X.-H. Zhang et al. / Dyes and Pigments 93 (2012) 1408e1415
1409
CH3
the structure, theoretical predictions of vibrational spectra are of
OHC
+
R
R
practical value for the identification of known and unknown
compounds [20e22]. Thus, theoretical predictions, preferably those
used with DFT methods, are advantageous. In this work, we fol-
lowed this approach, and the detailed results and discussion are
elaborated in the following sections.
O
O
N
O
Pyridine, EtOH
Reflux
CH3CCH2COC2H5
NH2OH
+
N
H
N
H
O
1: R = H
1: R = H
2: R = OCH2Ph
2: R = OCH2Ph
Scheme 1. Synthesis of merocyanine dyes (1) and (2).
2. Experimental
sulphoxide, methanol, ethanol and ethyl acetate as solvents, each at
a concentration of 10ꢁ5 M, in 1 cm quartz cells.
2.1. Synthesis
Crystals with approximate dimensions of 0.38
ꢂ
0.25
ꢂ
The general route for the synthesis of dyes (1) and (2) is shown
in Scheme 1. To a stirred mixture of hydroxylamine hydrochloride
(4 mmol), pyridine (4 mmol) in EtOH (10 mL), ethyl acetoacetate
(4 mmol) was added via a dropping funnel over a 30 min time span.
Then, either 1H-indole-3-carbaldehyde (3.5 mmol) or 5-benzyloxy-
1H-indole-3-carbaldehyde (3.5 mmol) was added, and the mixture
was stirred under reflux for 2 h [23]. After cooling, the precipitated
crude dyes were filtered and then washed thoroughly with ether
and ethanol. The solid was purified by recrystallization using
EtOHeMeOH, resulting in pure dyes (1) and (2) (yields of 67% and
60%, respectively). Single crystals of dyes (1) and (2) were grown
from an EtOHeMeOH mixture (1:2) or EtOHeacetone mixture
(1:1), respectively, for X-ray diffraction experiments.
0.13 mm3 for dye (1) and 0.31 ꢂ 0.26 ꢂ 0.13 mm3 for dye (2) were
selected for data collection. The X-ray diffraction data were
collected using a Bruker SMART APEX II CCD X-ray crystallography
system that was equipped with graphite monochromated Mo K
a
radiation ( e2 scan technique at room
l
¼ 0.71073 Å) by using
u
q
temperature. The structures were solved by direct methods and
refined using the full-matrix least-squares method on F2 with
anisotropic thermal parameters for all non-hydrogen atoms.
Hydrogen atoms were generated geometrically. Crystallographic
computing was performed with the SHELXTL [24] and PLATON [25]
programs. The crystal data, including details concerning data
collection and structure refinement for dyes (1) and (2), are
summarized in Table 1. Parameters in CIF format are available as
Electronic Supplementary Information from Cambridge Crystallo-
graphic Data Center (CCDC 724598, 729689).
Dye (1) (4-[(1H-indole-3-yl)-methylene]-3-methyl-isoxazole-5-
one): Orange needle crystal, yield 67%, m.p.: 239e241 ꢀC. 1H NMR
(DMSO-d6, 400 MHz)
d (ppm): 2.35 (s, 3H, CH3), 7.32e7.36 (m, 2H,
ArH), 7.60 (s, 1H, eCH]), 8.16e8.21 (m, 2H, ArH,), 9.52 (s, 1H,
2.3. Computational details
J ¼ 2.4 Hz, pyrrole-H), 12.81 (s, 1H, NH). 13C NMR (DMSO-d6,
400 MHz) d (ppm): 10.7, 108.3, 112.2, 112.7, 118.4, 122.1, 123.5, 127.5,
The single molecular structures of dyes (1) and (2) were opti-
mized at the DFT level using 6-311G** and 6-31G* basis sets. DFT
calculations were carried out using a hybrid exchange-correlation
functional termed B3LYP, which refers to Becke’s three-parameter
exchange functional (B3) along with the nonlocal correlation
functional of Lee, Yang, and Parr (LYP). The PCM model [26] at the
B3LYP/6-311G** level was used to study the solvent polarity effect
135.9, 138.0, 140.0, 161.2, 169.9. IR (KBr)
3125, 3063 (m, ]CeH), 2939 (m, yCeH), 1701 (s, yC]O), 1599 (s, yC]
C), 1582, 1452 (vs, yC]C yC]N), 1377, 1348, 1298, 1219 (yC]C), 1109,
995 (dCH), 878 (yNeO), 812, 756 (m, ]CH). Anal. Calcd. for
y: 3458 (m. b, yNeH), 3157,
y
d
C13H10N2O2 ¼ 226.23: C, 69.02; H, 4.01; N,12.37; Found: C, 69.42; H,
4.26; N, 12.38. UVeVis (MeOH) lmax: 426.4 nm.
Dye
methyl-isoxazole-5-one): Red columnar crystal, yield 60%, m.p.:
240e242 ꢀC. 1H NMR (DMSO-d6, 400 MHz)
(ppm): 2.36 (s, 3H,
(2)
(4-[(5-Benzyloxy-1H-indole-3-yl)-methylene]-3-
Table 1
d
Crystal data of dyes (1) and (2).
CH3), 5.19 (s, 2H, CH2), 7.02 (dd, 1H, J1 ¼ 2.0 Hz, J2 ¼ 8.4 Hz, ArH),
7.36 (d, 1H, J ¼ 7.6 Hz, ArH), 7.42 (t, 2H, J1 ¼7.6 Hz, J2 ¼ 8.4 Hz, ArH),
7.52 (t, 3H, J1 ¼ J2 ¼ 8.4 Hz, ArH), 7.89 (d,1H, J ¼ 2.0 Hz, ArH), 8.20 (s,
1H, eCH]), 9.47 (s, 1H, Pyrrole-H), 12.71 (s, 1H, NH). 13C NMR
Identification code
(1)
(2)
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
C13H10N2O2
226.23
298 (2) K
0.71073
Orthorhombic
Cmca
C20H16N2O3
332.35
298 (2) K
0.71073
Monoclinic
P21/n
(DMSO-d6, 400 MHz)
113.5, 127.4, 128.0, 128.7,130.8, 136.7, 138.4, 140.0, 154.9, 161.2, 170.1.
IR (KBr) : 3454 (m. b, yNeH), 3119, 3094, 3063 (m, ]CeH), 2922 (m,
d (ppm): 10.9, 69.6, 102.5, 107.6, 112.4, 113.3,
y
y
Space group
Unit cell dimensions (Å)
a ¼ 6.6348 (15)
b ¼ 19.189 (4)
c ¼ 18.074 (4)
a ¼ 7.3056 (19)
b ¼ 19.681 (5)
c ¼ 11.445 (3)
yCeH), 1703 (s, yC]O), 1595 (s, yC]C), 1580, 1439 (s, yC]C yC]N), 1375,
1337, 1288, 1200, 1132(yC]C), 1107, 990 (dCH), 874 (yNeO), 789, 727
(m,
d
]CH). Anal. Calcd. for C20H16N2O3 ¼ 332.35: C, 72.28; H, 4.85;
b
¼ 90ꢀ
b
¼ 105.063 (4)ꢀ
Volume (Å3)
2301.1 (9)
1589.0 (7)
N, 8.43; Found: C, 72.42; H, 4.62; N, 8.39. UVeVis (MeOH) lmax
:
Z
8
4
433.6 nm.
Calculated density (g/cm3)
Absorption coefficient (mmꢁ1
F (0 0 0)
1.323
0.091
968
1.389
0.095
696
)
2.2. Measurements
Crystal size (mm3)
q
0.38 ꢂ 0.25 ꢂ 0.13
0.31 ꢂ 0.26 ꢂ 0.13
Range for data collection
2.12e25.10
2.07e25.10
The starting materials were commercially available and used as
received without additional purification. The solvents used were of
analytical grade. Melting points were taken using an XT-4 micro-
melting apparatus and were uncorrected. Elemental analyses were
performed using a Vario EL-III instrument, while IR spectra, in
cmꢁ1, were recorded on a Bruker Equiox-55 spectrometer. 1H NMR
and 13C NMR spectra were recorded at 400 MHz using a Varian
Inova-400 spectrometer, and chemical shifts were reported relative
to the internal Me4Si. The absorption spectra were recorded on
a Shimadzu UV-2450 UVeVis spectrometer using water, dimethyl
Limiting indices h, k, l
ꢁ6/7, ꢁ22/22, ꢁ21/16 ꢁ8/5, e23/23, e13/7
Reflections collected/unique/Rint 5619/1121/0.0270
6425/2692/0.0338
95.4%
Completeness to
q
¼ 25.10ꢀ
100%
Data/restraints/parameters
1121/0/114
1.072
2692/0/227
1.083
Goodness-of-fit on F2
Final R indices [I > 2
s
(I)]
R1 ¼ 0.0388,
wR2 ¼ 0.1115
R1 ¼ 0.0486,
wR2 ¼ 0.1187
0.142 and ꢁ0.158
R1 ¼ 0.0618,
wR2 ¼ 0.1635
R1 ¼ 0.0835,
wR2 ¼ 0.1830
0.437 and ꢁ0.230
R indices (all data)
Largest diff. peak and
hole (e Åꢁ3
)