Gao et al.
FULL PAPER
1
3
obtained as a deep red solid after twice recrystallization
(s, 1H, ArOH); C NMR (DMSO-d
6
, 125 MHz) δ:
1
in alcohol. Color: deep red, m.p. 234—235 ℃; H NMR
112.734, 116.123, 121.852, 123.653, 125.578, 127.096,
127.915, 128.130, 128.530, 131.081, 135.812, 150.381,
150.599, 159.490, 161.031. Anal. calcd for C23H N O:
22 2
3 3 2
(CDCl , 500 MHz) δ: 3.00 [s, 6H, Ar-N(CH ) ], 6.71 (d,
J=8.5 Hz, 2H, ArH), 6.93 (d, J=16.0 Hz, 1H, Ar-
CH=CH-Ar), 7.21 (d, J=16.0 Hz, 1H, Ar-CH=
CH-Ar), 7.45 (d, J=8.5 Hz, 2H, ArH), 7.56 (d, J=9.0
Hz, 2H, ArH), 8.18 (d, J=9.0 Hz, 2H, ArH). Anal.
C 80.67, H 6.48, N 8.18; found C 80.75, H 6.52, N 8.09.
Results and discussion
16 2
calcd for C16H N O: C 71.62, H 6.01, N 10.44; found
General remarks
C 71.57, H 5.96, N 10.53.
p-Amino-p'-N,N-dimethylamino-stilbene p-Nitro-
p'-N,N-dimethylamino-stilbene (1 g, 3.731 mmol) was
dissolved in 100 mL anhydrous ethanol. Under argon
atmosphere, stannous chloride dehydrate (1.684 g, 7.462
mmol) was added slowly. The mixture was kept re-
fluxed for 24 h and then concentrated in vacuum. The
solid was dissolved in 15% sodium hydroxide solution
and its pH was adjusted to 8—9 with the dilute hydro-
chloric acid solution. Brown solid was obtained after
filtration, and then it was washed by the distillated water
for three times (30 mL×3), which was further purified
with column chromatography using methylene chloride
The occurrence of ESIPT of a molecule is driven by
the electron density redistribution induced by photoex-
citation, which is accompanied by the large changes in
4
3
the acidity or basicity of the “ESIPT groups”. Nor-
mally, this process is completed barrierlessly or nearly
barrierlessly through a five or six-members ring state.
Thus, we anticipated that C1 could be able to undergo
ESIPT process with appreciable barrier via a six-mem-
ber ring state, while C2 would have to go through an
eight-member ring state if it underwent ESIPT process.
It meant that phenyl ring had to be twisted if eight-
member ring state was formed. Consequently, it would
be reasonable to expect the existence of a too large
energy barrier for C2. Hence, the occurrence of ESIPT
would be barely. While as contrast, C1 was able to
undergo ESIPT process with appreciable barrier via a
reasonable six-member ring state.
as eluent. Yield 46%, m.p. 160—162 ℃; Color: yel-
1
lowish brown; H NMR (Benzene-d
6
, 500 MHz) δ: 2.63
[
s, 6H, N(CH
3
)
2
], 6.45 (d, J=8.5 Hz, 2H, ArH), 6.72 (d,
J=8.5 Hz, 2H, ArH), 7.264 (s, 2H, Ar-CH=CH-Ar),
7
.41 (d, J=8.5 Hz, 2H, Ar-H), 7.55 (d, J=9.0 Hz, 2H,
18 2
ArH). Anal. calcd for C16H N : C 80.63, H 7.61, N
Spectroscopic properties
1
1.75; found C 80.59, H 7.52, N 11.83.
2
-[(4'-N,N-Dimethylamino-diphenylethylene-4-
Absorption spectroscopy A typical comparison of
the absorption spectroscopy of C1 and C2 in ethyl ace-
tate was presented in Figure 2. Clearly, C1 and C2 ex-
hibited similar absorption spectroscopy from 275 to 500
nm. The maximal absorption of the compounds could be
ylimino)methyl]phenol (C1) p-Nitro-p'-N,N-dime-
thylamino-stilbene (0.100 g, 0.42 mmol) was dissolved
in 30 mL absolute ethanol. o-Hydroxy-benzaldehyde
0.051 g, 0.42 mol) was added into the mixture slowly
(
4
4
under argon atmosphere. The reactant was kept refluxed
for 3 h. After cooling, yellow solid was precipitated and
filtered and washed with anhydrous alcohol three times
from overall molecular (π, π*) transition. The maximal
absorption wavelength and the molar extinction coeffi-
cients of C1 and C2 in various solvents are listed in Ta-
ble 1. The data showed that the maximal absorption
wavelength of C1 displayed approximate 10 nm batho-
chromic shift with respect to C2 in various solvents.
Furthermore, the maximal absorption wavelength of C1
and C2 exhibited very small change in different solvents.
In other words, the absorption spectra of C1 and C2
were weakly dependent on the solvent polarity and the
absorption maxima were less sensitive to the solvent
polarity.
Fluorescence spectroscopy As expected, C1 and
C2 exhibited remarkably different fluorescence spec-
troscopy. C1 showed well-separated dual fluorescence
emission in aprotic solvents, while C2 displayed single
fluorescence emission band in various solvents. In
low-polar solvents, the fluorescence emission of C1 and
C2 generally showed a shoulder peak. A typical com-
parison of the fluorescence spectroscopy of C1 and C2
in ethyl acetate is shown in Figure 3. The first emission
band of C1 was almost identical to the fluorescence
spectroscopy of C2. They were effectively the same as
(30 mL per time). 0.1 g product was obtained after twice
recrytallization in ethanol. Yield 68%, m.p. 233—234
1
℃
; Color: orange yellow; H NMR (CDCl
3
, 500 MHz)
δ: 3.00 [s, 6H, Ar-N(CH
3
)
2
], 6.75 (s, 2H, ArH), 6.91—
6
.99 (m, 2H, Ar-CH=CH-Ar), 7.01—7.08 (m, 2H,
ArH), 7.28 (d, J=8.5 Hz, 2H, ArH), 7.35—7.40 (m, 2H,
ArH), 7.43 (d, J=8.5 Hz, 2H, ArH), 7.53 (d, J=8.5 Hz,
2
H, ArH), 8.76 (s, 1H, Ar-CH=N-Ar), 13.34 (s, 1H,
22 2
Ar-OH). Anal. calcd for C23H N O: C 80.67, H 6.48, N
8
.18; found C 80.78, H 6.39, N 8.27.
4
-[(4'-N,N-Dimethylamino-diphenylethylene-4-
ylimino)methyl]phenol (C2) The synthesis is similar
to that of C1 except for p-hydroxy-benzaldehyde as
staring material. Yield 53%, m.p. 237—238 ℃; Color:
1
dark yellow; H NMR (DMSO-d
6
, 500 MHz) δ: 2.93 [s,
6
H, Ar-N(CH
3
)
2
], 6.72 (d, J=7.5 Hz, 2H, ArH), 6.88 (d,
J=8.5 Hz, 2H, ArH), 6.98 (d, J=17.0 Hz, 1H, Ar-
CH=CH-Ar), 7.11 (d, J=16.0 Hz, 1H, Ar-CH=CH-
Ar), 7.21 (d, J=7.0 Hz, 2H, Ar-H), 7.40 (t, J=18.0 Hz,
2
8
H, Ar-H), 7.54 (d, J=8.0 Hz, 2H, Ar-H), 7.77 (d, J=
.0 Hz, 2H, Ar-H), 8.51 (s, 1H, Ar-CH=N-Ar), 10.13
0 1
the S →S absorption spectral feature, which demon-
1
060
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Chin. J. Chem. 2010, 28, 1057— 1068