X. Qin et al. / Dyes and Pigments 132 (2016) 27e40
31
HO
(1) Dry THF 40 mL K2CO3/18-C-6 (4h)
(2) anhydrous Na2SO4, PBr3 (80 0C 3h)
O
C3 (22.3 %), R, H
+
Br
(3) KOH + HO
NO2
R
OH
C4 (19.7 %), R, OH
Scheme 2. The one-pot preparation method of new photoinitiators C3 and C4.
J ¼ 6.5 Hz, AreH), 7.248e7.221 (d, 1H, J ¼ 13.5 Hz, AreCH]CHe),
7.121 (s, 1H, AreH), 7.039e6.975 (m, 4H, AreH), 5.228 (s, 2H,
eCH2eOe), 5.111 (s, 2H, eCH2eOe); 13C NMR (D6-DMSO, 125 MHz)
bond. It was noticed that the eOCH2- segments in C3 or C4 obvi-
ously displayed two separated peaks, reflecting that they are
located in different chemical environments. The 1H NMR spectral
integration area ratio of different hydrogen atoms was consistent
with that of the numbers of hydrogen atoms. We also found that
carbonyl group led to the movement of 1H NMR peaks of its adja-
cent hydrogen atoms to the down magnetic field due to its electron
withdrawing effect. Furthermore, the stronger electron accepting
role of nitro group caused the greater shift 1H NMR peaks of its
adjacent hydrogen atoms to the lower magnetic field.
d(ppm): (195.918, 159.302, 158.740, 146.282, 144.960, 142.470,
139.088, 137.493, 136.835, 133.449, 133.179, 130.360, 130.163,
130.086, 129.636, 129.101, 129.066 128.798, 127.860, 127.370,
124.620, 124.519, 120.687, 115.686, 114.639, 114.581, 69.555,
69.043). IR (cmꢀ1): 3129.6, 3035.5, 1649.9, 1586.7, 1508.5, 1400.5,
1340.9, 1306.6, 1256.4, 1174.4, 1154.7, 1109.5, 1047.9, 1021.1, 941.5,
844.5, 737.3, 705.8. Anal. Calcd for C35H27NO5 (541.19): C, 77.62, H,
5.02, N, 2.59, Found: C, 77.71, H, 4.91, N, 2.67.
Therefore, the successful synthesis of the target photoinitators
means the possibility of the large scale preparation of the new
dyads C3 and C4, which affords the great potentials for the further
applications.
2.8.10. Synthesis of 1-(4-(4-nitrostyrolene)-phenoxymethylene)-
3,5-bis((4-benzoyl)benzyloxy)- benzene (C4)
The reaction of 3,5-bis((4-benzoyl)-benzyloxy)-benzyl bromide
1 g (1.7 mmol) and 4-nitrostyryl-phenol 0.61 g (2.5 mmol) was
3.2. UV/visible absorption properties of the new dyads
mixed in acetone including potassium carbonate 0.468
g
(3.3 mmol) and a little 18-Crown-6 under Ar atmosphere at room
temperature overnight. The purification of C4 was carried out as
that of C3, color: yellow; yield: 52.1%; m.p: 142.8e144.5 ꢁC; 1H NMR
The UV/visible absorption spectra of C1~C5 were determined in
various organic solvents. The typical absorption spectra of these
molecules in ethyl acetate were presented in Fig. 3. The results
showed that C3 and C4 yielded the remarkable absorption in the
above 400 nm region. We need to point out that the molar
extinction coefficients of C3 and C4 at around 400 nm are two or-
ders of magnitude larger than that of the commercial photoinitiator
(D6-DMSO, 500 MHz)
d(ppm): 8.190e8.176 (d, 2H, J ¼ 7.0 Hz, AreH),
7.777e7.762 (d, 2H, J ¼ 7.5 Hz, AreH), 7.742e7.728 (d, 4H, J ¼ 7.0 Hz,
AreH), 7.710e7.679 (d, 4H, J ¼ 15.5 Hz, AreH), 7.662e7.637 (t, 2H,
J ¼ 6.5 Hz, AreH), 7.600e7.571 (m, 6H, AreH), 7.544e7.518 (m, 4H,
J ¼ 13.0 Hz, AreH), 7.444e7.416 (d, 1H, J ¼ 14.0 Hz, AreCH]CHe),
7.235e7.207 (d, 1H, J ¼ 14.0 Hz, AreCH]CHe), 7.023e7.009 (d, 2H,
J ¼ 7.0 Hz, AreH), 5.216 (s, 4H, eCH2eOe), 5.080 (s, 2H, eCH2eOe);
titanocene (~105 cmꢀ1
M
ꢀ1, versus ~103 cmꢀ1 Mꢀ1 [19]). The
representative absorption parameters of these molecules in various
solvents were given Table 1.
13C NMR (D6-DMSO, 125 MHz)
d(ppm): (195.399, 159.405, 158.787,
Fig. 1 showed that C1 and C2 possessed the single absorption
band peaked at near 260 nm, which was generated by benzophe-
none part. While in contrast, C3 and C4 displayed the double ab-
sorption bands, which included the first absorption band peaked at
about 260 nm yielded by benzophenone part, and the second ab-
sorption band peaked at approximate 370 nm produced by chro-
mophore part.
C4 exhibited the similar maximal molar extinction coefficients
at around 260 nm as C2 in various solvents. The maximal molar
extinction coefficients of C2 and C4 at about 260 nm were
approximate two times as large as those of C1 and C3 (such as in
EtOAc, C4, 0.395 at 256 nm, C3, 0.198 at 256 nm, C2, 0.383 at
258 nm, C1, 0.188 at 256 nm). This further demonstrated that
benzophenone part was covalently attached to the dye molecular
backbone. The presence of two benzophenone parts in C2 and C4
produced nearly twice molar extinction coefficients at near 260 nm
comparing to C1 and C3.
On the other hand, to C3 and C4, the maximal absorption
wavelengths and the maximal molar extinction coefficients of the
second absorption band peaked at around 370 nm were close with
each other (such as in EtOAc, C4, 0.198 at 373 nm, C3, 0.179 at
374 nm, C5, 0.200 at 377 nm). This is mainly due to the presence of
single chromophore part in C3 and C4. As a consequence, C5 pro-
duced the similar absorption spectral properties as C3 and C4 in the
long wavelength region in various solvents. It was observed that the
maximal absorption wavelength of C3 and C4 shifted to the longer
wavelength in polar solvents (such as to C4, in 1,4-dioxane, 360 nm,
in ACN, 371 nm), which could be caused by the presence of intra-
molecular charge transfer in the ground state of the entire
145.815, 144.469, 141.839, 139.574, 136.985, 136.355, 132.925,
132.670, 129.855, 129.559, 129.157, 128.589, 128.551, 128.313,
127.959, 127.774, 127.58, 127.370, 126.864, 124.132, 124.006,
115.202, 106.690, 101.264, 69.029, 69.207). IR (cmꢀ1): 3430.6,
3128.0, 3032.7, 1655.5, 1596.2, 1508.9, 1448.2, 1407.2, 1337.4, 1318.6,
1277.9, 1248.2, 1163.2, 1145.9, 1109.1, 1047.8, 824.7, 788.3, 705.9;
Anal. Calcd for C49H37NO7 (751.26): C, 78.28, H, 4.96, N, 1.86, Found:
C, 78.37, H 4.87, N 1.94.
3. Results and discussion
3.1. Synthesis and 1H NMR characterization of the new target dyads
The multi-step synthesis strategy has been established to pre-
pare the new dyads C3 and C4. The reaction was mainly involved
with bromination of hydroxy group as well as the following
condensation reaction between phenolic hydroxy and benzyl bro-
mide derivatives. Fortunately, the purified yields of C3 and C4 were
reasonable in both the last steps and the total routes (such as C4,
the last step, 52.1%, the total route, 24.0%).
In order to simplified the preparation route, one-pot synthesis of
C3 and C4 was made based on the optimized experimental condi-
tions. Scheme 2 showed one-pot preparation process developed in
our lab, which provide the similar yields of C3 and C4 as the multi-
step synthesis method.
Fig. 2 gave the representative 1H NMR spectra of the target
dyads C3 and C4. The results demonstrated that benzophenone was
attached to the dye molecular scaffold through chemical covalent