L. Cai, H. Du, D. Wang et al.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 249 (2021) 119297
+
chemical sensors and photoluminescent materials [15–18].
Recently, several new diacetoxyboron complexes with curcumin
derivatives were reported by our group and their photophysical
and solvatochromic properties were also investigated [19]. As a
continuation of our work, we designed and synthesized some novel
ditrifluoroacetoxyboron complexes with curcumin analogues by
replacing C–H bonds of acetoxy groups with C–F bonds to improve
their luminescent behaviors because the high-energy oscillators of
C–H bonds in molecules can result in the lower photoluminescent
properties [20,21]. In addition, the structures of ditrifluoroacetoxy-
boron complexes were identified and their solvatochromic fluores-
cent behaviors were investigated in solution, powders and PMMA
films in detail.
103.5 ppm; ESI–MS m/z: 534.83 [M+Na] ; Anal. calcd. for C23
H
15
-
BF
6
O
6
: C 53.94, H 2.95; found C 54.21, H 2.92.
Ditrifluoroacetoxyboron 1,7-di-p-tolylhepta-1,6-diene-3,5-dionate
(2b): Orange powder, yield 64%, m.p. 231–232 °C; IR (KBr):
1784 (s), 1601 (s), 1549 (s), 1501 (s), 1398 (s), 1353 (s), 1220 (s),
1159 (s), 1057 (s), 1020 (m), 976 (m), 821 (m), 746 (m) cm
NMR (300 MHz, CDCl ): d 7.96 (d, 2H, J = 15.5 Hz, C@CAH), 7.51
(d, 4H, J = 7.7 Hz, ArAH), 7.23 (d, 4H, J = 7.8 Hz, ArAH), 6.72 (d,
2H, J = 15.5 Hz, C@CAH), 6.28 (s, 1H, enol C@CAH), 2.41 (s, 6H,
3 3
ArACH ) ppm; C NMR (75 MHz, CDCl ): d 178.9, 157.2 (q,
J = 41.4 Hz), 148.9, 143.6, 131.2, 130.1, 129.6, 118.8, 114.2 (q,
J = 282.3 Hz), 103.2, 21.8 ppm; ESI–MS m/z: 562.67 [M+Na] ; Anal.
m
ꢁ1 1
; H
3
1
3
+
6 6
calcd. for C25H19BF O : C 55.58, H 3.54; found C 55.86, H 3.57.
Ditrifluoroacetoxyboron 1,7-Bis(4-methoxyphenyl)hepta-1,6-dien
e-3,5-dionate (2c): Purple powder, yield 67%, m.p. 236–237 °C; IR
2
. Experimental
(
KBr):
m
1779 (s), 1599 (s), 1547 (s), 1490 (s), 1397 (s), 1351 (s),
1
7
261 (s), 1216 (s), 1157 (s), 1057 (s), 1023 (s), 974 (m), 828 (s),
2.1. Materials and methods
ꢁ1
1
46 (m) cm
;
3
H NMR (300 MHz, CDCl ): d 7.94 (d, 2H,
J = 15.4 Hz, C@CAH), 7.58 (d, 4H, J = 8.5 Hz, ArAH), 6.94 (d, 4H,
J = 8.6 Hz, ArAH), 6.61 (d, 2H, J = 15.5 Hz, C@CAH), 6.21 (s, 1H, enol
All reagents and solvents were analytically pure and purchased
from commercial suppliers (Sun Chemical Technology or J&K Sci-
entific Ltd.). UV–vis absorption spectra were recorded on a Hitachi
U-3010 spectrophotometer. FT-IR spectra were measured on a
1
3
C@CAH), 3.88 (s, 6H, OCH
78.3, 157.1 (q, J = 41.2 Hz), 157.8, 143.7, 130.5, 126.7, 118.2,
115.1, 113.9 (q, J = 282.1 Hz), 102.9, 56.6 ppm; ESI–MS m/z:
3 3
) ppm; C NMR (75 MHz, CDCl ): d
1
1
Nicolet FTIR 5700 spectrophotometer from KBr disks. NMR ( H
+
1
3
TM
594.70 [M + Na] ; Anal. calcd. for C25
found C 52.17, H 3.39.
6 8
H19BF O : C 52.48, H 3.35;
and
C) spectra were carried out on a Bruker Avance III
3
00 MHz NMR spectrometer in CDCl
3
solution. ESI–MS spectra
Ditrifluoroacetoxyboron 1,7-Di(naphthalen-1-yl)hepta-1,6-diene-
were obtained with a Finnigan LCQ Advantage Max spectrometer.
Emission spectra were measured with a Varian Cary Eclipse fluo-
3,5-dionate (2d): Purple powder, yield 78%, m.p. 218–219 °C; IR
(
1
KBr):
m
1778 (s), 1596 (s), 1572 (s), 1500 (s), 1408 (s), 1356 (s),
rescence spectrometer and Quantum yields (
by the standard method using quinine sulfate in 0.1 M sulfuric acid
= 0.55, kex = 366 nm) as a standard [22]. Fluorescence lifetimes
U) were determined
ꢁ1
1
220 (s), 1158 (s), 1046 (s), 956 (m), 828 (m), 718 (m) cm ; H
NMR (300 MHz, CDCl
d, 2H, J = 5.0 Hz, ArAH), 7.49–7.36 (m, 6H, ArAH), 7.24–7.14 (m,
H, ArAH), 6.51 (d, 2H, J = 15.2 Hz, C@CAH), 6.19 (s, 1H, enol
3
): d 8.11 (d, 2H, J = 15.2 Hz, C@CAH), 7.60
(U
s
(
were measured with an Edinburgh FS5 spectrofluorometer by the
time-correlated single-proton counting (Instrument response
function, IRF = 150 ps, picoseconds pulsed diode laser EPL-450,
ex = 450 nm). Elemental analyses were performed with a Per-
kin–Elmer 2400CHN elemental analyzer. Melting points were
determined on Beijing Tech X-4 digital melting-point apparatus.
6
1
3
C@CAH) ppm; C NMR (75 MHz, CDCl
J = 42.1 Hz), 147.8, 142.8, 140.1, 139.7, 135.3, 134.8, 132.9, 132.6,
29.3, 129.0, 128.6, 120.1, 114.1 (q, J = 282.8 Hz), 103.3 ppm;
3
): d 177.9, 157.2 (q,
k
1
+
ESI–MS m/z: 634.91 [M+Na] ; Anal. calcd. for C31
0.81, H 3.13; found C 61.16, H 3.18.
Ditrifluoroacetoxyboron 1,11-Diphenyl-undeca-1,3,8,10-tetraene-
,7-dionate (2e): Purple powder, yield 72%, m.p. 227–228 °C; IR
6 6
H19BF O : C
6
2
.2. Synthesis of curcumin analogues (1a–1e)
5
(
1
(
(
KBr):
m
1783 (s), 1586 (s), 1530 (s), 1399 (s), 1351 (s), 1215 (s),
The curcumin analogues (1a–1e) were synthesized by conden-
sation reaction of the aromatic aldehydes with acetylacetone
according to our publication [19].
ꢁ1
1
149 (s), 1053 (s), 1002 (s), 752 (m), 685 (m) cm ; H NMR
300 MHz, CDCl
m, 4H, ArAH), 7.41–7.39 (m, 6H, ArAH), 7.19 (d, 2H, J = 15.4 Hz,
3
): d 7.79 (d, 2H, J = 14.7 Hz, C@CAH), 7.54–7.51
C@CAH), 6.98 (dd, 2H, J = 15.3, 11.3 Hz, C@CAH), 6.30 (d, 2H,
J = 14.7 Hz, C@CAH), 6.12 (s, 1H, enol C@CAH) ppm; 13C NMR
2.3. Synthesis of ditrifluoroacetoxyboron complexes (2a–2e)
(
3
75 MHz, CDCl ): d 178.4, 157.3 (q, J = 41.8 Hz), 146.9, 144.5,
Boric acid (0.09 g, 1.5 mmol) was added to 15 mL of benzene
136.1, 130.2, 129.3, 128.2, 127.7, 125.3, 114.2 (q, J = 282.5 Hz),
+
solution containing trifluoroacetic anhydride (1.3 mL, 9.0 mmol).
The mixture was heated to 50 °C and stirred for 1 h to obtain a pink
solution of boron trifluoroacetate. The curcumin analogues 1a–1e
103.2 ppm; EI–MS m/z: 586.68 [M+Na] ; Anal. calcd. for C27
: C 57.47, H 3.39; found C 57.73, H 3.35.
6
H19BF -
O
6
(
5
(
0.5 mmol) were dissolved in 15 mL of benzene and heated to
0 °C, then the above pink solution of boron trifluoroacetate
1.5 mmol) in benzene was added dropwise over 1 h. The mixture
3. Results and discussion
was kept stirring for 5 h at 50 °C and the purplish-red solids were
formed after cooling to room temperature. The solids were filtered
off and recrystallized from chloroform to give ditrifluoroacetoxy-
boron complexes (2a–2e).
3.1. Chemistry
The synthesis of ditrifluoroacetoxyboron complexes with cur-
cumin analogues was depicted in Scheme 1. Firstly, the curcumin
analogues (1a–1e) were synthesized by condensation of acetylace-
tone with the aromatic aldehydes according to our previous paper
[19]. Secondly, ditrifluoroacetoxyboron complexes with curcumin
analogues (2a–2e) were obtained by the chelation reaction with
boron trifluoroacetate in benzene. These reaction products were
Ditrifluoroacetoxyboron 1,7-diphenylhepta-1,6-diene-3,5-dionate
(2a): Orange powder, yield 62%, m.p. 205–206 °C; IR (KBr):
m
1
780 (s), 1603 (s), 1579 (s), 1553 (s), 1495 (m), 1390 (s), 1351
ꢁ1
(
s), 1220 (s), 1162 (s), 1059 (s), 998 (s), 826 (m), 733 (m) cm ;
1
H NMR (300 MHz, CDCl
3
): d 8.02 (d, 2H, J = 15.6 Hz, C@CAH),
7
2
.65 (d, 4H, J = 6.2 Hz, ArAH), 7.50–7.45 (m, 6H, ArAH), 6.79 (d,
1
3
H, J = 15.7 Hz, C@CAH), 6.33 (s, 1H, enol C@CAH) ppm;
): d 179.4, 157.3 (q, J = 41.7 Hz), 149.1,
33.7, 132.5, 129.5, 129.1, 119.8, 114.1 (q, 282.6 Hz),
C
recrystallized from chloroform to give the pure ditrifluoroacetoxy-
1
NMR (75 MHz, CDCl
1
3
boron complexes and their structures were confirmed by IR,
H
1
3
J
=
NMR, C NMR, ESI–MS spectroscopy and elemental analysis.
2