3
90
H. Chen et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 116 (2013) 389–393
to cyanide anions with obvious color and fluorescence changes,
which allows naked eye detection of cyanide anions.
Edinburgh FLS 920 spectrometer, respectively. The compounds
were titrated with cyanide anions by addition of a solution TBACN
in acetonitrile.
Experimental
Structure determination
Chemical and instruments
Single crystal of compound 1 was obtained by slow diffusion of
the compound in dichloromethane. X-ray diffraction of a red single
crystal of 1 (0.5 mm ꢁ 0.5 mm ꢁ 0.2 mm) was collected on a Bru-
ker Smart APEX-II CCD X-ray single crystal diffractometer. The
0
0
2
,6 -Dihydroxyacetophenone, p-dimethylaminobenzaldehyde,
p-bromobenzaldehyde and 4-formylbenzonitrile were purchased
from Aladdin Reagents. Other reagents were purchased from
Shanghai Reagents and were used as received directly without fur-
ther purification. NMR spectra were recorded on a Bruker Avance
III 400 MHz spectrometer at ambient temperature. Mass spectra
were recorded on an Agilent Q-TOF6510 spectrometer. Elemental
analyses were carried out on a PE 2400 autoanalyzer.
crystal belongs to the monoclinic system, P 2
1
/n space group, with
formula C17 and molecular weight 281.30; T = 296.0 (2) K,
H
15N0 O3
0
0
a = 7.5419 (2) ÅA , b = 23.7783 (8) ÅA , c = 8.4789 (2) ÅA , b = 110.193
0
3
ꢂ1
(
d
2)°, V = 1427.09(9) ÅA , Z = 4, F(000) = 592,
calcd. = 1.309 Mg m , R
l
= 0.090 mm
,
ꢂ3
1
= 0.0439, wR
2
= 0.1483.
Synthesis and characterization
Results and discussion
Synthesis and crystal structure
The hydroxyl aurone compounds 1–3 were synthesized via four
steps with 2 ,6 -dihydroxyacetophenone and p-substituted benzal-
dehyde as the starting materials with high yield. All the new com-
pounds were fully characterized by NMR, mass spectra and
elemental analyses.
The molecular structure of compound 1 along with the atom
labeling is shown in Fig. 1. Benzofuran group possesses perfect pla-
narity with the maximum deviation for the non-hydrogen atoms
being 0.017 Å for O1. Atoms O1 and O2 are also almost in benzofu-
ran plane with the deviations are 0.006 Å (O1) and 0.019 Å (O2),
respectively. The molecular backbone exhibits perfect planarity
with the dihedral angle between benzofuran and benzene group
being 7.62°, which is much larger than that of aurone without hy-
droxyl group (5.80°) [30]. That means that the import of hydroxyl
group slightly decreases the molecular planarity.
The synthetic routes to compounds 1–3 is outlined in
Scheme S1. The compounds were synthesized via four steps [29].
Firstly, one hydroxyl group in 2 ,6 -dihydroxyacetophenone was
0
0
0
0
0
0
protected using methoxymethoxy group by the reaction of 2 ,6 -
dihydroxyacetophenone with methyl chloromethyl ether in ace-
0
0
tone to afford 2 -hydroxy-6 -methoxymethoxy acetophenone (S-
) as colorless oil with a high yield (83%). Secondly, S-1 reacts with
1
0
0
the aldehydes to afford the corresponding 2 -hydroxy-6 -methoxy-
methoxy chalcone compounds (S-2). Thirdly, 4-methoxymethoxy
0
0
aurone compounds (1 –3 ) were obtained by the cyclization of
chalcones using mercury (II) acetate in pyridine according to Ref.
0
0
[
30]. Finally, the methoxymethoxy group in 1 –3 was deprotected
to afford the 4-hydroxy products 1–3 with high yield.
0
4
-N,N-Dimethylamino-4-hydroxy-aurone (1) Compound 1 was
1
red solid in 92% yield. H NMR (CDCl
H), 6.58 (d, J = 8.2 Hz, 1H), 6.76(d, J = 8.9 Hz, 2H), 6.77(d,
J = 8.1 Hz,1H), 6.85(s, 1H), 7.46 (t, J = 8.2 Hz, 1H), 7.83(d,
3
, 400 MHz), d (ppm): 3.07(s,
6
1
3
J = 8.9 Hz, 2H), 7.97 (s, 1H). C NMR (CDCl
3
, 100 MHz), d (ppm):
4
1
0.18, 103.60, 109.16, 110.47, 112.10, 115.55, 119.90, 133.89,
38.18, 144.62, 151.65, 156.69, 164.36, 185.00. MS for (M + H) ,
Linear absorption and steady fluorescence properties
+
Calcd exact mass: 282.1130, found 282.1119. Anal. Calcd for
Linear absorption and steady fluorescence properties of the
compounds in acetonitrile are shown in Table 1 and the spectra
are shown in Fig. 2. Compound 1 can be classified as D-p-A type
C
4
17
H
15NO
3
: C, 72.58; H, 5.37; N, 4.98. Found C, 72.71; H, 5.39; N,
.99.
0
4
-Bromide-4-hydroxy-aurone (2). Compound 2 was yellow so-
of molecule with dimethylamino and benzofuran as electron-
1
3
lid in 97% yield. H NMR (CDCl , 400 MHz), d (ppm): 6.64(d,
donating and withdrawing groups, respectively. But compounds
J = 8.4 Hz, 1H), 6.76(s, 1H), 6.81(d, J = 8.4 Hz, 1H), 7.54(t,
J = 8.4 Hz, 1H), 7.59(d, J = 8.8 Hz, 2H), 7.77(d, J = 8.8 Hz, 2H), 7.78
0
2
and 3 can be classified as A-
p
-A type of molecules with two elec-
tron-withdrawing groups (2: bromide and benzofuran; 3: cyano
and benzofuran). From Fig. 2, we can see that compound 1 exhibits
strong linear absorption in blue region with the main absorption
peak at 449 nm, which can be ascribed to charge transfer from
dimethylamino to benzofuran. Compounds 2 and 3 possess similar
absorption spectra with the main absorption peak at 389 nm,
which also can be ascribed to intramolecular charge transfer and
1
3
(
s, 1H). C NMR (CDCl
3
, 100 MHz), d (ppm): 103.78, 109.56,
1
1
3
10.31, 111.80, 124.72, 131.06, 132.36, 132.96, 139.60, 146.98,
+
56.84, 164.94, 185.63. MS for (M + H) , Calcd exact mass:
16.9813, found 316.9825. Anal. Calcd for C15 BrO : C, 56.81;
H
9
3
H, 2.86. Found C, 56.92; H, 2.87.
0
4
-Cyano-4-hydroxy-aurone (3) Compound 3 was yellow solid
1
in 96% yield.
3
H NMR (CDCl , 400 MHz), d (ppm): 6.67(d,
J = 8.4 Hz, 1H), 6.78(s, 1H), 6.82(d, J = 8.0 Hz, 1H), 7.57(t,
J = 8.0 Hz, 1H), 7.73(d, J = 8.4 Hz, 2H), 7.75(s, 1H), 7.98(d,
1
3
J = 8.4 Hz, 2H).
1
1
C NMR (CDCl
09.11, 110.00, 110.72, 112.82, 118.50, 131.57, 132.52, 136.47,
39.94, 148.05, 156.86, 164.91, 185.36. Anal. Calcd for C16 NO
3
, 100 MHz), d (ppm): 103.72,
H
9
3
:
C, 73.00; H, 3.45; N, 5.32. Found C, 73.16; H, 3.46; N, 5.31.
Photophysical properties and response to cyanide anions
Solutions of compounds 1–3 with 10
3
lM in acetonitrile (CH CN)
or CH CN–H O solution were prepared for photophysical measure-
3
2
ments. UV–vis absorption and steady-state fluorescence spectra
were recorded on a Shimadzu UV2550 spectrophotometer and an
Fig. 1. The molecular structure of compound 1.