Microwave-assisted solvent-free catalyzed synthesis and luminescence properties of 1,2,4,5-tetrasubstituted imidazoles bearing a 4-aminophenyl substituent

Article abstract of DOI:10.1007/s11696-016-0051-1

A solvent-free microwave-assisted four-component synthesis of 1,2,4,5-tetrasubstituted imidazoles bearing a 4-aminophenyl substituent was studied by condensation of p-phenylenediamine, aryl diketone, benzaldehyde derivatives and ammonium acetate in the presence of solid support silica gel and catalyst Keggin-H₃[PW₁₂O₄₀]. The effects of four components molar ratio along with catalyst loading, irradiation time on the yields were investigated. Also, the structures of synthesized compounds were characterized by FT-IR, HRMS, ¹H NMR and ¹³C NMR spectroscopy. Furthermore, their ultraviolet-visible maximum absorption, liquid fluorescence emission maximum and quantum yields were, respectively, measured in 0.05 M H₂SO₄ aqueous solution and in dichloromethane. Simultaneously, solid fluorescence spectra were determined in the powder state. The relationships between the optical behavior and the polarity of the solvents for some compounds were assessed. The results showed that the fluorescence quantum efficiency was increased by introducing amino phenyl in comparison with benzyl on 1-position of trisubstitued imidazoles. The compounds synthesized were sensitive to the polarity of the solvents.

Full text of DOI:10.1007/s11696-016-0051-1

Chem. Pap.
DOI 10.1007/s11696-016-0051-1
ORIGINAL PAPER
Microwave-assisted solvent-free catalyzed synthesis
and luminescence properties of 1,2,4,5-tetrasubstituted imidazoles
bearing a 4-aminophenyl substituent
Liu-qing Yan1 Yao Chen1 Xiao-fu Sun2 Mao-jun You2 Xiao-dong Chen1
•
•
•
•
•
Qiang Gu1 Yu-min Zhang1
•
Received: 20 April 2016 / Accepted: 27 July 2016
Ó Institute of Chemistry, Slovak Academy of Sciences 2016
Abstract A solvent-free microwave-assisted four-compo-
nent synthesis of 1,2,4,5-tetrasubstituted imidazoles bear-
Introduction
ing
a
4-aminophenyl substituent was studied by
Tetrasubstituted imidazole compounds have been widely
studied in chemistry, biology and materials science, such as
plasma reactors (Heung and Urban 1999), corrosion inhi-
bitors (Liu et al. 2014), anticancer drugs (Wagner et al.
2003), anti-inflammatory agents (Na et al. 2007) and
modulators of Pgp-mediated multidrug resistance (Smith
et al. 2009). Besides, their attractive emitting properties
and the high conjugation degree aromatic nature have
received great attention in the last few years. Masaru
Kimura et al. studied the functional imidazole derivatives
condensation of p-phenylenediamine, aryl diketone, ben-
zaldehyde derivatives and ammonium acetate in the pres-
ence of solid support silica gel and catalyst Keggin-
H3[PW12O40]. The effects of four components molar ratio
along with catalyst loading, irradiation time on the yields
were investigated. Also, the structures of synthesized
compounds were characterized by FT-IR, HRMS, 1H NMR
and 13C NMR spectroscopy. Furthermore, their ultraviolet–
visible maximum absorption, liquid fluorescence emission
maximum and quantum yields were, respectively, mea-
sured in 0.05 M H2SO4 aqueous solution and in dichlor-
omethane. Simultaneously, solid fluorescence spectra were
determined in the powder state. The relationships between
the optical behavior and the polarity of the solvents for
some compounds were assessed. The results showed that
the fluorescence quantum efficiency was increased by
introducing amino phenyl in comparison with benzyl on
1-position of trisubstitued imidazoles. The compounds
synthesized were sensitive to the polarity of the solvents.
ˇ´
on chemiluminescent reactions (Kimura et al. 2007); Jirı
´ ˇ
Kulhanek and Filip Bures researched imidazole as a parent
p-conjugated backbone in charge-transfer chromophores
´
ˇ
(Kulhanek and Bures 2012); Tian M. et al. focused on the
structure–effect relationship of multi-aryl imidazoles with
their fluorescence properties (Tian et al. 2014), etc.
Therefore, the synthesis and property of substituted imi-
dazoles had become an important part of modern organic
synthesis, and attracted more and more chemists, biologists
and materials scientists.
Generally, 1,2,4,5-tetrasubstituted midazoles were syn-
thetically obtained by the multicomponent reactions
(MCRs) of 1,2-diketone, a-hydroxy/acetoxy/silyloxyke-
tone or 1,2-ketomonoxime, aldehyde, amine and ammo-
nium acetate carried out by microwave irradiation in the
presence of silica gel/zeolite HY(Balalaie and Arabanian
2000), silica gel–NaHSO3 (Balalaie et al. 2003; Karimi
et al. 2006), etc., along with traditional heating in a suit-
able solvent using different catalysts (Chhanda and Pradip
2012; Heravi et al. 2007a, b; Jaberi and Barekat 2010;
Javid et al. 2011; Kidwai and Mothsra 2006; Mohammadi
et al. 2012; Murthy et al. 2010; Siddiqui et al. 2005;
Subhasis et al. 2009; Nasr-Esfahani et al. 2015), such as
Keywords Tetrasubstituted imidazole Á Microwave
radiation Á H3[PW12O40] Á Solid support SiO2 Á Solvent
free Á Luminescence property
& Yu-min Zhang
zhang_ym@jlu.edu.cn
1
College of Chemistry, Jilin University, Qianjin Street 2699,
Changchun 130012, People’s Republic of China
2
College of Life Science, Jilin University, Qianjin Street 2699,
Changchun 130012, People’s Republic of China
123

Chem. Pap.
KHSO4/DB18C6, Keggin-type heteropolyacid, NaH2PO4,
poly(AMPS-co-AA), molecular iodine, DABCO, NiCl2/
AlCl3, L-proline and nanorod vanadatesulfuric acid (Nasr-
Esfahani et al. 2015). The clean, high-yielding, time-saving
(reaction time had been shortened to 5–120 min) and
environmentally friendly heteropolyacid (HPA) approaches
by traditional heating (Javid et al. 2011; Heravi et al.
2007b) attracted us into evaluating the catalysis of HPA
under microwave-assisted solvent-free condition. Micro-
wave-assisted solvent-free reaction (Bhoi et al. 2016;
Zhang et al. 2016) could decrease the use of organic sol-
vent and expensive catalysts, shorten reaction time and
facilitate the separation of products (Baghbanzadeh et al.
2011). It was reported that microwave irradiation as a
dielectric heating is a process in which the organic com-
pounds consume electromagnetic energy, which can
accelerate the reaction rate several times, ten times or even
tens of thousands of times compared with conventional
heating (Jin et al. 1999).
enhance the photoluminescence properties of 1,2,4,5-te-
trasubstituted imidazoles in continuation of our search, a
series of new tetrasubstituted imidazoles without benzyl
but an 4-amino phenyl as an auxochrome group on
1-position and different 4-, 5-substituted groups were
prepared, and their photoluminescence properties in solid
state and in the different solvents were studied. The
results of these studies are reported herein.
Experimental
All reagents obtained from commercial companies (Tianjin
Fuyu Chemical Reagent Company, China; Aladdin-reagent
Co.) were of analytical grade and used without further
purification. Aryl diketones were synthesized by referring
to the reported literature (Gao et al. 1998). All reported
yields were isolated yields. A MCL-3-type microwave
reactor in Sichuan University, with a thermometer for
microwave application, was used in all experiments. All
melting points were determined with an XT-4 melting
point apparatus and were uncorrected. High resolution
mass spectrometry (HRMS) was collected on an Agilen-
t1290-micrOTOF Q II spectrometer. 1H and 13C NMR
spectra were measured using a Bruker AVANCE-500
NMR spectrometer with TMS as an internal standard. FT-
IR spectra were obtained with KBr pellets using a Shi-
madzu IRAffinity-1 instrument in the range between 500
and 3500 cm-1. Fluorescence spectra were recorded with a
FLS920 spectrofluorimeter. The absorption spectra were
recorded on a GBC Cintra 10e UV–Vis spectrometer
within the wavelength range from 200 to 800 nm. Fluo-
rescence strengths in solid state were determined at the
corresponding excitation wavelength by a Horiba Fluoro-
max-4 spectrofluorometer.
Consequently, it is very necessary to study new, green
synthetic processes to construct fused tetraimidazole deriva-
tives in higher yields and short reaction time. Moreover, the
used nitrogen sources in the above reactions were ammonia,
aniline, aliphatic amine, etc. However, p-phenylenediamine
has been rarely used, except byChhanda Mukhopadhyay etal.
who reported the synthesis starting from p-substituted aniline
using KHSO4/DB18C6 as catalyst by traditional heating for
4–8 h (Chhanda and Pradip 2012). Herein, one-pot four-
component condensation of p-phenylenediamine, aryl dike-
tone, benzaldehyde derivatives and ammonium acetate cat-
alyzed and dispersed by H3[PW12O40] and a mixture of silica
gel under microwave irradiation and solvent-free conditions
was explored (Scheme 1).
Furthermore, substituted imidazole exhibited favor-
able luminescence (Nagarapu et al. 2007; Buttke et al.
1997). It was reported that the emission spectra were
redshifted when substituted benzyls were introduced into
1-position of 2,4,5-trisubstituted imidazoles containing
furan rings or benzene rings (Chen et al. 2013). How-
ever, the fluorescence quantum yields (Au) of these
compounds were lower in 0.05 M H2SO4 aqueous solu-
tion, probably because methylene on 1-benzyl resulted in
bad coplanarity of tetrasubstituted imidazoles. To
Synthesis and characterization
General synthesis approach for aryl diketones
Aryl diketones were synthesized according to the reported
literature (Gao et al. 1998). A mixture of CuSO4•5H2O
Scheme 1 Synthesis of 1, 2, 4, 5-tetrasubstituted imidazoles bearing a 4-aminophenyl substituent
123

Chem. Pap.
15.80 g (0.0633 mol), pyridine 21.54 g (0.272 mol), and
H2O 10.26 dm3 (0.520 mol) were taken in a three-necked
bottle with a thermometer and a spherical condenser, and
was fully stirred in a water bath. 2-hydroxy-1,2-diaryl-
ethanone (0.0302 mol) was added to the three-necked
bottle when the blue solution became colorless, and then
stirred at 98–100 °C for 1.5 h. The reaction slurry was
poured into cold water for crystallization, then filtered and
washed with plenty of water. Sequentially, the filter cake
was recrystallized in ethanol. The desired aryl diketones
were obtained in 84–93% yield.
alkali. The method for synthesizing 1,2,4,5-tetrasubstituted
imidazoles required not only a long reaction time
(12–24 h), but also a base as an acid-binding agent and
plenty of solvent (Chen et al. 2013). Besides, the fluores-
cence quantum yields of the compounds reported were
lower. In the present work, the corresponding aryl dike-
tones (benzil, furil and 1,2-bis-(4-chlorophenyl)-2-hy-
droxy-ethanone) were synthesized, respectively, in 84, 91
and 93% yields. 1,2,4,5-Tetrasubstituted imidazoles bear-
ing a 4-aminophenyl substituent were synthesized using
silica gel as solid support and H3[PW12O40] as a catalyst
through the condensation of aryl diketones, p-phenylene-
diamine, benzaldehyde and ammonium acetate under
microwave irradiation and solvent-free condition.
General synthesis approach for tetrasubstituted
imidazoles with different substituted groups
It was reported that HPA was an effective catalyst to
synthesize 1,2,4,5-tetrasubstituted imidazole derivatives
starting from benzil, aniline or benzyl amine or methyl
amine in ethanol (Javid et al. 2011; Heravi et al. 2007b). At
the beginning of our investigation, to obtain imidazole
derivative with good luminescence property, bis(1,2,4,5-
tetrasubstituted imidazole) connected by a benzene ring
was designed and synthesized, changing conventional
heating into microwave irradiation. Unfortunately, the
target product was not obtained starting from benzil, p-
phenylenediamine and benzaldehyde using SiO2 or
H3[PW12O40] as a solid support or a catalyst. The obtained
product was confirmed to be 4-(2,4,5-triphenyl-1H-imida-
zol-1-yl)aniline by detection with HRMS and NMR. The
possible reason was that the 2,4,5-triphenyl-1H-imidazol-
1-yl group resulted in the poor nucleophilicity of the amino
group on the benzene ring, along with the steric hindrance
of 4-(2,4,5-triphenyl-1H-imidazol-1-yl)aniline. Sequen-
tially, the synthesis of 1,2,4,5-tetrasubstituted imidazole
was attempted in ethanol using H3[PW12O40] as a catalyst,
starting from benzil and aniline or p-phenylenediamine
referring to the literatures (Javid et al. 2011; Heravi et al.
2007b). As a result, 1,2,4,5-tetraphenyl-1H-imidazole was
obtained with a 82.8% yield in 15 min. Nonetheless, the
yields of obtained 4-(2,4,5-triphenyl-1H-imidazol-1-yl)
aniline (2a) only was 39.8% for 30 min and 50.3% for 6 h
(repeated twice), respectivly. To obtain a higher yield,
H3[PW12O40] as a catalyst and silica gel as a solid support
were explored under microwave irradiation. Herein, the
effects of catalyst loading, microwave irradiation time and
the molar ratio of the reactant on the yield of the synthe-
sizing 4-(2,4,5-triphenyl-1H-imidazol-1-yl)aniline (2a)
were explored by employing benzil, p-phenylenediamine,
benzaldehyde and ammonium acetate (Table 1).
A mixture of p-phenylenediamine (1 mmol), aryl diketone
(2 mmol), benzaldehyde derivatives (2 mmol), ammonium
acetate (8 mmol), silica gel (1 g) and H3[PW12O40] (0.7%)
was fully ground in a mortar, then transferred to a 50 mL
dried round-bottomed flask and heated with microwave
irradiation for 15 min (the reaction temperature was
130 °C). The reaction progress was monitored by TLC on
Silufol-254 plates. When the microwave-assisted reaction
was over, the residue was cooled to room temperature and
purified by column chromatography on Chemapol
(200–300 mesh) silica gel (petroleum ether/ethyl acet-
ate = 3/1) and then recrystallized in ethanol to give the
desired products.
Determination of fluorescence quantum yield
The fluorescent quantum yields were measured against
quinine sulfate (Au = 0.55 in 0.05 M sulfuric acid,
200 nm B k B 400 nm) as a standard (Gill 1969; Fletcher
1969) and was calculated according to the literature (Ci and
Jia 1986).
Results and discussion
Synthesis of the compounds
In our previous work, some 2-substituted-4,5-di(2-furyl)-
1H-imidazoles were synthesized using Al2O3 as solid
supports starting from 1,2-di(furan-2-yl)-2-oxoethyl car-
boxylates (Li et al. 2012) or furil (Zhang et al. 2015) under
microwave irradiation and solvent-free conditions. Herein,
the reactions were accelerated which might be because of
the action of microwave to decrease the activation energy
of the reaction. Furthermore, some corresponding tetra-
substituted imidazoles containing furan rings were syn-
thesized via condensation of 2-substituted-4,5-di(2-furyl)-
1H-imidazoles and benzyl chloride in the presence of
As shown in Table 1, we successfully synthesized the
desired product 2a in 23.5–78.3% using p-phenylenedi-
amine (A), benzil (B), benzaldehyde (C) and ammonium
acetate (D) in the presence of H3[PW12O40] as a catalyst
(Table 1, entries 3–12) and in catalyst-free condition
123

Chem. Pap.
Table 1 Effect of reaction factors on synthesizing 2a
Entry
Substrate A:B:C:D
Catalyst
Catalyst
T (°C)
Time (min)
Yielda (%)
Equiv (%)
1
1:2:2:8
1:2:2:8
1:2:2:8
1:2:2:8
1:2:2:8
1:2:2:8
1:2:2:8
1:2:2:8
1:2:2:8
1:1:1:4
1:1:1:8
1:1.3:1.3:8
None
–
130
130
130
130
130
130
130
130
130
130
130
130
15
20
15
15
15
5
56.8
57.3
78.3
63.7
78.1
23.5
47.3
78.3
78.9
71.2
69.6
72.2
2
None
–
3
H3[PW12O40
H3[PW12O40
H3[PW12O40
H3[PW12O40
H3[PW12O40
H3[PW12O40
H3[PW12O40
H3[PW12O40
H3[PW12O40
H3[PW12O40
]
]
]
]
]
]
]
]
]
]
0.7
0.2
1.2
0.7
0.7
0.7
0.7
0.7
0.7
0.7
4
5
6
7
10
18
20
15
15
15
8
9
10
11
12
a
Isolated product yield
(Table 1, entries 1, 2), respectively. Further, the reaction
condition was optimized. The influence of catalyst loading
on the yield was investigated. The yield of 2a was
increased significantly with increasing catalyst loading
from 0 to 0.7% mol of p-phenylenediamine or benzil
(Table 1, entries 1, 3 and 4). Nevertheless, the yield of 2a
was basically the same when H3[PW12O40] was loaded to
1.2% (Table 1, entry 5). Also, the effect of microwave
irradiation times on the yields of the product was observed.
The yield of 2a was substantially increased under micro-
wave irradiation for 15 min (78.3%) compared with that of
shorter irradiation time. However, the yield was not obvi-
ously enhanced when the reaction time was further
increased to 18 min (78.3%) and 20 min (78.9%) (Table 1,
entries 3 and 6–9). Further, the effects of the different
molar ratios of A, B, C, D (1:1:1:4, 1:1:1:8 and 1:1.3:1.3:4)
on the yield were investigated (Table 1, entries 3 and
10–12), and the target product was, respectively, obtained
with 71.2, 69.6 and 72.2% yield. Therefore, from the per-
spective of economic and environmental considerations,
the optimized reaction conditions were identified as fol-
lows: The molar ratio of the four components was 1:1:1:4,
microwave irradiation 15 min and catalyst load 0.7% mol
of aryl diketone.
Subsequently, a series of novel 1,2,4,5-tetrasubstituted
imidazoles bearing 4-amino phenyl had been synthesized
in 46.4–79.1% yields under the optimized reaction condi-
tions (Table 2). As shown in Table 2, aromatic aldehydes
bearing both electron-donating and electron-withdrawing
groups readily underwent the reaction and obtained the
target products in a moderate to good yield. Better yields
were obtained when using p-substituted benzaldehyde
containing electron-donating groups and without substitu-
tents (Table 2, –CH3, entries 3 and 8; –H, entries 1, 5 and
10) as starting materials than that containing electron-
withdrawing groups (Table 2, –NO2, –Cl, –Br, entries 2, 4,
6, 7 and 9). When R was furyl, the yield was much lower
than that of phenyl and substituted phenyl (Table 2, entries
1–4 and 10–12), because lower conjugation energy and rich
p electron feature of the furan ring reduced the stability and
eletrophilicity of carbonyl carbon. Furthermore, the struc-
tures of the synthesized 1,2,4,5-tetrasubstituted imidazoles
1
bearing 4-amino phenyl were confirmed by FT-IR, H and
13C NMR and HRMS analysis (Table 3). The resonances
of aryl-NH2 proton of the synthesized compounds exhib-
ited at 5.29–5.47 ppm, while the resonances for the aryl-N–
RC = N–carbon atom on imidazole ring were observed at
145.4–147.9 ppm (DMSO as the solvent).
123

Chem. Pap.
Table 2 Synthesis of
compounds of 1,2,4,5-
tetrasubstituted imidazoles
bearing 4-amino phenyl
Entry
1
R─
R1
H
Produce
Yield b (%)
71.2
M.p. (oC)
224-226
220-222
237-239
2a
2b
2c
2
3
Br
56.6
CH3
67.0
4
5
NO2
H
53.8
79.1
60.9
46.4
74.3
58.9
62.4
56.4
48.7
244-246
225-227
218-220
217-218
241-243
234-236
244-246
198-201
212-214
2d
2e
2f
l
C
l
C
l
C
l
C
l
C
6
Cl
7
Br
2g
2h
2i
8
CH3
NO2
H
9
O
10
11
12
2j
O
Cl
2k
2l
O
Br
Reaction conditions: p-phenylenediamine (1 mmol), aryl diketone (1 mmol), benzaldehyde derivatives
(1 mmol), ammonium acetate (4 mmol), silica gel (1 g), H3[PW12O40] (0.7%), MW heating 15 min
a
Isolated product yield
corresponding excitation wavelength were measured and
are summarized in Table 4. Besides, Au were measured
and calculated against quinine sulfate as a standard
(Table 4) according to the literature (Gill 1969; Fletcher
1969; Ci and Jia 1986). The maximum emission wave-
lengths of 2a–2l in 0.05 M H2SO4 aqueous solution red-
shifted, and their Au decreased comparing with that of in
DCM. The main reason was that H2SO4 protonated amino
Luminescence properties of the synthesized
compounds
Substituted groups effects on the spectral properties
The absorbance and fluorescence properties of compounds
2a–2l (1.0 9 10-6 mol/L) in 0.05 M H2SO4 aqueous
solution and in dichloromethane (DCM) excited at
123

Chem. Pap.
Table 3 Characterization data of synthesized compounds
Compound Characterizing data
2a
IR(KBr) m (cm-1): 3445, 3053, 1599, 1514, 1287, 1169, 1072, 961, 835, 692, 538.
1H NMR (500 MHz, DMSO) d (ppm): 7.46 (dd, J = 6.2, 3.5 Hz, 4H), 7.30 (dd, J = 7.1, 5.5 Hz, 6H), 7.26–7.20 (m, 4H), 7.15 (t,
J = 7.9 Hz, 1H), 6.86 (d, J = 8.6 Hz, 2H), 6.42 (d, J = 8.6 Hz, 2H), which were ascribed to H on benzene rings. 5.30 (s, amino
2H)
13C NMR (125 MHz, DMSO) d (ppm): 149.3 (1-phenyl–C4), 146.5 (imidazole–C2), 137.0 (2-phenyl–C1), 135.2 (imidazole–C5,
4-phenyl–C1), 132.2 (5-phenyl–C1), 131.6 (2-phenyl–C4), 129.5 (imidazole–C4), 128.8, 128.6, 128.5, 126.8 (ascribed to non-
quaternary carbon of 2-phenyl, 4-phenyl and 5-phenyl.), 126.7 (1-phenyl–C3, C5) 125.0 (1-phenyl–C1), 114.1 (1-phenyl–C2, C6)
HRMS, m/z: (M ? H)? calcd for C27H22N3 388.1814, found 388.1791
2b
IR(KBr) m (cm-1): 3441, 3319, 3207, 3040, 1638, 1516, 1442, 1294, 1167, 1074, 964, 822, 777, 700, 640, 536
1H NMR (500 MHz, DMSO) d (ppm): 7.52 (d, J = 8.6 Hz, 2H), 7.46 (d, J = 8.4 Hz, 2H), 7.39 (d, J = 8.7 Hz, 2H), 7.35–7.29 (m,
3H), 7.28–7.19 (m, 4H), 7.16 (t, J = 7.3 Hz, 1H), 6.87 (d, J = 8.6 Hz, 2H), 6.43 (d, J = 8.6 Hz, 2H), which were ascribed to H
on benzene rings. 5.33 (s, amino 2H).13C NMR (125 MHz, DMSO) d(ppm): 149.38(1-phenyl–C4), 145.36 (imidazole–C2),
137.08 (2-phenyl–C1), 134.96 (imidazole–C5), 133.29 (4-phenyl–C1), 132.52 (5-phenyl–C1), 131.10 (2-phenyl–C4), 130.07
(imidazole–C4), 131.56, 130.02, 129.45, 128.82, 128.71, 128.71, 128.65, 126.82(ascribed to non-quaternary carbon of 2-phenyl,
4-phenyl and 5-phenyl.) 126.77 (1-phenyl–C3, C5), 124.68(1-phenyl–C1), 114.15 (1-phenyl–C2, C6)
HRMS, m/z: (M ? H)? calcd for C27H21BrN3 466.0919, found 466.1142
2c
IR(KBr) m (cm-1): 3441, 3321, 3207, 3049, 2957, 2875, 1628, 1514, 1477, 1290, 1139, 1010, 961, 827, 750, 696, 518
1H NMR (500 MHz, DMSO) d (ppm): 7.49–7.44 (m, 2H), 7.36–7.28 (m, 5H), 7.25–7.19 (m, 4H), 7.15 (t, J = 7.3 Hz, 1H), 7.10 (d,
J = 8.1 Hz, 2H), 6.83 (d, J = 8.6 Hz, 2H), 6.42 (d, J = 8.6 Hz, 2H), which were ascribed to H on benzene rings. 5.29 (s, amino
2H), 2.27 (s, 3H)
13C NMR (125 MHz, DMSO) (ppm): 149.18(1-phenyl–C4), 146.65 (imidazole–C2), 137.92 (2-phenyl–C1), 136.76 (imidazole–
C5), 135.21 (4-phenyl–C1), 131.97 (5-phenyl–C1), 131.59 (2-phenyl–C4), 131.37 (imidazole–C4), 128.46 (2-phenyl–C4),
129.52, 129.11, 128.78, 128.57, 128.52, 126.76(ascribed to non-quaternary carbon of 2-phenyl, 4-phenyl and 5-phenyl.),
126.65(1-phenyl–C3, C5), 125.10(1-phenyl–C1), 114.08(1-phenyl–C2, C6), 21.22(CH3–C)
HRMS, m/z: (M ? H)? calcd for C28H24N3 402.1970, found 402.1961
2d
2e
2f
IR(KBr) m (cm-1): 3441, 3327, 3211, 3026, 1622, 1514, 1475, 1290, 1167, 1090, 1010, 829, 773, 635, 509
1H NMR (500 MHz, DMSO) d (ppm): 8.20–8.16 (m, 2H), 7.73–7.69 (m, 2H), 7.50–7.47 (m, 2H), 7.36–7.32 (m, 3H), 7.28–7.23 (m,
4H), 7.19 (t, J = 7.3 Hz, 1H), 6.92 (d, J = 8.6 Hz, 2H), 6.46 (d, J = 8.7 Hz, 2H), which were ascribed to H on benzene rings
5.39 (s, amino 2H)
13C NMR (125 MHz, DMSO) d (ppm): 149.67(2-phenyl–C4), 146.93 (1-phenyl–C4), 144.31 (imidazole–C2), 138.01 (imidazole–
C5), 137.15 (4-phenyl–C1), 134.63 (2-phenyl–C1), 133.78 (5-phenyl–C1), 130.73 (imidazole–C4), 131.54, 129.38, 128.99,
128.84, 128.88, 128.65 127.10 (ascribed to non-quaternary carbon of 2-phenyl, 4-phenyl and 5-phenyl.), 126.83((1-phenyl–C3,
C5), 124.32(1-phenyl–C1), 123.90 (2-phenyl–C3, C5), 114.24 (1-phenyl–C2, C6)
HRMS, m/z: (M ? H)? calcd for C27H21N4O2 433.1665, found 433.1685
IR (KBr) m (cm-1): 3474, 3385, 3041, 1618, 1514, 1285, 1285, 1136, 1090, 957, 831, 773, 692, 500
1H NMR (500 MHz, DMSO) d (ppm): 7.49–7.43 (m, 4H,), 7.39 (d, J = 8.4 Hz, 2H,), 7.34 (d, J = 8.6 Hz, 2H), 7.32–7.29 (m,
3H,), 7.25 (d, J = 8.4 Hz, 2H), 6.87 (d, J = 8.6 Hz, 2H), 6.44 (d, J = 8.6 Hz, 2H), which were ascribed to H on benzene rings.
5.35 (s, amino 2H)
13C NMR (125 MHz, DMSO) d(ppm): 149.43 (1-phenyl–C4), 147.00 (imidazole–C2,), 136.11(2-phenyl–C1), 133.80(4-phenyl–
C1), 133.61(imidazole–C5), 131.44 and 131.21(4,5-phenyl–C4), 130.92(2-phenyl–C4), 129.85 (5-phenyl–C1), 133.30, 129.50,
129.06, 128.78, 128.57, 128.56 and 128.55(ascribed to non-quaternary carbon of 2-phenyl, 4-phenyl and 5-phenyl.), 128.42(1-
phenyl–C3, C5), 124.60(1-phenyl–C1), 114.14(1-phenyl–C2, C6)
HRMS, m/z: (M ? H)? calcd for C27H20Cl2N3 456.1034, found 456.1023
IR (KBr) m (cm-1): 3441, 3319, 3206, 3040, 1638, 1516, 1443, 1294, 1167, 1074, 964, 822, 777, 700, 640, 536
1H NMR (500 MHz, DMSO) d (ppm): 7.53 (d, J = 1.9 Hz, 1H), 7.52–7.51 (m, 1H), 7.46 (d, J = 2.0 Hz, 1H), 7.46–7.44 (m, 1H),
7.39 (dd, J = 7.0, 1.6 Hz, 4H), 7.35 (d, J = 2.1 Hz, 1H), 7.33 (s, 1H), 7.25 (s, 1H), 7.23 (s, 1H), 6.88 (d, J = 8.6 Hz, 2H), 6.45
(d, J = 8.7 Hz, 2H), which were ascribed to H ascribe to on benzene rings. 5.38 (s, amino 2H)
13C NMR (125 MHz, DMSO) d(ppm): 149.58 (1-phenyl–C4), 145.92(imidazole–C2,), 136.32 (2-phenyl–C1), 133.72 (imidazole–
C5), 133.62 (4-phenyl–C1), 131.55 (2-phenyl–4C), 130.08 (4-phenyl–4C, 5-phenyl–4C), 129.67 (imidazole–C4), 133.29, 131.62,
130.38, 129.42, 129.09 and 128.81(ascribed to non-quaternary carbon of 2-phenyl, 4-phenyl and 5-phenyl.), 128.43 (1-phenyl–
C3, C5), 124.27 (5-phenyl–C1), 122.25 (1-phenyl–C1), 114.20 (1-phenyl–C2, C6)
HRMS, m/z: (M ? H)? calcd for C27H19Cl3N3 490.0645, found 490.1003
123

Chem. Pap.
Table 3 continued
Compound Characterizing data
2g
IR(KBr) m (cm-1): 3458, 3319, 3204, 3053, 1622, 1516, 1296, 1138, 1094, 1015, 837, 759, 640
1H NMR (500 MHz, DMSO) d (ppm): 7.53 (d, J = 1.9 Hz, 1H), 7.52–7.51 (m, 1H), 7.46 (d, J = 2.0 Hz, 1H), 7.46–7.44 (m, 1H),
7.40 (d, J = 2.0 Hz, 1H), 7.39 (d, J = 1.1 Hz, 2H), 7.38–7.36 (m, 1H), 7.35 (d, J = 2.1 Hz, 1H), 7.33 (s, 1H), 7.24 (d,
J = 8.5 Hz, 2H), 6.88 (d, J = 8.6 Hz, 2H), 6.45 (d, J = 8.7 Hz, 2H), which were ascribed to H on benzene rings. 5.38 (s, amino
2H)
13C NMR (125 MHz, DMSO) d(ppm): 149.58(1-phenyl–C4), 145.87 (imidazole–C2,), 136.29 (2-phenyl–C1), 133.71 (imidazole–
C5), 133.63 and 133.52(4-phenyl–C4 and 5-phenyl–C4), 131.55 (4-phenyl–C1), 131.51 (imidazole–C4), 129.73 (5-phenyl-C1),
129.68 (2-phenyl-C4), 133.29, 130.12, 129.43, 129.09, 128.81, 128.71, 128.43 (ascribed to non-quaternary carbon of 2-phenyl,
4-phenyl and 5-phenyl.), 124.29 (1-phenyl–C1), 114.20(1-phenyl–C2,C6)
HRMS, m/z: (M ? H)? calcd for C27H19BrCl2N3 534.0139, found 534.0175
2h
IR (KBr) m (cm-1): 3431, 3341, 3233, 3052, 2931, 2873, 1597, 1516, 1342, 1093, 1013, 833, 719, 624, 514
1H NMR (500 MHz, DMSO) d (ppm): 7.46 (d, J = 8.7 Hz, 2H), 7.38 (d, J = 8.5 Hz, 2H), 7.33 (d, J = 8.8 Hz, 4H), 7.23 (d,
J = 8.5 Hz, 2H), 7.11 (d, J = 8.0 Hz, 2H), 6.85 (d, J = 8.6 Hz, 2H), 6.44 (d, J = 8.7 Hz, 2H), which were ascribed to H on
benzene rings. 5.34 (s, amino 2H), 2.27 (s, 3H, CH3 H)
13C NMR (125 MHz, DMSO) d(ppm): 149.39 (1-phenyl–C4), 147.17 (imidazole–C2), 138.19 (2-phenyl–C1), 135.98 (imidazole–
C5), 133.87 and 133.57 (4,5-phenyl–C1), 131.38 and 130.98 (4,5-phenyl–C4), 129.93 (imidazole–C4), 133.31, 129.51, 129.05,
128.76 and 128.50 (ascribed to non-quaternary carbon of 2-phenyl, 4-phenyl and 5-phenyl.), 128.42 (1-phenyl–C3,C5), 128.14 (2-
phenyl–C1), 124.70 (1-phenyl–C1), 114.14 (1-phenyl–C2,C6), 21,23 (CH3–C)
HRMS, m/z: (M ? H)? calcd for C28H22Cl2N3 470.1191, found 470.1109
2i
IR (KBr) m (cm-1): 3474, 3381, 3053, 1624, 1518, 1477, 1292, 1169, 1092, 1074, 961, 831, 729, 698, 500
1H NMR (500 MHz, DMSO) d(ppm): 8.18 (d, J = 9.0 Hz, 2H), 7.70 (d, J = 9.1 Hz, 2H), 7.48 (d, J = 8.7 Hz, 2H), 7.42 (d,
J = 8.5 Hz, 2H), 7.37 (d, J = 8.6 Hz, 2H), 7.27 (d, J = 8.5 Hz, 2H), 6.93 (d, J = 8.6 Hz, 2H), 6.48 (d, J = 8.6 Hz, 2H), which
were ascribed to H on benzene rings. 5.44 (s, amino 2H)
13C NMR (125 MHz, DMSO) d (ppm): 149.84 (1-phenyl–C4, 2-phenyl–C4), 147.09 (2-phenyl–C1), 144.80(imidazole–C2), 137.14
(imidazole–C5), 136.85(4-phenyl–C1), 133.95 and 133.31 (4,5-phenyl–C4), 132.70 (imidazole–C4), 131.83 (5-phenyl–C1),
129.32 (1-phenyl–C1), 133.29, 129.11, 128.89 and 123.93 (ascribed to non-quaternary carbon of 2-phenyl, 4-phenyl and
5-phenyl.), 128.49 (1-phenyl–C3, C5), 114.29 (1-phenyl–C2, C6)
HRMS, m/z: (M ? H)? calcd for C27H19Cl2N4O2 501.0885, found 501.1028
2j
IR (KBr) m (cm-1): 3421, 3325, 3221, 3043, 3128, 1631, 1516, 1469, 1292, 1168, 1072, 1010, 887, 775, 740, 594, 540
1H NMR (300 MHz, DMSO) d (ppm): 7.71–7.66 (m, 1H), 7.66–7.61 (m, 1H), 7.45 (dd, J = 6.6, 3.2 Hz, 2H), 7.34–7.29 (m, 3H),
6.94–6.89 (m, 2H), 6.49 (ddd, J = 11.1, 3.4, 1.8 Hz, 5H), 6.27 (d, J = 3.1 Hz, 1H), which were ascribed to H on benzene rings
and furan rings. 5.42 (s, amino 2H)
13C NMR (125 MHz, DMSO) d(ppm): 149.75 and 149.29 (4-furyl–C2, 5-furyl–C2), 147.89(1-phenyl–C4), 142.96 (imidazole–C2),
132.43 (2-phenyl–C1), 130.53(imidazole–C4), 129.12, 128.97 (4-furyl–C5, 5-furyl–C5), 128.66 128.65 (1-phenyl–C2,
C6),128.60 (imidazole–C5), 122.40 (1-phenyl–C1), 114.18 (1-phenyl–C2, C6), 112.64, 111.73, 111.57, 107.15(4-furyl–C3,C4
and 5-furyl–C3,C4)
HRMS, m/z: (M ? H)? calcd for C23H18N3O2 368.1399, found 368.1398
2k
IR (KBr) m (cm-1): 3448, 3317, 3212, 3136, 3037, 1635, 1519, 1300, 1168, 1090, 1014, 833, 736, 594, 520
1H NMR (300 MHz, DMSO) d (ppm): 7.69 (dd, J = 1.9, 0.8 Hz, 1H), 7.65 (dd, J = 1.8, 0.9 Hz, 1H), 7.42 (d, J = 6.6 Hz, 4H),
6.93 (d, J = 8.7 Hz, 2H), 6.55–6.47 (m, 5H), 6.27 (dd, J = 3.4, 0.8 Hz, 1H), which were ascribed to H on benzene rings and
furan rings.5.46 (s, amino 2H)
13C NMR (125 MHz, DMSO) d(ppm): 149.89 and 149.13(4-furyl–C2, 5-furyl–C2), 146.77 (1-phenyl–C4), 142.79 (imidazole–C2),
133.82 (1-phenyl–C1), 132.53(imidazole–C4), 130.27 (5-furyl–C5, 4-furyl–C5), 129.35 (2-phenyl–C2,C6), 129.06 (imidazole–
C5), 128.74 (2-phenyl–C3,C5), 124.31 (2-phenyl–C4), 122.65 (1-phenyl–C1), 114.24 (1-phenyl–C2, C6), 112.73, 111.75, 111.59,
107.27 (4-furyl–C3,C4 and 5-furyl–C3,C4)
HRMS, m/z: (M ? H)? calcd for C23H17ClN3O2 402.1009, found 402.1023
2l
IR (KBr) m (cm-1): 3441, 3309, 3209, 3136, 3051, 1635, 1519, 1296, 1165, 1068, 1010, 829, 748, 594, 516
1H NMR (300 MHz, DMSO) d (ppm): 7.70 (dd, J = 1.9, 0.7 Hz, 1H), 7.65 (dd, J = 1.7, 0.8 Hz, 1H), 7.56–7.52 (m, 2H),
7.40–7.34 (m, 1H), 6.97–6.90 (m, 2H), 6.55–6.46 (m, 3H), 6.28 (d, J = 0.8 Hz, 1H), which were ascribed to H on benzene rings
and furan rings.5.47 (s, amino 2H)
13C NMR (125 MHz, DMSO) d(ppm): 149.90 and 149.11 (4-furyl–C2, 5-furyl–C2), 146.78 (1-phenyl–C4), 142.78 (imidazole–
C2), 132.56 (1-phenyl–C1), 131.65 and 130.51 (5-furyl–C5, 4-furyl–C5), 129.70 (imidazole–C4), 129.05 (2-phenyl–C3,C5),
128.7 (2-phenyl–C2,C6) 124.30 (imidazole–C5), 122.69 (1-phenyl–C1), 122.57 (2-phenyl–C4), 114.23 (1-phenyl–C2, C6),
112.74, 111.76, 111.60, 107.28 (4-furyl–C3,C4 and 5-furyl–C3,C4)
HRMS, m/z: (M ? H)? calcd for C23H17BrN3O2 446.0504, found 446.0532
123

Chem. Pap.
Table 4 Fluorescence
properties of compounds of
1,2,4,5-tetrasubstituted
imidazoles bearing 4-amino
phenyl
Compound
kmax (nm)
Fsmax (nm)
FWlmax (nm)
AuW
FDlmax (nm)
AuD
2a
2b
2c
2d
2e
2f
2g
2h
2i
276
268
267
260
286
281
286
280
283
297
299
298
311
287
384
397
385
396
389
394
394
386
394
411
393
397
–
405
415
417
411
418
419
419
417
414
487
486
488
460
467
0.273
0.195
0.332
0.002
0.215
0.239
0.134
0.487
0.004
0.133
0.115
0.086
0.376
0.101
381
385
381
380
392
387
388
401
400
408
419
422
415
411
0.406
0.189
0.468
0.009
0.406
0.380
0.125
0.633
0.011
0.399
0.334
0.053
0.744
0.145
2j
2k
2l
m
n
–
AWu and ADu are the fluorescence quantum yields in 0.05 M H2SO4 aqueous solution H2SO4 and in
dichloromethane (DCM) using quinine sulfate as standard
FWlmax, FDlmax Fsmax are the emission wavelengths excited at corresponding wavelength with gap 3 and 1 mm,
respectively, in 0.05 M H2SO4 aqueous solution H2SO4, in dichloromethane (DCM) and in the solid state
group of 4-amino phenyl group in 0.05 M H2SO4 aqueous
solution, which led to fluorescence quenching (Huang et al.
2012). Also, the emission of the synthesized compounds
bearing furan rings redshifted about 20 nm compared to the
corresponding compounds with 1-benzyl (Chen et al. 2013)
in the above H2SO4 solution. This was because of the
interaction of n–p and p–p electrons, along with copla-
narity between 4-amino phenyl and trisubstituted imidazole
(Huang, et al., 2012). In addition, compared to our previous
work, Au of 2j (0.133 in 0.05 M H2SO4 aqueous solution
and 0.399 in DCM) was lower than that of 4,5-di(furan-2-
yl)-2-phenyl-1H-imidazole (Li et al. 2012) (m, Table 4)
(0.376 in 0.05 M H2SO4 aqueous solution and 0.744 in
DCM), but higher than that of 1-benzyl-4,5-di(furan-2-yl)-
2-phenyl-1H-imidazole (Nagarapu et al. 2007) (n, Table 4)
(0.101 and 0.145). This is likely because the coplanarity of
trisubstituted imidazole is superior to tetrasubstituted imi-
dazole. Also, the conjugate effect of amino phenyl is
superior to benzyl, which improved the fluorescence
properties and enhanced Au of the synthesized compounds.
Furthermore, as shown in Table 4, the emission wave-
consistent with the literature (Chen et al. 2013). In H2SO4
aqueous solution, Au of imidazole derivatives bearing
furan rings on 4,5-position of imidazole (Table 4, entries
2j–2l) were lower than that bearing the benzene ring and
substituted benzene ring (Table 4, entries 2a–2i). This was
because the oxygen atom of furan rings contains a pair of
non-bonding n-electron and p-electron engender n–p* and
p–p* transitions in the excitation, whereas the n–p* and p–
p* energy of the furan ring was much lower than the p–p*
transition energy of benzene ring. In the 2e–2i series, 2h
bearing -CH3 similarly had the highest Au (0.487) fol-
lowed by 2f (-Cl, 0.239) rather than 2e (-H, 0.215) and
then in turn 2g (-Br, 0.134) and 2i(-NO2, 0.004)
(Table 3, entries 2e–2i). The n-electron cloud of the chloro
lengths of 2a–2l in 0.05 M H2SO4 aqueous solution (Flwmax
)
and in DCM (FDlmax) were, respectively, from 405 to
488 nm and from 381 to 422 nm. They emitted purple
light. Herein, Au (from 0.002 to 0.487 and from 0.009 to
0.633) of 2a–2l, respectively, in 0.05 M H2SO4 aqueous
solution and in DCM changed depending on the sub-
stituents investigated. The effects of substituents on the
maximal emission wavelength and Au were mainly relative
to the 2-position substituent groups of imidazoles when 4-
and 5-substituted groups were the same, which was
Fig. 1 The emission spectra of 2c in the solvents with different
polarities (kex = 300 nm)
123

Chem. Pap.
molecular planarity. Additionally, compared with solid-
state emission spectra, in the DCM solvent, the emission of
the compounds redshifted 3–26 nm (Table 4, entries 5, 8,
9, 11, 12), indicating that there was a little interaction
between DCM and the reported compounds (Ho et al.
2005). On the other hand, it also suggested that these
compounds had strong p–p* interaction in the solid state
(Table 4, entries 1–4, 6, 7, 10).
Effects of solvent polarity on photoluminescence
Furthermore, the fluorescence emission spectra of 2c and
2h (1.0 9 10-6 mol/dm3) in the solvents with different
polarity (toluene, dichloromethane, THF, methanol and
acetonitrile) under the same test condition are shown in
Fig. 1 and 2, respectively. The corresponding data are
summarized in Table 5.
Fig. 2 The emission spectra of 2 h in the solvents with different
polarities (kex = 300 nm)
group on 2-substituted phenyl of imidazole is almost par-
allel with that of the p orbit of aromatic rings, which
increased the conjugated effect and coplanarity of the
molecule (Table 3, entries 2e–2i) (Xu and Wang 2006). In
addition, the reason for fluorescence quenching (Table 4,
entries 2d, 2i) was that compounds bearing nitro group
could switch from the excited singlet (n, p*1) to triple state
under light irradiation (Huang et al. 2012). However, when
benzene was replaced by a low electron-withdrawing
substituent, such as a halogen (entries 2f and 2g; 2j and
2 k), Au gradually decreased with 2-position of tetrasub-
stituted imidazoles bearing 4-chlorophenyl and 4-bro-
mophenyl, which was derived from the introduction of
heavy atoms (Cl and Br) resulting in a great enhancement
of the rate of S1-T1 spin-forbidden process (Chen et al.
1990; Chen and Tong 2014; Chandra et al. 1978). In DCM,
Au of the synthesized compounds was basically dependent
on the electron-donating ability of the substituent. How-
ever, Au of 2e and 2f showed abnormal change rule, and Au
of imidazole derivatives bearing 2-furyl on 4,5-position of
imidazole (Table 4, entries 2j–2l) were about equal to that
of compounds bearing phenyl and substituted phenyl
(Table 4, entries 2a–2i). It was likely due to the repelling
effect between n-electrons of oxygen atom on 2-furyl and
that of chlorine atom on DCM which improved the
Notably, the Au of compounds 2c and 2h were
decreased significantly with increasing solvent polarity
(toluene, dichloromethane, THF and methanol). In toluene,
Au of 2c (0.587) and 2h (0.648) was highest and decreased
with increasing solvent polarity. In methanol, the values
were reduced to 0.257 (2c) and 0.407 (2h), respectively. It
suggested that the polarity of the ground state molecule
was much lower than the singlet excited one in the course
of an intramolecular charge transfer, and stronger electro-
static interactions between the excited molecule and polar
solvent were proposed to result in a decrease in Au. Higher
polar acetonitrile showed an anomalous increase compared
to methanol and THF, maybe because of intermolecular
hydrogen bonding between the acidic hydrogen of com-
pounds 2c and 2h and the cyano groups of acetonitrile
(Shirai et al. 2000). However, the emission bands of
compound 2c and 2h were redshifted slightly with an
increase of the solvent polarity. In toluene, the emission of
2c and 2h were at 383 nm (Fig. 1) and 390 nm (Fig. 2),
respectively. However, in methanol, they were, respec-
tively, redshifted to 399 nm (2c) and 406 nm (2h) due to
the stronger interaction between the solvent and the excited
state molecules in p–p* transition. The excited state was
more stabilized in polar solvents than that in lower polar
solvents. In acetonitrile, an anomalous decrease was shown
Table 5 The emission wavelength and Au of 2c and 2h in the solvents with different polarities (kex = 300 nm)
Solvents
Dipole moment (Debye)
2c
2h
Emission wavelength (nm)
Au
Emission wavelength (nm)
Au
Toluene
DCM
0.43
1.60
1.63
1.70
3.45
383
381
389
399
395
0.587
0.468
0.288
0.257
0.322
390
401
399
406
401
0.648
0.633
0.456
0.407
0.546
THF
Methanol
Acetonitrile
123

Chem. Pap.
polyarylierten Imidazolen und Oxazolen. J Fu¨r Prakt Chem
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Chandra AK, Turro NJ, Lyons AL, Stone P (1978) The intramolecular
external heavy atom effect in bromo-, benzo-, and naphthonor-
compared to methanol for intermolecular hydrogen bond-
ing. Also, compounds 2c and 2h possessed higher Au. Au
of 2h was obviously higher for the chloro group introduced
into the imidazole ring which made the coplanarity of
tetrasubstituted imidazole better.
bornenes. J Am Chem Soc 100:4964–4968. doi:10.1021/
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Chen XT, Tong AJ (2014) Halogenated salicylaldehyde azines: the
heavy atom effect on aggregation-induced emission enhance-
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2013.08.051
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Chen GZh, Huang XZh, Zhang ZhZ, Xu JG, Wang JB (1990)
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synthesis of 1-R1-2-R-4,5-di(furan-2-yl)-1H–imidazoles and
their luminescence properties. Comptes Rend Chim
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Fletcher AN (1969) Quinine sulfate as a fluorescence quantum yield
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Gill JE (1969) The fluorescence excitation spectrum of quinine
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1097.1969.tb07295.x
Heravi MM, Bakhtiari K, Oskooie HA Taheri S et al (2007a)
Synthesis of 2,4,5-triaryl-imidazoles catalyzed by NiCl2Á6H2O
under heterogeneous system. J Mol Catal A Chem 263(1):
279–281. doi:10.1016/j.molcata.2006.08.070
Heravi MM, Derikvand F, Bamoharram FF (2007b) Highly efficient,
four-component one-pot synthesis of tetrasubstituted imidazoles
using Keggin-type heteropolyacid as green and reusable cata-
lysts. J Mol Catal A-Chem 263:112–114. doi:10.1016/j.molcata.
2006.08.048
A facile and efficient one-pot MCRs microwave-irradiated
method for synthesizing 1,2,4,5-tetrasubstituted imidazoles
bearing auxochrome 4-amino phenyl (1-position) was
revealed. Twelve 1,2,4,5-imidazoles bearing a 4-amino-
phenyl substituent were successfully synthesized in
56.8–74.3% using H3[PW12O40] as a catalyst and silica gel
as solid support, and Au values were measured against
quinine sulfate in the 0.05 M H2SO4 aqueous solution and
the different solvents. The effects of different substituted
groups on the emission and Au in the 0.05 M H2SO4
aqueous solution, in DCM and in the solid state, were
investigated. The highest Au was up to 0.487 in H2SO4
solution, 0.648 in toluene and 0.633 in DCM. It was found
that 2- and 4,5-substituents of 1,2,4,5-tetrasubstituted imi-
dazoles with a 4-aminophenyl substituent, respectively,
had much influence on Au, and the emission and Au of
tetraimidazole compounds in solution could be restricted
by the polarity of the solvents. It suggested that the syn-
thesized compounds would have potential applications in
the metal ion detection, biological pharmaceutical and
material fields. In addition, the applications of 1,2,4,5-
trisubstituted imidazoles bearing 4-amino phenyl in metal
ion detection is being studied in our laboratory.
Heung K, Urban MW (1999) Effect of discharge gases on microwave
plasma reactions of imidazole on poly(dimethylsiloxane) sur-
faces: quantitative ATR FT-IR spectroscopic analysis. Langmuir
15:3499–3505. doi:10.1021/la970039q
Acknowledgements We are grateful to Mr. Ch. Y. Wang for the
NMR spectra and Mr. Zh. L. Wei for the MS spectra.
Ho TI, Elangovan A, Hsu HY, Yang SW (2005) Highly Fluorescent
N, N-dimethylaminophenylethynylarenes: synthesis, photophys-
ical properties, and electrochemiluminescence. J Phys Chem B
109:8626–8633. doi:10.1021/jp0444518
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