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J Fluoresc (2012) 22:1159–1164
photon excited fluorescence sensors for ions have been
reported [8, 10].
Synthesis
In order to be compatible with existing semiconductor
processing technology, organic NLO chrompohores for de-
vice application are required to be highly thermally stable for
sustaining the processing and operating temperatures [7].
Heterocyclic imidazoles based on NLO chromophores have
received increasing interest due to their excellent thermal
stability, improved molecular nonlinearity and high solubility
[1,6,8-11].
We report here the synthesis of four new Y-shaped deriva-
tives of 4- {4,5-[2,2′-Bis(2,4,6-trimethoxyphenyl)vinyl]-1-H-
imidazole-2-yl}benzonitrile 1a, 2-phenyl-{4,5-[2,2′-Bis(2,4,6-
trimethoxyphenyl)vinyl]-1-H-imidazole} 1b, 2- (9-anthryl)-
{4,5-[2,2′-Bis(2,4,6-trimethoxyphenyl)vinyl] }-1-H-imidazole
1c and 2- (4-nitrophenyl) – {4,5-[2,2′-Bis(2,4,6-trimethoxy-
phenyl)vinyl] -1-H-imidazole 1d, having an imidazole core.
Their optical properties such as absorption maxima, fluores-
cence emission maxima, Stokes’ shifts, singlet energies, fluo-
rescence quantum yield values and photostabilities in
tetrahydrofuran, toluene and acetonitrile were also investigated.
1,6-Bis(2,4,6-trimethoxyphenyl)hexa-1,5-diene-3,4-dione
(2). 2,3-butanedione (0.36 ml , 5 mmol) was added to the
methanol (20 ml) solution of 2,4,6- trimethoxybenzaldehyde
(2 g , 10 mmol). Then, piperidine (0.56 ml, 5.56 mmol) and
glacial acetic acid (0.32 ml, 5.55 mmol) were added as catalyst
to the stirred mixture. The mixture was refluxed for 6 h under
nitrogen atmosphere, during which orange crystals started to
form. After cooling to room temperature, the crystals were
filtered and washed with methanol for several times to obtain
the title compound with a yield of 30 %; mp 223–224 °C;
FT-IR (KBr): νmax 1650, 1551, 1207 cm-1; 1H NMR
(500 MHz, DMSO-d6): δ 3.88 (s, 6H), 3.90 (s, 12 H), 6.33
(s, 4H), 7.38 (d, J08.3 Hz, 2H), 8.02 (d, J08.3 Hz, 2H),; 13
C
NMR (500 MHz, DMSO-d6): δ 53.7, 56.4, 91.4, 105.1, 119.6,
138.3, 161.9, 164.2, 193.2; HRMS (ESI-TOF): m/z Anal.
Calcd. for C24H27O8 (M+ + H)0443.1706; Found: 443.1712.
General methods for the synthesis of 1a-d Glacial acetic
acid (1.91 ml) and 2 (0.1 g , 0.23 mmol) were added to a
50 mL round bottom flask. The mixture was allowed to stir
at room temperature until the entire solid was dissolved.
Aldehyde (0.23 mmol) was then added, followed by the
addition of ammonium acetate (0.28 g, 3.6 mmol). The
reaction mixture was magnetically stirred at 118 °C under
nitrogen atmosphere for 6 h and then cooled to room tem-
perature. The mixture was poured into 19,1 ml of ice water
and neutralized by %10 of sodium carbonate solution to a
pH 6.5-7.0. The formed precipitate was filtered and washed
with water for several times. Then redissolved in ethyl
acetate and purified by column chromatography using ethyl
acetate / hexane as eluent.
4- {4,5-[2,2′-Bis(2,4,6-trimethoxyphenyl)vinyl]-1-H-
imidazole-2-yl}benzonitrile (1a) Yield 49 %; mp 174 °C;
FT-IR (KBr): νmax 3204, 2223, 1630, 1454, 1328, 1204, cm-1;
1H NMR (500 MHz, DMSO-d6): 3.84 (s, 6H), 3.84 (s,
12H), 6.56 (s, 4H), 7.33 (d, J08.3 Hz, 2H), 7.48 (d, J0
3.4 Hz, 2H), 7.51 (d, J03.4 Hz, 2H), 7.58 (d, J08.3 Hz, 2H),
12.65 (s, 1H); 13C NMR (500 MHz, DMSO-d6): δ 55.2, 55.8,
91.2, 105.2, 118.1, 119.1, 123.6, 125.7, 130.8, 132.4, 132.8,
144.4, 149.7, 159.1, 161.9; HRMS (ESI-TOF): m/z Anal.
Calcd. for C32H32N3O6 (M+ + H)0554.2291; Found:
554.2354.
Experimental
General
All solvents were of analytical grade and purchased from
Merck (Darmstadt, Germany), Fluka (Buchs, Switzerland),
and Riedel (Seelze, Germany). All melting points were mea-
sured in sealed tubes using an electrothermal digital melting
points apparatus (Southend, UK) and are uncorrected. Infrared
spectra were recorded on a Perkin Emler (Massachusetts,
1
USA) FTIR infrared spectrometer (spectrum BX-II). H-
NMR and 13C-NMR spectra were recorded on Bruker
AC500 (500 MHz) (Coventry, UK). Ultra performance liquid
chromatography coupled to mass spectrometry detection
(UPLC-MS) was performed with a Waters Alliance systems
(gradient mixtures of acetonitrile/water) equipped with Acq-
uity UPLC columns. The Waters systems consisted of a
Waters Separations Module 2695, a Waters Diode Array de-
tector 996, a LCT Premier XE mass spectrometer, and a
Waters Mass Detector ZQ 2000. Analytical and preparative
thin layer chromatography (TLC) were carried out using silica
gel 60F254 (Merck). Column chromatography was carried out
by using 70–230 mesh silica gel (0.063-0.2 mm, Merck). UV/
visible absorption spectra were recorded with Schimadzu UV-
1601 spectrophotometer (Tokyo, Japan). All fluorescence
measurements were undertaken by using Varian-Carry Eclipse
spectrofluorimeter (Mulgrave, Australia). 1-hydroxypyrene-
3,6,8-trisulfonate trisodium salt (HPTS) purchased from Fluka
was used as reference standard for fluorescence quantum
yield calculations of 1a-d.
2-phenyl-{4,5-[2,2′-Bis(2,4,6-trimethoxyphenyl)vinyl]-1-
H-imidazole} (1b) Yield 78 %; mp 135 °C; FT-IR (KBr):
1
νmax 3200, 1602, 1454, 1327, 1203; H NMR (500 MHz,
DMSO-d6): 3.83 (s, 6H), 3.91 (s, 12H), 6.32 (s, 4H), 7.27
(d, J08.2 Hz, 2H), 7.41-7.38 (m, 5H), 7.51 (d, J04.4 Hz,
2H), 12.36 (s, 1H); 13C NMR (500 MHz, DMSO-d6): δ
55.2, 55.9, 91.2, 117.4, 125.5, 126.4, 127.6, 128.2, 128.5,
130.4, 136.1, 146.4, 158.1, 163.3; HRMS (ESI-TOF): m/z
Anal. Calcd. for C31H33N2O6 (M+ + H)0529.2339; Found:
529.2189.