Synthesis, crystal structure and spectroscopic study of novel benzimidazoles and benzimidazo[1,2-a]quinolines as potential chemosensors for different cations

Article abstract of DOI:10.1016/j.dyepig.2012.05.024

In this manuscript the synthesis, crystal structure, spectroscopic characterization and titration with several metal chloride salts of novel E-3-phenyl-2-(1-phenylbenzimidazol-2-yl)acrylonitriles and 5- phenylbenzimidazo[1,2-a]quinoline derivatives are described. All compounds were characterized by means of ¹H, ¹³C NMR, MS, UV/Vis and fluorescence spectroscopy. Crystal and molecular structures of E-3-(4-nitrophenyl)-2-(1-phenyl-benzimidazol-2-yl)acrylonitrile and 5-phenylbenzimidazo[1,2-a]quinoline-6-carbonitrile were determined by single-crystal X-ray diffractometry. The molecular assembly is characterized by the C-H···O and C-H···N intermolecular hydrogen bonds in E-3-(4-nitrophenyl)-2-(1-phenyl-benzimidazol-2-yl) acrylonitrile and 5-phenylbenzimidazo[1,2-a]quinoline-6-carbonitrile, respectively. Spectroscopic characterization of the prepared compounds was performed by using UV/Vis and fluorescence spectroscopy in ethanol. In order to determine a selectivity towards a variety of cations, to explore their use as potential chemosensors, the amino substituted 5-phenylbenzimidazo[1,2-a] quinoline-6-carbonitrile was chosen for a titration with metal chloride salts using fluorescence spectroscopy. The fluorescence intensity significantly increased upon addition of Zn²⁺ and Ag⁺ cations while decreased by addition of Mn²⁺, Co²⁺, Cu²⁺, Hg²⁺, Li⁺ and Fe³⁺ cations.

Full text of DOI:10.1016/j.dyepig.2012.05.024

Dyes and Pigments 95 (2012) 644e656
Contents lists available at SciVerse ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Synthesis, crystal structure and spectroscopic study of novel benzimidazoles and
benzimidazo[1,2-a]quinolines as potential chemosensors for different cations
,
a
a
a
ꢀ b
Marijana Hranjec a , Ema Horak , Martina Tireli , Gordana Pavlovic , Grace Karminski-Zamola
*
a
ꢀ
Department of Organic Chemistry, Faculty of Chemical Engineering and Technology, University of Zagreb, Marulicev trg 19, P. O. Box 177, HR-10000 Zagreb, Croatia
Faculty of Textile Technology, Department of Applied Chemistry, University of Zagreb, Prilaz baruna Filipovica 28a, HR-10000 Zagreb, Croatia
b
ꢀ
a r t i c l e i n f o
a b s t r a c t
Article history:
In this manuscript the synthesis, crystal structure, spectroscopic characterization and titration with
several metal chloride salts of novel E-3-phenyl-2-(1-phenylbenzimidazol-2-yl)acrylonitriles and
5-phenylbenzimidazo[1,2-a]quinoline derivatives are described. All compounds were characterized by
means of 1H, 13C NMR, MS, UV/Vis and fluorescence spectroscopy.
Crystal and molecular structures of E-3-(4-nitrophenyl)-2-(1-phenyl-benzimidazol-2-yl)acrylonitrile
and 5-phenylbenzimidazo[1,2-a]quinoline-6-carbonitrile were determined by single-crystal X-ray
diffractometry. The molecular assembly is characterized by the CeH$$$O and CeH$$$N intermolecular
hydrogen bonds in E-3-(4-nitrophenyl)-2-(1-phenyl-benzimidazol-2-yl)acrylonitrile and 5-phenylbenzimidazo
[1,2-a]quinoline-6-carbonitrile, respectively.
Spectroscopic characterization of the prepared compounds was performed by using UV/Vis and
fluorescence spectroscopy in ethanol. In order to determine a selectivity towards a variety of cations, to
explore their use as potential chemosensors, the amino substituted 5-phenylbenzimidazo[1,2-a]quino-
line-6-carbonitrile was chosen for a titration with metal chloride salts using fluorescence spectroscopy.
The fluorescence intensity significantly increased upon addition of Zn2þ and Agþ cations while decreased
by addition of Mn2þ, Co2þ, Cu2þ, Hg2þ, Liþ and Fe3þ cations.
Received 23 March 2012
Received in revised form
22 May 2012
Accepted 23 May 2012
Available online 13 July 2012
Keywords:
Benzimidazoles
Benzimidazo[1,2-a]quinolines
Crystal structure
UV/Vis and fluorescence spectroscopy
Chemosensors
Zinc
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
a recognition site linked to a fluorophore as the signal source which
translates the recognition event into the fluorescence signal [9].
The permanent and growing interest in recent years for the
synthesis of sensitive and selective chemosensors that are capable
of assaying cations or anions in solution is a direct consequence of
their great importance in the areas of biological, medicinal and
environmental science [1e3]. Heterocyclic sensors with excellent
spectroscopic properties, capable of detecting versatile ions with
different spectral responses, have been one of the most extensively
studied classes of organic compounds [4,5]. Fluorescence spec-
troscopy as a very sensitive, efficient and economic method has
been widely used for a quantification of biologically important ions
[6]. Fluorescent sensors have many advantages including high
sensitivity, easy availability and possible multiple modes of detec-
tion like fluorescence quenching and enhancing or fluorescence
lifetime [7,8]. Usually, a typical fluorescent chemosensor contains
The benzimidazole unit is one of the most important key
building blocks for a variety of compounds which have crucial roles
in the functions of biologically important molecules [10,11]. Mostly,
benzimidazole derivatives display diverse biological activities such
as antibacterial [12,13], antitumor [14e16], antifungal [17] or anti-
viral [18] and furthermore due to the structural similarity of
benzimidazole nuclei with naturally occurring compounds such as
purine, they can easily interact with biomolecules of the living
systems [10]. Besides, benzimidazoles have found applications in
several other areas such as optical lasers and polymer dyes in
optoelectronics [19,20], fluorescent probes for detection of bio-
logical important molecules as DNA, RNA or proteins in biomedical
diagnostics [21,22], efficient and selective chemosensors for cation
or anion detection [23,24] and as efficient ligands in metal-
lochemistry [25]. Benzannulated benzimidazole analogues such as
benzimidazo[1,2-a]quinolines, are highly conjugated planar chro-
mophores and very important fluorophores with excellent spec-
troscopic characteristics including high fluorescence intensity
which is very important in their possible application as fluorescent
probes in homogeneous assays of biological molecules [26,27].
* Corresponding author. Department of Organic Chemistry, Faculty of Chemical
ꢀ
Engineering and Technology, University of Zagreb, Marulicev trg 20, P.O. Box 177,
HR-10000 Zagreb, Croatia. Tel.: þ385 14597245; fax: þ385 14597250.
E-mail address: mhranjec@fkit.hr (M. Hranjec).
0143-7208/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.dyepig.2012.05.024

M. Hranjec et al. / Dyes and Pigments 95 (2012) 644e656
645
Additionally, fluorescence can be significantly altered by additional
substituents placed on different positions of the planar chromo-
phore. We have recently reported on the synthesis of amino
substituted benzimidazo[1,2-a]quinolines which significantly
enhanced fluorescence emission intensity upon addition of calf
thymus DNA and thus offer the potential applications as a DNA-
specific fluorescent probes [28].
Prompted by the aforementioned considerations and as a part of
our continuing research on the synthesis and spectroscopic char-
acterization of benzimidazole derivatives, we set out to explore and
synthesize novel acyclic E-3-phenyl-2-(1-phenylbenzimidazol-2-
yl)acrylonitriles and 5-phenyl-benzimidazo[1,2-a]quinolines. The
prepared compounds were characterized by means of UV/Vis and
fluorescence spectroscopy while amino substituted 5-phenyl-ben-
zimidazo[1,2-a]quinoline 5 was investigated as a potential che-
mosensor, by fluorescence spectroscopy in the presence of several
metal chloride salts to determine its selectivity towards versatile
cations. Compound 5 showed the highest enhancement of fluo-
rescence intensity in the presence of Zn2þ cations and almost the
total quenching of fluorescence intensity in the presence of Cu2þ
cations.
for 3e3.5 h. After reaction mixture was cooled to the room
temperature, the crude product was filtered off and recrystallized
from ethanol.
2.2.2.1. E-3-phenyl-2-(1-phenylbenzimidazol-2-yl)acrylonitrile
3a. Compound 3a was prepared from 1 (1.00 g, 4.33 mmol) and
benzaldehyde 2a (0.46 g, 4.33 mmol) in absolute ethanol (20 mL)
and piperidine (0.15 mL) after heating under reflux for 3 h and
recrystallization from ethanol to yield 0.90 g (65%) of yellow crys-
tals; m.p.136e138 ꢀC; 1H NMR (300 MHz, DMSO-d6):
d
¼ 7.91 (s,1H,
Harom.), 7.88e7.38 (m, 2H, Harom), 7.81 (d, 1H, J ¼ 7.68 Hz, Harom),
7.69e7.65 (m, 3H, Harom), 7.64 (d, 2H, J ¼ 1.84 Hz, Harom), 7.56e7.52
(m, 3H, Harom), 7.40e7.34 (m, 2H, Harom), 7.23 (dd, 1H, J1 ¼ 7.60 Hz,
J2 ¼ 1.83 Hz, Harom); 13C NMR (150 MHz, DMSO-d6):
d
¼ 150.9 (d),
147.1 (s), 142.4 (s), 137.3 (s), 135.6 (s), 132.9 (s), 132.5 (d), 130.7 (d,
2C), 130.0 (d, 3C), 129.7 (d, 2C), 127.9 (d, 2C), 124.9 (d), 123.9 (d),
120.1 (d), 116.0 (s), 111.1 (s), 101.1 (s); MS (m/z): 322 ([Mþ1]þ); UV
(EtOH) lmax: 337; Anal. Calcd for C22H15N3 (321.1): C, 82.22; H, 4.70;
N, 13.08. Found: C, 82.10; H, 4.62; N, 13.25.
2.2.2.2. E-3-(2-chlorophenyl)-2-(1-phenylbenzimidazol-2-yl)acrylo-
nitrile 3b. Compound 3b was prepared from 1 (0.69 g, 3.00 mmol)
and 2-chlorobenzaldehyde 2b (0.65 g, 3.00 mmol) in absolute
ethanol (15 mL) and piperidine (0.10 mL) after heating under reflux
for 3 h and recrystallization from ethanol to yield 0.49 g (77%) of
yellow powder; m.p. 163e164 ꢀC; 1H NMR (600 MHz, DMSO-d6):
2. Experimental
2.1. General methods
All chemicals and solvents were purchased from commercial
suppliers Acros, Aldrich or Fluka. Melting points were recorded on
SMP11 Bibby and Büchi 535 apparatus. The 1H and 13C NMR spectra
were recorded on a Varian Gemini 300 or Varian Gemini 600 at
300, 600 and 150 and 75 MHz, respectively. All NMR spectra were
measured in DMSO-d6 solutions using TMS as an internal standard.
d
¼ 7.93 (d, 1H, J ¼ 8.19 Hz, Harom.), 7.85 (s, 1H, Harom), 7.69 (d, 2H,
J ¼ 8.20 Hz, Harom), 7.64e7.53 (m, 2H, Harom), 7.46e7.40 (m, 4H,
Harom), 7.27 (d, 2H, J ¼ 7.80 Hz, Harom), 7.08 (d, 1H, J ¼ 7.76 Hz,
Harom), 6.83 (d, 1H, J ¼ 7.70 Hz, Harom)
;
13C NMR (150 MHz, DMSO-
d6):
d
¼ 150.0 (d), 147.0 (s), 142.6 (s), 137.3 (s), 137.0 (s), 135.6 (s),
131.7 (d), 131.6 (d, 2C), 130.6 (d, 2C), 130.2 (s), 129.9 (d, 2C), 128.0 (d,
2C), 125.0 (d), 123.8 (d), 120.1 (d), 115.6 (s), 111.2 (s), 101.4 (s); MS
(m/z): 356 ([Mþ1]þ); UV (EtOH) lmax: 264; Anal. Calcd for
C22H14ClN3 (355.1): C, 74.26; H, 3.97; N, 11.81. Found: C, 74.14; H,
4.09; N, 11.66.
Chemical shifts are reported in ppm (d) relative to TMS. In prepar-
ative photochemical experiments the irradiation was performed at
room temperature with a water-cooled immersion well with
“Origin Hanau” 400-W high pressure mercury arc lamp using Pyrex
glass as a cut-off filter of wavelengths below 280 nm. Mass spectra
were recorded on an Agilent 1200 series LC/6410 QQQ instrument.
The electronic absorption spectra were recorded on Varian Cary 50
spectrometer using quartz cuvette (1 cm). All compounds were
routinely checked by TLC with Merck silica gel 60F-254 glass plates.
Elemental analysis for carbon, hydrogen and nitrogen were per-
formed on a PerkineElmer 2400 elemental analyzer. Where anal-
yses are indicated only as symbols of elements, analytical results
obtained are within 0.4% of the theoretical value.
2.2.2.3. E-3-(4-chlorophenyl)-2-(1-phenylbenzimidazol-2-yl)acrylo-
nitrile 3c. Compound 3c was prepared from 1 (1.50 g, 6.50 mmol)
and 4-chlorobenzaldehyde 2c (1.42 g, 6.50 mmol) in absolute
ethanol (20 mL) and piperidine (0.15 mL) after heating under reflux
for 3.5 h and recrystallization from ethanol to yield 1.60 g (69%) of
yellow crystals; m.p. 146e148 ꢀC; 1H NMR (600 MHz, DMSO-d6):
d
¼ 7.94 (s, 1H, Harom.), 7.83 (d, 3H, J ¼ 8.67 Hz, Harom), 7.67e7.60 (m,
7H, Harom.), 7.40e7.34 (m, 2H, Harom.), 7.23 (dd, 1H, J1 ¼ 7.80 Hz,
J2 ¼ 1.70 Hz, Harom.); 13C NMR (150 MHz, DMSO-d6):
d
¼ 149.5 (d),
2.2. Synthesis
146.9 (s), 142.4 (s), 137.4 (s), 137.0 (s), 135.5 (s), 131.7 (d), 131.5 (d,
2C), 130.7 (d, 2C), 130.0 (s), 129.8 (d, 2C), 128.0 (d, 2C), 124.9 (d),
123.7 (d), 120.2 (d), 115.7 (s), 111.2 (s), 101.7 (s); MS (m/z): 356
([Mþ1]þ); UV (EtOH) lmax: 344, 287; Anal. Calcd for C22H14ClN3
(355.1): C, 74.26; H, 3.97; N, 11.81. Found: C, 74.12; H, 4.13; N, 11.69.
2.2.1. 2-Cyanomethyl-N-phenylbenzimidazole 1
A
mixture of equimolar amounts of N-phenyl-1,2-
phenylenediamine (3.00 g, 16.30 mmol) and 2-cyanoacetamide
(2.70 g, 16.30 mmol) was heated in an oil bath for 20 min at
200 ꢀC. After cooling, the reaction mixture was treated with 50%
ethanol/water (100 mL) and resulting product was filtered off. After
recrystallization from ethanol/water the green crystals (2.50 g, 66%)
2.2.2.4. E-3-(4-nitrophenyl)-2-(1-phenylbenzimidazol-2-yl)acryloni-
trile 3d. Compound 3d was prepared from 1 (0.66 g, 2.86 mmol)
and 4-nitrobenzaldehyde 2d (0.43 g, 2.86 mmol) in absolute
ethanol (15 mL) and piperidine (0.10 mL) after heating under reflux
for 3.5 h and recrystallization from ethanol to yield 0.33 g (31%) of
yellow crystals; m.p. 179e181 ꢀC; 1H NMR (600 MHz, DMSO-d6):
obtained. m.p. 118e120 ꢀC; 1H NMR (300 MHz, DMSO-d6):
d
¼ 7.76
(dd, 1H, J1 ¼ 6.90 Hz, J2 ¼ 2.07 Hz, Harom.), 7.69e7.62 (m, 3H, Harom),
7.58 (d, 2H, J ¼ 7.10 Hz, Harom.), 7.31e7.27 (m, 2H, Harom), 7.16 (dd,
1H, J1 ¼ 6.93 Hz, J2 ¼ 2.31 Hz), 4.37 (s, 2H, CH2); MS (m/z): 233
([M]þ); UV (EtOH) lmax: 338.
d
¼ 8.36 (d, 2H, J ¼ 8.88 Hz, Harom.), 8.08 (s, 1H, Harom), 8,03 (d, 2H,
J ¼ 8.90 Hz, Harom.), 7.85 (dd, 1H, J1 ¼ 7.98 Hz, J2 ¼ 2.10 Hz, Harom.),
7.67e7.65 (m, 4H, Harom.), 7.63e7.61 (m, 4H, Harom.), 7.41e7.36 (m,
4H, Harom.), 7.24 (d, 1H, J ¼ 7.98 Hz); 13C NMR (150 MHz, DMSO-d6):
2.2.2. General procedure for synthesis of compounds 3ae3e
A solution of equimolar amounts of 2-cyanomethyl-N-phenyl-
benzimidazole 1, corresponding heteroaromatic aldehydes 2ae2e
and a few drops of piperidine in absolute ethanol, were refluxed
d
¼ 146.9 (s), 143.7 (s), 141.7 (s), 133.7 (d), 132.3 (d), 131.4 (s), 131.3
(d), 130.5 (s), 129.5 (d), 126.7 (d), 125.6 (d), 125.3 (d), 124.2 (d), 123.6
(s), 123.4 (d), 120.4 (d), 115.6 (d), 115.0 (d), 114.5 (s); MS (m/z): 367

646
M. Hranjec et al. / Dyes and Pigments 95 (2012) 644e656
([Mþ1]þ); UV (EtOH) lmax: 360, 276; Anal. Calcd for C22H14N4O2
chromatography to yield 0.19 g (48%) of yellow powder; m.p.
>280 ꢀC; 1H NMR (600 MHz, DMSO-d6):
¼ 8.98 (d, 1H, J ¼ 8.46 Hz,
(366.1): C, 72.12; H, 3.85; N,15.29. Found: C, 72.30; H, 4.05; N,14.98.
d
Harom.), 8.82 (d,1H, J ¼ 8.40 Hz), 8.07 (dt,1H, J1 ¼7.40 Hz, J2 ¼ 1.56 Hz,
Harom), 8.04 (dt, 1H, J1 ¼ 7.60 Hz, J2 ¼ 1.60 Hz, Harom), 7.80 (d, 1H,
J ¼ 8.28 Hz, Harom), 7.71e7.67 (m, 2H, Harom), 7.67e7.61 (m, 2H,
Harom), 7.59 (dd, 1H, J1 ¼ 7.90 Hz, J2 ¼ 1.60 Hz, Harom), 7.59 (d, 1H,
J ¼ 7.90 Hz, Harom), 7.37 (dd, 1H, J1 ¼ 8.10 Hz, J2 ¼ 1.77 Hz); 13C NMR
(150 MHz, DMSO-d6): 151.2 (s), 147.6 (s), 145.0 (s), 136.0 (s), 135.5 (s),
134.3 (s), 134.0 (d), 132.0 (d), 131.3 (s), 130.1 (d, 2C), 128.7 (d), 128.6
(d), 125.6 (d, 2C), 124.4 (d), 121.7 (s), 120.9 (d), 116.9 (d), 115.4 (s),
115.3 (d), 102.5 (s); MS (m/z): 354 ([Mþ1]þ); UV (EtOH) lmax: 255,
265; Anal. Calcd for C22H12ClN3 (353.1): C, 74.68; H, 3.42; N, 11.88.
Found: C, 74.85; H, 3.20; N, 11.60.
2.2.2.5. E-3-(4-N,N-dimethylaminophenyl)-2-(1-phenylbenzimidazol-
2-yl)acrylonitrile 3e. Compound 3e was prepared from 1 (0.70 g,
3.03 mmol) and 4-N,N-dimethylamino- benzaldehyde 2e (0.44 g,
3.03 mmol) in absolute ethanol (15 mL) and piperidine (0.15 mL)
after heating under reflux for 3.5 h and recrystallization from ethanol
to yield 0.26 g (21%) of orange crystals; m.p. 216e218 ꢀC; 1H NMR
(600 MHz, DMSO-d6):
d
¼ 7.75 (d, 1H, J ¼ 7.92 Hz, Harom.), 7.70 (d, 2H,
J ¼ 9.06 Hz, Harom), 7.69 (s, 1H, J ¼ 5.64 Hz, Harom.), 7.64 (t, 2H,
J ¼ 6.72 Hz, Harom.), 7.61e7.57 (m, 3H, Harom.), 7.32 (dt, 1H,
J1 ¼7.53 Hz, J2 ¼ 1.15 Hz, Harom.), 7.26 (dt,1H, J1 ¼7.60 Hz, J2 ¼ 1.04 Hz,
Harom.), 7.15 (d,1H, J ¼ 7.87 Hz, Harom.), 6.78 (d, 2H, J ¼ 9.12 Hz, Harom.),
3.03 (s, 6H, CH3); 13C NMR (150 MHz, DMSO-d6):
d
¼ 153.1 (s), 150.5
2.2.4.3. 2-Chloro-5-phenylbenzimidazo[1,2-a]quinoline-6-carbonitrile
4c. Compound 4c was prepared from 3c (0.40 g, 1.10 mmol) in
ethanol (400 mL) after irradiation for 5 h and separation by column
chromatography to yield 0.18 g (45%) of yellow powder; m.p.
(d), 148.7 (s),147.6 (s),142.6 (s), 137.4 (s),136.0 (s),132.5 (d, 2C), 130.6
(d, 2C), 129.7 (d), 128.0 (d, 2C), 124.4 (d), 120.1 (d), 119.7 (d), 117.6 (s),
112.1 (d), 110.8 (d), 91.9 (s), 83.6 (s), 47.7 (q, 2C); MS (m/z): 365
([Mþ1]þ); UV (EtOH) lmax: 421; Anal. Calcd for C24H20N4 (364.2): C,
79.10; H, 5.53; N, 15.37. Found: C, 79.30; H, 5.67; N, 15.60.
>280 ꢀC; 1H NMR (600 MHz, DMSO-d6):
d
¼ 8.96 (d, 2H, J ¼ 8.49 Hz,
Harom.), 8.81 (dd, 1H, J1 ¼ 8.50 Hz, J2 ¼ 1.78 Hz), 8.08e8.00 (m, 2H,
Harom.), 7.74 (d, 2H, J ¼ 8.34 Hz, Harom.), 7.63e7.61 (m, 2H, Harom.),
7.59e7.56 (m, 3H, Harom.); 13C NMR (150 MHz, DMSO-d6): 150.5 (s),
148.0 (s), 144.5 (s), 136.1(s), 135.2 (s), 134.1 (d), 133.6 (s), 131.9 (d),
131.0 (s), 130.2 (d, 2C), 129.1 (d, 2C), 127.6 (d), 125.5 (d), 124.3 (d),
121.9 (s), 120.8 (d), 116.8 (d), 115.4 (d), 115.3 (s), 102.4 (s); MS (m/z):
354 ([Mþ1]þ); UV (EtOH) lmax: 355, 266, 254; Anal. Calcd for
C22H12ClN3 (353.1): C, 74.68; H, 3.42; N, 11.88. Found: C, 74.89; H,
3.25; N, 11.65.
2.2.3. E-3-(4-N,N-dimethylaminophenyl)-2-(1-phenylbenzimidazol-
2-yl)acrylonitrile hydrochloride 3f
A stirred suspension of compound 3e (0.05 g, 0.10 mmol) in
absolute ethanol (5 mL) was saturated with HCl(g). After 24 h of
stirring at room temperature, the resulting product was filtered off
and washed with diethylether (10 mL) to yield 0.04 g (73%) of red
powder; m.p. >280 ꢀC; 1H NMR (600 MHz, DMSO-d6):
d
¼ 1H NMR
(DMSO-d6) (
d
/ppm) 7.88 (s, 1H, Harom.), 7.78 (d, 1H, J ¼ 8.10 Hz),
7.67e7.64 (m, 2H, Harom.), 7.63e7.61 (m, 2H, Harom.), 7.41 (dt, 1H,
J1 ¼7.60 Hz, J2 ¼1.60 Hz, Harom.), 7.35 (dt,1H, J1 ¼7.75 Hz, J2 ¼1.80 Hz,
Harom.), 7.20 (d, 1H, J ¼ 8.28 Hz, Harom.), 6.80 (d, 2H, J ¼ 9.10 Hz), 3.90
2.2.4.4. 2-Nitro-5-phenylbenzimidazo[1,2-a]quinoline-6-carbonitrile
4d. Compound 4d was prepared from 3d (0.30 g, 0.80 mmol) in
ethanol (400 mL) after irradiation for 3 h and separation by column
chromatography to yield 0.18 g (60%) of yellow powder; m.p.
(brs,1H, NHþ); 13C NMR (150 MHz, DMSO-d6):
d
¼ 154.6 (s),152.8 (d),
149.9 (s),148.5 (s),144.0 (s),137.6 (s),136.9 (s),133.2 (d, 2C),130.9 (d,
2C), 130.5 (d), 129.1 (d, 2C), 126.0 (d), 122.7 (s), 120.4 (d), 118.8 (d),
114.3 (d), 112.4 (d), 97.2 (s), 90.6 (s), 48.5 (q, 2C); MS (m/z): 365
([Mþ1-HCl]þ); UV (EtOH) lmax: 421; Anal. Calcd for C24H21ClN4
(400.2): C, 71.90; H, 5.28; N,13.98. Found: C, 71.75; H, 5.49; N,13.75.
>280 ꢀC; 1H NMR (600 MHz, DMSO-d6):
d
¼ 9.00 (d, 1H, J ¼ 8.52 Hz,
Harom), 8.79 (d, 1H, J ¼ 7.74 Hz, Harom), 8.42 (d, 1H, J ¼ 8.76 Hz,
Harom), 8.41 (d, 1H, J ¼ 8.52 Hz, Harom), 8.16e8.05 (m, 2H, Harom),
7.98 (d, 1H, J ¼ 8.88 Hz, Harom), 7.78 (d, 2H, J ¼ 8.98 Hz, Harom),
7.64e7.57 (m, 2H, Harom), 7.37 (d, 1H, J ¼ 8.64 Hz, Harom); 13C NMR
(150 MHz, DMSO-d6):
d
¼ 149.0 (s), 146.9 (s), 143.7 (s), 141.6 (s),
2.2.4. General procedure for synthesis of compounds 4ae4d
135.6 (s), 133.7 (d), 132.3 (d, 2C), 131.6 (s), 131.4 (d), 129.0 (d), 126.7
(d), 125.4 (d), 124.6 (d), 123.6 (s), 123.2 (d, 2C), 121.1 (s), 120.4 (d),
117.3 (s), 115.6 (d), 114.5 (s); MS (m/z): 365 ([Mþ1]þ); UV (EtOH)
lmax: 264; Anal. Calcd for C22H12N4O2 (364.1): C, 72.52; H, 3.32; N,
15.38. Found: C, 72.77; H, 3.11; N, 15.55.
Ethanolic solutions of compounds 3ae3d and small amount of
iodine (5%), were irradiated at room temperature, with 400-W high-
pressure mercury lamp, using a Pyrex filter for about 3e5 h, until the
UV spectra shown that the reaction of dehydrocyclizationwas finished.
Air was bubbled through the solution. The solutions were concen-
trated under reduced pressure and resulting product was separated by
column chromatography on SiO2 using dichlormethane as eluent.
2.2.5. 2-Amino-5-phenylbenzimidazo[1,2-a]quinoline-6-carbonitrile
5
Compound 4d (0.11 g, 0.30 mmol) and solution of SnCl2 ꢁ 2H2O
(0.54 g, 2.4 mmol) in MeOH (0.9 mL) and concentrated HCl (0.9 mL)
were heated under reflux for 0.5 h. After cooling, the reaction
mixture was evaporated under vacuum and dissolved in water
(20 mL). The resulting solution was treated with 20% NaOH to
pH ¼ 14. Resulting product was filtered off and washed with water
to yield 0.03 (69%) of yellow powder; m.p. >280 ꢀC; 1H NMR
2.2.4.1. 5-Phenylbenzimidazo[1,2-a]quinoline-6-carbonitrile
4a. Compound 4a was prepared from 3a (0.30 g, 0.90 mmol) in
ethanol (400 mL) after irradiation for 4 h and separation by column
chromatography to yield 0.15 g (50%) of yellow powder; m.p.
>280 ꢀC; 1H NMR (600 MHz, DMSO-d6):
d
¼ 8.95 (d, 1H, J ¼ 8.46 Hz,
Harom.), 8.80 (d, 1H, J ¼ 7.80 Hz, Harom), 8.05e8.00 (m, 2H, Harom.),
7.69e7.64 (m, 4H, Harom.), 7.61e7.59 (m, 3H, Harom.), 7.19e7.11 (m,1H,
(600 MHz, DMSO-d6):
d
¼ 8.92 (d, 1H, J ¼ 8.70 Hz, Harom), 8.03 (dd,
Harom.); 13C NMR (150 MHz, DMSO-d6):
d
¼ 151.7 (s), 144.6 (s), 139.0
2H, J1 ¼ 8.98 Hz, J2 ¼ 1.78 Hz, Harom), 7.83 (dd, 2H, J1 ¼ 8.70 Hz,
J2 ¼ 1.38 Hz, Harom), 7.64e7.51 (m, 2H, Harom), 7.39 (d, 1H,
J ¼ 8.76 Hz, Harom), 7.30 (d, 1H, J ¼ 8.80 Hz, Harom), 7.07 (d, 2H,
J ¼ 8.37 Hz, Harom), 6.71 (d, 1H, J ¼ 8.34 Hz, Harom), 5.70 (brs, 2H,
(s), 136.2 (s), 134.8 (s), 133.9 (d), 131.6 (s), 131.5 (d), 130.8 (d), 129.9
(d), 129.6 (d), 129.3 (d), 128.2 (d), 126.2 (s), 125.7 (d), 125.6 (d), 124.3
(d), 122.1 (s), 120.9 (d), 116.7 (d), 115.4 (d), 115.3 (s); MS (m/z): 320
([Mþ1]þ); UV (EtOH) lmax: 353, 265, 243; Anal. Calcd for C22H13N3
(319.1): C, 82.74; H, 4.10; N, 13.16. Found: C, 82.89; H, 4.33; N, 13.40.
NH2); 13C NMR (150 MHz, DMSO-d6):
d
¼ 149.6 (s), 147.2 (s), 144.1
(s), 142.0 (s), 135.5 (s), 134.1 (d), 133.1 (d, 2C), 131.9 (d), 131.7 (s),
129.4 (d), 127.1 (d), 125.6 (d), 124.8 (d), 124.4 (s), 123.7 (d, 2C), 121.8
(s), 120.9 (d), 118.0 (s), 116.1 (d), 115.0 (s); MS (m/z): 335 ([Mþ1]þ);
UV (EtOH) lmax: 360, 344, 260; Anal. Calcd for C22H14N4 (334.1): C,
79.02; H, 4.22; N, 16.76. Found: C, 79.32; H, 4.13; N, 16.55.
2.2.4.2. 4-Chloro-5-phenylbenzimidazo[1,2-a]quinoline-6-carbonitrile
4b. Compound 4b was prepared from 3b (0.40 g, 1.10 mmol) in
ethanol (400 mL) after irradiation for 4 h and separation by column

M. Hranjec et al. / Dyes and Pigments 95 (2012) 644e656
647
Table 1
2.2.6. 2-Amino-5-phenylbenzimidazo[1,2-a]quinoline-6-
carbonitrile hydrochloride 6
General and crystal data and summary of intensity data collection and structure
refinement for compounds 3d and 4a.
A stirred suspension of compound 5 (0.03 g, 0.09 mmol) in
absolute ethanol (5 mL) was saturated with HCl(g). After 24 h of
stirring at room temperature, the resulting product was filtered off
and washed with diethylether (5 mL) to yield 0.02 g (61%) of yellow
3d
4a
Formula
Mr
C22H14N4O2
366.37
Monoclinic,
yellow prism
P 21/n
C22H13N3
319.35
Monoclinic,
yellow prism
P 21/c
0.38 ꢁ 0.22 ꢁ 0.16
Crystal system,
colour and habit
Space group
Crystal dimensions (mm3)
Unit cell parameters:
a (Å)
powder; m.p. >280 ꢀC; 1H NMR (600 MHz, DMSO-d6):
d
¼ 8.00 (d,
1H, J ¼ 8.68 Hz, Harom), 7.78 (d, 1H, J ¼ 7.98 Hz, Harom), 7.75 (d, 1H,
J ¼ 8.70 Hz, Harom), 7.67e7.63 (m, 3H, Harom), 7.41 (dt, 1H,
J1 ¼ 7.98 Hz, J2 ¼ 1.02 Hz, Harom), 7.35 (dt, 2H, J1 ¼ 7.98 Hz,
J2 ¼ 1.02 Hz, Harom), 7.19 (dd, 1H, J1 ¼ 8.10 Hz, J2 ¼ 1.40 Hz, Harom),
6.80 (d, 2H, J ¼ 8.80 Hz, Harom), 4,80 (brs, 3H, NHþ3 ); 13C NMR
0.42 ꢁ 0.18 ꢁ 0.15
5.4466(7)
26.373(3)
12.6600(16)
101.244(13)
1783.6(4)
4
1.364
0.091
760
4 to 25
9.6785(2)
16.3577(4)
10.4937(2)
103.910(2)
1612.62(6)
4
1.315
0.621
664
5 to 73
b (Å)
c (Å)
ꢀ
(150 MHz, DMSO-d6):
d
¼ 149.3 (s), 147.0 (s), 144.5 (s), 142.6 (s),
b
/
V (Å3)
135.6 (s), 134.4 (d), 133.3 (d, 2C), 132.2 (d), 131.9 (s), 129.3 (d), 126.2
(d), 125.4 (d), 124.6 (d), 124.6 (s), 123.8 (d, 2C), 121.9 (d), 121.7 (s),
118.4 (s), 116.3 (d), 114.7 (s); MS (m/z): 335 ([Mþ1-HCl]þ); UV
(EtOH) lmax: 361, 345, 264; C22H15ClN4 (370.1): C, 71.25; H, 4.08; N,
15.11. Found: C, 71.40; H, 4.33; N, 14.87.
Z
Dc (g cmꢃ3
)
m
(mmꢃ1
)
F(000)
q
range for data
collection (ꢀ)a
h,k,l range
ꢃ6 to 3,
ꢃ30 to 31,
ꢃ15to 14
u
ꢃ8 to 11,
ꢃ17 to 20,
ꢃ12 to 12
u
2.3. Spectroscopic characterization
Scan type
UV absorption spectra were recorded, against the solvent, at
(25 ꢂ 0.1) ꢀC, using a Varian Cary 50 spectrophotometer operated in
double-beam mode. The wavelength range covered was
200e450 nm. Quartz cells of 1-cm path length were used
throughout and absorbance values were recorded at 0.1 nm. Fluo-
rescence measurements were carried out on a Varian Cary Eclipse
fluorescence spectrophotometer at 25 ꢀC using 1-cm path quartz
cells. Excitation maxima were determined from excitation spectra
covering the range of 200e450 nm. Emission spectra were recor-
ded from 400 to 600 nm and corrected for the effects of time- and
wavelength-dependent light-source fluctuations using a standard
of rhodamine 101, a diffuser provided with the fluorimeter and the
software supplied with the instrument. The measurements were
performed in ethanol (HPLC grade). Relative fluorescence quantum
yields were determined according to Miller using Eq. (1):
No. measured
reflections
No. independent
reflections (Rint.
Data/restraints/
parameters
6843
7806
3125 (0.0898)
3125/0/254
1481
3169 (0.036)
3169/0/226
2456
)
No. observed
reflections, I ꢄ 2
Completeness (%)
g1, g2 in w
s(I)
99.4 (to
q
¼ 25.00ꢀ)
99.3(to
q
¼ 72.5ꢀ)
0.0314, 0.000
0.0505, 0.0709
0.1573, 0.0864
0.869
0.0101(9)
ꢃ0.135, 0.134
0.0798, 0.1647
0.0458, 0.1225
0.0614, 0.1492
1.053
R, wR [I ꢄ 2
s(I)]
R, wR [all data]
Goodness of fit on F2, S
Extinction coefficient
Min. and max. electron
e
ꢃ0.195, 0.145
density (e Åꢃ3
)
Maximum
D/s
<0.001
0.001
a
The data collection for compound 3d were collected by
u-scans on an Oxford
fX
¼
fS ꢁ ASDXn2X=AXDSn2S
Xcalibur diffractometer equipped with 4-circle kappa geometry and CCD Sapphire 3
detector and graphite-monochromated MoK radiation (
temperature (296 K) and for compound 4a on an Oxford Xcalibur diffractometer
equipped with 4-circle kappa geometry and CCD Ruby detector and graphite-
monochromated CuK
a
l
¼ 0.71073 Å) at ambient
where in
f is the emission quantum yield, A is the absorbance at the
excitation wavelength, D is the area under the corrected emission
curve and n is the refractive index of the solvents used. The
subscripts s and x refer to the standard and to the unknown,
respectively. The standard employed was quinine sulfate with
a published fluorescence quantum yield of 0.54 [28]. All samples
were purged with argon to displace oxygen. The reproducibility
(difference between the largest and the smallest value in a series of
three independent measurements, divided by their arithmetic
mean) of quantum yield measurements was better than 10%.
a
radiation (
l
¼ 1.5418 Å) at ambient temperature (296 K).
Structures were solved by direct methods and refined on F2 by
weighted full-matrix least-squares. Programs SHELXS97 [30] and
SHELXL97 [30] integrated in the WinGX (v. 1.70.01) [31] software
system were used to solve and refine structure. All non-hydrogen
atoms were refined anisotropically. Hydrogen atoms belonging to
Csp2 carbon atoms were placed in geometrically idealized positions
[Csp2-H 0.93 Å with Uiso(H) ¼ 1.2 Ueq(C)] and they were constrained
to ride on their parent atoms by using the appropriate SHELXL97
HFIX instructions. The molecular geometry calculations were done
using PLATON [32] and PARST [33] programs. Graphics were done
using ORTEP-3 [34] and PovRay [35] and Mercury [36]. All
programs are integrated in the WinGX software system [31].
2.4. Single-crystal X-ray diffraction experiment
Selected crystallographic and refinement data for structures 3d
and 4a obtained by the single-crystal X-ray diffraction experiment
are reported in Table 1. Tables 2 and 3 contain selected molecular
geometry parameters for structures 3d and 4a, respectively. Table 4
lists hydrogen bond and interaction geometry for 3d and 4a, while
3. Results and disscussion
Table 5 contains geometry of p$$$p interactions.
Data collection for both structures 3d and 4a, has been per-
formed by applying the CrysAlis Software system, Version
1.171.34.40 [29]. The Lorentz-polarization effect was corrected and
the intensity data reduced by the CrysAlis RED application of the
CrysAlis Software system, Version 1.171.34.40 [29]. The diffraction
data have been scaled for absorption effects by the multi-scanning
method.
3.1. Synthesis
All newly prepared compounds presented in Fig. 1. were
synthesized according to the two synthetic procedures shown in
Scheme 1 and Scheme 2.
Acyclic compounds 3ae3f were prepared by conventional
methods for the preparation of similar benzimidazole derivatives,

648
M. Hranjec et al. / Dyes and Pigments 95 (2012) 644e656
Table 2
Electronic absorption and fluorescence emission data of studied compounds in ethanol.
Comp.
3a
3c
3d
3e
3f
4a
4b
4c
4d
5
lmax/nm
332
277
339
281
230
205
361
278
205
408
241
476
353
268
244
209
354
263
241
356
265
244
361
245
261
363
343
266
ε ꢁ 103
30.05
23.05
13.55
17.50
13.65
49.40
27.60
11.80
46.50
7.10
11.15
27.00
28.85
16.35
44.20
38.45
9.20
8.85
29.25
9.50
8.80
33.00
(dm3 molꢃ1 cmꢃ1
)
10.00
16.60
37.70
481
22.80
19.00
25.95
483
lemiss/nm
Rel. Fluo. Int.
(arb. un.)
f
478
63.9
561
128.1
431
204.1
489
58.0
478
491.9
485
307.1
478
32.1
460
23.6
78.1
629.5
<0.01
146
<0.01
142
<0.01
200
<0.01
23
<0.01
13
0.40
130
0.53
124
0.58
94
0.05
117
0.06
97
Stokes
shift (nm)
Table 3
by mass spectroscopy. The photocyclization reaction leads to
a downfield shift of the signal of most aromatic protons in their 1H
NMR along with disappearance of one aromatic proton on the
acrylonitrile part of the molecule. Migration of a phenyl ring from
benzimidazole to acrylonitrile part of cyclic skeleton was addi-
tionally confirmed with 2D NMR spectroscopy based on NOE
interactions of specific aromatic signals. 1H NMR spectra of the
amino substituted benzimidazo[1,2-a]quinoline 5 showed appear-
ance of broad singlet which belong to two protons of amino group.
1H NMR spectra of amino substituted benzimidazo[1,2-a]quinoline
hydrochloride 6 showed a downfield shift of most of the signals in
comparison with 1H NMR spectra of compound 5.
Selected interatomic distances (Å) and valence and torsion
angles (ꢀ) for the compound 3d.
3d
Selected bond distances
C1eN1
C1eN2
C1eC8
C8eC9
C8eC16
C9eC10
Selected bond angles
C9eC8eC16
C9eC8eC1
C16eC8eC1
C8eC9eC10
Selected torsion angle
C18eC17eN1eC7
1.383(3)
1.311(3)
1.472(3)
1.346(3)
1.424(4)
1.465(3)
122.9(2)
119.4(2)
117.6(2)
130.7(2)
3.2. Spectroscopic characterization
105.7(3)
In order to study the spectroscopic properties of prepared
compounds 3a, 3c, 3d, 3e, 3f, 4a, 4c, 4d and 5, UV/Vis and fluo-
rescence emission spectra were recorded in ethanol. The stock
solutions of compounds were prepared in ethanol by concentꢃra3-
in a cyclocondensation starting from the 2-cyanomethyl-N-phe-
nylbenzimidazole 1 and the corresponding aromatic benzalde-
hydes 2ae2d. Cyclic benzimidazo[1,2-a]quinolines 4ae4d were
prepared by photochemical dehydrocyclization of an ethanolic
solution of compounds 3ae3d after separation on chromatography
silica gel. All photochemical reactions were followed by UV/Vis
spectroscopy. Amino substituted compound 5 was prepared from
nitro substituted compound 4d by reduction with SnCl2 ꢁ 2H2O in
MeOH and concentrated HCl. The hydrochloride salts 3f and 6 of
N,N-dimethylamino 3e and amino 5 substituted compounds were
prepared with HClgas. All structures of novel E-3substituted-2-(1-
tions as it follows: c(3a)
¼
4.05
ꢁ
10ꢃ3 mol dm
;
;
;
;
;
c(3c) ¼ 5.06 ꢁ 10ꢃ4 mol dmꢃ3; c(3d) ¼ 3.55 ꢁ 10ꢃ3 mol dmꢃ3
c(3e) ¼ 1,24 ꢁ 10ꢃ5 mol dmꢃ3; c(3f) ¼ 1.37 ꢁ 10ꢃ3 mol dmꢃ3
c(4a) ¼ 6.8 ꢁ 10ꢃ4 mol dmꢃ3; c(4b) ¼ 2.0 ꢁ 10ꢃ4 mol dmꢃ3
c(4c) ¼ 3.9 ꢁ 10ꢃ4 mol dmꢃ3; c(4d) ¼ 2.7 ꢁ 10ꢃ4 mol dmꢃ3
c(5) ¼ 5.1 ꢁ10ꢃ4 mol dmꢃ3. UV/Vis spectra of prepared compounds
were recorded at the same concentration of 2.0 ꢁ 10ꢃ5 mol dmꢃ3
and can be visualized in Fig. 2.
Acyclic compounds 3a and 3c showed one intense main
absorption band at 332 and 339 nm, nitro substituted compound
3d at 361 nm while N,N-dimethylamino substituted compounds 3e
and 3f showed intense bathochromic shift of w90 nm relative to 3a
and 3c and absorption maxima at 422 and 425 nm, respectively.
Heteroatoms, such as nitrogen, with non-bonding electrons which
can take part in the resonance and cause a bathochromic shift, can
absorb UV radiation when the electrons make a transition from n
phenylbenzimidazol-2-yl)acrylonitriles
3ae3e
and
2,4-
substituted-5-phenyl-benzimidazo[1,2-a]quinoline-6-carbonitriles
4ae4d and 5e6 were determined by the NMR analysis based on the
analysis of HeH coupling constants as well as chemical shifts and
Table 4
Selected interatomic distances (Å) and valence and torsion
angles (ꢀ) for the compound 4a.
Table 5
Hydrogen bond and weak interaction geometry (Å, ꢀ) for compounds 3d and 4a.
4a
DeH,,,A
DeH
H,,,A
D,,,A
:DeH,,,A
Symmetry
code
Selected bond distances
N1eC1
N1eC15
1.312(2)
1.383(2)
3d
N2eC1
N2eC9
N2eC10
C3eC16
1.3880(19)
1.3999(19)
1.4011(18)
1.491(2)
C9eH9$$$O1
0.93
0.93
2.57
2.68
3.477(3)
3.554(3)
165
157
ꢃ1/2 þ x,1/2ꢃ
y,1/2 þ z
C18eH18$$$N3
4a
x þ 1,þy,þz
Selected torsion angle
C2eC3eC16eC17
C8eH8$$$N3
C11eH11$$$N3
0.93
0.93
2.48
2.73
3.243(2)
3.655(2)
139
173
1 þ x,y,z
1 þ x,y,z
90.9(2)

M. Hranjec et al. / Dyes and Pigments 95 (2012) 644e656
649
R1
R1
R2
CN
R2
N
N
N
N
CN
3a R1=H, R2=H
3b R1=H, R2=Cl
3c R1=Cl, R2=H
4a R1=H, R2=H
4b R1=H, R2=Cl
4c R1=Cl, R2=H
4d R1=NO2, R2=H
3d R1=NO2, R2=H
3e R1=N(CH3)2, R2=H
3f R1=N(CH3)2×HCl, R2=H
5
6
R1=NH2, R2=H
R1=NH2×HCl, R2=H
Fig. 1. Synthesized acyclic benzimidazole derivatives 3ae3f and cyclic benzimidazo[1,2-a]quinolines 4ae4d, 5 and 6.
orbitals to
p* orbitals. Cyclic compounds 4a, 4c, 4d and 5 display
electronic transitions are made from
p
to
p* orbital of the tetra-
several absorption bands (Table 2), especially intense in the region
cyclic conjugated p-system. Conversion of nitro into the amino
from 240 to 275 nm with high extinction coefficients. Most of these
substituent did not resulted in changes in absorbance spectra while
introduction of a chlorine substituent resulted in a hypechromic
shift of the absorbance intensity and an increasing in the molar
extinction coefficients.
Fluorescence emission spectra were recorded at the same
concentration of 2.0 ꢁ 10ꢃ6 mol dmꢃ3 for acyclic compounds 3a, 3c,
3d, 3e and 3f, and 5.0 ꢁ 10ꢃ7 mol dmꢃ3 for cyclic compounds 4a,
4b, 4c, 4d and 5 and can be visualized in Fig. 3.
Fluorescence excitation was performed at the wavelength of
maximum absorption. All compounds exhibit characteristic fluo-
rescence emission with a single emission band. Nitro substituted
acyclic compound 3d showed an intense batochromic shift with
emission maxima at 561 nm, N,N-dimethylamino substituted
compound 3e showed one emission maxima at 431 nm while other
acyclic compounds showed low fluorescence intensity and emis-
sion maxima at w480 nm. Cyclic compounds also showed a single
emission band (Table 2). Compound 4a showed the highest fluo-
rescence intensity amongst all studied compounds. Additional
substituents did not yield any significant change of emission
maxima and have caused only hyperchromic shift of fluorescence
intensity. Electronic absorption and fluorescence data of studied
compounds recorded at the same concentration in ethanol,
quantum yield data 4 and Stokes shift values are summarized in
Table 2.
Excitation spectra of all studied compounds are in a good
agreement with their absorption spectra. The difference in energy
between the absorbed and emitted radiation is known as the Stokes
shift. All compounds except 3e and 3f possessed large Stokes shift
values (94e200 nm) which could be generally attributed to
a different charge distribution (or geometry) in the excited state of
molecules compared to the ground state.
3.3. Crystal structure analysis of compounds 3d and 4a
3.3.1. Crystal structure description of compound E-3-(4-nitrophenyl)-
2-(1-phenyl benzimidazol-2-yl)-acrylonitrile 3d
ORTEP-POV-Ray rendered view of the molecular structure of 3d
is depicted in Fig. 4.
The molecule deviates from planarity in the solid state which is
described by the dihedral angle [18.6(1)ꢀ] calculated between best
planes through the atoms of the phenyl (C10 e C15) and benz-
imidazole ring (C1, N1, N2, C2, C3, C4, C5, C6 and C7). We recently
published analogous structures belonging to the class of 2-
benzimidazolyl substituted acrylonitriles such as monohydrates
Scheme 1. Synthesis of compounds 3ae3f and 4ae4d.

650
M. Hranjec et al. / Dyes and Pigments 95 (2012) 644e656
NH3+Cl-
NO2
NH2
EtOH
HCl(g)
SnCl2×2H2O
MeOH, HCl
N
N
N
N
N
N
CN
4d
CN
CN
6
5
Scheme 2. Synthesis of compounds 5 and 6.
3a
4a
3c
4c
3d
4d
5
1,6
1,2
0,8
0,4
0,0
3e
3f
4b
250
300
350
400
450
500
/ nm
Fig. 2. UV/Vis spectra of compounds 3a, 3c, 3d, 3e, 3f, 4a, 4c, 4d and 5 in ethanol.
of 2-(1H-benzimidazol-2-yl)-3-(4-cyanophenyl)-acrylonitrile and
2-(1H-benzimidazol-2-yl)-3-(4-bromophenyl)-acrylonitrile [36]
which do not deviate significantly from planarity [5.6(1)o and
3.5(1)ꢀ, respectively] and 2-(2-benzimidazolyl)-3-(4-fluorophenyl)
acrylonitrile ethanol solvate which molecules deviate from
planarity by 13.11(2)ꢀ [27]. All three above-mentioned 2-
700
3a
4a
3c
4c
3d
5
600
500
400
300
200
100
0
3f
3e
4b
450
500
550
600
650
700
/ nm
Fig. 3. Fluorescence emission spectra of compounds 3a, 3c, 3d, 3e, 3f, 4a, 4b, 4c, 4d and 5 in ethanol.

M. Hranjec et al. / Dyes and Pigments 95 (2012) 644e656
651
Fig. 4. ORTEP-POV-Ray rendered view of the asymmetric unit of 3d with atom labeling schemes. The displacement ellipsoids are drawn at the 50% probability level at 296(2) K.
benzimidazolyl substituted acrylonitrile derivatives are differently
functionalized at position 4 of phenyl ring: by cyano group,
bromine atom, fluorine atom and nitro group in the case of
compound 3d. Compound 3d is additionally substituted by phenyl
group at the N1 atom of 2-benzimidazolyl moiety, while in the
previously published structures this is not the case. The spatial
orientation of phenyl ring in respect to the plane of benzimidazole
ring is given by the dihedral angle value of 67.2(1)ꢀ. The bond
distances C1eC8 and C9eC10 are predominantly
showing delocalization effect to a larger extent (1.472(3) Å and
in
s in character
1.465(3) Å, respectively). The C8 ¼ C9 bond is dominantly
p
character (1.346(3) Å; Table 3). The value of C8-C16 bond distance
(1.424(4) Å) is influenced by the presence of the nearby cyano
group. Since the groups attached to C8 and C9 with the higher
priority lie on the same side of a plane containing the double
C8 ¼ C9 bond, the stereoisomer 3d in the crystalline state is
designated as E.
Fig. 5. Crystal packing of 3d viewed down a axis. Dashed lines represent CeH$$$O inter-
molecular hydrogen bond linking molecules into infinite zig-zag chains spreading along caxis.
Fig. 6. ORTEP-POV-Ray rendered view of the asymmetric unit of 4a with atom labeling schemes. The displacement ellipsoids are drawn at the 50% probability level at 296(2) K.

652
M. Hranjec et al. / Dyes and Pigments 95 (2012) 644e656
Fig. 7. Crystal packing of 4a showing antiparallel layers of chains formed by CeH$$$Nhydrogen bonds (in dashed lines). The chains are spreading along a axis.
The crystal structure is dominated by the C9eH9$$$O1 (Table 4)
chlorine
atom
in
2-chlorobenzimidazo[1,2-a]quinoline-6-
intermolecular hydrogen bond between eCH proton donor group
and the oxygen atom from nitro group linking molecules into
infinite zig-zag chains spreading along the c axis (Fig. 5).
The very weak CeH$$$N interaction including one of the aryl
eCH group and the cyano nitrogen atom N3 as a proton acceptor is
carbonitrile [28] and by piperidine in 2-piperidinylbenzimidazo
[1,2-a]quinoline-6-carbonitrile [28]. The compound 4a is addi-
tionally substituted at position 5 by the phenyl ring which does not
lie in the plane defined by essentially planar benzimidazo[1,2-a]
quinoline-6-carbonitrile structural fragment (dihedral angle
calculated between two best planes amounts 89.0(1)ꢀ). The ben-
zimidazo[1,2-a]quinoline fragment contains an sp3 hybridized N2
also present (Table 4). No p$$$p interactions are found.
3.3.2. Crystal structure description of compound 5-phenyl-
benzimidazo [1,2-a]quinoline-6-carbonitrile 4a
ORTEP-POV-Ray rendered view of the molecular structure of 3d
is depicted in Fig. 6.
We have recently published the crystal and molecular structures
of the six compounds which belong to the class of benzimidazo[1,2-
atom, the lone pair electrons of which are delocalized within the p-
system of fused rings. The CeN bond distances with the sp3
hybridized N2 atom (C1-N2, C9-N2 and C10-N2) are significantly
longer than CeN bonds formed by the sp2 hybridized N1 atom
(shorter C1-N1 and longer C15-N1 in imidazolyl ring), which are
dominantly
p in character (Table 4), as it is found in analogous
a]quinoline-6-carbonitriles functionalized at position
2
by:
benzimidazo[1,2-a]quinolines [27,28,37]. The compound 4a does
not contain strong proton donors, therefore the molecular
assembly within crystal structure is characterized by the existence
of the weak CeH,,,N hydrogen bonds formed between phenyl
eCH groups and the N3 atom of the cyano group (Table 5, Fig. 7).
The N3 atom acts as a double proton acceptor forming stronger and
weaker CeH,,,N hydrogen bond linking molecules into infinite
chains along the a axis. The chains spread into layers along the c
bromine atom in the structure of 2-bromo-benzimidazo[1,2-a]
quinoline-6-carbonitrile [37], cyano group in the structure of ben-
zimidazo[1,2-a]quinoline-2,6-dicarbonitrile [37], methyl group in
2-methylbenzimidazo[1,2-a]quinoline-6-carbonitrile [27], fluorine
atom in 2-fluoro-benzimidazo[1,2-a]quinoline-6-carbonitrile [27],
Table 6
Geometrical parameters of
axis interacting mutually through p$$$p interactions (Table 6).
p,,,
p
interactionsa (Å, ꢀ) for compound 4a.
,c
Interactionb CgeCg
Cg,,,P1b
Cg,,,P2d
ae
bf
Slippage
3.4. Detection of different cations with compound 5
distance
4a
Cg1$$$Cg3
Cg3$$$Cg1
Cg3$$$Cg4
Cg4$$$Cg3
3.7696(9) 3.3021(7) 3.3982(7) 3.22(8) 25.65 1.632
3.7696(9) 3.3983(7) 3.3021(7) 3.22(8) 28.84 1.818
3.766(1) 3.4207(7) 3.4196(7) 4.84(8) 24.75 1.576
3.766(1) 3.4196(7) 3.4207(7) 4.84(8) 24.71 1.576
The changes in fluorescence properties of compound 5 upon
addition of different metal chloride salts were measured in ethanol
at room temperature, at concentration 1 ꢁ 10ꢃ6 mol dmꢃ3 of
compound 5 while for the titration with Zn2þ cations the concen-
a
tration of compound 5 was 5 ꢁ 10ꢃ7 mol dmꢃ3
.
Those possible interactions for which perpendicular distance between two
planes is longer than 3.8 Å (3.3e3.8 Å) (Cg,,,P1 and Cg,,,P2; the perpendicular
distance of corresponding centroid to a plane) and dihedral angles (between P1 and
P2) larger than 20ꢀ are not taken into account. The calculated slippage on the basis of
Cg...Cg distances as well as the value of the angle between Cg...Cg vector and vertical
line on corresponding plane has been taken into account as one of the geometrical
Stock solutions of various metal chloride salts (ZnCl2, MnCl2,
CuCl2, CoCl2, HgCl2, AgCl, LiCl and FeCl3) were prepared in ethanol.
Most of the results are presented in Fig. 8. As it can be viewed, the
fluorescence intensity of compound 5 decreased in the presence of
Mn2þ, Co2þ, Liþ and Fe3þ cations while significantly increased upon
addition of Zn2þ cation and Agþ cation. In Fig. 9. are presented
summarized results of fluorescence response of compound 5 in the
presence of all used cations at the same concentration of
1 ꢁ 10ꢃ6 mol dmꢃ3 (Fig. 10).
criteria, too (approx. 1.5 Å for p,,,p stacking interactions).
b
Rings Cg1,Cg3 and Cg4 are defined by the atoms N2, C1, C2, C3, C4 and C9; C10,
C11, C12, C13, C14 and C15; C16, C17, C18, C19, C20 and C21, respectively.
c
Cg,,,P1 is the perpendicular distance of corresponding centroid to a plane.
Planes P1 or P2 are defined by the atoms, which define the corresponding centroids.
d
Cg,,,P2 is the perpendicular distance of corresponding centroid to a plane.
Planes P1 or P2 are defined by the atoms, which define the corresponding centroids.
In the presence of Hg2þ and Liþ cations, the fluorescence
intensity of compound 5 decreased. The highest fluorescence
quenching of compound 5 was observed upon addition of Cu2þ
e
Dihedral angles between P1 and P2.
f
b
is the angle between Cg,,,Cg vector and vertical line on corresponding plane.
Symmetry code: i ¼ 2 þ x,1/2-y,3/2 þ z.

M. Hranjec et al. / Dyes and Pigments 95 (2012) 644e656
653
a
b
1000
900
800
700
600
500
400
300
200
100
0
compound 5
c (Ag )=5×10
c (Ag )=1×10
c (Ag )=3×10
c (Ag )=5×10
c (Ag )=1×10
c (Ag )=4×10
c (Ag )=7×10
c (Ag )=1×10
compound 5
c (Zn )=5×10
c (Zn )=1×10
c (Zn )=3×10
c (Zn )=5×10
c (Zn )=7×10
c (Zn )=1×10
450
400
350
300
250
200
150
100
50
M
M
M
M
M
M
M
M
2+
increasing Zn
M
M
M
M
M
M
+
increasing Ag
0
400
450
500
550
600
400
450
500
550
600
/ nm
/ nm
c
d
350
300
250
200
150
100
50
400
350
300
250
200
150
100
50
2+
compound 5
increasing Mn
compound 5
c (Fe )=1×10
c (Fe )=2×10
c (Fe )=3×10
c (Fe )=5×10
c (Fe )=7×10
c (Fe )=1×10
c (Mn )=5×10
c (Mn )=1×10
c (Mn )=2×10
c (Mn )=3×10
c (Mn )=5×10
c (Mn )=1×10
M
M
M
M
M
M
increasing Fe
M
M
M
M
M
M
0
0
400
450
500
550
600
400
450
500
550
600
/ nm
/ nm
e
f
+
300
250
200
150
100
50
increasing Li
300
250
200
150
100
50
compound 5
compound 5
c(Co )=5 × 10
c(Co )=1 × 10
c(Co )=2 × 10
c(Co )=3 × 10
c(Co )=5 × 10
c(Co )=1 × 10
M
2+
c(Li )=5 × 10
c(Li )=1 × 10
c(Li )=3 × 10
c(Li )=5 × 10
c(Li )=1 × 10
M
M
M
M
M
increasing Co
M
M
M
M
M
0
0
400
450
500
550
600
400
450
500
550
600
/ nm
/ nm
Fig. 8. Fluorescence intensity changes of compound 5 upon addition of different metal chloride salts in ethanol; a) Zn2þ; b) Agþ; c) Mn2þ; d) Fe3þ; e) Liþ; f) Co2þ; (lexc ¼ 363 nm).
cations (8 times). Moreover, the fluorescence maxima of compound
5 showed a slight red shift upon addition of Zn2þ (9 nm), Agþ
(7 nm), Hg2þ (9 nm), Co2þ (11 nm) and Cu2þ (14 nm).
The changes in fluorescence intensity upon addition of
different metal cations may be explained on the basis of a PCT
mechanism (photoinduced charge transfer). As it is well known,
when a fluorophore, which is benzimidazo[1,2-a]quinoline, is
directly attached to an electron donating receptor, which is amino
The selectivity of chemosensor 5 towards different cations is
presented in Fig. 11. After addition of the same amount of different
cation solutions (30
m
l, concentration of 1 ꢁ 10ꢃ6 mol dmꢃ3),
group, to form a new p-electron conjugation system which results
respectively, only Zn2þ and Agþ enhanced fluorescence emission at
460 nm for 3,51 and 1.46 times. All other cations quenched fluo-
rescence emission at 460 nm Cu2þ almost totally quenched fluo-
rescence at experimental conditions.
in electron rich and electron poor terminals, it undergoes intra-
molecular charge transfer (ICT) from the donor to the acceptor
upon excitation by light. Since a slight red shift in emission is
observed, we could assume that an interaction between the

654
M. Hranjec et al. / Dyes and Pigments 95 (2012) 644e656
compound 5
2+
Zn
2+
1000
800
600
400
200
0
Co
2+
Cu
3+
Fe
2+
Hg
+
Li
2+
Mn
+
2+
Zn
Ag
+
Ag
5
3+
Fe
+
2+
Li
Hg
2+
Co
2+
Mn
2+
Cu
400
450
500
550
600
/ nm
Fig. 9. Fluorescence response of compound 5 in the presence of different metal cations at the same concentration of 1 ꢁ 10ꢃ6 mol dmꢃ3 in ethanol (lexc ¼ 363 nm).
a
b
Co2+
Cu2+
Fe3+
Hg2+
Li+
300
250
200
150
100
50
1000
900
800
700
600
500
400
300
200
100
Zn2+
Ag+
Mn2+
0
0,0
0,0
2,0x10
4,0x10
6,0x10
8,0x10
1,0x10
2,0x10
4,0x10
6,0x10
8,0x10
1,0x10
1,2x10
concentration of cations (mol dm-3)
concentration of cations (mol dm-3)
Fig. 10. Changes in fluorescence emission of compound 5 at 463 nm in the presence of different concentration of cations.
Zn2+
cation and receptor strengthens the pushepull effects and
change the photophysical properties of fluorophore. To confirm
our assumption, that amino group is responsible for interaction
with cations, we have perform some additional experiments
with 5-phenylbenzimidazo[1,2-a]quinoline-6-carbonitrile 4a, un-
substituted derivative on quinoline nuclei, and 2-chloro-5-
phenylbenzimidazo[1,2-a]quinoline-6-carbonitrile 4b. Fluori-
metric titrations with metal chloride salts of compounds 4a and
4c did not cause any significant changes in fluorescent intensities
of compounds 4a and 4c.
3,5
3,0
2,5
2,0
1,5
1,0
0,5
0,0
Ag+
Fe3+
Li+
Hg2+
Co2+
Mn2+
Cu2+
4. Conclusion
In this work, we have presented the synthesis of novel E-3-
phenyl-2-(1-phenyl-benzimidazol-2-yl)acrylonitriles 3ae3f and
Fig. 11. The selectivity of chemosensor 5 towards different cations.

M. Hranjec et al. / Dyes and Pigments 95 (2012) 644e656
655
[3] Jeong J, Yoon J. Recent progress on fluorescent chemosensors for metal ions.
Inorganica Chimica Acta 2012;381:2e14.
[4] Boca M, Jameson RF, Linert W. Fascinating variability in the chemistry and
5-phenylbenzimidazo[1,2-a]quinolines 4ae4d,
5
and 6. All
prepared compounds, especially the cyclic derivatives, showed
interesting spectroscopic characteristic which were studied by UV/
Vis and fluorescence spectroscopy in ethanol. Amongst all of the
acyclic compounds, the nitro substituted compound 3d showed an
intense batochromic shift with emission maxima at 561 nm, while
the cyclic compound 4a showed the highest fluorescence intensity
amongst all of the studied compounds. In comparison to unsub-
stituted 4a and chloro substituted 4b and 4c benzimidazo[1,2-a]
quinolines, nitro 4d and amino 5 substituted compounds showed
very low fluorescence quantum yield.
The crystal and molecular structures of two compounds 3d and
4a have been determined. Since the groups attached to C8 and C9
with the higher priority lie on the same side of a plane containing
double C8 ¼ C9 bond, the stereoisomer 3d in the crystalline state is
designated as E. The molecules are assembled in the crystal via
weak CeH$$$O in 3d and CeH$$$N intermolecular hydrogen bonds
in 4a.
To shed more light on the possibility of benzimidazo[1,2-a]
quinolines for their application as a chemosensors for a variety of
cations, amino substituted cyclic compound 5 was chosen for
a spectroscopic study of its fluorescence properties in the pres-
ence of different metal chloride salts. Fluorescence emission
spectra revealed that in the presence of Zn2þ and Agþ cations,
fluorescence intensity of compound 5 is significantly enhanced
while in the presence of Mn2þ, Co2þ, Cu2þ, Hg2þ, Liþ and Fe3þ
cations, fluorescence intensity is quenched. The observed changes
together with bathochromic shifts of fluorescence intensity may
be attributed to PCT process. Quinolines and its derivatives,
despites of their disadvantages such as poor fluorescence or
solubility, are well known fluorogenic chelators for transition
metal ions and particularly for Zn2þ cation. Incorporation of
benzimidazole nuclei with a quinoline units leads to improve-
ment of photophysical properties. Thus, compound 5 showed
special sensitivity for Zn2þ cation which could offer the possibility
for its application for imaging and quantification Zn2þ in biolog-
ical samples since, it is well known from the literature data that
zinc is one of the most important transition metal ions in
the human body, essential for the many biological processes such
as brain function, gene transcription, immune function and
mammalian reproduction [38].
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Supplementary material
CCDC numbers 870440 & 870441 for compounds 3d and 4a
respectively, contains the supplementary crystallographic data for
this paper. These data can be obtained free of charge at www.ccdc.
cam.ac.uk/conts/retrieving.html [or from the Cambridge Crystal-
lographic Data Centre (CCDC), 12 Union Road, Cambridge CB2 1EZ,
UK; fax: þ44 (0)1223-336033; email: deposit@ccdc.cam.ac.uk].
Structure factors table is available from the authors.
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Acknowledgments
[26] Hranjec M, Karminski-Zamola G. Synthesis of novel benzimidazolyl
substituted acrylonitriles and amidino substituted benzimidazo[1,2-a]quino-
lines. Molecules 2007;12:1817e28.
This study was supported by grants 125-0982464-1356 and
098-1191344-2943 by the Ministry of Science, Education and Sports
of the Republic of Croatia.
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azole derivatives related to 2,3-acrylonitriles, benzimidazo[1,2-a]quinolines and
fluorenes: synthesis, antitumor evaluation in vitro and crystal structure deter-
mination. European Journal of Medicinal Chemistry 2010;45:2405e17.
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