Thermal, optical and Photophysical behaviour of some Mesogenic Benzimidazole-based Schiff-bases

Article abstract of DOI:10.1016/j.molliq.2017.10.051

A series of luminescent benzimidazole-based Schiff-bases, 5-(alkyloxy)-2-(((2-(4-(alkyloxy)phenyl)-1H–benzimidazol-5-yl)imino)methyl)phenol, with different alkyl chains was synthesized and characterized by ¹H & ¹³C NMR, UV–Vis, fluorescence and mass spectrometry. All the compounds were found to be mesogenic (smectic A₁), as studied by POM and DSC techniques, and their green emission was implied by fluorescence studies. Electrochemical study of one of the compounds, 3d, shows a band gap of 2.56 eV with HOMO and LUMO energy levels at ? 5.22 eV and ? 2.67 eV, respectively.

Full text of DOI:10.1016/j.molliq.2017.10.051

Accepted Manuscript
Thermal, optical and Photophysical behaviour of some Mesogenic
Benzimidazole-based Schiff-bases
Rajasekhar Yerrasani, M. Karunakar, Ragini Dubey, Angad
Kumar Singh, T.R. Rao
PII:
DOI:
Reference:
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doi:10.1016/j.molliq.2017.10.051
MOLLIQ 8013
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Journal of Molecular Liquids
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Accepted date:
21 February 2017
26 September 2017
10 October 2017
Please cite this article as: Rajasekhar Yerrasani, M. Karunakar, Ragini Dubey, Angad
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ACCEPTED MANUSCRIPT
[Re-revised Manuscript MOLLIQ_2017_723_R1]
Thermal, Optical and Photophysical Behaviour of Some Mesogenic
Benzimidazole-based Schiff-Bases
Rajasekhar Yerrasani, M. Karunakar, Ragini Dubey, Angad Kumar Singh and T. R.
Rao*
Department of Chemistry, Centre of Advanced Studies, Institute of Science,
Banaras Hindu University, Varanasi-221005, India
*E-mail: drtrrao@gmail.com
Abstract
A series of luminescent benzimidazole-based Schiff-bases, 5-(alkyloxy)-2-
(((2-(4-(alkyloxy)phenyl)-1H-benzimidazol-5-yl)imino)methyl)phenol, with different
1
alkyl chains was synthesized and characterized by H & 13C NMR, UV-Vis,
fluorescence and mass spectrometry. All the compounds were found to be mesogenic
(smectic A1), as studied by POM and DSC techniques, and their green emission was
implied by fluorescence studies. Electrochemical study of one of the compounds, 3d,
shows a band gap of 2.56 eV with HOMO and LUMO energy levels at 5.22 eV and
2.67 eV, respectively.
Keywords: Liquid crystal; fluorescence; benzimidazole; Schiff-base.
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1. Introduction
Over many years, heterocyclic mesogenic compounds were being synthesized
by replacing mesogenic core unit (benzene or naphthalene) by species such as
oxadiazoles, benzimidazoles, triazoles, coumarin and pyridine. Incorporation of
heterocycles into liquid crystals holds special scientific and technological interest,
since their known electron deficiency can be used to generate intrinsically
luminescent mesogens with high charge carrier mobility. Liquid crystals containing
extended π-conjugated systems have attracted special attention owing to their ability
to generate highly ordered structures presenting both luminescence and conductivity
properties in an anisotropic manner1-4. Hetrocyclic liquid crystals were used in
additional applications such as optical devices in dye lasers, liquid crystal displays,
electron transport systems and organic light-emitting diodes (OLEDs)5-10
.
Benzimidazole-based compounds were found to possess several kinds of applications
particularly in optical sensors11-14, medicinal chemistry13 and also as OLEDs because
of their good electron mobility14-17. Nevertheless, only a few reports on the
incorporation of benzimidazole as a core or end-group in liquid crystalline
compounds can be found in literature despite their thermal stability18. Zhang et al.
synthesized benzimidazole based (end-group) compounds and investigated their
thermal properties only not optical properties 18a
.
In the present work, we report synthesis of a homogeneous series of
mesogenic benzimidazole-based (core) fluorescent Schiff bases which were found to
possess a electrical band gap of 2.56 eV. The structures of the compounds were
characterized by 1H & 13C NMR, IR and mass spectrometry.
2. Experimental
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2.1. Materials
All the required reagents of analytical grade (AR) obtained from commercial
sources were used as such; 1-bromohexane, 1-bromooctane, 1-bromododecane, 2,4-
dihydroxybenzaldehyde, 4-hydroxybenzaldehyde and 4-nitro-o-phenylenediamine are
from Sigma–Aldrich, USA; KHCO3 and KI are from Merck. The organic solvents
obtained from commercial vendors were dried, when required, using standard
methods19.
2.2. Instruments and measurements
1
The H and 13C NMR spectra were recorded on a JEOL AL-300 MHz FT-
NMR multinuclear spectrometer; C, H, N contents were micro analysed on an
Elemental Vario EL III Carlo Erba 1108 analyzer. Infrared spectra were recorded on a
JASCO FT-IR (model-5300) spectrophotometer in 4000-400 cm-1 region. ESI-MS
measurements were carried out using a WATERS Q-TOF premier mass spectrometer.
UV-VIS spectra were recorded on a Shimadzu spectrophotometer, model,
Pharmaspec UV-1700. Emission spectra were recorded on JY HORIBA Fluorescence
spectrophotometer. Mesophases were identified by using polarized hot-stage
microscope (LOMO, USA) equipped with digital camera (Nikon Coolpix 4500).
Differential scanning calorimetry studies were made on METTLER DSC-25 unit.
Thermo gravimetric analysis (TGA) was performed using a Perkin-Elmer-STA 6000
apparatus under high purity nitrogen over a temperature range, RT to 600 °C, with a
heating rate of 10 °C/min. Powder XRD studies were measured by Panalytical
(Empyrean) Cu-Kα (1.54 Å) X-ray diffractometer. Electrochemical measurements
were made in THF solutions on a potentiostat, CH Instruments Model CHI 610E,
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using tetrabutylammonium perchlorate (TBAP, 0.1M) as supporting electrolyte; the
instrument was pre-calibrated using ferrocene as internal standard.
2.3. Synthesis
The synthetic route for preparation of 5-(alkyloxy)-2-(((2-(4-
(alkyloxy)phenyl)-1H-benzimidazol-5-yl)imino)methyl)phenols
and
their
intermediates is depicted in Scheme 1. The general procedures for alkylation of 2,4-
dihydroxybenzaldehyde and 4-hydroxybenzaldehyde were reported earlier20-22
.
2.3.1. General procedure for synthesis of precursor materials, 2-(4-(alkyloxy)phenyl)-
5-nitro-1H-benzimidazoles, 1(a-b): These compounds were synthesized following
the literature procedure23; the crude product was purified by column chromatography
on silica gel using n-hexane/chloroform (1:3, v/v) as eluent; evaporation of the
solvent gave a light orange solid.
2-(4-(dodecyloxy)phenyl)-5-nitro-1H-benzimidazole, 1a: Yield: 2.87 g, 68
%. Anal. Calc. for C25H33N3O3: C, 70.89; H, 7.85; N, 9.92. Found: C, 70.84; H, 7.83;
1
N, 9.89. H NMR (300 MHz, DMSO-d6) δ (ppm): 13.34 (s, 1H), 8.36 (s, 1H), 8.10
(m, 3H), 7.67 (d, J = 8.7 Hz, 1H), 7.07 (d, J = 8.4 Hz, 2H), 3.99 (t, J = 6.0 Hz, 2H),
1.67-1.17 (m, 20H), 0.81 (t, J = 5.1 Hz, 3H).
2-(4-(hexyloxy)phenyl)-5-nitro-1H-benzimidazole, 1b: Yield: 2.44 g, 72 %.
Anal. Calc. for C19H21N3O3: C, 67.24; H, 6.24; N, 12.38. Found: C, 67.23; H, 6.22; N,
12.36. 1H NMR (300 MHz, DMSO-d6) δ (ppm): 13.46 (s, 1H), 8.38 (s, 1H), 8.11 (m,
3H), 7.69 (d, J = 8.7 Hz, 1H), 7.08 (d, J = 8.4 Hz, 2H), 3.99 (t, J = 6.0 Hz, 2H), 1.68-
1.18 (m, 8H), 0.803 (t, J = 5.1 Hz, 3H).
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2.3.2. General procedure for synthesis of precursor materials, 2-(4-(alkyloxy)phenyl)-
1H-benzimidazol-5-amine, 2(a-b): To a solution of 2-(4-(alkyloxy)phenyl)-5-nitro-
1H-benzimidazole (5 mmol in ethanol) was added SnCl2.2H2O (25 mmol); the
reaction mixture was refluxed for 4h until completion as indicated by TLC. The
resulting solution was allowed to cool to room temperature and neutralised with 10%
aqueous sodium hydroxide solution. The precipitate formed was filtered off, dried and
extracted with chloroform; evaporation of the solvent gave the final product which
was recrystallised from ethanol.
2-(4-(dodecyloxy)phenyl)-1H-benzimidazol-5-amine, 2a: Yield: 1.17 g,
60%. Anal. Calc. for C25H35N3O: C, 76.29; H, 8.96; N, 10.68. Found: C, 76.27; H,
1
8.95; N, 10.66. H NMR (300 MHz, CDCl3), δ (ppm): 7.95 (d, J = 8.7 Hz, 2H), 7.37
(d, J = 8.4 Hz , 1H), 6.85 (d, J = 8.4 Hz, 2H), 6.73 (s, 1H), 6.59 (d, J = 8.4 Hz, 1H)
3.92 (t, J = 6.3 Hz, 2H), 1.76-1.25 (m, 20H), 0.87 (t, J = 6.0 Hz, 3H).
2-(4-(hexyloxy)phenyl)-1H-benzimidazol-5-amine, 2b: Yield: 0.927 g, 60%.
Anal. Calc. for C19H23N3O: C, 73.76; H, 7.49; N, 13.58. Found: C, 73.75; H, 7.48; N,
13.57. 1H NMR (300 MHz, CDCl3), δ (ppm): 7.92 (d, J = 9 Hz, 2H), 7.41 (d, J = 8.4
Hz, 1H), 6.92 (d, J = 9 Hz, 2H), 6.79 (s, 1H), 6.63 (d, J = 8.1 Hz, 1H) 3.96 (t, J = 5.4
Hz, 2H), 1.768-1.25 (m, 8H), 0.90 (t, J = 5.4 Hz, 3H).
2.3.3. General method for synthesis of the Schiff bases, 2-(((2-(4-(alkyloxy)phenyl)-
1H-benzimidazol-5-yl)imino)methyl)-5-(alkylyloxy)phenol, 3(a-d): All the Schiff
bases were prepared by a general procedure by adding, drop wise, 1 mmol of 2-(4-
(alkyloxy)phenyl)-1H-benzimidazol-5-amine to a methanolic solution of 4-
alkyloxysalicylaldehyde (1 mmol) followed by addition of two drops of glacial acetic
acid to the mixture. The reaction mixture was refluxed for 4h, cooled to room
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temperature and vacuum filtered to get the product as yellow solid in each case, which
was purified by column chromatography on silica gel using n-hexane/chloroform (1:2,
v/v) as eluent.
2-(((2-(4-(dodecyloxy)phenyl)-1H-benzimidazol-5-yl)imino)methyl)-5-
(octyloxy)phenol, 3a, Yield: 0.44 g, 70%. Anal. Calc. for C40H55N3O3: C, 76.76; H,
1
8.86; N, 6.71. Found: C, 76.75; H, 8.86; N, 6.70. H NMR (300 MHz, CDCl3), δ
(ppm): 14.17 (br, 1H), 8.43 (s, 1H), 8.04 (d, J = 7.5 Hz, 2H), 7.58 (d, J = 5.4 Hz, 1H),
7.34 (s, 1H), 7.22 (m, 2H) 6.93(d, J =7.5 Hz, 2H), 6.47 (m, 2H), 3.92 (t, J = 6.0 Hz,
13
4H), 1.76-1.26 (m, 32H), 0.88 (t, J = 6.0 Hz, 6H); C NMR (75.45 MHz, CDCl3), δ
(ppm): 163.66, 161.30, 160.97, 159.83, 153.11, 148.34, 141.97, 133.38, 128.24,
121.89, 115.02, 112.92, 107.56, 105.82, 101.65, 68.26. ESI-MS: m/z 626.44 [(M+H)+,
calcd. 626.43]. IR (cm−1, KBr pellet): 3425, 1615, 1254.
2-(((2-(4-(dodecyloxy)phenyl)-1H-benzimidazol-5-yl)imino)methyl)-5-
(dodecyloxy)phenol, 3b: Yield: 0.46 g, 68%. Anal. Calc. for C44H63N3O3: C, 77.49;
1
H, 9.31; N, 6.16; Found: C, 77.47; H, 9.29; N, 6.15. H NMR (300 MHz, CDCl3), δ
(ppm): 14.05 (br, 1H), 8.52 (s, 1H), 8.00 (d, J = 8.7 Hz, 2H), 7.62 (d, J = 5.4 Hz, 1H),
7.61 (s, 1H), 7.26 (m, 2H) 6.94 (d, J = 9.0 Hz, 2H), 6.46 (m, 2H), 3.95 (t, J = 5.4 Hz,
13
4H), 1.78-1.26 (m, 40H), 0.90 (t, J = 6.0 Hz, 6H); C NMR (75.45 MHz, CDCl3), δ
(ppm): 163.66, 162.98, 160.37, 159.59, 152.95, 146.60, 142.77, 133.00, 128.06,
122.26, 114.42, 112.85, 109.07, 106.95, 101.32, 67.84. ESI-MS: m/z 682.50 [(M+H)+,
calcd, 682.49]. IR (cm−1, KBr pellet): 3432, 1615, 1254.
2-(((2-(4-(hexyloxy)phenyl)-1H-benzimidazol-5-yl)imino)methyl)-5-
(octyloxy)phenol, 3c: Yield: 0.38 g, 72%. Anal. Calc. for C34H43N3O3: C, 75.38; H,
1
8.00; N, 7.76. Found: C, 75.36; H, 7.98; N, 7.75. H NMR (300 MHz, CDCl3), δ
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(ppm): 14.09 (br, 1H), 8.49 (s, 1H), 7.98 (d, J = 8.7 Hz, 2H), 7.78 (d, J = 5.4 Hz, 1H),
7.61 (s, 1H), 7.26 (m, 2H) 6.94 (d, J = 8.7 Hz, 2H ), 6.46 (m, 2H), 3.97 (t, J = 5.4 Hz,
13
4H), 1.77-1.33 (m, 20H), 0.90 (t, J = 6.0 Hz, 6H); C NMR (75.45 MHz, CDCl3), δ
(ppm): 163.62, 162.94, 161.18, 160.12, 158.12, 147.52, 140.49, 133.45, 129.11,
117.11, 116.51, 115.05, 114.31, 112.99, 109.85, 107.56, 103.97, 68.23. ESI-MS: m/z
542.35 [(M+H)+, calcd, 542.34]. IR (cm−1, KBr pellet): 3435, 1615, 1254.
2-(((2-(4-(hexyloxy)phenyl)-1H-benzimidazol-5-yl)imino)methyl)-5-
(dodecyloxy)phenol, 3d: Yellow solid, yield: 0.41 g, 70% Anal. Calc. for
1
C38H51N3O3: C, 76.34; H, 8.60; N, 7.03. Found: C, 76.33; H, 8.58; N, 7.02. H-NMR
(300 MHz, CDCl3), δ (ppm): 14.09 (br, 1H), 8.49 (s, 1H), 8.01(d, J = 8.7 Hz, 2H),
7.61 (d, J = 8.1 Hz, 1H), 7.38 (s, 1H), 7.27 (m, 2H), 6.96 (d, J = 8.7 Hz, 2H) 6.46 (m,
2H), 3.97 (t, J = 5.7 Hz, 4H), 1.82-1.26 (m, 28H), 0.92 (t, J = 6.0 Hz, 6H); 13C NMR
(75.45 MHz, CDCl3), δ (ppm): 163.20, 162.25, 160.12, 158.77, 153.22, 143.10,
133.38, 128.16, 127.00, 122.72, 119.90, 115.05, 100.73, 100.54, 68.95; IR (cm−1, KBr
pellet): 3421, 1615 & 1145.
3. Results and Discussion
3.1. Chemical structure characterisation
The benzimidazole based Schiff-base compounds, 3(a-d) (Scheme 1), were
1
13
1
studied by IR, H & C NMR and mass spectral techniques. In the H NMR spectra
the two triplets (around δ, 0.90 and 3.98) correspond to –CH2CH3 and –OCH2–CH2
protons respectively), multiple peaks (around δ 6.45-8.00) imply aromatic protons,
and the singlets (at δ, 8.49-8.52) correspond to the imine (–CH=N) while the broad
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signal at 14.05-14.17 arises due to Ph–OH protons. The position and broadness of the
IR spectral peak centred at 3432 cm-1 may be inferred for ν(O-H)phenolic with
considerable amount of inter/intra molecular H-bonding to the imine group. The
strong absorption at 1615 cm-1 arises due to ν(C=N) of the azomethine moiety.
3.2. Mesomorphic properties
The mesogenic behaviour, phase transition temperatures and thermal stability
data of 3(a–d) were presented in Table 1 and in Figs. 1–3; all the compounds showed
fan-shaped texture implying smectic A (SmA1) mesophase; DSC studies implied
enantiotropic mesomorphism. All the DSC data are in concurrence with POM studies.
Further, TGA studies show that all the compounds are thermally stable up to 320 °C.
These compounds (core based) possess low isotropic points (193-200 °C) when
compared with previously reported compounds (end-group) 18a
.
XRD patterns (Fig. 4) of a representative compound (3d, un-oriented sample
filled in Lindemann capillary) at 190 °C show sharp reflection peak, due to smectic
layer spacing, in small angle region (d = 36.17 Å) and a diffuse wide-angle maximum
(d = 4.67 Å), probably owing to fluid-like correlation of the molecules in the layers.
The DFT calculated length (of the optimized structure, monomer) is given by, L =
40.07 Å, which is comparable with the interlayer distance (d = 36.17 Å) calculated
from the XRD patterns of the sharp reflection peak in the small angle region. The fact
that d  L may imply that the molecular unit in the layers exists as monomer. Based
upon the magnitudes of (d) and (L), SmA1, SmA2 and SmAd phases were defined as:
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SmA1 phase is a mono layer smectic phase with d  L where L is molecular length
calucalted from DFT and d is the inter layer distance caluculated from XRD; SmA2
phase is a bilayer smectic phase with d  2L and SmAd phase is a partially bilayer
smectic phase with a layer period incommensurate with the length of individual
molecules (L < d < 2L). In our work, since the inter layer distance is comparable to
the molecular length (L  d), based on the above definitions the present case may be
understood as SmA1 phase which is corroborated by XRD technique 24.
3.3. Photo-physical properties
The photo-physical properties of the compounds were measured by UV-Vis
and fluorescence spectroscopy in solution (spectra of the representative compound 3d
shown in Fig. 5 and the data in Table 2. The UV-Vis spectral peaks around 270-280
nm and 360 nm may be due to π-π* transitions. The fluorescence spectra (in 10 µM
chloroform solutions at excitation wavelength of 350 nm) show green emission
centred at 506-510 nm (with large stoke’s shift of 147-150 nm and quantum yield up
to 0.16-0.20, estimated by using quinine sulphate as a reference (Φ = 0.54 in 0.1N
H2SO4)). It was observed that the length of alkyl chain had no effect on the emission
spectra of these molecules in solution. The targeted compounds 3(a-d) may be found
useful in electroluminescent devices because of their green emission.
In order to better understand the relationship between the photo physical
properties and the electronic structures, quantum mechanical computations were
performed with TD-DFT/B3LYP/6-311G(d, p) Gaussian method to obtain the lowest
energy spatial conformation of the compound 3d in the ground state; the HOMO-
LUMO plot (Fig. 6) implies that the electron density in the HOMO is confined
mainly onto the benzimidazole and benzene moieties, while that of LUMO is
9

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distributed onto the benzene moiety (imine system). Further, the DFT generated
theoretical spectrum shows strong absorption at 362 nm which may be due to the
energetically more favourable π→π* transition arising from the highest energy
bonding pi-orbital (HOMO) to the lowest energy anti-bonding pi-orbital (LUMO).
The theoretical spectrum is in accordance with the experimentally obtained absorption
band of 360 nm. The theoretically calculated values of HOMO (-5.71 eV), LUMO (-
2.29 eV) are close to the experimental CV values (-5.22 and -2.67 eV) but the energy
gap value (3.42 eV) is much higher than the experimental values (2.56 eV from CV
data and 2.87 eV from UV-Vis data).
3.4. Cyclic Voltammetry
The cyclic voltammogram of 3d (Fig. 7) represents two single electron ‘onset
oxidation potentials’ at +0.98 and +1.57 V during the anodic cycle and one ‘onset
reduction potential’ at -1.57 V during the cathodic cycle. The first onset oxidation and
reduction potential values were used for calculating HOMO and LUMO energy levels
using the equations25 reported earlier, accordingly, the HOMO and LUMO energy
levels were found to be at -5.22 and -2.67 eV respectively, with the electrochemical
band gap of 2.56 eV. These compounds may be potentional candidates in the field of
optoelectronic devices, especially as OLEDs26-28. In analogy, the other compounds in
the series are expected to show a similar behaviour in CV experiments, because of
their structural similarities and the expected negligible influence of variable terminal
alkoxy chains on their electronic properties.
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4. Conclusion
A series of luminescent benzimidazole-based Schiff-base materials, 5-
(alkyloxy)-2-(((2-(4-(alkyloxy)phenyl)-1H-benzimidazol-5-yl)imino)methyl)phenols,
with different alkyl chains was synthesized and characterized by spectral methods. All
the compounds exhibit enantiotropic liquid crystalline behaviour (smectic A1 phase)
as revealed by POM, DSC and PXRD. TGA studies reveal thermal stability while
optical studies imply that the compounds are green emissive materials with good
quantum yields in solution.
Acknowledgements
RY gratefully acknowledges funding by the UGC, India in the form of
Research fellowship (No.18-12/2011(ii)EU-V). The authors gratefully acknowledge
the cooperation and help of Prof. Sandeep Kumar, Raman Research Institute,
Bangalore in arranging recording of PXRD patterns in his laboratory.
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O2N
NH2
NH2
O2N
N
O
KI,DMF
OR1
24h refulx
OR1
N
H
S
1
E
n
4
1a: R1 = C12H25
1b: R1 = C6H13
h
C
t
h
l
r
a
2
e
.
n
2
f
l
o
H
u
l
x
2
O
O
O
H2N
N
CnH2n+1Br
OR1
KHCO3, DMF
4h reflux
N
H
R2O
OH
HO
OH
2a: R1 = C12H25
2b: R1 = C6H13
2
NH
R2O
N
N
OR1
OH
3
3a: R1= C12H25, R2= C8H17
3b: R1= C12H25, R2= C12H25
3c: R1= C6H13, R2= C8H17
3d: R1= C6H13, R2= C12H25
Scheme 1. Synthesis of targeted compounds (3a-d)
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Fig. 1. Optical texture for the compound 3d in heating cycle:
fan shaped texture (SmA1 phase) at 190 °C.
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Fig. 2. DSC thermograms of 3(a-d): (i) Second heating cycle and (ii) Second cooling
cycle [with scan rate of 5 °C min-1]
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Fig. 3. TGA thermograms of compound 3a, 3b, 3c and 3d.
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Fig. 4. PXRD pattern for Smectic A1 phase of compound 3d at 190 °C
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Fig. 5. UV-Vis and fluorescence spectra of compound 3d; (a) UV-Vis spectrum and
(b) Fluorescence spectrum
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Fig. 6. Frontier molecular orbital of 3d optimized by DFT
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Fig. 7. Cyclic voltogram of compound 3d
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Table 1. Phase transitions and enthalpies
Compound
T °C [ΔH, kJ/mol]
Heating
Cooling
Cr 175.4 (30.3) SmA1
194.6 (2.2) I
Cr 146.6 (12.2) Cr' 170.9
(26.4) SmA1 193.1 (3.0) I
Cr 189.0 (36.6) SmA1
200.0 (3.5) I
I 193.8 (2.6) SmA1 159.2
(31.7) Cr
I 191.5 (2.6) SmA1 151.9
(21.2) Cr' 144.9 (10.57) Cr
I 197.9 (3.3) SmA1 164.2
(30.4) Cr
3a
3b
3c
3d
Cr 181.4 (34.2) SmA1
200.7 (3.7) I
I 197.7 (2.9) SmA1 156.1
(30.5) Cr
Cr = crystalline state, SmA1 = smectic A1 mesophase, I = istropic liquid.
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Table 2 UV-visible absorption and fluorescence emission properties of 3(a-d)
a
compound λabs (nm)
λemi (nm)
Stokes
shift (nm)
150
Quantum
yield (Φ)
0.19
ΔEg,opt
(eV)
2.87
360
360
359
360
510
508
506
508
3a
3b
3c
3d
148
0.20
2.87
147
0.16
2.87
148
0.18
2.87
a Calculated from absorption onset
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Graphical abstract
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Research Highlights
 Some benzimidazole-based SmA Schiff-bases with different alkyl chains
synthesized
 Intercalation of alkyl chains exists between the layers
 Fluorescence spectra show green emission with quantum yield up to 0.16-0.20
 Calculated values of HOMO and LUMO are close to experimental CV values
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