(4-bromophenyl)amino]benzaldehyde was synthesized in a
yield of 63%. In the present work, 4-N-(p-bromophenyl)-
N-phenylaminobenzaldehyde (9) was obtained by the bromi-
nation of 4-(N,N-diphenylamino)benzaldehyde (8) in a yield of
94%, which is higher than that reported in ref. 20. In our case,
the dropping rate of bromine in diluted methylene chloride was
very slow to prevent the formation of the 4-[N,N-di(4-bromo-
phenyl)amino]benzaldehyde as the by-product. After the reac-
tion was completed, the crude product was not washed with
methanol, as was done in ref. 20, because we found that our
crude product could slightly dissolve in methanol. So this may
be the reason for the higher yield of compound 4 than that of
4-[N,N-di(4-bromophenyl)amino]benzaldehyde in ref. 20.
The five chromophores were synthesized by the Knoevenagel
reaction between 3,5-dicyano-2,4,6-trimethylpyridine (2) and
aromatic aldehydes with piperidine as a catalyst. Compounds
4 and 6 were prepared simultaneously in yields of 27% and
66%, respectively, with a molar ratio of reagents of 1 : 3.1 (Table
1). The structure of 6 was proved by its 1H NMR spectrum with
the chemical shift of the unsubstituted methyl group being
around 2.83 ppm, and also by its 13C NMR spectrum with the
CN group of the compound 6 split into two peaks at 102.24 and
103.19 ppm, as theoretically the CN group of the 2,6-disubsti-
tuent could not be split in its 13C NMR spectrum. Also, the CN
group of tri-substituted 4 only had its chemical shift at 104.47
ppm. Compounds 3 and 5 were also prepared simultaneously in
yields of 22% and 57%, respectively, with a molar ratio of the
reagents of 1 : 3.1 also (Table 1). However, when a molar ratio
for 3,5-dicyano-2,4,6-trimethylpyridine (2) and N-ethyl-N-cetyl-
aminobenzaldehyde (10) of 1 : 3.1 was used, the main product
was 7; its 2,4,6-trisubstituted derivative cannot be obtained and
some unreacted 10 was also recovered. The possible reason the
trisubstituted derivative was not obtained might be related to its
distorted structure due to its long alkyl group, which prevents
the reaction from occurring. So, in this study, a molar ratio of
1 : 2.1 for compounds 2 and 10 was used (Table 1) to prepare 7,
3,5-Dicyano-2,4,6-tri[N-(p-bromophenyl)-N,N-diphenylamino]
styrylpyridine (4) and 3,5-dicyano-2,4-di[N-(p-bromophenyl)-
N,N-diphenylamino]styryl-6-methylpyridine (6). After 2 and
4-N-(p-bromophenyl)-N-phenylaminobenzaldehyde (9) reacted
completely, the crude product was chromatographed as de-
scribed above. The first band was collected to give 4 as a red
1
solid; 27% yield (0.19 g); m.p. 257–259 1C and Td 359 1C. H
NMR (CDCl3, 300 MHz, d): 8.12 (d, 2H, J = 14.5 Hz, o-Py–
CH CH), 7.85 (d, 1H, J = 15.5 Hz, p-Py–CH CH), 7.54 (m,
Q
4H, o-Py–CH CH and Ar–H), 7.46 (m, 3H, p-Py–CH CH
Q
Q
Q
and Ar–H), 7.36 (t, 4H, J = 7.5 Hz, Ar–H), 7.29 (t, 4H, J = 6.5
Hz, Ar–H), 7.10 (dd, 12H, J = 6.5 Hz, Ar–H), 7.01 (q, 15H, J =
8.0 Hz, Ar–H). 13C NMR (CDCl3, 300 MHz, d): 104.47, 114.89,
114.97, 115.97, 116.73, 117.17, 118.12, 119.28, 122.71, 122.93,
124.01, 124.26, 124.48, 125.36, 125.73, 126.07, 126.41, 126.68,
129.09, 129.28, 129.53, 130.14, 132.54, 132.67, 132.81, 139.01,
141.91, 145.44, 145.63, 145.81, 146.20, 147.77, 149.21, 150.83,
154.41, 155.05, 164.44, 165.02, 165.27. FTIR (cmꢀ1):1622, 967
(CH CH), 2214 (CN). Anal. calcd for C H N Br : C, 68.54;
Q
H, 3.84; N, 7.16. Found: 68.76; H, 4.02; N, 6.91. The second band
67 45
6
3
gave compound 6 as a red solid; 66% yield (0.32 g); m.p. 196–198
1
1C and Td 249 1C. H NMR (CDCl3, d): 8.07 (d, 1H, J = 14.5
Hz, o-Py–CH CH–), 7.86 (d, 1H, J = 15.5 Hz, o-Py–CH
Q
CH–), 7.48 (m, 3H, p-Py–CH CH and Ar–H–), 7.36 (m, 3H, p-
Q
Q
Py–CH CH– and Ar–H), 7.28 (m, 4H, J = 6.5 Hz, Ar–H), 7.12
Q
(t, 8H, J = 8.1 Hz, Ar–H), 7.03 (t, 10H, J = 7.2 Hz, Ar–H), 2.83
(s, CH3). 13C NMR (CDCl3, 300 MHz, d): 25.42, 102.24, 103.19,
116.67, 117.68, 118.16, 119.73, 120.18, 121.71, 121.89, 122.22,
122.40, 124.32, 124.68, 125.66, 126.67, 129.01, 129.45, 129.68,
129.84, 132.66, 132.84, 141.03, 141.68, 146.09, 146.52, 146.89,
149.43, 149.63, 149.99, 151.46, 159.81, 164.95. FTIR (cmꢀ1):
1630, 967 (CH CH), 2217 (CN). Anal. calcd for C H N Br :
5
Q
C, 68.65; H, 3.93; N, 8.34. Found: 68.78; H, 4.16; N, 7.89.
48 33
2
3,5-Dicyano-2,4-di(N-ethyl-N-cetylaminobenzylstyryl)-6-me-
thylpyridine (7). After 2 and N-ethyl-N-cetylaminobenzalde-
hyde (10) reacted completely, the crude product was chroma-
tographed as described above to give compound 7 as a red
1
whose structure was proved by its H NMR spectrum with the
chemical shift of the unsubstituted methyl group being around
2.78 ppm, and also proved by the peak at 882 (M + 1) in the
mass spectrum; no higher mass peaks appear.
1
solid; 36% yield (0.19 g); m.p. 123–125 1C and Td 317 1C. H
NMR (CDCl , d): 8.04 (d, 1H, J = 15.5 Hz, o-Py–CH CH–),
Q
7.94 (d, 1H, J = 15.5 Hz, p-Py–CH CH–), 7.48 (t, 4H, J = 8.5
3
All of the above compounds are characterized by 1H NMR,
FTIR, UV-Vis and elemental analysis; some compounds have
13C NMR analysis; these data are given above in the Experi-
mental. Characteristic resonances of the vinylic protons of
these compounds at 8.12–7.03 ppm with large trans coupling
Q
Hz, Ar), 7.25 (d, 1H, J = 15.5 Hz, o-Py–CH CH–), 7.03 (d,
Q
1H, J = 15.5 Hz, p-Py–CH CH–), 6.60 (d, 4H, J = 8.5 Hz,
Q
Ar), 3.40 (d, 4H, J = 7.5 Hz, N–CH2), 3.29 (t, 4H, J = 7.2 Hz,
N–CH2), 2.78 (s, 3H, CH3–Py), 1.25 (m, 56H, CH2), 0.88 (t, 12H,
Q
1
J = 6.6 Hz, CH3). FTIR (cmꢀ1): 1598, 967 (CH CH), 2216
(CN). Anal. calcd for C60H91N5: C, 81.73; H, 10.33; N, 7.95.
Found: 81.84; H, 10.52; N, 8.22. FAB-MS (m/z) 882 (M + 1).
constants were evident in their H NMR spectra; the shift of
the unsubstituted methyl groups of these compounds were
around 2.8 ppm. The absorptions around 2221 and 969 cmꢀ1
in their FTIR spectra correspond to CN stretching and out-
of-plane bending motions, respectively, of trans-vinylene.
Thermogravimetric analyses of these compounds show they
all have a relatively high thermal stability with a 5% weight
loss at relatively high temperatures in argon. All of the
compounds are soluble in common organic solvents such as
toluene, chloroform, acetone, THF, DMF and DMSO.
Results and discussion
Syntheses and structural characterization
The synthetic routes to the aromatic aldehydes and compounds
3–10 are shown in Scheme 1. In the literature20 4-[N,N-di
Table 1 Syntheses and experimental photophysical properties of compounds 3–7 in chloroform solution
abs
b
spf
b
tpf
l
max
b
Molar ratioa
1 : 3.1
Product
l
l
Ff/%c
d/GM (at 10ꢀ4 M)d
d0/GM (at 10ꢀ4 M)e
max
max
3
5
4
6
7
480
471
476
468
482
586
581
575
570
569
592
f
—
54
50
51
45
38
187
f
—
101
f
—
1 : 3.1
587
588
575
204
118
109
110
53
1 : 2.1
66
a
When the molar ratio of the regents [3,5-dicyano-2,4,6-trimethylpyridine (2) and aromatic benzylaldehydes] was 1 : 3.1, the first product was 3 or 4, and
b
the second product was 5 or 6; when the molar ratio of the regents was 1 : 2.1, the first product was 7. lambasx, lmspafx, ltmpafx: peak wavelengths in the linear
absorption, single photon fluorescence emission, two-photon absorption (at 800 nm) induced fluorescence emission. Rhodamine B was used as in ref.
c
27. TPA cross-section values are given in GM at 800 nm, measured at a concentration of 10ꢀ4 M, with Rhodamine 6G used as in ref. 1. GM (Goppert–
d
¨
Mayer) = 10ꢀ50 cm4 s photonꢀ1
.
Two-photon-excited fluorescence (TPEF) action cross section at a concentration of 10ꢀ4 M. Not obtained.
e
f
794
N e w J . C h e m . , 2 0 0 5 , 2 9 , 7 9 2 – 7 9 7