Synthesis and fluorescent properties of 2-(1H-benzimidazol-2-yl)-phenol derivatives

Article abstract of DOI:10.1002/jhet.5570410309

A high yield one pot synthesis of 2-(2-hydroxyaryl)-1H-benzimidazole derivatives by 2-hydroxy aromatic aldehydes with aromatic 1,2-diamines in the presence of manganese(III) acetate at room temperature was developed. Nine fluorescencers 2-(2-hydroxyaryl)-1H-benzimidazoles with substituent(s) X (X = H, CH₃, CH₃O, Cl) and two fluorescencers 2-(2-hydroxyaryl)-1H-naphth[2,3-d]imidazoles with substituent of H or Cl were prepared in 38-87% yield and the ultraviolet absorption and fluorescent spectra of the eleven compounds synthesized were measured in methanol. The fluorescent characteristics of the 2-(2-hydroxyaryl)benzimidazole derivatives prepared were investigated on the basis of excited-state intramolecular proton transfer mechanism, Stokes' shift, quantum yield, and the relationship between fluorescent intensity and the substituents were derived.

Full text of DOI:10.1002/jhet.5570410309

May-Jun 2004
359
Synthesis and Fluorescent Properties of
2-(1H-Benzimidazol-2-yl)-phenol Derivatives
Jie Ouyang
Department of Biological and Chemical Engineering, Tianjin University of Technology,
263 Hongqi Nan Road, Tianjin 300191, P. R. of China
Chenguang Ouyang
Department of Biological Science and Technology, Nanjing University,
22 Hankou Road, Nanjing 210093, P. R. of China
Yuki Fujii,* Yoshiharu Nakano
Department of Chemistry, Faculty of Science, Ibaraki University, 2-1-1 Bunkyo, Mito 310 - 8512, Japan
Takuji Shoda, Tetsuo Nagano
Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku,
Tokyo 113-0033, Japan
Received December 5, 2003
A high yield one pot synthesis of 2-(2-hydroxyaryl)-1H-benzimidazole derivatives by 2-hydroxy aromatic
aldehydes with aromatic 1,2-diamines in the presence of manganese(III) acetate at room temperature was
developed. Nine fluorescencers 2-(2-hydroxyaryl)-1H-benzimidazoles with substituent(s) X (X = H, CH ,
CH O, Cl) and two fluorescencers 2-(2-hydroxyaryl)-1H-naphth[2,3-d]imidazoles with substituent of H or
3
3
Cl were prepared in 38 - 87% yield and the ultraviolet absorption and fluorescent spectra of the eleven com-
pounds synthesized were measured in methanol. The fluorescent characteristics of the 2-(2-
hydroxyaryl)benzimidazole derivatives prepared were investigated on the basis of excited-state intramolec-
ular proton transfer mechanism, Stokes' shift, quantum yield, and the relationship between fluorescent inten-
sity and the substituents were derived.
J. Heterocyclic Chem., 41, 359 (2004).
Introduction.
synthesis, recently, it has been widely employed in the syn-
thesis of many kinds of heterocyclic compounds [23-27].
Herein, we wish to report an one-pot synthesis of HPBI
and its derivatives in higher yield by the oxidative conden-
sation of 2-hydroxybenzaldehyde or substituted 2-
hydroxy-benzaldehydes with corresponding aromatic 1,2-
diamines using manganese triacetate as a relatively benign
oxidizing reagent under milder reaction conditions and the
fluorescent properties of some prepared HPBI derivatives.
The synthesis and development of fluorescence sensors
for biological applications have been an important field of
chemistry and pharmaceutics, recently, many novel series
of fluorescent probes have been designed and synthesized
[1-8]. 2-(2-Hydroxy-phenyl)benzimidazole (HPBI) and its
derivatives were a series of important fluorescent com-
pounds, these compounds have generated a lot of interest
[ 9 - 11] because of their intense emission property via
excited-state intramolecular proton transfer (ESIPT). The
HPBI derivatives were useful as a new series of fluores-
cent probes [12-14], high-energy radiation detector, plastic
scintillators [15-18] and polymer ultraviolet stabilizers
[10], as well as for their implications in biology and poten-
tial applications as molecular switches in logic or memory
circuits [19]. Recently we there have been very interest in
the development and synthesis of HPBI and its derivatives.
The HPBI is usually prepared from salicylic acid and 1,2-
phenylenediamine in polyphospholic acid at high tempera-
ture (150-250 °C) in 14-30% yield [17,20-21]. Our labora-
tory has reported the photolysis method of [N, N'-o-
phenylenebis(salicylideneaminato)]diaqua manganese(III)
at room temperature for effective formation of HPBI in
40% yield [22]. Manganese triacetate is rapidly evolving
as a new and exceptionally versatile reagent in org a n i c
Results and Discussion.
I. Synthesis.
Reactions of 2-Hydroxy Aromatic Aldehydes with
Aromatic 1,2-Diamines in the Presence of Manganese(III)
Acetate.
When the reaction of benzene-1,2-diamine (1A) with 2-
hydroxybenzaldehyde (2a) in the presence of man-
ganese(III) acetate was carried out by stirring for 12 hours
in acetic acid at room temperature until the dark brown
colored solution of manganese (III) acetate turned trans-
parent, the corresponding product 2-(1H-benzoimidazol-2-
yl)-phenol (3A-a) was obtained in 85 % yield (Scheme 1
and Table 1). Similarly, the reaction of 1A separately with
2-hydroxy-4-methoxybenzaldehyde (2 b), 2-hydroxy-4,6-
dimethoxybenzaldehyde (2 c), 5-chloro-2-hydroxybenz-

360
J. Ouyang, C. Ouyang, Y. Fujii, Y. Nakano, T. Shoda, and T. Nagano
Vol. 41
aldehyde (2 d), 2-hydroxy-3-methoxybenzaldehyde (2 e) ,
2,4-dihydroxy-benzaldehyde (2f) for a period of time gave
corresponding phenol ring substituted 2-(1H- b e n z i m i d a-
zol-2-yl)-phenols 3A-b-3A-f in 38-87 % yield (Scheme 1
and Table 1). The reaction of 4-methylbenzene-1,2-
diamine (1B) with 2a and substituted 2-hydroxy-benzalde-
hydes 2b, 2d gave the corresponding HPBI derivatives 3B-
a, 3B-b and 3B-d in 68-86 % yield (Scheme 1 and
Table 1). Also the reaction of naphthalene-2,3-diamine
(1C) with 2a and 2d gave the corresponding analogous
compounds of HPBI 3C-a and 3C-d in 69 and 60 % yield
(Scheme 2 and Table 1).
Scheme 1
genated further by manganese (III) acetate to deliver benz-
imidazoles 3 (Scheme 1 and Scheme 2).
II. Spectroscopic Properties.
A. Ultraviolet and Fluorescent Spectra.
All 1H-benzimidazole and 1H-naphthoimidazole deriv-
atives reported in this paper have fluorescent properties,
h o w e v e r, the fluorescent intensity is largely different
among the derivatives. In order to evaluate the fluorescent
properties, the absorption and emission spectra of these
2-(2-hydroxyaryl)-benzimidazoles 3 were measured in
methanol, the data are listed in Table 2.
The reaction pathways for the formation of 2-(2-hydrox-
yaryl)benzimidazoles 3 could be explained as the follow-
ing [27-28]. The reaction of 1 with 2 gives a Schiff base.
Then the nucleophilic addition of the second amino group
to the imide in the presence of manganese(III) acetate to
give a cyclic intermediate, which is subsequently dehydro-
Table 2, which lists the photophysical characteristics of
the compounds studied, clearly demonstrates the depen-
dence of fluorescent properties on the structure of hydrox-
yaryl groups and benzimidazole ring (or naphthoimidazole
ring). All eleven compounds 3 display an intense fluores-
cence emission with a quantum yield ranging 0.157 to

May-Jun 2004
Fluorescent Properties of 2-(1H-Benzimidazol-2-yl)-phenol Derivatives
361
0.694 for total fluorescence and show large Stokes' shifts
from 6112 to 9906 cm-1, a typical characteristic shift for
emission of the corresponding excited-state intramolecular
proton transfer (ESIPT) fluors [9-11]. These products dis-
play special photophysical properties which render them
potentially suitable as fluorescent probes. It was found
from the data in Table 2 that when it is a product which
bearing the electron-attracting chlorine atom at the C-5
position in 2-hydroxyphenyl, such as 3A-d, 3B-d and
3C-d, their maximum absorption wavelength and maxi-
mum emission wavelength are shifted approximately 5-10
nm toward longer wavelength relative to values of the 3A-
a, 3B-a and 3C-a, but their Stokes' shift relatively decrease,
the differences in Stokes' shift of 3 A - d, 3B-d and 3C-d
with 3 A - a, 3B-a and 3C-a are respectively 645, 348, 238
(cm–1). On the other hand, when a methoxy group which is
an electron-donating group is attached to the benzene ring
of 2-hydroxyphenyl group of the 2-(2-hydroxyaryl) benz-
imidazoles 3 at the C-4 or C-6 position, such as 3 A - b, 3 A - c
or 3B-b , their maximum absorption wavelength and
absorption coefficient (ε) were increased, but the maximum
emission wavelength, Stokes' shift and quantum yield were
decreased relative to those of the 3A-a or 3 B - a. When a
methoxy group is attached to the benzene ring of 2-hydrox-
yphenyl group at the C-3 position that is an ortho - position
of the hydroxy group, such as the compound 3A-e, its max-
imum absorption wavelength and corresponding maximum
emission wavelength is respectively 302 nm and 361 nm, a
blue-shift was shown, and both the Stokes' shift (6112
cm-1) and the quantum yield (0.157) were decreased rela-
length, absorption coefficient (ε) and the maximum emis-
sion wavelength respectively were increased approximately
30 nm, 6300-7700 Lmol-1cm-1 and 25 nm, but, Stokes' shift
and quantum yield respectively were decreased relative to
these values of the 3 A - a and 3 A - d.
B. Dependence of Normal and Tautomer Emission on the
Structure of o-Hydroxyaryl Groups in Methanol at 25 °C.
In recent years, the dual emission characteristics, normal
and tautomer, of the HPBI in many cases at room tempera-
ture has been studied and reported [11]. It is known that the
HPBI can have two intramolecular hydrogen bonded
rotamers I, II and one tautomer III in the ground state as
shown in Scheme 3. I is more stable than II and I I I, the tau-
tomer III has a higher energy than both I and II in the
ground state [11a]. Quantum chemical calculations indicate
that the barrier for the interconversion between I and II
increases in the excited electronic state, and hence I and II
are not freely interconvertible in the excited singlet state. It
has been also demonstrated that only II on excitation
undergoes ESIPT to form a tautomer I I I, which gives rise
to an emission (tautomer emission) with large Stokes' shift.
Rotamer I does not undergo ESIPT and is responsible for
the short wavelength normal emission (Figure 1). The dri-
ving force of ESIPT is the nitrogen atoms of the five-mem-
bered ring of HPBI becoming richer in π- electrons than the
oxygen atom of the hydroxyl group in the S1 state [11b].
tive to
electron-
those of 3A-a. When a methyl group which is an
donating group is added to the benzene ring at the
C-6) position, that is a benzene ring of benzimida-
C-5 (or
zole struc
ture in the compounds 3, such as compounds 3B-
a, 3B-b or
3B-d, their absorption coefficient (ε) were
increased (the
Δε are respectively 3700, 3600 and 1100
Lmol-1cm-1), but
Stokes' shift values were decreased rela-
tive to the values of
the 3 A - a, 3A-b and 3 A - d. When a
structure is connected respectively to
ring and naphthoimidazole ring at the 2
compounds 3C-a and 3 C - d, a larg e r
rescence properties is observed as show
example, their maximum absorption wave-
same 2-hydroxyaryl
the benzimidazole
position, such as
change of their fluo
in Table 2. For

362
J. Ouyang, C. Ouyang, Y. Fujii, Y. Nakano, T. Shoda, and T. Nagano
Vol. 41
In relation to this dual emission property of HPBI, it has
Table 3 clearly demonstrates the dependence of fluores-
cent quantum yield on the structure of hydroxyaryl groups.
When an electron-donating group (OH or OCH3) is
attached to the benzene ring of 2-hydroxyphenyl group of
the 2-(2-hydroxyaryl) benzimidazoles 3, such as 3A-f, 3A-
b and 3A-e or 3B-b, the eleactron density of lone pair of
the OH of 2-hydroxyphenyl group is increased relative to
that of 3A-a or 3B-a, the population of the rotamer I
increases. Hence the normal emission of the corresponding
compounds 3 is relatively enhanced, the ratio values
(ΦΝ/ΦΤ) become large compared with that of 3A-a (0.180)
such as the ΦΝ/ΦΤ of 3 A - f, 3A-b and 3A-e are respec-
tively 0.320, 0.240 and 1.617. The ΦΝ/ΦΤ of 3B-b is
0.179, which is also larger than that of 3B-a (0.163). Here
the donor electron effect of OH is stronger than that of
OCH3, hence the ΦΝ/ΦΤ of 3A-f becomes even larger than
that of the 3A-b or 3B-b. Since the OCH3 of the 3A-e is
attached to ortho - position relative to the hydroxy group,
the donor conjugation effect (+M effect) is stronger than
that of 3A-b in which the OCH3 is attached to meta - posi-
tion relative to the hydroxy group, consequently the
ΦΝ/ΦΤ of 3A-e becomes larger by about 9 times compared
with that of the 3A-a. In the case of 3A-e, the normal emis-
sion dominates over the tautomer emission as shown in
Figure 2. The ΦΝ/ΦΤ of 3A-c is very low (0.087), which is
an exception, because two kinds of the intramolcular
been reported that the relative intensities of the two kinds
of emission largely change with the temperature and sol-
vents [11]. Herein we wish to report a dependence of nor-
mal and tautomer emissions on the structure of o-hydrox-
yaryl groups for HPBI and its derivatives in methanol at 25
°C, because the relative intensities also depend on the sub-
stituents as is exemplified in Figure 2. We have evaluated
respectively quantum yield of the normal emission (ΦN)
and quantum yield of the tautomer emission (ΦT) for the
all HPBI and its derivatives synthesized, and have calcu-
lated a ratio (ΦN/ΦT) of the corresponding compounds, the
data are listed in Table 3.
3A-a
3A-c
3A-f
3A-d
…
…
hydrogen bonds (N–H O C H 3 and O–H N) exist
simultaneously in 3A-c [29]. On the other hand, when an
electron-withdrawing group such as Cl is attached to the
para - position relative to the OH of the 2-hydroxyphenyl
group, such as 3A-d, 3B-d and 3C-d, the electron density
of the oxygen atom of OH is decreased relative to that of
the 3 A - a, 3B-a or 3 C - a, and the acidity of the OH is
increased. Hence the intramolecular hydrogen bond of the
Figure 2. The fluorescent spectra of compounds 3A-a, 3A-f, 3A-e and
3 A-d in methanol at 25 C. The spectra near 355 nm correspond to normal
emission and the spectra near at 430 – 480 nm to tautomer emission.
°
…
form of the O–H N is enhanced in the corresponding
compounds 3, the population of the rotamer II, which is
responsible for the tautomer emission, becomes more pre-
dominant. Thus, the ΦΝ/ΦΤ of the compounds 3A-d, 3B-d
and 3C-d is less than that of 3A-a, 3B-a and 3C-a (the data
see Table 3). Evidently, the normal emission is inhibited in
3A-d, 3B-d and 3C-d. In this case, it gives predominantly
a high intensity emission with a high Stokes' shift due to
ESIPT transform, useful for fluorescent molecular sensors.
EXPERIMENTAL
Measurements.
1 13
All H and C nmr spectra were taken with a GSX-400 nmr
1
13
(400MHz for H and 100 MHz for C) spectrometer with tetram-
ethylsilane being used as the internal standard. Chemical shifts are
shown in δ values (ppm) and the coupling constants are expressed
in J values (Hz). Mass spectra were taken with a JMS-DX300
mass spectrometer at an ionizing voltage of 70 eV. All of the melt-
ing points were determined with a yanagimoto micromelting-

May-Jun 2004
Fluorescent Properties of 2-(1H-Benzimidazol-2-yl)-phenol Derivatives
363
point apparatus MP-J3. Elemental analyses were performed by the
Instrumental Analysis Center, Ibaraki University, Mito, Japan.
The ultraviolet absorption spectra were recorded at 25 °C using a
UV-1600 UV-Visible spectrometer (Shimadzu, Kyoto, Japan).
The fluorescence measurements were made on a F-4500 model
spectrophotometer (Hitachi, Tokyo, Japan). The slit width was 2.5
nm for both excitation and emission. The photomultiplier voltage
was 700 V. All compounds were dissolved in DMSO to obtain 10
mM stock solutions, the absorption and emission spectra were
recorded in methanol, the methanol is a solvent for fluorescence
analysis (Dojindo Laboratory, Kumamoto, Japan), the concentra-
tion of DMSO as co-solvent in methanol is 0.1% (v/v). Quantum
yields were determined using quinine sulfate in 0.1 N H SO
2-(1H-Benzoimidazol-2-yl)-5-methoxy-phenol (3A-b).
This compound was obtained as colorless microcrystals, 149
1
mg (62%), mp 233-234 °C (from ethanol); H nmr (400 MHz,
deuteriodimethyl sulfoxide):δ = 13.35 (br s, 1H, OH), 13.00 (s,
1H, NH), 7.95 (d, 1H, arom H, J = 8.4 Hz), 7.62 (dd, 2H, arom H,
J = 3.2, 9.2 Hz), 7.25 (dd, 2H, arom H, J = 3.2, 9.2 Hz), 6.62 (dd,
1H, arom H, J = 2.4, 8.4 Hz), 6.58 (d, 1H, arom H, J = 2.4 Hz),
13
3.80 (s, 3H, CH O); C nmr (100 MHz, deuteriodimethyl sul-
3
foxide) δ = 162.2, 159.7, 151.6, 139.9, 132.8, 127.5, 127.3,
122.6, 122.4, 106.5, 105.3, 101.4, 101.3, 55.4; EI-MS: m/z (rela-
+
tive intensity) = 240 (100, M ), 197 (24), 169 (7), 143 (5), 120
(6), 106 (7), 65 (7).
A n a l. Calcd. for C
2
4
H N O : C, 69.99; H, 5.03; N, 11.66.
14 12 2 2
Found: C, 69.68; H, 5.11; N, 11.43.
(from measurements using 350 nm excitation wavelength, Φ =
0.577). The working equation was:
2-(1H-Benzoimidazol-2-yl)-3,5-dimethoxy-phenol (3A-c).
This compound was obtained as colorless needles, 103 mg
1
(38%), mp 177-178 °C (from ethanol); H nmr (400 MHz, deu-
2
Φ
(Area
. = (Φ )(Area )(Absorbance )(n
std
) /
spl
spl
std.
)(Absorbance ) (n
spl
2
)
std.
The n is an index of refraction of solvent used.
std.
spl
teriodimethyl sulfoxide): δ = 14.68 (br s, 1H, NH), 12.09 (br s,
1H, OH), 7.64 (dd, 2H, arom H, J = 3.2, 9.2Hz), 7.23 (dd, 2H,
arom H, J = 3.2, 9.2 Hz), 6.35 (s, 2H, arom H), 4.01 (s, 3H,
Materials.
Manganese(III) acetate hydrate, o-phenylenediamine, 2,4-
dihydroxybenzaldehyde and salicylaldehyde were commercially
available and used as they were received (Wako). 3,4-Diamino-
toluene, 5-chlorosalicylaldehyde, and 4,6-dimethoxysalicyl-
aldehyde were purchased from Aldrich Chemical Co. Inc.. 2,3-
Diaminonaphthalene and 2-hydroxy-4-methoxybenzaldehyde
were purchased from Tokyo-kasei Co. Ltd. and used as received.
13
CH O), 3.80 (s, 3H, CH O); C nmr (100 MHz, deuteriodi-
3
methyl sulfoxide): δ = 162.3, 161.6, 158.8, 150.2, 139.0, 132.4,
3
122.3, 122.2, 116.8, 111.9, 95.3, 94.3, 90.2, 55.6, 55.1; EI-MS:
+
m/z (relative intensity) = 270 (100, M ), 240 (16), 193 (20), 143
(12), 136 (20), 121 (17), 78 (6), 65 (5), 58 (10).
A n a l. Calcd. for C
H N O : C, 66.66; H, 5.22; N, 10.36.
15 14 2 3
Found: C, 66.38; H, 5.31; N, 10.13.
Reaction of Aromatic 1,2-Diamines 1a-c with 2-Hydroxy
Aromatic Aldehydes 2 in the Presence of Manganese(III) Acetate.
2-(1H-Benzoimidazol-2-yl)-4-chloro-phenol (3A-d).
This compound was obtained as colorless needles, 212 mg
1
(87%), mp 301-303 °C (from ethanol) (lit 302-304 °C)[15]; H
The general procedure for the reaction of aromatic 1,2-
diamines 1A~C with 2-hydroxy aromatic aldehydes 2 in the pres-
ence of manganese(III) acetate was as follows. Manganese(III)
acetate (2 mmol) was added to a stirred solution of diamine (1
mmol) and 2-hydroxyaldehyde (1 mmol) in the acetic acid (30 ml)
in a flask equipped with a dry-air inlet tube. The mixture was
stirred at room temperature for the period of time shown in Table
1. The reaction was monitored by TLC. The reaction was
quenched by adding water (60 ml) and the mixture was then
extracted with ether and ethyl acetate and the combined extract
was washed with a saturated solution of sodium hydrogen carbon-
ate, and dried over sodium sulfate. After removing the ether and
ethyl acetate, the resulting products were separated by silica gel
column (Wakogel C - 200) while eluted with a mixture of hexane-
ethyl acetate (2:1 v/v). The products were further purified for ana-
lytical samples by recrystallization from appropriate solvents. The
yields are listed in Table 1. Specific details are given below.
nmr (400 MHz, deuteriodimethyl sulfoxide): δ = 13.26 (br s, 2H,
OH and NH), 8.15 (d, 1H, arom H, J = 2.8 Hz), 7.80 (d, 1H, arom
H, J = 8.4Hz), 7.69 (d, 1H, arom H, J = 8.4 Hz), 7.47 (dd, 1H,
arom H, J =2.8, 8.8 Hz), 7.37 (br s, 2H, arom H), 7.14 (d, 1H,
13
arom H, J = 8.8 Hz); C nmr (100 MHz, deuteriodimethyl sul-
foxide): δ = 156.5, 150.1, 133.2, 133.1, 125.5, 125.4, 123.1,
123.0, 122.6, 122.5, 119.0, 118.9, 113.9;EI-MS: m/z (relative
+
+
intensity) = 246 (33, M +2), 244 (100, M ), 216 (8), 181 (16),
149 (7), 90 (11), 57 (10).
2-(1H-Benzoimidazol-2-yl)-6-methoxy-phenol (3A-e).
This compound was obtained as colorless microcrystals, 127
1
mg (53%), mp 270-271 °C dec. (from ethanol); H nmr
(400MHz, deuteriodimethyl sulfoxide): δ = 13.25 (br s, 1H, OH),
13.17 (br s, 1H, NH), 7.72 (d, 1H, arom H, J = 8.4 Hz), 7.63 (dd,
1H, arom H, J = 1.6, 8.0 Hz), 7.59 (d, 1H, arom H, J = 8.4 Hz),
Products.
7.30 (br s, 2H, arom H), 7.15 (dd, 1H, arom H, J = 1.6, 8.0 Hz),
13
7.02 (t, 1H, arom H, J = 8.0 Hz), 3.84 (s, 3H, CH O); C nmr
3
(100 MHz, deuteriodimethyl sulfoxide): δ = 151.7, 148.4, 148.1,
139.0, 132.9, 123.5, 122.8, 122.7, 118.6, 117.5, 117.4, 113.8,
2-(1H-Benzoimidazol-2-yl)-phenol (3A-a).
This compound was obtained as colorless microcrystals,
178mg (85%), mp 240-242 °C (from ethanol) (lit 241-242
1
°C)[15]; H nmr (400 MHz, deuteriodimethyl sulfoxide):δ =
13.22 (br s, 2H, OH and NH), 8.10 (dd, 1H, arom H, J = 1.6, 7.2
Hz), 7.76 (d, 1H, arom H, J =5.6 Hz), 7.65 (d, 1H, arom H, J =5.6
Hz), 7.44-7.32 (m, 3H, arom H), 7.10-7.04 (m, 2H, arom H);
nmr (100 MHz, deuteriodimethyl sulfoxide): δ = 157.9, 151.6,
+
112.3, 55.7; EI-MS: m/z (relative intensity) = 240 (30, M ), 197
(13), 169 (6), 123 (17), 97 (42), 57 (100).
A n a l. Calcd. for C
H N O : C, 69.99; H, 5.03; N, 11.66.
14 12 2 2
Found: C, 69.65; H, 5.09; N, 11.48.
13
C
2-(1H-Benzoimidazol-2-yl)-benzene-1,3-diol (3A-f).
140.7, 133.0, 131.7, 126.2, 126.0, 123.2, 122.3, 119.0, 117.1,
+
112.5, 111.4; EI-MS: m/z (relative intensity) = 210 (100, M ),
182 (20), 91 (18), 78 (14).
This compound was obtained as colorless microcrystals, 104
mg (46%), mp 279-282 °C dec. (from ethanol) (lit 280-284
1
°C)[30]; H nmr (400 MHz, deuteriodimethyl sulfoxide): δ =

364
J. Ouyang, C. Ouyang, Y. Fujii, Y. Nakano, T. Shoda, and T. Nagano
Vol. 41
13.17 (br s, 1H, OH), 12.88 (br s, 1H, NH), 9.96 (br s, 1H, OH),
7.82 (d, 1H, arom H, J = 8.8 Hz), 7.61 (br s, 1H, arom H), 7.53 (br
s, 1H, arom H), 7.21 (d, 2H, arom H), 6.43 (dd, 1H, arom H, J =
2.4, 8.8 Hz), 6.38 (d, 1H, arom H, J = 2.4 Hz); C nmr (100
MHz, deuteriodimethyl sulfoxide): δ = 160.7, 159.7, 152.2,
135.9, 129.8, 127.4, 127.3, 122.3, 107.5, 107.4, 104.3, 103.0,
126.7, 124.1, 123.4, 119.1, 117.3, 112.1, 107.4; EI-MS: m/z (rel-
+
ative intensity) = 260 (53, M ), 240 (100), 197 (21), 169 (6), 120
(5), 106 (6), 57 (12).
13
4-Chloro-2-(1H-naphtho[2,3-d]imidazol-2-yl)-phenol (3C-d).
This compound was obtained as light yellow microcrystals,
1
177 mg (60%), mp 360 °C dec. (from ethanol); H nmr
+
102.9; EI-MS: m/z (relative intensity) = 226 (100, M ), 169 (23),
149 (31), 99 (14), 69 (23), 55 (37).
(400MHz, deuteriodimethyl sulfoxide): δ = 13.33 (br s, 2H, OH
and NH), 8.27 (d, 1H, arom H, J = 2.8 Hz), 8.20 (br s, 2H, arom
H), 8.05 (m, 2H, arom H), 7.48 (dd, 1H, arom H, J = 2.8, 8.8 Hz),
2-(5(6)-Methyl-1H-benzoimidazol-2-yl)-phenol (3B-a).
This compound was obtained as colorless microcrystals, 195
1
mg (85%), mp 256-257 °C (from ethanol); H nmr (400 MHz,
13
7.43 (m, 2H, arom H), 7.12 (d, 1H, arom H, J = 8.8 Hz); C nmr
(100 MHz, deuteriodimethyl sulfoxide): δ = 157.3, 154.3,
132.02, 132.0, 130.21, 130.20, 127.70, 127.66, 127.60, 126.12,
126.07, 123.88, 123.84, 122.7, 119.1, 119.0, 113.5; EI-MS: m/z
deuteriodimethyl sulfoxide): δ = 13.17 (br s, 1H, OH), 13.03 (br
s, 1H, NH), 8.00 (dd, 1H, arom H, J = 1.6, 7.6 Hz), 7.57-7.32 (m,
13
+
+
3H, arom H), 7.11-6.96 (m, 3H, arom H), 2.43 (s, 3H, CH );
3
C
(relative intensity) = 296 (34, M +2), 294 (100, M ), 260 (10),
231 (10), 149 (12), 140 (16), 115 (20), 57 (12).
A n a l. Calcd. for C H ClN O: C, 69.28; H, 3.76; N, 9.50.
nmr (100 MHz, deuteriodimethyl sulfoxide): δ = 157.8, 151.2,
132.5, 131.5, 131.4, 126.0, 125.9, 124.2, 119.0, 117.0, 112.6,
111.4, 111.3, 21.3; EI-MS: m/z (relative intensity) = 224 (100,
17 11
2
Found: C, 68.98; H, 3.83; N, 9.25.
+
M ), 196 (14), 149 (8), 98 (9), 77 (9), 57 (6).
A n a l. Calcd. for C H N O: C, 74.98; H, 5.39; N, 12.49.
14 12 2
Found: C, 74.78; H, 5.53; N, 12.25.
REFERENCES AND NOTES
5-Methoxy-2-(5(6)-methyl-1H-benzoimidazol-2-yl)-phenol (3 B-b).
This compound was obtained as colorless microcrystals, 173
[1] V. Bernard, Molecular Fluorescence Principles and
Application, Wiley-Vch., New York, NY, 2002, pp 273-384.
[2] T. Hirano, K. Kikuchi, Y. Urano, T. Higuchi and T.
Nagano, J. Am. Chem. Soc., 122, 12399 (2000).
[3] T. Hirano, K. Kikuchi, Y. Urano and T. Nagano, J. Am.
Chem. Soc., 124, 6555 (2002).
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Yamada, N. Nishiyama, T. Nagano, N. Matsuki and Y. Ikegaya, J.
Cell. Boil., 158, 215 (2002).
[5] T. Hirano, K. Kikuchi, Y. Urano, T. Higuchi and T.
Nagano, Angew. Chem. Int. Ed., 39, 1052 (2000).
[6] S. Maruyama, K. Kikuchi, T. Hirano, Y. Urano and T.
Nagano, J. Am. Chem. Soc., 124, 10650 (2002).
[7] H. Takakusa, K. Kikuchi, Y. Urano, S. Sakamoto, K.
Yamaguchi and T. Nagano, J. Am. Chem. Soc., 124, 1653 (2002).
[8] T. Shoda, K. Kikuchi, H. Kojima, Y. Urano, H. Komatsu,
K. Suzuki and T. Nagano Analyst, 128, 719 (2003).
[9] M. Forés, M. Duran, M. Solà, M. Orozco and F. F. Luque,
J. Phys. Chem. A, 103, 4525 (1999).
[10] M. A. Ríos and M. C. Ríos, J. Phys. Chem. A, 102, 1560
(1998).
[11a] K.Das, N. Sarkar, D. Majumdar and K. Bhattacharyya,
Chem. Phys. Lett., 1 9 8, 443 (1992); [b] K. Das, N. Sarkar, A. K.
Ghosh, D. Majumdar, D. N. Nath and K. Bhattacharyya, J. Phys.
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[12] A. Sytnik and M. Kasha, Proc. Natl. Acad. Sci. U.S.A., 91,
8627 (1994).
[13] A. Sytnik, D. Gormin and M. Kasha, Proc. Natl. Acad. Sci.
U.S.A., 91,11968 (1994).
1
mg (68%), mp 220-221 °C (from ethanol); H nmr (400 MHz,
deuteriodimethyl sulfoxide): δ = 13.35 (br s, 1H, OH), 12.87 (br
s, 1H, NH), 7.90 (d, 1H, arom H, J = 8.8 Hz), 7.46 (br s, 1H, arom
H), 7.37 (br s, 1H, arom H), 7.04 (d, 1H, arom H, J = 8.0 Hz),
6.59 (dd, 1H, arom H, J = 2.8, 8.8 Hz), 6.55 (d, 1H, arom H, J =
13
1
2.0 Hz), 3.79 (s, 3H, CH O), 2.42 (s, 3H, CH ); C nmr (100
3
MHz, deuteriodimethyl sulfoxide): δ = 161.9, 159.7, 151.6,
3
132.0, 127.0, 126.9, 123.8, 111.4,106.3, 106.2, 105.7, 101.4,
+
101.3, 55.3, 21.3; EI-MS: m/z (relative intensity) = 254 (12, M ),
193 (92), 164 (18), 136 (100), 107 (65), 585 (55).
A n a l. Calcd. for C
H N O : C, 70.85; H, 5.55; N, 11.02.
15 14 2 2
Found: C, 70.78; H, 5.43; N, 11.25.
4-Chloro-2-(6-methyl-1H-benzoimidazol-2-yl)-phenol (3B-d).
This compound was obtained as colorless needles, 222 mg
1
(86%), mp 299-300 °C (from ethanol); H nmr (400 MHz, deu-
teriodimethyl sulfoxide): δ = 13.25 (br s, 1H, OH), 13.10 (br s,
1H, NH), 8.12 (d, 1H, arom H, J = 2.8 Hz), 7.58 (d, 1H, arom H,
J = 8.0Hz), 7.50 (d, 1H, arom H, J = 8.0 Hz), 7.37 (dd, 1H, arom
H, J = 2.8, 8.4 Hz), 7.10 (br s, 1H, arom H), 7.04 (d, 1H, arom H,
13
J = 8.4 Hz), 2.45 (s, 3H, CH ); C nmr (100 MHz, deuteriodi-
3
methyl sulfoxide): δ = 156.4, 149.5, 133.2, 131.2, 131.1, 125.5,
125.4, 124.7, 122.6, 122.5, 118.9, 113.9, 113.8, 21.3; EI-MS: m/z
+
+
(relative intensity) = 260 (33, M +2), 258 (100, M ), 193 (42),
164 (8), 136 (42), 107 (30), 77 (19), 58 (22).
Anal. Calcd. for C H ClN O: C, 65.00; H, 4.29; N, 10.83.
[14] A. Sytnik and J. C. Del Valle, J. Phys. Chem., 99, 13028
(1995).
14 11
2
[15] A. Douhal, F. Amat-Guerri, P. Lillo and A. U. Acuña, J.
Photochem. Photobiol. Part. A,Chem., 78, 127 (1994).
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Chem. Int. Ed. Engl., 36, 1514 (1997).
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[20] C. M. Orlando Jr., J. G. Wirth and D. R. Heath, J. Org.
Chem., 35, 3147 (1970).
Found: C, 64.69; H, 4.41; N, 10.50.
2-(1H-Naphtho[2,3-d]imidazol-2-yl)-phenol (3C-a).
This compound was obtained as light yellow microcrystals,
180 mg (69%), mp 334-335 °C dec. (from ethanol) (lit 340-346
1
°C)[31]; H nmr (400MHz, deuteriodimethyl sulfoxide): δ =
13.28 (br s, 1H, OH), 13.21 (br s, 1H, NH), 8.25 (br s, arom H,
1H), 8.14 (dd, 1H, arom H, J = 1.6, 7.6 Hz), 8.05-8.00 (m, 3H,
1
arom H), 7.46-7.41 (m, 3H, arom H), 7.09-7.04 (m, 2H, arom H);
13
C nmr (100 MHz, deuteriodimethyl sulfoxide): δ = 158.6,
155.7, 141.2, 133.5, 132.6, 130.4, 129.9, 127.9, 127.4, 126.8,
[21] D. W. Hein, R. J. Alheim and J. J. Leavitt, J. Am. Chem.
Soc., 79, 427 (1957).

May-Jun 2004
Fluorescent Properties of 2-(1H-Benzimidazol-2-yl)-phenol Derivatives
365
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27, 3167 (1979).
[29] The protons of OH and NH of 3A-c both show a broad sin-
1
glet peak at 12.09 ppm (OH) and 14.68 ppm (NH), respectively in H
[24] J. Ouyang, H. Nishino and K. Kurosawa, J. Heterocyclic.
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Nishino, J. Ouyang and K. Kurosawa, J. Heterocyclic. Chem., 37,
269 (2000).
NMR spectrum, and the chemical shift of NH-proton is much more
low-field than that of the other members of the family (e.g. 13.22
ppm (3A-a), 13.00 ppm (3A-b)), indicating that 3A-c exists in the
form of two kinds of intramolecular hydrogen bond (N–H…OCH
and O–H N).
[30] J. Beger, G. Wagner, E. Uhlig and U. Dinjus, J. Prakt.
3
…
Chem., 325, 708 (1983).
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1539 (1998).
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Heterocyclic. Chem., 7, 1385 (1970).