4
22
D. Sarkar et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 115 (2013) 421–425
antimicrobial, anticancer, anti-inflammatory, antivirus and anti-
convulsant [1–10]. Benzimidazole based ligands can be used to
prepare luminescent metal complexes and form supramolecular
architectures. Planar benzimidazole based ligands can engage in
p–p stacking interactions and have also shown LMCT charge trans-
fer properties in the complexes [11–14].
Proton transport in bio-molecules is of utmost importance for
bioenergetics [15,16]. This stimulates high research activity in
the field of proton-transfer dynamics in organic molecules
Table 1
Crystallographic data and refinement parameters for HL.
Empirical formula
Moiety formula
Formula weight
Crystal system
Space group
a (Å)
8
C30H30N O3
2(C15
14 4 2
H N O), H O
533.99
Triclinic
P ꢁ 1
8.590(5)
b (Å)
c (Å)
11.789(5)
14.670(5)
76.674(5)
86.065(5)
88.027(5)
1441.9(11)
2
1.268
0.086
293(2)
a
(°)
b (°)
(°)
[
17–19]. Aromatic weak acids and bases have found use as
proton-transfer fluorescent probes for surfactants and macromole-
cules [18,20,21]. Such probes have been utilized by several groups
to elucidate the effects of microenvironment on the equilibrium
and rate constants of the excited-state proton transfer in micelles,
liposomes, microemulsions and LB films [22–27]. Effects of the sur-
face potential on apparent pK and protolytic photodissociation rate
constants, correlation between rate constants and apparent pK in
micelles of different charge, and kinetic nonequivalence of pro-
ton-transfer probes in liposomes have been revealed [22,28–30].
The present work describes the synthesis and characterizations
of 2-[(1-Methyl-2-benzimidazolyl)azo]-p-cresol (HL), containing
phenolic-OH function and benzimidazole moiety. The chemical,
electronic structure and photophysical properties have been stud-
ied by spectroscopic analysis abetted with DFT and TDDFT
calculations.
c
3
V (Å )
Z
3
q
l
calcd (g cm )
(mm 1
ꢁ
)
T (K)
hkl range
F(000)
h range (°)
Reflns collected
Unique reflns (Rint
Observed data (I > 2
ꢁ10 to 10, ꢁ14 to 14, ꢁ17 to 17
580
1.78–25.99
13,930
5600 [0.0622]
2030
5600/0/372
0.0641, 0.1182
0.1978, 0.1467
1.092
)
r(I))
Data/restraints/parameters
a
b
R
R
1
, wR
, wR
2
(I > 2
(all data)
r(I))
1
2
c
GOF
Largest diff. peak/hole (e Å )
3
0.237/ꢁ0.187
P
P
a
R
1
¼
jðjF
o
j ꢁ jF
c
jÞj= jF
o
j.
ꢂ
ꢃ
ꢂ
ꢃ
ꢀ
ꢁ
ꢀ
ꢁ
1=2
h
ꢀ
ꢁ
i
P
2
P
2
b
w F ꢁ F2c
2
o
2
; w ¼ 1= r2
2
o
2
wR
2
¼
=
w F
F
þ ð0:0345PÞ
;
Experimental
o
ꢀ
ꢁ
2
o
2
where P ¼
F
þ 2Fc =3.
Material and methods
ꢂ
ꢃ
ꢀ
ꢁ
1=2
P
2
c
2
o
2
GOF ¼
w F ꢁ Fc
=ðn ꢁ pÞ
;
2
-Amino-4-methylphenol and benzimidazole were purchased
where n ¼ number of measured data and p ¼ number of parameters.
from Aldrich. All other organic chemicals and inorganic salts were
available from Sisco Research Lab, Mumbai, India and used without
further purification. Commercially available SRL silica gel (60–120
mesh) was used for column chromatography.
Anal. Calc. for C15
Found: C, 67.82; H, 5.32; N, 21.11%. IR data (KBr, cm ): 3373
14 4
H N O (HL): C, 67.65; H, 5.30; N, 21.04%.
Microanalytical data (C, H, N) were collected on Perkin–Elmer
ꢁ1
2
400 CHNS/O elemental analyzer. ESI mass spectra were recorded
1
t(OAH); 1620
3
t(C@N); 1419 t(N@N). H NMR data (CDCl ,
on a micromass Q-TOF mass spectrometer. Infrared spectra were
taken on a RX-1 Perkin Elmer spectrophotometer with samples
prepared as KBr pellets. Electronic spectral studies were performed
on a Perkin Elmer Lambda 25 spectrophotometer. NMR spectra
were recorded using a Bruker (AC) 300 MHz FTNMR spectrometer
ppm): 13.45 (1H, s), 7.84 (1H, s), 7.78 (1H, d, J = 7.5 Hz), 7.64
(
(
1H, d, J = 8.0 Hz), 7.37 (1H, d, J = 7.5 Hz), 7.23–7.33 (3H, m), 3.79
3H, s), 2.14 (3H, s).
in CDCl
pH System 361. Triply distilled water was used wherever
required.
3
. The pH of the solutions was measured on a Systronics
l
Crystallography
Details of crystal analysis, data collection and structure refine-
ment data for HL is given in Table 1. Crystal mounting was done
on glass fibers with epoxy cement. Single crystal data collections
were performed with an automated Bruker SMART APEX CCD dif-
Synthesis of 2-[(1-Methyl-2-benzimidazolyl)azo]-p-cresol (HL)
2
-Amino-4-methylphenol (4.0 g, 32.4 mmol) was dissolved in
5
mL conc. HCl and 10 mL distilled water and cooled to 0 °C.
fractometer using graphite monochromatized Mo K
(k = 0.71073 Å). Reflection data were recorded using the
technique. Unit cell parameters were determined from least-
a
radiation
Sodium nitrite (2.8 g, 42.12 mmol) was dissolved in minimum vol-
ume of water and cooled to 0 °C. The diazotized solution was added
dropwise with constant stirring to benzimidazole (4.0 g,
x
scan
squares refinement of setting angles with
1:78 6 h 6 25:99 . Out of 13,930 collected data 5600 with I > 2
h in the range
ꢂ
3
4.0 mmol) dissolved in aqueous solution of sodium carbonate
r
(
5.1 g, 48.0 mmol). The product was purified by column chroma-
(I) were used for structure solution. These were in the
tography using silica gel (60–120 mesh) and eluted by 20% (v/v)
ethyl acetate petroleum ether mixture. Yield was, 5.1 g 64%.
ꢁ10 6 h 6 10; ꢁ14 6 k 6 14; ꢁ17 6 l 6 17. The structures were
2
solved and refined by full-matrix least-squares techniques on F
3
.2 g (12.6 mmol) of the diazo-coupled product was taken and
using the SHELXS-97 program [32]. The absorption corrections
were done by the multi-scan technique. All data were corrected
for Lorentz and polarization effects, and the non-hydrogen atoms
were refined anisotropically. Hydrogen atoms were generated
using SHELXL-97 [32] and their positions calculated based on the
riding mode with thermal parameters equal to 1.2 times that of
associated C atoms, and participated in the calculation of the final
R-indices.
N-methylation was performed with MeI (1.8 g, 13.0 mmol) using
NaH (1.0 g, 25.1 mmol) as base in dry THF medium following the
reported methods [31]. The product was subjected to chromato-
graphic separation on a silica gel column (60–120 mesh). The de-
sired red band of HL was eluted with 10% (v/v) ethyl acetate
petroleum ether mixture. Evaporation of the solvent under reduced
pressure afforded pure compound. Yield was 2.1 g, 62%.
Sarkar, Deblina
