Lifetime time measurements, Kamlet-Taft and Catalan solvatochromism of some 2-aryl benzimidazole derivatives

Article abstract of DOI:10.1016/j.saa.2012.09.073

Some 2-aryl benzimidazole derivatives (1-6) have been prepared and characterized by different spectral techniques. Fluorescence lifetime of synthesized 2-aryl benzimidazole derivatives was calculated. Kamlet-Taft and Catalan solvatochromism of synthesized

Full text of DOI:10.1016/j.saa.2012.09.073

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 101 (2013) 156–161
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Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Lifetime time measurements, Kamlet–Taft and Catalan solvatochromism of some
2-aryl benzimidazole derivatives
⇑
J. Jayabharathi , K. Jayamoorthy, V. Thanikachalam
Department of Chemistry, Annamalai University, Annamalainagar 608 002, Tamilnadu, India
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
"
Fluorescence lifetime has been
discussed.
"
Kamlet–Taft and Catalan
solvatochromism have been
discussed.
"
1-(4-Methylbenzyl)-2-p-tolyl-1H-
benzo[d]imidazole is triclinic
crystals.
a r t i c l e i n f o
a b s t r a c t
Article history:
Some 2-aryl benzimidazole derivatives (1–6) have been prepared and characterized by different spectral
techniques. Fluorescence lifetime of synthesized 2-aryl benzimidazole derivatives was calculated. Kam-
let–Taft and Catalan solvatochromism of synthesized 2-aryl benzimidazole derivatives have been dis-
cussed. Crystal structure of 1-(4-methylbenzyl)-2-p-tolyl-1H-benzo[d]imidazole has been studied.
Ó 2012 Elsevier B.V. All rights reserved.
Received 27 August 2012
Received in revised form 20 September
2012
Accepted 22 September 2012
Available online 29 September 2012
Keywords:
Fluorescence lifetime
Kamlet–Taft
Catalan
2-Aryl benzimidazole
XRD
Introduction
the solvent nature [3]. In order to correlate the polarity influence
of the solvent on the absorption maxima and fluorescence emis-
Solvents influence the reaction rates, the equilibria and the
mechanisms for many compounds. Major interests to explain
many processes and applications in this field assume to under-
stand solute–solvent interactions and measure them quantita-
tively. The emission and absorption spectroscopy is the widely
used method for investigating the intermolecular interactions
and solvatochromism [1,2]. Usually, the electronic absorption band
characteristics are strongly sensitive to organic ligand and also to
sion wavelengths, we used the polarity parameters which ex-
pressed the best local interactions between the solute and the
solvent, i.e., the
p values from Kamlet et al. [4,5]. The p scale is
based on solvent-induced shifts of the longest wavelength
p
? p
absorption band of seven nitro aromatic indicators 1, in which this
electronic transition is connected with an intramolecular charge
transfer from the electron–donor part (–OMe, –NR2, –alkyl). The
values of their solvatochromic shifts are averaged to prevent the
inclusion of specific probe/solvent interactions. It is accepted that
p
values measure dispersive, inductive, and electrostatic probe/sol-
⇑
Corresponding author. Mobile: +91 9443940735.
E-mail address: jtchalam2005@yahoo.co.in (J. Jayabharathi).
vent interactions and correspond to a blend of polarisability and
1386-1425/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2012.09.073

J. Jayabharathi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 101 (2013) 156–161
157
dipolarity of the solvent. For non-aromatic and non-polyhalogenat-
ed aliphatic solvents correlates approximately linearly with the
kin Elmer Lambda 35) and corrected for background absorption
due to solvent. Photoluminescence (PL) spectra were recorded on
a (Perkin Elmer LS55) fluorescence spectrometer. NMR spectra
were recorded on Bruker 400 MHz NMR spectrometer. Mass spec-
tra were recorded on a Varian Saturn 2200 GCMS spectrometer.
The lifetime spectra have been recorded on Fluorocube-01-NL life-
time system provided with emission monochromator and diode
excitation.
p
permanent dipole moment of the solvent molecules. In this work,
we report the synthesis of six solvatochromic fluorescent probes,
as well as the influence of solvents of various polarities on the elec-
tronic absorption and fluorescence spectra and fluorescence
lifetime.
Experimental
General procedure for the synthesis of ligands
Spectral measurements
A mixture of corresponding aldehyde (2 mmol), o-phenylenedi-
amine (1 mmol) and ammonium acetate (2.5 mmol) has been re-
fluxed at 80 °C in ethanol. The reaction was monitored by TLC
The ultraviolet–visible (UV–vis) spectra of the benzimidazole
derivatives were measured in an UV–vis spectrophotometer (Per-
Table 1
Adjusted coefficients ((
t
x)0, ca, cb and cc) for the multilinear regression analysis of the absorption tab and fluorescence
t
fl wavenumbers and Stokes shift (
Dtss) of benzimidazole
derivatives 1, 2, 3, 4, 5 and 6 with the solvent polarity/polarizability, and the acid and base capacity using the Taft (pꢀ
,
a
and b) and the Catalan (SPPN, SA and SB) scales.
(tx)
(tx)
cmꢁ
(
pꢀ
)
c
cb
0
a
1
kab
kfl
(3.42 0.020) ꢂ 104
(2.89 0.065) ꢂ 104
(0.52 0.075) ꢂ 104
(2.67 3.56) ꢂ 103
(2.28 11.56) ꢂ 103
(2.67 13.38) ꢂ 103
ꢁ(7.37 11.37) ꢂ 103
ꢁ(8.49 36.94) ꢂ 103
(1.12 42.76) ꢂ 103
(5.24 8.86) ꢂ 103
(7.27 28.65) ꢂ 103
ꢁ(2.03 33.18) ꢂ 103
D
tss
=
=
tab
ꢁ
ꢁ
tfl
(tx)
(
tx
)
0 cmꢁ1
cSA
cSB
cNSPP
kab
kfl
(3.42 0.015) ꢂ 104
(2.95 0.045) ꢂ 104
(0.47 0.050) ꢂ 104
(9.60 5.30) ꢂ 103
ꢁ(45.62 15.43) ꢂ 103
(55.21 17.13) ꢂ 103
ꢁ(44.04 22.09) ꢂ 103
(167.80 64.26) ꢂ 103
ꢁ(211.84 21.37) ꢂ 103
(49.17 22.96) ꢂ 103
ꢁ(163.71 66.80) ꢂ 103
(212.98 24.19) ꢂ 103
D
tss
tab
tfl
2
(
kab
kfl
D
tx
)
(
tx
)
0 cmꢁ1
(
pꢀ
)
c
cb
a
(3.44 0.014) ꢂ 104
(2.92 0.027) ꢂ 104
(0.52 0.039) ꢂ 104
(3.78 2.52) ꢂ 103
ꢁ(1.27 4.89) ꢂ 103
(5.06 7.03) ꢂ 103
ꢁ(10.80 8.11) ꢂ 103
(0.32 15.75) ꢂ 103
ꢁ(11.13 22.61) ꢂ 103
(7.91 6.35) ꢂ 103
ꢁ(0.20 12.33) ꢂ 103
(8.17 17.71) ꢂ 103
tss
=
=
tab
ꢁ
ꢁ
tfl
0 cmꢁ1
cSA
cSB
cNSPP
(tx
)
(
tx
)
kab
kfl
D
(3.44 0.015) ꢂ 104
(2.93 0.019) ꢂ 104
(0.51 0.031) ꢂ 104
(4.88 5.01) ꢂ 103
ꢁ(19.57 6.50) ꢂ 103
(24.45 107.112) ꢂ 103
ꢁ(16.47 21.08) ꢂ 103
(69.12 27.34) ꢂ 103
ꢁ(85.61 45.05) ꢂ 103
(14.37 22.16) ꢂ 103
ꢁ(65.81 28.73) ꢂ 103
(80.18 47.34) ꢂ 103
tss
tab
tfl
3
4
5
6
(
kab
kfl
D
tx
)
(
tx
)
0 cmꢁ1
(
pꢀ
)
c
cb
a
(3.46 0.057) ꢂ 104
(2.78 0.088) ꢂ 104
(6.84 0.133) ꢂ 104
(4.37 10.24) ꢂ 103
(2.19 15.86) ꢂ 103
(2.18 23.89) ꢂ 103
ꢁ(14.86 32.97) ꢂ 103
ꢁ(16.00 51.07) ꢂ 103
(1.15 76.90) ꢂ 103
(16.98 25.82) ꢂ 103
(12.61 40.00) ꢂ 103
(4.37 60.02) ꢂ 103
tss
=
=
tab
ꢁ
ꢁ
tfl
0 cmꢁ1
cSA
cSB
cNSPP
(tx
)
(
tx
)
kab
kfl
D
(3.43 0.038) ꢂ 104
(2.85 0.061) ꢂ 104
(0.57 0.088) ꢂ 104
(33.63 13.17) ꢂ 103
ꢁ(59.07 20.99) ꢂ 103
(92.70 30.16) ꢂ 103
ꢁ(7.69 55.36) ꢂ 103
(218.91 88.24) ꢂ 103
ꢁ(29.59 126.86) ꢂ 103
(40.24 58.18) ꢂ 103
ꢁ(213.50 92.74) ꢂ 103
(253.75 133.32) ꢂ 103
tss
tab
tfl
(tx
)
(tx
)
0 cmꢁ1
(
pꢀ
)
c
cb
a
kab
kfl
D
(3.40 0.077) ꢂ 104
(2.86 0.021) ꢂ 104
(5.37 0.026) ꢂ 104
(3.59 1.37) ꢂ 103
ꢁ(1.65 3.89) ꢂ 103
(5.24 4.66) ꢂ 103
ꢁ(6.74 4.39) ꢂ 103
(2.07 12.43) ꢂ 103
ꢁ(8.81 14.89) ꢂ 103
(3.28 3.41) ꢂ 103
ꢁ(0.97 16.54) ꢂ 103
(3.75 21.84) ꢂ 103
tss
=
=
tab
ꢁ
tfl
0 cmꢁ1
cSA
cSB
cNSPP
(tx
)
(
tx
)
kab
kfl
D
(3.39 0.009) ꢂ 104
(2.89 0.026) ꢂ 104
(0.50 0.032) ꢂ 104
(9.62 3.50) ꢂ 103
ꢁ(17.40 9.64) ꢂ 103
(27.09 11.99) ꢂ 103
ꢁ(36.35 14.73) ꢂ 103
(64.18 40.53) ꢂ 103
ꢁ(101.33 50.42) ꢂ 103
(37.51 15.39) ꢂ 103
ꢁ(63.44 42.34) ꢂ 103
(101.25 52.67) ꢂ 103
tss
tab
–
tfl
(tx
)
(tx
)
0 cmꢁ1
(p
ꢀ)
c
cb
a
kab
kfl
D
(3.40 0.014) ꢂ 104
(2.86 0.037) ꢂ 104
(5.41 0.049) ꢂ 104
ꢁ(0.36 2.58) ꢂ 103
(0.02 6.68) ꢂ 103
ꢁ(0.41 8.22) ꢂ 103
(3.26 8.28) ꢂ 103
ꢁ(1.59 21.38) ꢂ 103
(4.93 28.24) ꢂ 103
ꢁ(6.71 6.40) ꢂ 103
(0.97 16.54) ꢂ 103
ꢁ(3.75 21.84) ꢂ 103
tss
=
=
tab
ꢁ
ꢁ
tfl
0 cmꢁ1
cSA
cSB
cNSPP
(tx
)
(
tx
)
kab
kfl
D
(3.39 0.009) ꢂ 104
(2.89 0.026) ꢂ 104
(0.50 0.032) ꢂ 104
(9.62 3.50) ꢂ 103
ꢁ(17.40 9.64) ꢂ 103
(27.09 11.99) ꢂ 103
ꢁ(36.35 14.73) ꢂ 103
(64.18 40.53) ꢂ 103
ꢁ(101.33 50.42) ꢂ 103
(37.51 15.39) ꢂ 103
ꢁ(63.44 42.34) ꢂ 103
(101.25 52.67) ꢂ 103
tss
tab
tfl
(tx
)
(tx
)
0 cmꢁ1
(
pꢀ
)
c
cb
a
kab
kfl
D
(0.34 0.015) ꢂ 104
(2.82 0.039) ꢂ 104
(0.55 0.048) ꢂ 104
(0.71 2.70) ꢂ 103
ꢁ(0.19 6.98) ꢂ 103
(0.90 8.64) ꢂ 103
ꢁ(0.13 8.65) ꢂ 103
(4.80 22.35) ꢂ 103
ꢁ(4.93 27.67) ꢂ 103
ꢁ(0.13 6.69) ꢂ 103
ꢁ(4.84 17.29) ꢂ 103
(4.71 21.41) ꢂ 103
tss
=
=
tab
ꢁ
ꢁ
tfl
0 cmꢁ1
cSA
cSB
cNSPP
(tx
)
(
tx
)
kab
kfl
D
(3.38 0.010) ꢂ 104
(2.89 0.025) ꢂ 104
(0.48 0.028) ꢂ 104
(6.21 3.78) ꢂ 103
ꢁ(27.95 9.18) ꢂ 103
(34.17 10.30) ꢂ 103
ꢁ(21.18 15.92) ꢂ 103
(117.58 38.63) ꢂ 103
ꢁ(138.76 43.32) ꢂ 103
(21.20 16.62) ꢂ 103
ꢁ(119.49 40.35) ꢂ 103
(140.70 45.25) ꢂ 103
tss
tab
tfl

158
J. Jayabharathi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 101 (2013) 156–161
2-(Naphthalen-1-yl)-1-((naphthalen-1-yl)methyl)-1H-
benzo[d]imidazole (3)
Yield: 60%. mp = 130 °C, Anal. calcd. for C28H20N2: C, 87.47; H,
5.24; N, 7.29. Found: C, 87.67; H, 5.10; N, 7.23. 1H NMR
(400 MHz, CDCl3): d 5.75 (s, 2H), 7.24–7.32 (m, 4H), 7.37–7.41 (t,
3H), 7.44–7.47 (m, 1H) 7.50–7.57 (m, 4H), 7.75–7.76 (t, 2H),
7.88–7.94 (m, 4H), 7.98–8.01 (t, 2H). 13C (400 MHz, CDCl3): d
46.12 (–CH2 carbon), 110.78, 120.25, 122.06, 122.68, 123.15,
123.61, 124.85, 124.91, 125.43, 125.58, 126.07, 126.33, 126.42,
126.50, 127.42, 127.78, 128.12, 128.22, 128.36, 128.97, 130.18,
130.28, 131.21, 133.59, 133.67, 135.42, 143.38, 151.36, 153.17
(Aromatic carbons). MS: m/e 384.1, calcd. 385.16 [M+1].
Fig. 1. Stabilization of solvated isomers of 4.
1-(2-Hydroxy-5-bromobenzyl)-2-(2-hydroxy-5-bromophenyl)-1H-
benzo[d]imidazole (4)
Yield: 40%. mp = 141 °C, Anal. calcd. for C20H14Br2N2O2: C,
50.66; H, 2.98; Br, 33.70 N, 5.91; O, 6.75. Found: C, 50.73; H,
2.99; Br, 33.60 N, 5.92; O, 6.76. 1H NMR (400 MHz, CDCl3): d 5.40
(s, 2H), 7.00–7.06 (m, 2H), 7.10–7.15 (t, 3H), 7.18–7.20 (d, 1H)
7.22–7.26 (m, 1H), 7.28–7.32 (m, 1H), 7.55–7.57 (m, 1H), 7.77–
7.80 (s, 1H), 12.97 (s, 2H). 13C (400 MHz, CDCl3): d 47.49 (–CH2 car-
bon), 109.31, 114.93, 115.23, 115.71, 118.00, 121.92, 122.30,
125.76, 126.93, 127.07, 130.59, 131.02, 152.09, 152.99, 160.27,
160.36, 162.58, 163.48, 164.67 (Aromatic carbons). MS: m/e
474.0, calcd. 474.94 [M+1].
and purified by column chromatography using petroleum ether:-
ethyl acetate (9:1) as the eluent.
1-Benzyl-2-phenyl-1H-benzo[d]imidazole (1)
Yield: 50%. mp = 124 °C, Anal. calcd. for C20H16N2: C, 84.48; H,
5.67; N, 9.85. Found: C, 84.12; H, 5.79; N, 10.09. 1H NMR
(400 MHz, CDCl3): d 5.43 (S, 2H), 7.13 (d, 2H), 7.23–7.28 (m, 2H),
7.32–7.37 (m, 4H), 7.45–7.50 (m, 3H), 7.71–7.72 (t, 2H), 7.90–
7.91 (S, 1H). 13C (400 MHz, CDCl3):
d 48.39 (–CH2 carbon),
1-(4-Methyl benzyl)-2-p-tolyl-1H-benzo[d]imidazole (5)
110.53, 120.02, 122.68, 123.04, 125.99, 127.78, 128.76, 129.06,
129.28, 129.91, 130.14, 136.10, 136.43, 143.24, 154.19 (aromatic
carbons). MS: m/e 284.3, calcd. 285.13 [M+1].
Yield: 50%. mp = 114 °C, Anal. calcd. for C22H20N2: C, 84.58; H,
6.45; N, 8.97. Found: C, 84.88; H, 6.55; N, 8.57. 1H NMR
(400 MHz, CDCl3): d 2.32 (s, 3H), 2.39 (s, 3H), 5.39 (s, 2H), 6.97–
6.99 (d. 2H), 7.11–7.13 (d, 2H), 7.17–7.20 (t, 2H), 7.23–7.30 (m,
4H), 7.57–7.59 (d, 2H), 7.84–7.86 (d, 1H). 13C (400 MHz, CDCl3): d
21.47, 21.13 (methyl carbons), 47.71 (–CH2 carbon), 110.54,
119.86, 122.57, 122.86. 125.93, 127.23, 129.20, 129.47, 123.73,
133.50, 136.15, 137.46, 140.05, 143.23, 154.38 (Aromatic carbons).
MS: m/e 312.1, calcd. 313.16 [M+1].
1-(4-Fluorobenzyl)-2-(4-fluorophenyl)-1H-benzo[d]imidazole (2)
Yield: 55%. mp = 84 °C, Anal. calcd. for C20H14F2N2: C, 74.98; H,
4.41; F, 11.86; N, 8.75. Found: C, 74.49; H, 4.51; F, 11.95; N, 9.05. 1H
NMR (400 MHz, CDCl3): d 5.41 (s, 2H), 7.02–7.08 (m, 4H), 7.15–7.18
(t, 3H), 7.22–7.23 (d, 1H) 7.26–7.29 (m, 1H), 7.33–7.36 (m, 1H),
7.65–7.67 (m, 2H), 7.87–7.88 (s, 1H). 13C (400 MHz, CDCl3): d
47.71 (–CH2 carbon), 110.33, 115.93, 116.03, 116.21, 120.07,
122.92, 123.30, 126.16, 126.19, 127.60, 127.63, 127.67, 131.19,
131.25, 131.93, 131.95, 135.89, 143.06, 153.08, 161.31, 162.78,
163.28, 164.77 (Aromatic carbons). MS: m/e 320.1, calcd. 321.11
[M+1].
1-(4-Methoxybenzyl)-2-(4-methoxyphenyl)-1H-benzo[d]imidazole
(6)
Yield: 60%. mp = 162 °C, Anal. calcd. for C22H20N2O2: C, 76.72; H,
5.85; N, 8.14; O, 9.29. Found: C, 77.02; H, 5.29; N, 8.33; O, 9.36. 1H
NMR (400 MHz, CDCl3): d 3.78 (s, 3H), 3.85 (s, 3H), 5.38 (s, 2H),
6.84–6.86 (d, 2H), 6.96–6.98 (d, 2H), 7.02–7.04 (d, 2H), 7.21–7.22
Fig. 2. ORTEP diagram of 1-(4-methylbenzyl)-2-p-tolyl-1H-benzo[d]imidazole with 30% probability.

J. Jayabharathi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 101 (2013) 156–161
159
Table 2
Selected bond lengths (Å), bond angles (°) and torsional angles (°) of 5.
N1A–C2A
N1A–C8A
N1A–C1A
N3A–C2A
N3A–C9A
N1B–C2B
N1B–C8B
N1B–C1B
N3B–C2B
N3B–C9B
C1A–C11A
C2A–C21A
C7A–C8A
C8A–C9A
C14A–C17A
C24A–C27A
1.3782(1.4972)
1.3833(1.4584)
1.4537(1.4700)
1.3163(1.3671)
1.3881(1.4606)
1.3795(1.4972)
1.3863(1.4584)
1.4550(1.4700)
1.3174(1.3671)
1.3866(1.4606)
1.5135(1.5400)
1.4729(1.5400)
1.3921(1.3862)
1.3999(1.4763)
1.5089(1.5400)
1.5078(1.5400)
C2A–N1A–C8A
C2A–N1A–C1A
C8A–N1A–C1A
C2A–N3A–C9A
C2B–N1B–C8B
C2B–N1B–C1B
C8B–N1B–C1B
C2B–N3B–C9B
N1A–C1A–C11A
N3A–C2A–N1A
N3A–C2A–C21A
N1A–C2A–C21A
N1A–C8A–C3A
N1A–C8A–C9A
N3A–C9A–C4A
N3A–C9A–C8A
106.23(101.69)
128.33(113.71)
124.79(113.33)
104.77(105.49)
106.27(101.69)
129.32(113.71)
123.98(113.33)
105.12(105.41)
115.07(109.47)
113.25(113.53)
123.44(123.23)
123.30(123.24)
131.76(130.72)
103.49(108.25)
129.91(130.69)
110.26(108.25)
C2A–N1A–C1A–C11A
C8A–N1A–C1A–C11A
C9A–N3A–C2A–N1A
C9A–N3A–C2A–C21A
C8A–N1A–C2A–N3A
C1A–N1A–C2A–N3A
C8A–N1A–C2A–C21A
C1A–N1A–C2A–C21A
C9A–C4A–C5A–C6A
C2A–N1A–C8A–C7A
C1A–N1A–C8A–C7A
C2A–N1A–C8A–C9A
C1A–N1A–C8A–C9A
C6A–C7A–C8A–N1A
C2B–N1B–C1B–C11B
C8B–N1B–C1B–C11B
C9B–N3B–C2B–N1B
C9B–N3B–C2B–C21B
C8B–N1B–C2B–N3B
C1B–N1B–C2B–N3B
C8B–N1B–C2B–C21B
C1B–N1B–C2B–C21B
C9B–C4B–C5B–C6B
C2B–N1B–C8B–C7B
C1B–N1B–C8B–C7B
C2B–N1B–C8B–C9B
C1B–N1B–C8B–C9B
C6B–C7B–C8B–N1B
109.45(ꢁ177.75)
ꢁ81.12(ꢁ62.25)
ꢁ0.02(ꢁ13.69)
ꢁ178.71(165.91)
0.59(17.54)
171.55(139.72)
179.28(ꢁ162.06)
ꢁ9.75(ꢁ39.88)
0.1(ꢁ0.1581)
178.45(166.15)
7.08(43.71)
ꢁ0.88(13.70)
ꢁ172.25(136.15)
179.75(176.19)
108.10(ꢁ177.75)
ꢁ79.66(ꢁ62.25)
ꢁ0.86(ꢁ13.69)
177.35(165.91)
1.24(17.54)
173.85(139.72)
ꢁ176.90(162.06)
ꢁ4.29(ꢁ39.88)
0.25(ꢁ0.1581)
176.39(166.15)
3.28(43.71)
ꢁ1.05(ꢁ13.70)
ꢁ174.15(ꢁ136.15)
177.76(176.19)
Values within the parenthesis corresponds to theoretical values.
Fig. 3a. Fluorescence decay of 1 and 2.
(d, 2H), 7.24–7.31 (m, 2H), 7.62–7.64 (d,2H), 7.83–7.85 (s, 1H). 13
C
Catalan et al. [7] suggest the SPPN, SA and SB scales to described
the polarity/polarizability, the acidity and basicity of the solvents
as shown as
(400 MHz, CDCl3): d 47.91 (–CH2 carbon), 55.32, 55.40 (methoxy
carbons), 110.43, 114.20, 114.44, 119.73, 122.47, 122.54, 122.75,
127.23, 128.51, 130.73, 136.11, 143.19, 154.15, 159.12, 160.91
(Aromatic carbons). MS: m/e 344.2, calcd. 345.15 [M+1].
y ¼ y0 þ aSASA þ bSBSB þ cSPPSPP ðCatalanÞ
ð2Þ
The correlation of the absorption and fluorescence wave num-
bers obtained by the multi-component linear regression employing
the Taft and Catalan solvent parameters with the experimental val-
ues given in Table 1. The polarity/polarizability of the solvent coef-
Results and discussion
Taft and Catalan solvatochromism
ficient [C ꢀ or CNSPP] value correlating the solvatochromic shifts with
p
Solvent properties mainly affect the photophysical properties of
compounds are polarity, H-bond donor capacity and electron do-
nor ability. Different scales for such parameters can be found in
the solvent polarity. The coefficient controlling the H-donor capac-
ity or acidity of the solvent [C or CSA], has a negative value for 1–6.
a
This is interpreted in terms of the stabilization of the resonance
structures of the chromophore (Fig. 1). Resonance structure ‘‘II’’
has the negative charge located at the carbon atom and it will be
stabilized in acidic solvents. Because these resonance structures
is predominant in the S1 state and the stabilization of the S1 state
with the solvent acidity would be more important than that of
the literature, Kamlet and Taft [6] propose the pꢀ
,
a
and b scales,
shown as
ꢀ
ꢀ
y ¼ y0 þ aa þ bbb þ cp p ðKamlet—TaftÞ
a
ð1Þ

160
J. Jayabharathi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 101 (2013) 156–161
Fig. 3b. Fluorescence decay of 3 and 4.
Fig. 3c. Fluorescence decay of 5 and 6.
Table 3
Fluorescence decay time constants
of two exponentials, their associated pre-exponential factors a1
s
1 calculated assuming a bi-exponential decay and corresponding v2; decay time constants
a2 parameters of 1–6.
s1 and s2 assuming the observed decay to be a sum
,
Compound
1
Excitation (nm)
360
s1 (ns)
s2 (ns)
a1
a2
v2
1.3393
2.0531
ꢁ3.283 ꢂ 10ꢁ2
(ꢁ49.42)
6.4767 ꢂ 10ꢁ2
ꢁ149.42
1.1162
2
3
4
5
6
354
390
357
351
363
1.3038
1.1593
8.867
1.41
2.0661
1.7605
4.2237
1.6407
1.3439
ꢁ4.3942 ꢂ 10ꢁ2
(ꢁ60.44)
7.3611 ꢂ 10ꢁ2
ꢁ160.44
1.1825
0.9946
1.1067
1.0251
1.1282
ꢁ6.3082 ꢂ 10ꢁ2
(ꢁ85.11)
9.0349 ꢂ 10ꢁ2
ꢁ185.11
ꢁ1.2879 ꢂ 10ꢁ2
(ꢁ8.18)
3.5767 ꢂ 10ꢁ2
ꢁ108.18
ꢁ9.5886 ꢂ 10ꢁ2
(ꢁ170.48)
0.1307
ꢁ270.48
1.2824
ꢁ03039 ꢂ 10ꢁ2
(ꢁ564.52)
0.3414 ꢂ 10ꢁ2
ꢁ664.52
Values within the parenthesis corresponds to relative amplitude.
the S0 state. Consequently, the energy gap between the S1 and S0
states decreases and the absorption and fluorescence wavelengths
shift to longer wavelength with increasing solvent acidity.
the benzene rings of the 4-methylbenzyl and the p-tolyl groups
are 76.64 (3)° and 46.87 (4)°, respectively, in molecule A. The cor-
responding values in molecule B are 86.31 (2)° and 39.14 (4)°. The
dihedral angle between the planes of the two benzene rings is
73.73 (3)° and 80.69 (4)° in molecules A and B, respectively. Opti-
mization of 5 have been performed by DFT at B3LYP/6-31G(d,p)
using Gaussian-03. All these XRD data are in good agreement with
the theoretical values (Table 2). However, from the theoretical val-
ues it can be found that most of the optimized bond lengths, bond
angles and dihedral angles are slightly higher than that of XRD val-
ues. These deviations can be attributed to the fact that the theoret-
Crystal structure
Crystalline benzimidazole derivative (5) [8] are triclinic crystals.
It crystallizes in the space group P1ꢀ. The cell dimensions are
a = 9.6610 Å, b = 10.2900 Å, c = 17.7271 Å. ORTEP diagram of (5)
(Fig. 2) shows that the benzimidazole ring is essentially planar.
The dihedral angles between the planes of the benzimidazole and

J. Jayabharathi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 101 (2013) 156–161
161
ical calculations were aimed at the isolated molecule in the gas-
eous phase and the XRD results were aimed at the molecule in
the solid state.
to lower energies with the increasing acidity of the solvent. The
analysis of the fluorescence decay gave a poor fit with a mono-
exponential decay. Fitting our decay curve to a sum of two expo-
nents and considerably improved the v2 value.
Fluorescence lifetime measurements
Acknowledgments
The experimental decay curves were first fitted to
exponentials:
a
bi
One of the authors Dr. J. Jayabharathi is thankful to DST [No. SR/
S1/IC-73/2010], UGC (F. No. 36-21/2008 (SR)) and DRDO (NRB-213/
MAT/10-11) for providing funds to this research study. Mr. K. Jaya-
moorthy is thankful to DST [No. SR/S1/IC-73/2010] for providing a
fellowship.
fðtÞ ¼
a1 expðꢁt=s1Þ þ
a2 expðꢁt=s2Þ þ
a
3 expðꢁt=s3
Þ
ð3Þ
where a1 and s1 are respectively, the pre-exponential factor and
lifetime of the various excited states involved.
X
2
v2
¼
ðactual deviation=expected deviationÞ
ð4Þ
Appendix A. Supplementary material
n
This model is based on the assumption that one, two or three
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.saa.2012.09.073.
fluorescent substances are present in the solution. If Ni molecules
are excited at zero time, the fluorescence quantum yield of the ith
component ai is proportional to the ratio aisi/N [9] and the ai fac-
tors are related to the absorbances of the various substances at the
excitation wavelength. The fluorescence decay curves (Figs. 3a, 3b
and 3c) of all benzimidazole derivatives were recorded in ethanol.
Laser excitation was set at 270 nm and the fluorescence signal was
measured at emission wavelength of individual compound. The
fluorescence decay was fitted with a biexponential function decay
time are provided in the Table 3.
References
[1] J. Jayabharathi, V. Thanikachalam, K. Jayamoorthy, Spectrochim. Acta Part A 89
(2012) 168–176.
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Acta A 95 (2012) 446–451.
[3] V. Pop, D. Dorohoi, V. Holban, Spectrochim. Acta A 50 (1994) 2281–2289.
[4] M.J. Kamlet, J.-L.M. Abboud, R.W. Taft, J. Am. Chem. Soc. 99 (1977) 6027–6038.
[5] M.H. Abraham, G.J. Buist, P.L. Grellier, R.A. McGill, D.V. Prior, S. Oliver, E. Turner,
J.J. Morris, P.J. Taylor, P. Nicolet, P.-C. Maria, J.-F. Gal, J.-L.M. Abboud, R.M.
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552.
[6] M.J. Kamlet, R.W. Taft, J. Am. Chem. Soc. 98 (1976) 377–383.
[7] J. Catalan, V. Lopez, P. Perez, J. Fluoresc. 6 (1996) 15–22.
[8] S. Rosepriya, A. Thiruvalluvar, K. Jayamoorthy, J. Jayabharathi, Antony Linden,
Acta Cryst. E67 (2011) o3519.
Conclusions
1-(4-Methylbenzyl)-2-p-tolyl-1H-benzo[d]imidazole is triclinic
crystal. All these XRD data are in good agreement with the theoret-
[9] A. Grinvald, I.Z. Steinberg, Anal. Biochem. 59 (1974) 583–598.
ical values. The acidity of the solvent, C or CSA has a negative va-
a
lue, suggesting that the absorption and fluorescence bands shifted