polarity indicated the
enhancement or diminished the electron density in the struc-
ture, as well as the intermolecular charge transfer (ICT) due to
the strong interaction with the solvent.
2.5 The effect of pH on absorption and emission spectra
There is one basic centre in the compound 2, i.e., imidazole NH
group. As mentioned above both absorption and emission
spectra showed a bathochromic shi in a polar aprotic solvent.
To study the effect of pH on the absorption spectrum of
compound 2 and to understand the effect of the electronic
density on the p-conjugated through the donor to acceptor part.
Fig. 7a shows the proposed mechanism of equilibrium between
protonation at pH ¼ 2 and deprotonation at pH ¼ 14 of
compound 2 in 5 mL of solvent's mixture THF–water (1 : 1). The
experiments were carried out using solutions diluted with HCl
and NaOH. Fig. 7b shows appearance of the solutions under
normal and UV illumination.
The maxima absorption wavelength as free nitrogen forms of
compound 2 appeared at 305 and 381 nm, which corresponding
to the n–p* and p–p* transition respectively (Fig. 8a) and
exhibit a high molar extinction coefficient (36 070 Mꢀ1 cmꢀ1).
When increased the hydrogen ion concentration, (pH ¼ 2), the
cation species 2a is formed due to the protonation of the
nitrogen atom and the absorption attribute to the n–p* tran-
sition vanished, as well as the absorption band due to p–p*
transition moves toward to blue region (23 nm) as compared to
the neutral compound 2. The formation of species 2a observed
by a colour change from greenish yellow to colourless in the
visible light (Fig. 7b). The blue shi was obtained due to
absence of lone pair in the imidazole which in turn to prevent
the charge transfer and acts as acceptor (A). However, at a low
concentration of hydrogen ion the bands appeared at 384 nm,
and a new broad band was appeared at 467 nm as compared to
Fig.
6 (a) Solvatochromism (b) normalized emission spectra of
compound 2 in several solvents.
The compound 2 exhibited a highest quantum yield value of
0.21 and 0.20 in DCM and DMSO respectively, whereas it is
found to be lowest value of 0.07 in CHCl3. These results are
indicated solute and solvents interaction leads to change in the
transition state which was responsible for the shi in the
emission maxima.
For optical properties, solvents play an important role
because it stimulates major changes in the position, intensity
and shape of the absorption and emission bands.55 The effect of
solvent polarity on emission spectra is shown in Fig. 6a, a sol-
vatochromic shi from green to yellowish orange was clearly
visible upon UV irradiation. Compound 2 exhibited positive
solvatochromism effect conrmed by the red-shi (66 nm) with
increasing the polarity of the solvents and Fig. S1† showed the
variation in the emission wavelength with different solvents
polarity. The interaction of compound 2 with different polar
solvents is mostly stabilized by the local excited states and thus
lead to the bathochromic emission.56 Stokes shi was calcu-
lated for the different the solvents and the values are obtained
Table 5 The data of absorption, emission and spectroscopic deter-
mined Egap for the compound 2 in the THF–H2O mixture at the
different pH valuesa
Medium
pH
labs (nm)
lem (nm)
FF
Egap (eV)
Acidic
Neutral
Basic
2a
2
2b
357
305, 381
308, 384, 467
476
530
546, 671
0.07
0.10
0.15
2.99
2.81
2.19
a
labs ¼ maximum absorption wavelength, c ¼ 1.0 ꢂ 10ꢀ3 mol Lꢀ1; lem
¼
maximum absorption wavelength, c ¼ 1.0 ꢂ 10ꢀ3 mol Lꢀ1; Egap ¼ optical
band gap derived from onset wavelength of the UV-Vis absorption
spectra.
Fig. 7 (a) Plausible mechanism of protonation and deprotonation of
compound
2 with different pH. (b) Halochromic effect of the
compound 2.
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the neutral species 2 (Fig. 8a). At pH ¼ 7 to 12, the absorption
The emission spectra of compound 2 at pH ¼ 8–11, the band
wavelength for n–p* and p–p* transition was almost the same. was moved to lower energy from 520 nm to 548 nm, but the
Further, with the decreasing of the hydrogen ion concentration, band is broad with emission from 500 nm to 700 nm with
(i.e.) pH ¼ 11 to 14, the species 2b was detected when the colour increasing intensity. It shows the charge transfer take place in
changes of the greenish-yellow solution to reddish-orange. The the initial level (i.e., D–p–A structural motif). According to the
absorption maxima for the solution (species 2b) appeared at measurement, aer the pH 12–14, the species 2b was formed
308, 384 and 467 nm and corresponding to the n–p*, p–p* and which is not making more changes in emission but it could be
possibility of inter- and intra-molecular charge transfers, ne-tuned from greenish-yellow to dark reddish-violet (Fig. 7b).
respectively. Theses red shis appeared due to great extent of The emission maxima moved from 546 to 561 nm with
intramolecular charge transfer (ICT) from donor to acceptor.57 decreasing intensity meanwhile another peak appeared at
The lone pair electron of the anionic species (D) 2b was showed 659 nm and it shied to 671 nm with increasing intensity
more contribution in the CT compared to the lone pair electron (Fig. 8b). It indicated that N-3 position of the imidazole ring was
of the neutral species 2.
deprotonated, and it can induce the intramolecular charge
The uorescence spectra of compound 2 at different pH are transfer (ICT), between the anion nature of the imidazole ring
shown in the Fig. 8b. The species 2a (pH ¼ 2) showed sharp (D) to phenylacrylonitrile (A).
band at 476 nm with a shi to higher energy region of 54 nm
The alteration of [H+] ion concentration can alter push–pull
compare to the neutral species 2. In the acidic medium (pH ¼ nature (ICT) between the donor to acceptor. It was well corre-
2), it is possible that due to protonation of imidazole part lating with optical band (Egap) values, calculated by absorption
generating a positive charge 2a and it was reducing the onset (Fig. S4 in ESI†). The Egap values of species 2, 2a and 2b
donating character in the structure and presents a strong pull– were obtained as 2.81, 2.99 and 2.19 eV respectively (Table 5).
push effect more than in neutral species 2 (i.e., A0–p–A struc- The Egap values were changed through the modifying the [H+]
tural motif), which observed through the emission changing the ion concentration. The Egap values are higher in acidic medium
colour from uorescence greenish-yellow to cyan (Fig. 7b).
(pH ¼ 2) than the basic medium (pH ¼ 14). This indication
observed in the absorption maxima by blue shi at the acidic
medium whereas red shi occurred at the basic medium
compared to the neutral condition. These results indicated the
compound 2 was able to act as D–p–A or A0–p–A structural motif
based on the pH nature and hence it showed a promising
candidate for the pH sensor.
2.6 Solid state photoluminescence
From our group previous experiences, phenyl acrylonitrile
derivatives (a-cyanostilbene) exhibited the good solid-state
emission which used to make for a better organoelctronic
device. In order to examine how imidazole based phenyl-
acrylonitrile showed its solid-state emission properties in the
thin lm (TF) and powder form. Thin lms were deposited onto
cleaned glass substrates by two process, one is the spin coating
method (solution) and other is the thermal vacuum deposition
method. Absorption and emission spectra of the thin lm and
powder are shown in Fig. 9. The powder showed a spectrum
with a broad shape (420 nm), but in thin lm showed a dened
shape with labs value at 388 nm. The powder form showed
a broadening shape of the absorption maxima may be due to the
intermolecular interaction or intramolecular interaction took
place. The absorbance and emission spectra are shown in Fig. 9
and corresponding data are listed in Table S6.† The emission
spectra of the powder and lm showed lem band around 563 nm
and 540 nm respectively. The quantum yield of the powder was
found to be 16% and, in the solution is 21%.
The surface morphology of the lms by solution-processed
and vacuum evaporation are compared in the Fig. 10. The
evaporation process leads to form morphology with agglomer-
ates of about 300 nm and the morphology by solution process
showed an arrangement alignment as herringbone. Optical
properties, absorption and emission were like the solution-
Fig. 8 (a) Absorption (b) emission spectra of compound 2 at different
pH.
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processed lms. The thin lms prepared by high vacuum
deposition were exposed to HCl, H2SO4, HNO3 vapours. Aer
few minutes, the sample exposed to HNO3 only showed the
transformation.
It was followed by absorption measurements and exposed
the lms under UV lamp was examined to see the change of the
uorescence. Fig. 11a showed a pure lm for the reference and
Fig. 11b showed exposed to HNO3 vapor lm. It can be seen the Fig. 10 (a) and (b) AFM image of the compound 2 thin film by solution
process and (c) morphology image of evaporated films.
blue-shi in uorescence emission, at same wavelength as the
compound 2 in solution at pH ¼ 2. The observed phenomenon
also was reversible, because aer 4 days the lms come to the
original colour and the uorescence, Fig. 11c.
For making the OLED of compound 2 using the vacuum
deposition lm and its photo luminance (PL) and electro
Absorption (solid line) and emission (short dashed line) spectra
luminance (EL) spectra are shown in Fig. 13a. The wavelength of
were measured and shown in the Fig. 12. Aer exposure both
maximum emission was about 550 nm. The J–V curve for OLED
spectra showed a hypsochromic effect, for absorption a maximum
is shown in Fig. 13b, the threshold voltage was about 4 V, the
inset shows a picture for OLED. The average luminance for
absorption showed a shi of 37 nm while the emission shis to
52 nm. As mentioned above, the change in uorescence was
devices was about 450 cd mꢀ2. It indicates that compound 2 had
reversible, Fig. 12, showed the absorbance and uorescence
promising candidate for an electronic device as well as the
vapour sensor device.
spectra for the compound in thin lm exposed to HNO3 and kept
at normal atmosphere for four days. Interestingly, the emission is
like the original one (lPL ¼ 545 nm). However, the absorbance
2.7 Theoretical calculation
remains as like the exposed lm. It could be the transformation of
the organic compound lm was not completed. However, the
experiment show that it is possible tuning the uorescence as well
as the application as vapor senor uorescence (Fig. 12).
To understand the electronic properties of compound 2, we
carried out the TD-DFT calculations in the gas phase and
solution state (1,4-dioxane, chloroform, ethyl acetate, THF,
DCM, methanol, DMF, and DMSO). It's corresponding to the
cation and anion structures with B3LYP/6-311++G (d, p) level of
theory. The calculated absorption wavelength (labs), oscillator
strengths (f), and major orbital transitions (in %) for compound
2 is presented in Tables S8 and S9 ESI.† The most important the
Frontier molecular orbital (FMO) (Highest Occupied Molecular
Orbital, HOMO and Lowest Unoccupied Molecular Orbital,
LUMO) are presented in Fig. 14. The computed absorption of
the compound 2 in gas phase and in the solutions state showed
around 450 nm. These values may be due to the intramolecular
charge transfer (H / L transition with 100%) arise from the
electron pulling nature of phenylacrylonitrile moiety (acceptor).
This CT was observed in the absorption spectrum of powder
form but did not observe in the solution and TF (Fig. 9a). The
second absorption peaks in the both states showed around
340 nm are corresponding to p / p* transition (H ꢀ 1 / L
with 86–100%). Another weak transition around 319–330 nm, it
belongs to n / p* transition (H / L + 1 with 90–100%). On the
other hand, when increasing the solvent polarity, the computed
lmax value showed slightly blue shi as like experiment results.
To understand the effect of pH on molecular structure, we
computed to the absorptions for the compound 2 in the form of
Fig. 9 (a) Absorption and (b) emission spectra of compound 2 in the Fig. 11 (a) Thin film (TF) as reference (b) exposed to HNO3 (c) exposed
powder and thin film.
TF after 4 days.
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the strong Stokes shi observed at pH 14. It was performed the
HOMO–LUMO analysis for the compound 2 at neutral, cation
and anion environment. The HOMO and LUMO energy level of
compound 2 (at neutral) was of ꢀ5.67 eV and ꢀ2.59 eV
respectively, and it's DEgap of 3.08 eV. These results were closer
to the experimental results of the CV measurements (Fig. S5,†
HOMO is ꢀ5.677 eV and LUMO is ꢀ2.868 eV; DEgap of 2.81 eV).
It noted that the HOMO and LUMO of cation is more stabilized
with 3.05 eV than the neutral molecule. Whereas HOMO of
anion is less stabilized with 3.60 eV and 2.69 eV for LUMO of
anion than neutral molecule. These variations in energy level of
FMO is might be reason for the blue shi absorption and
emission in acidic and red shi in the basic medium.
To recognise that the origin of intramolecular charge trans-
fer in the title molecule, we carried out the NBO analysis for
neutral, cation and anionic state of the molecule (Tables S8 and
S9†). The result suggested that the whole molecule involved in
the intramolecular charge transfer process. Briey, the phe-
nylacrylnitrile moiety in the neutral molecule is predominately
involved in the charge transfer process with the strong stabili-
zation energy. Whereas the imidazole moiety is strongly or
moderately involved in the intramolecular charge transfer
process with moderate stabilization energy in the cation and
anion environment. The NBO analysis suggested that the phe-
nylacrylonitrile moiety acts as a strong electron withdrawing
moiety and it enhanced the intramolecular charges transfer
along the whole molecule.
Fig. 12 Absorption and emission spectra of compound 2 in thin film
(TF).
Finally, the optoelectronic calculations with the aid
Fig. 13 (a) Photoluminescence and electroluminescence spectra of
thin film and OLEDs respectively. (b) Electrical characteristics J–V for
OLEDs (the inset shows an OLED picture).
¨
Schrodinger programme, we compute the oxidation potential
and reduction potential values of compound 2 help us to see
that the compound to loose/gain electrons. From the CV values
are of 1.455 eV and ꢀ1.354 eV respectively, that compared with
the calculated are closer for the reduction potential with
a difference ꢀ0.0461 eV between the calculated and experi-
mental. That is an indication that the compound 2 acta more
acceptor than donating. The presence of the electro with-
drawing CN group in the molecule is responsible for an oxida-
tion potential higher than similar molecule imidazole groups.58
In the Table S5,† exhibits hole and electron reorganization
energies (HRE and ERE). It is worth to notice that the reorga-
nization energy (RE) is one of the parameters governing the
hopping rate. It has long been recognized that HRE and ERE are
closely related to the geometries of cation and anion states. In
fact, the RE is dened as the energy difference between the
charged and neutral systems. The molecules with small RE
possess high carrier mobility and these energies are in
proportion to the deformation of the geometries in charge
transfer process. In compound 2 the HRE is 0.1064 smaller than
the ERE indicating a smaller geometrical deformation upon
electron injection compared to hole injection. This value is
remarkably small, indicated that the hole extraction potential of
6.368 eV, which demonstrates that the injection of hole into
compound 2 is slightly easier. On the contrary, compound 2 has
maximum electron extraction potential of ꢀ1.2032 eV, indi-
cating that the injection of electron into the compound 2
becomes much difficult.
the cation and anion environment (Table S9†). From the results,
the H / L transition went to blue shi (440 nm in gas and
417 nm in THF), for the cationic environment whereas for the
anionic environment absorption moved to a strong red shi (at
582 nm in gas and 562 nm in THF). These results are matched
with in the pH experimental values. In order to understand for
Fig. 14 The HOMO–LUMO diagram of the compound 2 in neutral,
acidic and basic condition.
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measurements were carried out with
a
potentiostat
3. Conclusion
(PGSTAT128N), using
a
three-electrode cell assembly
comprising Ag/Ag+ in a 3 M solution of KCl as a reference
In summary, it was designed a novel Imidazole based lumino-
genic compound was characterized by SCXRD, FT-IR, 1H NMR,
13C NMR and EIMS. We investigated the photophysical prop-
erties of compound 2 in solution state with various solvents and
in the solid states (TF and powder). In the solution state, it
showed the positive solvatochromic behaviour and it had
a solid-state emission too. Furthermore, by varying the pH
medium to observe the intramolecular charge transfer in solu-
tion and solid state (TF) and it resulted the halochromic
behaviour. The phenyl rings of imidazole moiety trigged by
protonation and deprotonation of the imidazole group and its
reason for the electronic transition (ICT) via C-2 phenyl ring to
the acceptor of phenyl acrylonitrile group. Based on that
compound 2 can be used as pH sensor for solution and vapor
medium. Optical band gap values are estimated from cyclic
voltammetry and the absorption onset. Overall, compound 2
can able to act as D–p–A as well as A0–p–A based on the pH
nature. In addition, the compound was used as emitting layer in
OLEDs with acceptable performance. TD-DFT computations
and the energy levels of FMO are very closer to the experimental
results and it aid to give an insight idea to support the studies.
Therefore, it can act as a new multi-functional material for the
eld of sensor and organo-electronic application.
electrode, a platinum wire (f ¼ 0.2 mm) as the working elec-
trode,
a 0.1 M solution of tetrabutylammonium hexa-
uorophosphate (TBAFP6) CH2Cl2 as a supporting electrolyte
and a platinum wire as the counter electrode. Ferrocene was
used as an external standard. The scanning rate was 50 mV sꢀ1
.
Single crystal X-ray diffraction (SCXRD). All reection
intensities were measured at 110(2) K using a SuperNova
diffractometer (equipped with Atlas detector) with Cu Ka radi-
˚
ation (l ¼ 1.54178 A) under the program CrysAlisPro (Version
CrysAlisPro 1.171.39.29c, Rigaku OD, 2017)59 The same program
was used to rene the cell dimensions and for data reduction.
The structure was solved with the program SHELXS-2018/3
(Sheldrick, 2018) and was rened on F2 with SHELXL-2018/3
(Sheldrick, 2018). Analytical numeric absorption correction
using a multifaceted crystal model was applied using CrysA-
lisPro. The temperature of the data collection was controlled
using the system Cryojet (manufactured by Oxford Instru-
ments). The H atoms were placed at calculated positions (unless
otherwise specied) using the instructions AFIX 43 with
isotropic displacement parameters having values 1.2 Ueq. of the
attached C atoms. The H atoms attached to N1, O1W and O2W
were found from difference Fourier maps, and their coordinates
were rened pseudo freely using the DFIX instruction to keep
the N–H, O–H and H/H distances within acceptable ranges.
The structure is ordered.
4. Experimental section
4.1 Materials and instruments
OLEDs: thin lm and devices fabrication. For OLEDs ITO/
Benzil(1,2-diphenylethane-1,2-dione), phenylacetonitrile, 4-for- glass substrates with 5–15 U per square were purchased from
mylbenzaldehyde (1,4-terephtaldehyde) and ammonium Delta Technologies. Poly(3,4-ethylenedioxythiophene) poly-
acetate were acquired from Aldrich Chemical Co. and Fermont. styrene sulfonate (PEDOT:PSS) (Clevios PVP AI4083) was ob-
The reagents and solvents were used as received without any tained from Heraeus–Clevios and this compound acts as hole
additional purication. Melting points were measured with an transport layer. Ca and Ag used as cathode were acquired from
SEV (0–300 ꢁC) apparatus and were reported as uncorrected Sigma Aldrich. Substrates, glass for lms and glass/ITO for
values. IR spectra of the products were recorded on a Vertex OLEDs were cleaned with ethanol in an ultrasonic bath and
(model 70, Bruker Optics, Germany) 750 FT-IR spectropho- rubbed with alcohol wetted cotton; aer this procedure,
tometer by attenuated total reectance (ATR). 1H NMR and 13
C
substrates were dried with clean and dry air and kept at 85 C,
ꢁ
NMR spectra were obtained in DMSO-d6 on a Bruker 500 MHz over 12 h. Before deposition of the organic layers, the substrates
NMR spectrometer. The electron ionization (EI) spectra were were treated with plasma-oxygen by 5 min. For OLEDs,
acquired on a Jeol MStation 700-D mass spectrometer (Jeol USA, PEDOT:PSS was deposited by spin coating and annealed at
Peabody, MA). Absorbance and emission (UV-Vis and PL). The 120 ꢁC by 15 min in air, thickness was about 45 nm. Then,
absorbance spectra were measured using a spectrometer Cary substrates were transferred to an evaporation chamber and
˚
300 (Agilent) equipped with a deuterium and halogen lamp. 100 nm of the uorescent compound was evaporated at 0.5 A
Emission spectra (PL) were acquired with a QE-Pro-FL (Ocean sꢀ1, the chamber pressure was 2 ꢂ 10ꢀ6 Torr. A double layer of
Optics, Dunedin, FL) an UV-Lamp Mineral Light with emission calcium (50 nm) and silver (100 nm) was used as cathode and
at 401 nm was used as excitation source. I–V curves were evaporated sequentially aer the organic layer. The thickness of
acquired with a source-meter Keithley 2450. Electrolumines- the organic layer was measured through Atomic Force Micros-
cence spectra were recorded with an Ocean Optics spectrom- copy (AFM) Nanosurf EasyScan. The emissive area of samples
eter. The morphology and thickness were analyzed using atomic was of 9 mm2. For recording, the I–V curves a source-meter
force microscopy (AFM) with the microscope EasyScan2 from Keithley 2450 was used. The photoluminescence, electrolumi-
Nanosurf operating in contact mode under ambient conditions. nescence (EL) and luminance were measured with an Ocean
This has a maximum square scanning area of 110 mm. The optics USB4000 spectrophotometer, calibrated with the HL-3P-
adjustment of pH solutions was achieved through the addition CAL lamp.
of NaOH or HCl solutions and monitored with the aid of Met-
Quantum chemical calculations. All the quantum chemical
rohm 716 DMS Titrino Titrator pH meter using buffers of pH 4.0 calculations were performed with the Gaussian 09 program.60
and pH 9.2 as calibrants. Cyclic Voltammetry (CV) The constrains free optimization was carried out by using M06-
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2X61,62 cc-PVTZ level of theory with Grimme's D3 dispersion ArH), 7.59–7.58 (m, 4H, ArH), 7.47 (s, 1H, ]CH), 7.40–7.24 (m,
corrections.63 The selection of M06-2X and basis set has been 11H); 13C NMR (100 MHz, CDCl3, d) 145.0, 141.6, 134.4, 133.6,
made on our earlier studies.64–69 The vibrational frequency was 131.6, 129.9, 129.1, 128.9, 128.4, 127.9, 126.0, 125.5, 118.2,
calculated for the optimized geometry in vacuum and solvent 111.4; IR (KBr, cmꢀ1) n: 3301(NH), 2211 (–C^N), 1593(–CH]N–
phases to determine the energy minima on the potential energy ), 1363(–C–N–); MS (ESI): [M+] calculated for C30H21N3 423.17,
surface and were found to have no negative frequencies. All the found 423.0, 154 (100%), 136 (72%), 307 (21%)
solution phase calculations were carried out by using the
conductor-like polarizable continuum model (CPCM).70,71 Time-
Conflicts of interest
dependent DFT (TDDFT)72 is used to calculate the absorption
properties from the optimized geometries All the absorption
values are not comparable with experimental result.
There are no conicts to declare.
Optoelectronic calculation. Optoelectronic calculation for
compound 2 was carried out in the materials science suite in the Acknowledgements
73
¨
Schrodinger program. The materials science suite provides
The authors wish to express their gratitude to VIEP-BUAP
(project PEZM-NAT16-G), to project fellowship-PRODEP-SEP
511-6/17-11066 and 511-6/18-16257, to Maxime Siegler for the
very accurate optoelectronic properties standard materials like
Ir(ppy)3 and AlQ3 compounds.74 For this calculation it was used
a gas phase optimized geometry of compound 2 which was
´
X-ray determination, Laboratorio Nacional de Supercomputo
73
¨
obtained from jaguar suite in the Schrodinger program, and
del Sureste (LNS-BUAP) to perform the calculations as well as to
Vladimir Carranza for technical assistance with mass
spectrometry.
the optimization process was carried out with MIDIX basis set
with gradient-corrected correlation functional of B3LYP.75–77 To
conrm the proper convergence to minima, it was computed
the vibrational frequencies with same level of theory to conrm
that no negative frequencies presented.
Notes and references
1 H. Schill, S. Nizamov, F. Bottanelli, J. Bierwagen, V. N. Belov
and S. W. Hell, Chem.–Eur. J., 2013, 19, 16556–16565.
2 D. Huang, T. Zhao, W. Xu, T. Yang and P. S. Cremer, Anal.
Chem., 2013, 85, 10240–10248.
3 X.-D. Liu, Y. Xu, R. Sun, Y.-J. Xu, J.-M. Lu and J.-F. Ge, Analyst,
2013, 138, 6542–6550.
4 G. Gryn’ova and C. Corminboeuf, J. Phys. Chem. Lett., 2018, 9,
2298–2304.
5 S. Sasaki, G. P. C. Drummen and G. Konishi, J. Mater. Chem.
C, 2016, 4, 2731–2743.
4.2 Synthesis of 4-(4,5-diphenyl-1H-imidazol-2-yl)
benzaldehyde (1)
A mixture of 4-formylbenzaldehyde (500 mg, 3.730 mmol),
benzil (627 mg, 3.730 mmol), NH4OAc (3.45 mg, 44.76 mmol) in
acetic acid (50 mL) was reuxed for 5 hours, and then cooled to
room temperature. The reaction mixture was poured into the
ice-cold water and allowed to be le for 1 h, ltered, and the
yellow precipitate was washed with water. The crude product
was suspended in EtOAc and lter it. The ltrate was concen-
trated by evaporation and the solid product washed with 5%
(EtOAc : Hex). The product was identied by their spectral
data.78 Pale yellow solid, yield: 42%, mp 233–235 ꢁC (lit. 72 233–
235 ꢁC); 1H NMR (500 MHz, DMSO) d 13.04 (s, 1H), 10.04 (s, 1H),
8.31 (d, J ¼ 8.3 Hz, 2H), 8.02 (d, J ¼ 8.5 Hz, 2H), 7.55 (dd, J ¼
16.8, 7.4 Hz, 4H), 7.47 (t, J ¼ 7.4 Hz, 2H), 7.42 (d, J ¼ 7.2 Hz, 1H),
7.33 (t, J ¼ 7.5 Hz, 2H), 7.26 (d, J ¼ 7.2 Hz, 1H). IR (KBr, cmꢀ1):
1696(–CHO), 1605(–C]NH–), 1309 (–C–N).
6 C. Wu, J. Wei, D. Tian, Y. Feng, R. H. Miller and Y. Wang, J.
Med. Chem., 2008, 51, 6682–6688.
7 G. Cheng, D. Wenyue, Y. Liang, L. Ying, Z. Zhongbo, L. Dan
and M. Yuguang, Adv. Mater., 2012, 24, 2413–2417.
8 J. S. Wilson, M. J. Frampton, J. J. Michels, L. Sardone,
G. Marletta, R. H. Friend, P. Samori, H. L. Anderson and
F. Cacialli, Adv. Mater., 2005, 17, 2659–2663.
9 P. Zrazhevskiy, M. Sena and X. Gao, Chem. Soc. Rev., 2010, 39,
4326–4354.
10 H. Sasabe and J. Kido, Chem. Mater., 2011, 23, 621–630.
11 D. Ding, J. Liang, H. Shi, R. T. K. Kwok, M. Gao, G. Feng,
Y. Yuan, B. Z. Tang and B. Liu, J. Mater. Chem. B, 2014, 2,
231–238.
4.3 Synthesis of (Z)-3-(4-(4,5-diphenyl-1H-imidazol-2-yl)
phenyl)-2-phenylacrylonitrile (2)
A mixture of the compound 1 (50 mg, 0.1542 mmol), 2-phenyl
acetonitrile (18 mg, 0.1542 mmol), KOH (1.7 mg, 0.03084 mmol)
´
ˇ
in MeOH (2 mL) was reuxed for 6 hours to get compound 2 as 12 M. Klikar, P. Solanke, J. Tydlitat and F. Bures, Chem. Rec.,
a yellow solid. Aer completion, the reaction mixture was dried, 2016, 16, 1886–1905.
added a water to lter the resulting precipitate. For neutralize 13 W. Aigner, O. Bienek, B. P. Falcao, S. U. Ahmed, H. Wiggers,
˜
the precipitate, water was used to wash. In order to recrystalli-
M. Stutzmann and R. N. Pereira, Nanoscale, 2018, 10, 8042–
zation, briey, 0.05 g of the title compound was dissolved in
20 mL commercial MeOH, heated at 85 C for 2 h, lter it and 14 S. Jhulki and J. N. Moorthy, J. Mater. Chem. C, 2018, 6, 8280–
8057.
ꢁ
allowed to evaporate the ltrate slowly at room temperature.
8325.
The expected product was obtained as crystal. Yellow solid, 15 P. Kan-Yi and L. Bin, Adv. Funct. Mater., 2009, 19, 277–284.
yield: 65%, mp. 244–246 ꢁC; 1H NMR (500 MHz, CDCl3, d) 9.92 16 T. P. I. Saragi, T. Spehr, A. Siebert, T. Fuhrmann-Lieker and
(s, 1H, –NH), 7.95 (d, 2H, J ¼ 10 Hz, ArH), 7.90 (d, 2H, J ¼ 10 Hz,
J. Salbeck, Chem. Rev., 2007, 107, 1011–1065.
12094 | RSC Adv., 2019, 9, 12085–12096
This journal is © The Royal Society of Chemistry 2019

View Article Online
Paper
RSC Advances
´
´
17 A. Kundu, S. Karthikeyan, Y. Sagara, D. Moon and 40 M. J. Percino, V. M. Chapela, L.-F. Montiel, E. Perez-Gutierrez
S. P. Anthony, Phys. Chem. Chem. Phys., 2018, 20, 27385–
27393.
18 G. Wiethaus, J. M. Toldo, F. da Silveira Santos, R. da Costa
and J. L. Maldonado, Chem. Pap., 2010, 64, 360–367.
41 Z.-Q. Yan, Z.-Y. Yang, H. Wang, A.-W. Li, L.-P. Wang, H. Yang
and B.-R. Gao, Spectrochim. Acta, Part A, 2011, 78, 1640–1645.
Duarte, P. F. B. Gonçalves and F. S. Rodembusch, Phys. 42 Y. Li, F. Li, H. Zhang, Z. Xie, W. Xie, H. Xu, B. Li, F. Shen,
Chem. Chem. Phys., 2019, 21, 4408–4420.
19 Z. Fang, S. Wang, L. Zhao, Z. Xu, J. Ren, X. Wang and
Q. Yang, Mater. Chem. Phys., 2008, 107, 305–309.
20 A. Hariharasubramanian and Y. D. Ravichandran, RSC Adv.,
2014, 4, 54740–54746.
L. Ye, M. Hanif, D. Ma and Y. Ma, Chem. Commun., 2007,
231–233.
43 B.-R. Gao, H.-Y. Wang, Y.-W. Hao, L.-M. Fu, H.-H. Fang,
Y. Jiang, L. Wang, Q.-D. Chen, H. Xia, L.-Y. Pan, Y.-G. Ma
and H.-B. Sun, J. Phys. Chem. B, 2010, 114, 128–134.
21 Y. Zhang, S.-L. Lai, Q.-X. Tong, M.-F. Lo, T.-W. Ng, 44 F. H. Allen, O. Kennard, D. G. Watson, L. Brammer,
M.-Y. Chan, Z.-C. Wen, J. He, K.-S. Jeff, X.-L. Tang,
W.-M. Liu, C.-C. Ko, P.-F. Wang and C.-S. Lee, Chem.
Mater., 2012, 24, 61–70.
A. G. Orpen and R. Taylor, J. Chem. Soc., Perkin Trans. 2,
1987, S1–S19.
ˇ
´
´
´
45 K. Molcanov, I. Sabljic and B. Kojic-Prodic, CrystEngComm,
22 H.-M. Zhang, W.-F. Fu, S.-M. Chi and J. Wang, J. Lumin.,
2009, 129, 589–594.
2011, 13, 4211–4217.
46 O. V Dolomanov, L. J. Bourhis, R. J. Gildea, J. A. K. Howard
and H. Puschmann, J. Appl. Crystallogr., 2009, 42, 339–341.
47 T. Steiner, Angew. Chem., Int. Ed., 2002, 41, 48–76.
´
ˇ
23 J. Kulhanek and F. Bures, Beilstein J. Org. Chem., 2012, 8, 25–
49.
24 J. Jayabharathi, V. Thanikachalam, N. Srinivasan and M. V 48 M. Inoue and I. Hirasawa, J. Cryst. Growth, 2013, 380, 169–
Perumal, Spectrochim. Acta, Part A, 2012, 90, 125–130. 175.
25 J. Mandal, P. Ghorai, P. Brandao, K. Pal, P. Karmakar and 49 Z.-B. Cai, L. Bai, Y.-L. Pan, F.-F. Ma, S.-L. Li and Y.-P. Tian, J.
A. Saha, New J. Chem., 2018, 42, 19818–19826. Photochem. Photobiol., A, 2017, 346, 194–205.
26 R. Bag, Y. Sikdar, S. Sahu, D. K. Maiti, A. Frontera, A. Bauza, 50 G.-C. Zheng, Z.-B. Cai, Y.-L. Pan, L. Bai, Y.-T. Zhou, S.-L. Li
˜
´
M. G. B. Drew and S. Goswami, Dalton Trans., 2018, 47,
17077–17085.
and Y.-P. Tian, Tetrahedron, 2016, 72, 2988–2996.
´
51 M. J. Percino, M. Ceron, G. Soriano-Moro, M. E. Castro,
´
27 N. Fridman, M. Kaory, Y. Eichen and S. Speiser, J. Mol.
Struct., 2009, 917, 101–109.
V. M. Chapela, J. Bonilla, M. Reyes-Reyes and R. Lopez-
Sandoval, CrystEngComm, 2014, 16, 8591–8604.
28 M. Y. Berezin, J. Kao and S. Achilefu, Chem.–Eur. J., 2009, 15, 52 M. M. Duvenhage, M. Ntwaeaborwa, H. G. Visser,
3560–3566.
P. J. Swarts, J. C. Swarts and H. C. Swart, Opt. Mater., 2015,
42, 193–198.
29 K. Aggarwal and J. M. Khurana, J. Photochem. Photobiol., A,
2015, 307–308, 23–29.
30 A. Safavi and M. Bagheri, Sens. Actuators, B, 2003, 90, 143–
150.
31 B. Kumari, S. P. Singh, R. Santosh, A. Dutta,
S. S. Mallajosyula, S. Ghosal and S. Kanvah, New J. Chem.,
2019, 43, 4106–4115.
32 L. Zhu and Y. Zhao, J. Mater. Chem. C, 2013, 1, 1059–1065.
33 J. N. Zhang, H. Kang, N. Li, S. M. Zhou, H. M. Sun, S. W. Yin,
N. Zhao and B. Z. Tang, Chem. Sci., 2017, 8, 577–582.
53 J. C. S. Costa, R. J. S. Taveira, C. F. R. A. C. Lima, A. Mendes
and L. M. N. B. F. Santos, Opt. Mater., 2016, 58, 51–60.
54 S. Dhami, A. J. De Mello, G. Rumbles, S. M. Bishop,
D. Phillips and A. Beeby, Photochem. Photobiol., 2018, 61,
341–346.
55 M. J. Wirth, TrAC, Trends Anal. Chem., 1982, 1, 383–386.
56 R. Ghosh and D. K. Palit, Photochem. Photobiol. Sci., 2013, 12,
987–995.
¨
57 A. O. Eseola, O. Adepitan, H. Gorls and W. Plass, New J.
´
´
´
34 M. Martınez-Abadıa, R. Gimenez and M. B. Ros, Adv. Mater.,
Chem., 2012, 36, 891–902.
2018, 30, 1704161.
35 C. Dou, L. Han, S. Zhao, H. Zhang and Y. Wang, J. Phys.
Chem. Lett., 2011, 2, 666–670.
36 R. Usman, A. Khan, M. Wang, Y. Luo, W. Sun, H. Sun, C. Du
and N. He, Cryst. Growth Des., 2018, 18, 6001–6008.
37 M. Wykes, S. K. Park, S. Bhattacharyya, S. Varghese,
58 J. J. Guerard, P. R. Tentscher, M. Seijo and J. Samuel Arey,
Phys. Chem. Chem. Phys., 2015, 17, 14811–14826.
59 G. M. Sheldrick, Acta Crystallogr., Sect. C: Struct. Chem., 2015,
71, 3–8.
60 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone,
B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato,
X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng,
J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota,
R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda,
O. Kitao, H. Nakai, T. Vreven, J. A. Montgomery,
J. E. Peralta, F. Ogliaro, M. Bearpark, J. J. Heyd,
E. Brothers, K. N. Kudin, V. N. Staroverov, R. Kobayashi,
J. Normand, K. Raghavachari, A. Rendell, J. C. Burant,
S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam,
M. Klene, J. E. Knox, J. B. Cross, V. Bakken, C. Adamo,
J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev,
¨
J. E. Kwon, D. R. Whang, I. Cho, R. Wannemacher, L. Luer,
S. Y. Park and J. Gierschner, J. Phys. Chem. Lett., 2015, 6,
3682–3687.
´
´
´
38 M. J. Percino, V. M. Chapela, E. Perez-Gutierrez, M. Ceron
and G. Soriano, Chem. Pap., 2011, 65, 42–51.
39 M. Castro, M. Percino, V. Chapela, M. Ceron, G. Soriano-
Moro, J. Lopez-Cruz, F. Melendez, M. E. Castro,
M. J. Percino, V. M. Chapela, M. Ceron, G. Soriano-Moro,
J. Lopez-Cruz and F. J. Melendez, Int. J. Mol. Sci., 2013, 14,
4005–4029.
This journal is © The Royal Society of Chemistry 2019
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RSC Advances
Paper
A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, 68 P. Venkatesan, V. Rajakannan, N. S. Venkataramanan,
R. L. Martin, K. Morokuma, V. G. Zakrzewski, G. A. Voth,
P. Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels,
A. Ilangovan, T. Sundius and S. Thamotharan, J. Mol.
Struct., 2016, 1119, 259–268.
O. Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski and 69 M. Udayakumar, J. Kothandapani, S. S. Ganesan,
D. J. Fox, Gaussian 09, Revis. B.01, Gaussian, Inc.,
N. S. Venkataramanan, S. Madan Kumar, K. Byrappa and
Wallingford CT, 2009.
S. Thamotharan, J. Mol. Struct., 2017, 1133, 510–518.
61 Y. Zhao, N. E. Schultz and D. G. Truhlar, J. Chem. Theory 70 J. Tomasi, B. Mennucci and R. Cammi, Chem. Rev., 2005,
Comput., 2006, 2, 364–382. 105, 2999–3094.
62 E. G. Hohenstein, S. T. Chill and C. D. Sherrill, J. Chem. 71 S. Miertus, E. Scrocco and J. Tomasi, Chem. Phys., 1981, 55,
Theory Comput., 2008, 4, 1996–2000. 117–129.
63 S. Grimme, J. Antony, S. Ehrlich and H. Krieg, J. Chem. Phys., 72 W. Kohn and L. J. Sham, Phys. Rev., 1965, 140, A1133–A1138.
ˇ
2010, 132, 154104.
64 J. Percino, M. Ceron, P. Venkatesan, P. Ceballos,
73 A. D. Bochevarov, E. Harder, T. F. Hughes, J. R. Greenwood,
D. A. Braden, D. M. Philipp, D. Rinaldo, M. D. Halls, J. Zhang
and R. A. Friesner, Int. J. Quantum Chem., 2013, 113, 2110–
2142.
´
˜
´
A. Banuelos, O. Rodrıguez, M. A. Siegler, F. Robles,
´
´
V. M. Chapela, G. Soriano-Moro, E. Perez-Gutierrez,
¨
J. Bonilla-Cruz and S. Thamotharan, Cryst. Growth Des., 74 J. Breu, P. Stossel, S. Schrader, A. Starukhin, W. J. Finkenzeller
2017, 17, 1679–1694. and H. Yersin, Chem. Mater., 2005, 17, 1745–1752.
65 M. J. Percino, M. Ceron, O. Rodrıguez, G. Soriano-Moro, 75 A. D. Becke, J. Chem. Phys., 1993, 98, 5648–5652.
´
´
´
M. E. Castro, V. M. Chapela, M. A. Siegler and E. Perez- 76 C. Lee, W. Yang and R. G. Parr, Phys. Rev. B: Condens. Matter
´
Gutierrez, Molecules, 2016, 21, 389.
Mater. Phys., 1988, 37, 785–789.
66 P. Venkatesan, M. Ceron, S. Thamotharan, F. Robles and 77 B. Miehlich, A. Savin, H. Stoll and H. Preuss, Chem. Phys.
M. J. Percino, CrystEngComm, 2018, 20, 2681–2697. Lett., 1989, 157, 200–206.
67 P. Venkatesan, S. Thamotharan, A. Ilangovan, H. Liang and 78 X. Chen, C. Jia, Z. Wan, J. Feng and X. Yao, Org. Electron.,
T. Sundius, Spectrochim. Acta, Part A, 2016, 153, 625–636. 2014, 15, 2240–2249.
´
12096 | RSC Adv., 2019, 9, 12085–12096
This journal is © The Royal Society of Chemistry 2019