Synthesis, crystal structures and photoluminescence of 7-(N,N′-diethylamino)-3-phenylcoumarin derivatives

Article abstract of DOI:10.1016/j.saa.2009.12.049

Two new coumarin derivatives, 7-(N,N′-diethylamino)-3-(4-hydroxyphenyl)-coumarin and 7-(N,N′-diethylamino)-3-(4-bromophenyl)-coumarin, were synthesized successfully. Their structures were verified by single crystal X-ray crystallography. The UV-vis absorp

Full text of DOI:10.1016/j.saa.2009.12.049

Spectrochimica Acta Part A 75 (2010) 1036–1042
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis, crystal structures and photoluminescence of
7-(N,Nꢀ-diethylamino)-3-phenylcoumarin derivatives
Tianzhi Yua,∗, Jing Menga, Peng Zhanga, Yuling Zhaob, Hui Zhanga, Duowang Fana,
Lili Chenc, Yongqing Qiuc
a Key Laboratory of Opto-Electronic Technology and Intelligent Control (Lanzhou Jiaotong University), Ministry of Education, 88 West Anning Road, Lanzhou 730070, Gansu, China
b School of Chemical and Biological Engineering, Lanzhou Jiaotong University, Lanzhou 730070, China
c Institute of Functional Material Chemistry, Faculty of Chemistry, Northeast Normal University, Changchun 130024, China
a r t i c l e i n f o
a b s t r a c t
Two new coumarin derivatives, 7-(N,Nꢀ-diethylamino)-3-(4-hydroxyphenyl)-coumarin and 7-(N,Nꢀ-
diethylamino)-3-(4-bromophenyl)-coumarin, were synthesized successfully. Their structures were
verified by single crystal X-ray crystallography. The UV–vis absorption and fluorescence of the compounds
were discussed. The compounds exhibit strong blue emission under ultraviolet light excitation. The
molecular structures, the lowest energy transitions and the UV–vis spectra of 7-(N,Nꢀ-diethylamino)-3-(4-
hydroxyphenyl)-coumarin and 7-(N,Nꢀ-diethylamino)-3-(4-bromophenyl)-coumarin have been studied
with density functional theory (DFT) and time-dependent density functional theory (TD-DFT) at B3LYP/6-
31G(d) level.
Article history:
Received 13 October 2009
Received in revised form 9 December 2009
Accepted 11 December 2009
Keywords:
Coumarin derivatives
Crystal structures
Photoluminescence
DFT studies
© 2009 Elsevier B.V. All rights reserved.
HOMO–LUMO energies
1. Introduction
emitting fluorescent materials, two new coumarin derivatives, 7-
(N,Nꢀ-diethylamino)-3-(4-hydroxyphenyl)-coumarin and 7-(N,Nꢀ-
Coumarinand its derivatives exist widelyin plant, andhavebeen
broadly studied due to their applications in biological, chemical and
physical fields. For example, they have wonderful biological and
medical activity [1–3], such as antitumor and anticoagulant effect
[4]. Furthermore, this series of compounds has prominent optical
properties, such as an extended spectral range, large Stokes shifts,
high quantum yields, superior photostability and good solubility
in common solvents [5–9]. As a result, the coumarin derivatives
are widely used as laser dyes [10,11], ionophores, colorants, non-
linear optical chromophores [12], fluorescent probes [13] and
fluorescent whiteners [14]. Since Tang et al. [15] first used 3-
(2-benzothiazolyl)-7-diethylaminocoumarin (coumarin 6) as an
electroluminescent (EL) material successfully, coumarin dyes have
attracted much interest owing to their potential application in
organic light-emitting diodes (OLEDs) [6,16–20].
diethylamino)-3-(4-bromophenyl)-coumarin, were synthesized.
They contained electron-releasing moieties (i.e., diethylamino) in
7-positions, but the difference between them is that in 3-position of
7-(N,Nꢀ-diethylamino)-3-(4-hydroxyphenyl)-coumarin is phenol
moiety, in the same position of 7-(N,Nꢀ-diethylamino)-3-(4-
bromophenyl)-coumarin is bromophenyl moiety. These moieties
could increase the conjugative effect and surely benefit the flu-
orescence of the compounds. We synthesize them in order to
understand the effect of substituents in coumarin skeleton on the
photoluminescent properties of coumarin.
2. Experimental
2.1. Materials and methods
4-(N,Nꢀ-Diethylamino)salicylaldehyde from Zhejiang Huadee
Dyestuff Chemical Co. Ltd. (China) was recrystallized from ethanol.
4-Hydroxyphenylacetonitrile was purchased from Jinan Haohua
Industrial Co. Ltd. (China). 4-Bromophenylacetonitrile was analyti-
cal grade reagent from Alfa Aesar China (Tianjin) Co. Ltd. The other
solvents were analytical grade reagents.
Although several coumarin derivatives which possess good
photoluminescence and electroluminescence properties were
investigated in our laboratory [5–9], there remain some interests
in the molecular design and synthesis of new coumarin deriva-
tives with high quantum yield of fluorescence and greater stability.
The present work is a continuation of our search for high efficient
IR spectra (400–4000 cm−1) were measured on a Shimadzu
IRPrestige-21 FT-IR spectrophotometer. 1H NMR spectra were
obtained on Unity Varian-500 MHz. C, H, and N analyses were
obtained using an Elemental Vario-EL automatic elemental
∗
Corresponding author. Tel.: +86 931 4956935; fax: +86 931 4938756.
E-mail address: ytz823@hotmail.com (T. Yu).
1386-1425/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2009.12.049

T. Yu et al. / Spectrochimica Acta Part A 75 (2010) 1036–1042
1037
Scheme 1. Synthetic route of 7-(N,Nꢀ-diethylamino)-3-(4-hydroxyphenyl)-coumarin and 7-(N,Nꢀ-diethylamino)-3-(4-bromophenyl)-coumarin.
analysis instrument. UV–vis absorption and photoluminescent
spectra were recorded on a Shimadzu UV-2550 spectrometer and
Perkin Elmer LS-55 spectrometer, respectively.
2.3. Crystallography
Suitable
single
crystal
of
and
7-(N,Nꢀ-diethylamino)-3-
7-(N,Nꢀ-diethylamino)-3-
(4-hydroxyphenyl)-coumarin
(4-bromophenyl)-coumarin were obtained by evaporation of
ethyl acetate solution, respectively. The diffraction data were
collected with a Bruker Smart Apex CCD area detector using
2.2. Synthesis and characterization of
7-(N,Nꢀ-diethylamino)-3-(4-hydroxyphenyl)-coumarin and
7-(N,Nꢀ-diethylamino)-3-(4-bromophenyl)-coumarin
a
graphite monochromated Mo K␣ radiation (ꢁ = 0.71073 Å)
at 20 ◦C. The structures were solved by using the program
SHELXL and Fourier difference techniques, and refined by
full-matrix least-squares method on F2. All hydrogen atoms
were added theoretically. The crystal and experimental data
of 7-(N,Nꢀ-diethylamino)-3-(4-hydroxyphenyl)-coumarin and
7-(N,Nꢀ-diethylamino)-3-(4-bromophenyl)-coumarin are shown
in Table 1. The selected bond lengths and bond angles of the
compounds are listed in Tables 2 and 3, respectively.
The synthetic routes were shown in Scheme 1.
7.2 g (37.6 mmol) of 4-(N,Nꢀ-diethylamino)salicylaldehyde and
5.0 g (37.6 mmol) of 4-hydroxyphenylacetonitrile were dissolved
in 30 mL of ethanol at room temperature and treated with piperi-
dine (0.5 mL). The reaction mixture was held for 24 h at 80 ◦C,
treated with HCl (50 mL, 7%) and boiled for 8–10 h to hydrolyze the
iminocoumarin. After the reaction was finished, the acidic solu-
tion was neutralised with aqueous ammonia until the pH was
7. Some of solvent was removed by rotary evaporation and the
resulting mixture was poured into 100 mL water and extracted
with dichlormethane (3× 60 mL). The organic phase was washed
with water (2× 50 mL) and dried over anhydrous MgSO4. After
filtering, the filtrate was evaporated to dryness under reduced
pressure. The crude was purified by chromatography on silica
gel using ethyl acetate/petroleum ether (1:5, v/v) as the elu-
ent to give 7-(N,Nꢀ-diethylamino)-3-(4-hydroxyphenyl)-coumarin
2.4. Quantum chemical calculations
The structure of 7-(N,Nꢀ-diethylamino)-3-(4-hydroxyphenyl)-
coumarin
and
7-(N,Nꢀ-diethylamino)-3-(4-bromophenyl)-
coumarin were optimized by semi-empirical density functional
theory (DFT) using a B3LYP/6-31G(d) basis set. The structural
energies of the compounds were calculated at B3LYP/6-31G(d)
levels. The structure optimizations and energy calculations were
performed with the GAUSSIAN 98 program.
(6.16 g, 53.4%). m.p. 187–189 ◦C. IR (KBr pellet, cm−1): 3298 (ꢀO–H
,
phenol), 1714 (ꢀC O, lactone), 1618 (ꢀC C), 1519, 1520, 1355, 1235.
1H NMR (Actone-D6, ı, ppm): 8.415 (s, 1H, 4-H), 7.839 (s, 1H,
–OH), 7.604 (d, J = 7.2 Hz, 2H, Aryl-H), 7.460 (d, J = 8.8 Hz, 1H, Aryl-
H), 6.868 (d, J = 7.2 Hz, 2H, Aryl-H), 6.734 (d, J = 8.8 Hz, 1H, Aryl-H),
6.525 (s, 1H, Aryl-H), 3.525 (m, 4H, N-CH2), 1.219 (t, J = 6.8 Hz, 6H,
CH3). Anal. Calc. for C19H19NO3 (%): C, 73.77; H, 6.19; N, 4.53. Found:
C, 74.20; H, 6.30; N, 4.23.
3. Results and discussion
3.1. X-ray crystal structures
The structure of 7-(N,Nꢀ-diethylamino)-3-(4-hydroxyphenyl)-
5.0 g (25.9 mmol) of 4-(N,Nꢀ-diethylamino)salicylaldehyde, 5.2 g
(26.5 mmol) of 4-bromophenylacetonitrile were placed into a
round bottom flask (100 mL) and dissolved in 50 mL of ethanol.
2 mL of piperidine was added into the mixed reaction, and then the
mixture was refluxed with stirring for 48 h. After the reaction was
complete, 10 mL of aqueous solution of HCl was added into reaction,
and then the mixture was refluxed with stirring for 24 h. The result-
ing solution was evaporated to dryness under reduced pressure.
The precipitate was recrystallized from ethyl acetate, and 6.01 g
of brown crystal was 7-(N,Nꢀ-diethylamino)-3-(4-bromophenyl)-
coumarin obtained (yield 63%). m.p.: 159–160 ◦C. IR (KBr pellet,
cm−1): 3421(ꢀN–H), 1716 (ꢀC O), 1128 (ꢀC–O–C), 719 (ꢀC–Br). 1H
NMR (500 MHz, CDCl3, ı, ppm): 7.472–7.678 (m, 4H, phenyl-
H), 7.261–7.315 (t, 1H, coumarin skeleton), 6.514–6.610 (m, 3H,
coumarin skeleton), 3.364–3.450 (m, 4H, CH2), 1.167–1.236 (m, 6H,
CH3). Anal. Calc. for C19H18NO2Br (%): C, 61.30; H, 4.87; N, 3.76.
Found: C, 61.83; H, 4.60; N, 3.43.
coumarin
and
7-(N,Nꢀ-diethylamino)-3-(4-bromophenyl)-
coumarin were measured by X-ray crystallography. Their crystal
structures and packing diagrams are given in Figs. 1–4 , respec-
tively. The crystal data and experimental details are shown
in Table 1. The selected bond lengths and bond angles of the
compounds are listed in Table 2.
The crystal of 7-(N,Nꢀ-diethylamino)-3-(4-hydroxyphenyl)-
coumarin belongs to the triclinic space group P-1. As shown in
Fig. 1, there is an asymmetric unit consisted of two molecules
in crystal structure of the compound due to the different space
configuration of hydroxy groups in 4ꢀ-position of benzene ring,
these two molecules are space conformers. In every molecule,
the phenol ring is not coplanar with the coumarin ring and the
dihedral angle is 38.13◦. As shown in Fig. 2, the distance of the
coumarin rings between two adjacent molecules along a-axis in
crystal lattice is about 3.8 Å, which means weak intermolecular
␲–␲ stacking interaction between 7-(N,Nꢀ-diethylamino)-3-(4-

1038
T. Yu et al. / Spectrochimica Acta Part A 75 (2010) 1036–1042
Table 1
Crystallographic data for 7-(N,Nꢀ-diethylamino)-3-(4-hydroxyphenyl)-coumarin (I) and 7-(N,Nꢀ-diethylamino)-3-(4-bromophenyl)-coumarin (II).
Compound
I
II
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
C19H19NO3
309.35
293(2)
0.71073
Triclinic
P-1
C19H18BrNO2
372.25
293(2)
0.71073
Monoclinic
P21/c
Unit cell dimensions
a (Å)
b (Å)
10.071(2)
11.670(3)
13.869(3)
92.707(4)
101.863(3)
97.796(4)
1575.7(6), 4
1.304
16.2673(19)
12.5722(15)
8.2004(10)
90
104.60(3)
90
1623.0(3), 4
1.523
2.542
c (Å)
˛ (◦)
ˇ (◦)
ꢂ (◦)
Volume (Å3), Z
Density (calculated) (g/cm3)
Absorption coefficient (mm−1
F (0 0 0)
)
0.088
656
760
Crystal size (mm)
0.45 × 0.28 × 0.21
0.42 × 0.29 × 0.05
ꢃ range for data collected (◦)
1.50–25.75
2.07–26.08
Limiting indices
−12 ≤ h ≤ 11,
−12 ≤ k ≤ 14,
−15 ≤ l ≤ 16
−19 ≤ h ≤ 20,
−15 ≤ k ≤ 15,
−8 ≤ l ≤ 10
Reflections collected
8698
8888
Independent reflections
Absorption correction
Max. and min. transmission
Refinement method
5882 (Rint = 0.0157)
Semi-empirical from equivalents
0.9821 and 0.9612
Full-matrix least-squares on F2
5882/0/421
3211 (Rint = 0.0252)
Semi-empirical from equivalents
0.8728 and 0.4170
Full-matrix least-squares on F2
3211/0/210
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2ꢄ (I)]
R indices (all data)
1.040
1.035
R1 = 0.0626, wR2 = 0.1682
R1 = 0.0835, wR2 = 0.1894
0.642 and −0.354
R1 = 0.0384, wR2 = 0.0957
R1 = 0.0606, wR2 = 0.1059
0.590 and −0.295
Largest diff. Peak and hole (eÅ−3
)
Table 2
Experimental and calculated structural parameters of 7-(N,Nꢀ-diethylamino)-3-(4-hydroxyphenyl)-coumarin (I) and 7-(N,Nꢀ-diethylamino)-3-(4-bromophenyl)-coumarin
(II).
I
II
Exp.
Calcd.
Exp.
Calcd.
Bond length (Å)
C(1)–O(1)
C(7)–O(2)
Bond length (Å)
Br(1)–C(1)
C(7)–O(1)
1.377(2)
1.3676
1.3973
1.2108
1.3637
1.3729
1.4634
1.4629
1.902(3)
1.9130
1.2109
1.3972
1.3633
1.3784
1.4625
1.4630
1.385(2)
1.206(2)
1.382(2)
1.366(3)
1.459(3)
1.468(3)
1.205(3)
1.383(3)
1.378(3)
1.374(3)
1.461(3)
1.459(3)
C(7)–O(3)
C(7)–O(2)
C(15)–O(2)
C(13)–N(1)
C(16)–N(1)
C(18)–N(1)
C(11)–O(2)
C(13)–N(1)
C(16)–N(1)
C(18)–N(1)
Bond angles (◦)
Bond angles (◦)
C(6)–C(1)–O(1)
O(1)–C(1)–C(2)
O(3)–C(7)–O(2)
O(3)–C(7)–C(8)
O(2)–C(7)–C(8)
O(2)–C(15)–C(10)
C(14)–C(15)–O(2)
C(7)–O(2)–C(15)
C(13)–N(1)–C(16)
C(13)–N(1)–C(18)
N(1)–C(13)–C(14)
N(1)–C(13)–C(12)
C(16)–N(1)–C(18)
N(1)–C(16)–C(17)
N(1)–C(18)–C(19)
121.71(19)
118.78(19)
115.63(19)
126.8(2)
117.52(18)
119.67(19)
117.05(19)
122.98(16)
121.1(2)
122.2(2)
121.8(2)
121.3(2)
116.7(2)
122.797
117.649
116.171
126.897
116.932
120.175
117.074
123.677
120.863
121.150
121.378
121.325
117.853
114.972
115.025
C(2)–C(1)–Br(1)
C(6)–C(1)–Br(1)
O(1)–C(7)–C(8)
O(1)–C(7)–O(2)
O(2)–C(7)–C(8)
C(11)–O(2)–C(7)
O(2)–C(11)–C(10)
C(12)–C(11)–O(2)
N(1)–C(13)–C(12)
N(1)–C(13)–C(14)
C(13)–N(1)–C(16)
C(13)–N(1)–C(18)
C(18)–N(1)–C(16)
N(1)–C(16)–C(17)
N(1)–C(18)–C(19)
120.4(2)
119.486
119.684
126.959
116.195
116.846
123.719
120.164
117.139
121.293
121.236
122.071
121.703
116.223
113.889
113.920
119.29(19)
127.2(2)
115.01(19)
117.80(19)
122.98(17)
119.7(2)
116.6(2)
121.3(2)
121.4(2)
122.4(2)
121.2(2)
115.5(2)
113.3(2)
113.9(2)
113.8(3)
114.4(2)
Hydrogen bonds
D–H· · ·A
d(D–H)
0.82
0.82
d(H· · ·A)
2.00
1.93
d(D· · ·A)
2.790(2)
2.739(3)
O(1)–H(1)· · ·O(6)a
O(4)–H(4)· · ·O(1)b
a
Symmetry transformations used to generate equivalent atoms: x + 1, y + 1, z.
Symmetry transformations used to generate equivalent atoms: −x + 2, −y + 1, −z + 2.
b

T. Yu et al. / Spectrochimica Acta Part A 75 (2010) 1036–1042
1039
Table 3
Absorption spectra data of 7-(N,Nꢀ-diethylamino)-3-(4-hydroxyphenyl)-coumarin and 7-(N,Nꢀ-diethylamino)-3-(4-bromophenyl)-coumarin.
Compound
1
Transition character
OSCa
ꢁmax, cal. (nm)
ꢁmax, exp. (nm)b
Transition feature
*
*
HOMO → LUMO
0.7848
0.1526
356.31
244.30
397
268
␲ → ␲
␲ → ␲
HOMO → LUMO + 3
*
HOMO → LUMO
0.9542
0.3392
372.07
204.06
403
273
␲ → ␲
␲ → ␲
2
*
HOMO − 2 → LUMO + 1
a
Oscillator strength coefficients (f).
ꢁmax in dichlormethane solvent.
b
Fig. 1. Crystal structure of 7-(N,Nꢀ-diethylamino)-3-(4-hydroxyphenyl)-coumarin.
hydroxyphenyl)-coumarin molecules in crystal lattice. In addition,
there are the formation of hydrogen bonds between molecules
in the crystal of 7-(N,Nꢀ-diethylamino)-3-(4-hydroxyphenyl)-
coumarin (Table 2).
bromophenyl)-coumarin belongs to the monoclinic space group
P21/c (Fig. 3). In the molecule, the phenol ring is also not coplanar
with the coumarin ring and the dihedral angle is 31.28◦. As shown
in Fig. 4, the distance of the coumarin rings between two adjacent
molecules along c-axis in crystal lattice is about 3.5 Å, which
means strong intermolecular ␲–␲ stacking interaction between
Compared with 7-(N,Nꢀ-diethylamino)-3-(4-hydroxyphenyl)-
coumarin,
the
crystal
of
7-(N,Nꢀ-diethylamino)-3-(4-
Fig. 2. Packing diagram of 7-(N,Nꢀ-diethylamino)-3-(4-hydroxyphenyl)-coumarin along a-axis. H atoms are omitted for clarity.

1040
T. Yu et al. / Spectrochimica Acta Part A 75 (2010) 1036–1042
Fig. 3. Crystal structure of 7-(N,Nꢀ-diethylamino)-3-(4-bromophenyl)-coumarin.
Fig. 4. Packing diagram of 7-(N,Nꢀ-diethylamino)-3-(4-bromophenyl)-coumarin along c-axis. H atoms are omitted for clarity.
7-(N,Nꢀ-diethylamino)-3-(4-bromophenyl)-coumarin molecules
in crystal lattice.
3.2. UV–vis absorption and photoluminescence
UV–vis absorption and photoluminescent spectra of
7-(N,Nꢀ-diethylamino)-3-(4-hydroxyphenyl)-coumarin and 7-
(N,Nꢀ-diethylamino)-3-(4-bromophenyl)-coumarin in diluted
dichloromethane solutions are shown in Fig. 5. The absorption
spectrum of coumarin was reported to have two peaks at 281 and
320 nm [21], while 7-(N,Nꢀ-diethylamino)-3-(4-hydroxyphenyl)-
coumarin has absorption peaks at 268 and 398 nm, respectively.
The second absorption band at 398 nm presents bathochromic shift
as the result of the electron-releasing diethylamino substituent in
7-position and a phenol group in 3-position which can increase
conjugative effect of the molecule. The absorption spectrum of
7-(N,Nꢀ-diethylamino)-3-(4-bromophenyl)-coumarin is similar
to that of 7-(N,Nꢀ-diethylamino)-3-(4-hydroxyphenyl)-coumarin,
there are two absorption at 273 and 403 nm.
Fig. 5. UV–vis absorption spectrum (5 × 10−5 mol/L) and fluorescence spectrum
(1 × 10−5 mol/L) of 7-(N,Nꢀ-diethylamino)-3-(4-hydroxyphenyl)-coumarin (I) and
7-(N,Nꢀ-diethylamino)-3-(4-bromophenyl)-coumarin (II).

T. Yu et al. / Spectrochimica Acta Part A 75 (2010) 1036–1042
1041
Fig.
5
also shows the photoluminescent spectra of 7-
and
(N,Nꢀ-diethylamino)-3-(4-hydroxyphenyl)-coumarin and 7-(N,Nꢀ-
diethylamino)-3-(4-bromophenyl)-coumarin are slightly lower
than that of coumarin 6.
(N,Nꢀ-diethylamino)-3-(4-hydroxyphenyl)-coumarin
7-(N,Nꢀ-diethylamino)-3-(4-bromophenyl)-coumarin in dilute
dichloromethane solutions. They all exhibit bright blue emission,
and the emission peaks of the compounds locate at around 472 and
462 nm, respectively. The emission peak of 7-(N,Nꢀ-diethylamino)-
3-(4-hydroxyphenyl)-coumarin was red-shifted by 10 nm with
respect to that of 7-(N,Nꢀ-diethylamino)-3-(4-bromophenyl)-
coumarin, it can be generally deduced that the conjugative effect
of the phenol derivative is larger than that of the bromophenyl
derivative.
3.4. Quantum chemical calculations
B3LYP/6-31G(d) optimized structure of 7-(N,Nꢀ-diethylamino)-
3-(4-hydroxyphenyl)-coumarin and 7-(N,Nꢀ-diethylamino)-3-(4-
bromophenyl)-coumarin are close to their X-ray crystal structures,
B3LYP/6-31G(d) optimized geometrical data of them are in good
agreement with the X-ray crystallographic data as listed in Table 2,
the average discrepancy of the selected bond lengths between the-
oretical and experimental data is less than 0.02 Å, and the average
discrepancy of the selected bond angles is less than 1.1◦.
3.3. Fluorescence quantum yield of the compounds (˚F)
Fluorescence
quantum
yields
of
7-(N,Nꢀ-
The orbital energy levels of HOMO (highest occupied molec-
ular orbital) and LUMO (lowest unoccupied molecular orbital)
of 7-(N,Nꢀ-diethylamino)-3-(4-hydroxyphenyl)-coumarin and 7-
(N,Nꢀ-diethylamino)-3-(4-bromophenyl)-coumarin were deduced
using the DFT method as shown in Figs. 6 and 7, respectively.
It can be seen that EHOMO and ELUMO values of 7-(N,Nꢀ-
diethylamino)-3-(4-hydroxyphenyl)-coumarin are −5.011 and
−1.278 eV, respectively. The energy gap between HOMO and LUMO
is about 3.733. For 7-(N,Nꢀ-diethylamino)-3-(4-bromophenyl)-
coumarin, the HOMO level of is −5.251 eV and the LUMO level is
−1.625, the energy gap between HOMO and LUMO is about 3.626.
The UV–vis absorption spectra of 7-(N,Nꢀ-diethylamino)-
diethylamino)-3-(4-hydroxyphenyl)-coumarin
and
7-(N,Nꢀ-diethylamino)-3-(4-bromophenyl)-coumarin in chlo-
roform solution were checked with anthracene, respectively. The
quantum yield (˚F) were calculated according to the relationship
[22,23]:
ꢀ
ꢁ
ꢂ
∞ IF(v˜)dv˜
IFS(v˜)dv˜
S
ꢃ
ꢄ
1 − 10−A
n
ns
2
0
˚
F
= ˚S
F
1 − 10−A
where ˚SF is the quantum yield of anthracene as standard, which
was assumed to be 0.25 for all environments [23]. The inte-
ꢀ
ꢀ ∞
gral ∞ IF(v˜)dv˜ and
IFS(v˜)dv˜ are the areas under the emission
0
0
curves of the investigated and standard compound, respec-
3-(4-hydroxyphenyl)-coumarin
and
7-(N,Nꢀ-diethylamino)-
tively.
A
and AS are the absorbances at the wavelength of
3-(4-bromophenyl)-coumarin were also calculated by the
time-dependent density functional theory (TD-DFT) at the
same level. The experimental and calculated ꢁmax (nm) for the
lower-lying singlet states of the compounds are listed in Table 3.
As shown in Table 3, there are some discrepancies between
theoretical and experimental data due to several influencing
factors, such as solvent effect and intermolecular interaction,
excitation, n and nS are the refractive indices for the inves-
tigated and standard, respectively. In the research, the
˚
F
of 7-(N,Nꢀ-diethylamino)-3-(4-hydroxyphenyl)-coumarin and 7-
(N,Nꢀ-diethylamino)-3-(4-bromophenyl)-coumarin are 0.49 and
0.52, respectively. Fluorescence quantum yields of coumarin 6
in acetonitrile is 0.63 [24]. Fluorescence quantum yields of 7-
Fig. 6. Frontier molecular orbitals of 7-(N,Nꢀ-diethylamino)-3-(4-hydroxyphenyl)-coumarin.

1042
T. Yu et al. / Spectrochimica Acta Part A 75 (2010) 1036–1042
Fig. 7. Frontier molecular orbitals of 7-(N,Nꢀ-diethylamino)-3-(4-bromophenyl)-coumarin.
etc. It has been found that the lowest energy absorption at
funds (QL-05-23A) by Lanzhou Jiaotong University. This work was
also supported by the Science Foundation for Young Teachers of
Northeast Normal University (NENU 20070313).
397 nm for 7-(N,Nꢀ-diethylamino)-3-(4-hydroxyphenyl)-coumarin
or
403 nm
for
7-(N,Nꢀ-diethylamino)-3-(4-bromophenyl)-
coumarin is an excitation from the HOMO to the LUMO. The
transition occurring at 268 nm for 7-(N,Nꢀ-diethylamino)-3-
(4-hydroxyphenyl)-coumarin is attributed to the electronic
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Two new coumarin derivatives, 7-(N,Nꢀ-diethylamino)-3-
(4-hydroxyphenyl)-coumarin and 7-(N,Nꢀ-diethylamino)-3-(4-
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in good agreement with experimental data.
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Acknowledgements
This work was supported by the National Natural Science Foun-
dation of China (Grant 60776006) and ‘Qing Lan’ talent engineering