Synthesis, crystal structure and photoluminescence of 3-(1-benzotriazole)-4-methyl-coumarin

Article abstract of DOI:10.1016/j.molstruc.2005.12.022

A novel coumarin derivative containing an electron-transporting moiety (benzotriazole), 3-(1-benzotriazole)-4-methyl-coumarin (BMC), was synthesized from starting substances, i.e. benzotriazole and 2-hydroxyacetophenone. The compound structure was verified by FT-IR, ¹H NMR, element analysis and single crystal X-ray crystallography. Crystallographic data reveal a dihedral angle of 108° between the coumarin and benzotriazole rings, which is attributed to the spatial hindrance of a 4-positioned methyl group. The fluorescence and UV-vis absorption of BMC were discussed. The compound exhibits a strong UV emission peak at 385 nm under 360 nm excitation. The molecular structure of BMC was optimized using density functional theory (DFT) at B3LYP/6-31G(d) level, showing that the optimized geometric parameters are in good agreement with experimental data. In addition, the HOMO and LUMO levels of BMC were deduced.

Full text of DOI:10.1016/j.molstruc.2005.12.022

Journal of Molecular Structure 791 (2006) 18–22
www.elsevier.com/locate/molstruc
Synthesis, crystal structure and photoluminescence
of 3-(1-benzotriazole)-4-methyl-coumarin
*
Tianzhi Yu , Yuling Zhao, Duowang Fan
Key Laboratory of Opto-Electronic Technology and Intelligent Control (Lanzhou jiaotong University),
Ministry of Education, Lanzhou 730070, China
Received 19 October 2005; received in revised form 29 December 2005; accepted 29 December 2005
Available online 14 February 2006
Abstract
A novel coumarin derivative containing an electron-transporting moiety (benzotriazole), 3-(1-benzotriazole)-4-methyl-coumarin (BMC), was
synthesized from starting substances, i.e. benzotriazole and 2-hydroxyacetophenone. The compound structure was verified by FT-IR, 1H NMR,
element analysis and single crystal X-ray crystallography. Crystallographic data reveal a dihedral angle of 1088 between the coumarin and
benzotriazole rings, which is attributed to the spatial hindrance of a 4-positioned methyl group. The fluorescence and UV–vis absorption of BMC
were discussed. The compound exhibits a strong UV emission peak at 385 nm under 360 nm excitation. The molecular structure of BMC was
optimized using density functional theory (DFT) at B3LYP/6-31G(d) level, showing that the optimized geometric parameters are in good
agreement with experimental data. In addition, the HOMO and LUMO levels of BMC were deduced.
q 2006 Elsevier B.V. All rights reserved.
Keywords: Benzotriazole; Coumarin derivative; Crystal structure; Photoluminescence
1. Introduction
(in absorption and fluorescence). Since 3-(2-benzothiazolyl)-7-
diehylaminocoumarin (coumarin 6) is widely used as an
emissive dopant in organic light–emitting diodes (OLEDs)
based on polymers [14–16] and small molecules [17–18],
coumarin derivatives have attracted much attention due to their
potential application for OLEDs [19–20].
Coumarin and its derivatives have been extensively
studied due to their commercial applications in several
fields. They possess excellent biological activity, such as
anticancer and anticoagulant activity [1]. Moreover, this
series of compounds has outstanding optical properties,
including an extended spectral range, high quantum yields,
superior photostability and good solubility in common
solvents. So these compounds are widely used as laser
dyes [2–3], nonlinear optical chromophores [4], fluorescent
whiteners [5], as well as fluorescent labels and probes for
physiological measurement [6–9]. Another feature of the
coumarin derivatives is that photophysical and spectroscopic
properties can be readily modified by the introduction of
substituents in the coumarin ring, giving themselves more
flexibility to fit well in various applications [10–13]. For
example, electron-releasing substituents in 3- or 7- positions
not only bring bathochromic shifts of the absorption edge
towards long wavelength side, but also enhance band intensity
In this study, we report on the synthesis and photophysical
properties of a novel coumarin derivative, 3-(1-benzotriazole)-
4-methyl-coumarin (BMC), containing an electron-accepting
moiety (benzotriazole). Benzotriazole moiety is chosen as a
substituent for the following reasons. First, UV emission of the
coumarins was less studied in spite of their well-known
fluorescence in visible range; second, the electron-accepting
benzotriazole moiety surely benefits the electron-transporting
properties of the compounds [21].
2. Experimental
2.1. Materials and methods
2-Hydroxyacetophenone from Acros Organics and
1H-benzotriazole (BTA) from Aldrich were used without
further purification. Chloroacetic acid and Phosphorus oxy-
chloride were analytical grade reagents from Tanjin Fuchen
*
Corresponding author. Tel. C86 931 4956935; fax: C86 931 4956030.
E-mail address: ytz823@hotmail.com (T. Yu).
0022-2860/$ - see front matter q 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2005.12.022

T. Yu et al. / Journal of Molecular Structure 791 (2006) 18–22
19
Table 1
Chemical Reagent Factory. Phosphorus oxychloride was dried
Crystal data and structure refinement for BMC
and redistilled before using.
IR spectra (400–4000 cmK1) were measured on a Nicolet
Magna FT-IR spectrophotometer. C, H, and N analyses were
obtained using an Elemental Vario-EL automatic elemental
analysis instrument. 1H NMR spectra were obtained on Unity
Varian-500MHz. UV–vis absorption and fluorescence spectra
were recorded on a Hitachi UV-3010PC spectrometer and on a
Hitachi MPF-4 spectrometer, respectively. Melting points were
observed by the capillary tube method.
Empirical formula
Formula weight
Temperature (K)
C16H11N3O2
277.28
293 (2)
˚
Wavelength (A)
0.71073
Orthorhombic
Pca21
Crystal system
Space group
o
˚
Unit cell dimensions
aZ18.303 (3) A, aZ90
bZ5.4256 (8) A, bZ90
cZ13.4928 (19) A, gZ90
1339.9 (3), 4
1.375
o
˚
o
˚
3
˚
Volume (A ), Z
Density (calculated) (g/cm3)
Absorption coefficient (mmK1
F (000)
2.2. (1-Benzotriazolyl) acetic acid (1)
)
0.094
576
Crystal size (mm)
q range for data collected (o)
0.31 ! 0.11 ! 0.08
2.23 to 26.04
K20%h%22, K6%k%6,
K13%l%16
7024
13.1 g(0.11 mol)of1H-benzotriazoleand9.45 g(0.1 mol)of
chloroacetic acid were dissolved in dry toluene (100 ml), and
then the solution was heated to 130 8C and refluxed for 18 h with
magnetic stirring. After cooling the solution to room tempera-
ture, it was poured into a concentrated aqueous solution of
NaHCO3. The water phase was separated and extracted with
dichloromethanethreetimes. Theaqueoussolutionwas adjusted
to a pH of 4 by adding 2N HCl and allowed to sit overnight. After
this, the precipitate was filtered and washed successively with
distilled water and methanol. The product was dried under
reduced pressure and purified with re-crystallization from
methanol to yield 10.6 g (60%) of white crystalline solid; m.p.
213–215 8C (Ref.[22]: 214–216 8C).
Limiting indices
Reflections collected
Independent reflections
Absorption correction
Max. and min. transmission
Refinement method
2295 (RintZ0.0372)
Semi-empirical from equivalents
0.9922 and 0.9716
Full-matrix least-squares on F2
2295/1/191
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [IO2s(I)]
R indices (all data)
1.024
R1Z0.0494, wR2Z0.1120
R1Z0.0700, wR2Z0.1238
0.147 and K0.125
K3
˚
Largest diff. Peak and hole (e A
)
69.16;H,3.94;N,15.04.IR(KBrpellet,cmK1):1718(nCZO).1H
NMR(500 MHz,CDCl3,d,ppm):2.32m(s,3H,CH3),7.25–8.21
(m, 8H, Ar-H). The compound is soluble in common organic
solvents such as chloroform, acetone and tetrahydrofuran.
2.3. (2-Acetyl) phenol 2-(1-benzotriazolyl) acetate (2)
To a stirred solution of 10 g (0.073 mol) of 2-hydroxyaceto-
phenone and 13.99 g (0.079 mol) of (1-benzotriazolyl) Acetic
acid (1) in 100 ml of dry pyridine cooled at 5–10 8C, 6 ml of
phosphorus oxychloride was added stepwise. The mixture was
stired for 10 h at room temperature. After the reaction was
complete, the mixture was allowed to sit overnight. Then the
mixture was poured into an aqueous solution of HCl containing
fragment ice with vigorous stirring, and a precipitate was
produced. The precipitate was filtered and washed successively
with diluted aqueous solution of NaHCO3 (10%) and distilled
water, respectively. After ethanol recrystallization, filtration and
drying in vacuum, 17.35 g (80%) of primrose fine crystals were
obtained. m.p. 136–138 8C (Lit. [23]: 137–138 8C).
2.5. Crystallography
A suitable single crystal of BMC was obtained from methanol
solution. The diffraction data were collected with a Bruker Smart
ApexCCDareadetectorusingagraphitemonochromatedMoKa
˚
radiation (lZ0.71073 A) at 20 8C. The structure was 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 are shown in Table 1.
N
N
N
2.4. 3-(1-Benzotriazole)-4-methyl-coumarin (3)
O
C
OH
COCH3
O
2
CH2
COCH3
6 g (0.02 mol) of (2-acetyl) phenol 2-(1-benzotriazolyl)
acetate was dissolved in 50 ml of dry pyridine, then 1.4 g
(0.025 mol) of potassium hydroxide was added stepwise and the
reaction mixture was stirred vigorously for 5 h at room
temperature. The mixture turned brown during the reaction,
andthesolutionbecame ropy. Aftercompleting, themixturewas
poured into the aqueous solution of HCl containing fragment ice
with vigorous stirringand a yellow precipitate was formed. Then
thecrudeproductwasfilteredandwashedwithdistilledwaterand
purified with recrystallization from ethanol to yield 4.61 g
(81.9%)ofyellowcrystallinesolid.m.p.172–174 8C.Anal.Calc.
for C16H11N3O2 (%): C, 69.31; H, 4.00; N, 15.15. Found: C,
N
N
N
ClCH2COOH
N
N
POCl3
N
H
CH2COOH
1
KOH
Py
N
N
CH3
N
O
O
3
Scheme 1. Synthetic route to the titled compound 3.

20
T. Yu et al. / Journal of Molecular Structure 791 (2006) 18–22
N
N
N
H3C
O
N
N
CH3
N
N
H
N
-
H-O-
O
C
N
CH
N
N
O
C
KOH
N
O
CH2
O
-H
O
O
O
O
COCH3
C
CH3
O
Scheme 2. The mechanism of cyclodehydration.
2.6. Quantum chemical calculations
structure was examined by a single-crystal X-ray diffraction
analysis. The crystal of BMC belongs to the orthorhombic
space group Pca21. As shown in Fig. 1, the benzotriazole group
is not coplanar with the coumarin ring and the dihedral angle is
1088. This is attributed to steric interaction between 4-posi-
tioned methyl group and benzotriazole group. There is an
intermolecular p–p stacking between the BMC molecules in
crystal lattice as shown in Fig. 2.
The structure of BMC was optimized by semiempirical
density functional theory (DFT) using a B3LYP/6-31G(d) basis
set. The structural energy of BMC was computed at B3LYP/6-
31G(d) levels. The structure optimization and energy calcu-
lations were performed with the GAUSSIAN 98 program.
3. Results and discussion
3.3. Absorption and fluorescence of BMC
3.1. Synthesis
UV–vis absorption spectra of BMC and coumarin in diluted
chloroform solutions are given in Fig. 3. Two intense
absorption bands are observed in the spectra of BMC and
coumarin and the spectral shape of BMC is similar to that of
coumarin. The absorption spectrum of coumarin has two peaks
at 281 and 320 nm, while BMC has two absorption peaks at
275 and 315 nm, respectively. Compared with coumarin, the
absorption peaks of BMC shift to blue due to the electron-
withdrawing benzotriazole substituent in 3-position. Charge
density decreases within the pyranone ring, and thus, there
appears a noticeable p-electron density transfer from carbonyl
oxygen to pyranone ring. The lower energy absorption
maximum of BMC (315 nm) corresponds to S0/S1 transition.
Fig. 4 shows fluorescence spectra of BMC and coumarin in
dilute solutions. It is shown that the emission peaks of BMC
and coumarin appeared at around 385 nm and 430 nm,
respectively. The emission of BMC was blue-shifted by
about 45 nm with respect to that of coumarin because of steric
hindrance resulting from benzotriazole and methyl group.
The BMC compound containing electron withdrawing
benzotriazole moiety was synthesized by the synthetic route
shown in Scheme 1. The first step was alkylation of 1H-
benzotriazole with chloroacetic acid in dry toluene. The second
step was esterification of (1-benzotriazolyl) acetic acid with
2-hydroxyacetophenone in the presence of phosphorus oxy-
chloride in dry pyridine. The final step was cyclodehydration of
(2-acetyl) phenol 2-(1-benzotriazolyl) acetate using potassium
hydroxide as catalyst in the dry pyridine.
The mechanism of cyclodehydration is shown in Scheme 2.
Bearing electron-withdrawing group, the alkylidene adjacent to
benzotriazole easily loses a proton when treated with base and
a carbanion forms stably. The carbanion connects to the
carbonyl group and the oxy anion attacks the hydrogen
intramolecularly. A H-OK is then eliminated and a new CZ
C bond is formed.
3.2. X-ray crystallographic analyse
The crystal structure and packing diagram of BMC are
given in Fig. 1 and Fig. 2, respectively. The crystal data and
experimental details are shown in Table 1. The bond lengths
and bond angles of BMC are listed in Table 2.
The single crystal of BMC, suitable for X-ray diffraction
analyse, was obtained from methanol solutions and the
Fig. 1. Crystal structure of BMC.
Fig. 2. Packing diagram along b-axis. H atoms are omitted for clarity.

T. Yu et al. / Journal of Molecular Structure 791 (2006) 18–22
21
Table 2
Experimental and calculated structural parameters of BMC molecule
1.0
0.5
0.0
Bond
Exp.
Calcd.
Bond angles (o) Exp.
Calcd.
length
˚
(A)
O1–C7
O1–C15
O2–C7
N1–C1
N1–N2
N1–C8
N2–N3
N3–C2
C1–C2
C1–C6
C2–C3
C3–C4
C4–C5
C5–C6
C7–C8
C8–C9
C9–C10
C9–C16
1.364(4) 1.3652
1.389(4) 1.3815
1.204(4) 1.2082
1.367(4) 1.3747
1.366(3) 1.3887
1.414(4) 1.4136
1.298(4) 1.2845
1.381(4) 1.3814
1.378(4) 1.408
1.405(4) 1.4021
1.399(4) 1.4038
1.364(5) 1.3849
1.394(5) 1.4163
1.362(5) 1.3868
1.445(4) 1.4712
1.349(4) 1.3671
1.451(4) 1.4554
1.483(4) 1.5045
C7–O1–C15
C1–N1–N2
C1–N1–C8
N2–N1–C8
N3–N2–N1
N2–N3–C2
N1–C1–C2
N1–C1–C6
C2–C1–C6
121.5(2)
122.8
109.4(2)
128.4(2)
122.2(2)
109.2(2)
107.8(2)
104.4(3)
132.9(3)
122.6(3)
109.2(3)
130.6(3)
120.3(3)
117.6(3)
121.2(3)
122.9(3)
115.4(3)
117.3(3)
125.6(3)
117.1(3)
122.0(3)
123.5(3)
114.5(3)
117.2(3)
122.2(3)
120.6(3)
116.7(3)
119.6(3)
123.6(3)
120.9(3)
120.5(3)
120.2(3)
118.4(3)
121.1(2)
123.3(3)
115.6(3)
109.4612
130.8264
119.6938
109.0601
109.0178
103.6797
134.4108
121.8905
108.7726
130.1688
121.0565
117.2709
121.2158
122.1957
116.3701
118.222
350
400
450
5 00
550
N3–C2–C1
N3–C2–C3
C1–C2–C3
Wavelength (nm)
Fig. 4. Fluorescence spectra of BMC (B) and coumarin (D) in dilute
chloroform solutions at room temperature. (CZ2!10K5 mol/l, lexZ360 nm.)
C4–C3–C2
C3–C4–C5
C6–C5–C4
C5–C6–C1
O2–C7–O1
O2–C7–C8
O1–C7–C8
C9–C8–N1
C9–C8–C7
125.6812
116.085
C10–C15 1.377(4) 1.4068
C10–C11 1.400(5) 1.4106
C11–C12 1.369(4) 1.3877
C12–C13 1.379(5) 1.4021
C13–C14 1.373(5) 1.3894
C14–C15 1.379(4) 1.3956
121.9677
122.8209
115.1706
117.9934
122.8028
119.2038
117.4891
118.7218
123.7887
121.0271
120.0709
120.2927
119.1197
121.4714
122.0002
116.528
N1–C8–C7
C8–C9–C10
C8–C9–C16
C10–C9–C16
C15–C10–C11
C15–C10–C9
C11–C10–C9
C12–C11–C10
C11–C12–C13
C14–C13–C12
C13–C14–C15
C10–C15–O1
C10–C15–C14
O1–C15–C14
Fig. 5. B3LYP/6-31G(d)-optimized structure of BMC.
optimized structure of BMC is shown in Fig. 5, indicating that
the DFT-optimized structure is close to the crystal structure.
Atomic charges of hetero atoms and dipole moment of BMC
molecule are listed in Table 3.
B3LYP/6-31G(d)-optimized geometrical data of BMC were
obtained. It was found that the B3LYP/6-31G(d) optimized
structure of BMC is in good agreement with the X-ray
crystallographic data as listed in Table 2. Therefore, the results
using density functional theory (DFT) at B3LYP/6-31G(d)
level is creditable. The HOMO and LUMO levels of BMC
were deduced using the DFT method as shown in Fig. 6, which
is essential for deducing its S0 and S1 states. This knowledge is
important for the better understanding of its fluorescence and
nonlinear optical properties.
3.4. Quantum chemical calculations
The total energy of BMC obtained at B3LYP/6-31G(d) level
of theory was K930.7834098 (au). The B3LYP/6-31G(d)-
2.0
1.5
1.0
0.5
0.0
Table 3
Atomic charges of hetero atoms and dipole moment of BMC
Atom
Mullikena
O(1)
K0.518559
K0.456091
K0.498957
K0.053297
K0.367091
7.0130
O(2)
N(3)
250
300
350
400
N(4)
Wavelength (nm)
N(5)
Dipole moment, D
Fig. 3. UV-vis absorption spectra of BMC (B) and coumarin (D) in chloroform
(2!10K5mol/l).
a
In hartree based on the B3LYP/6-31G(d) level.

22
T. Yu et al. / Journal of Molecular Structure 791 (2006) 18–22
Fig. 6. Frontier molecular orbitals of compound BMC.
¨
[2] K.H. Drexhage, in: F.P. Schafer (Ed.), Topics in Applied Physics Dye
From Fig. 6, it can be seen that the HOMO of BMC is
Lasers, vol. 1, Springer, Berlin, 1973.
K6.38 eV and the LUMO is K2.11 eV. The electron density
of the HOMO is localized mostly on the benzotriazole ring,
and inversely, the LUMO is localized mainly on the coumarin
ring. The presence of electron-withdrawing benzotriazole at
3-position has a large effect on frontier orbitals, and thus the
LUMO of BMC is higher than that of coumarin [10].
Further investigation on the electroluminescent properties
of BMC is being carried out.
[3] G. Jones, W.R. Jackson, C. Choi, W.R. Bergmark, J. Phys. Chem. 89
(1985) 294.
[4] T. Hiroshi, O. Yosho, I. Juzo, I. Masato, T. Atsushi, Jpn. Kokai Tokkyo
Koho, 1990 (1990) (CODEN JKXXAF JP 02126241 A2 19900515
Heisei).
[5] H.E. Patel, K.R. Desai, J. Inst. Chem. 68 (1996) 78.
[6] R.P. Haugland, Handbook of Fluorescent Probes and Research
Chemicals, Molecular Probes, Eugene (OR), 1994–1996.
[7] H. Schwander, P. Hendrix, in: Y.S. Yamamoto (Ed.), fifth ed. Ullmann’s
encyclopedia of industrial chemistry, vol. A11, VCH, Weinheim, 1988,
p. 280.
4. Conclusions
[8] H.K. Arora, A.R. Aggarwal, P. Singh, Indian J. Chem. 21A (1982) 844.
[9] O.S. Wolfbeis, E. Koller, P. Hochmuth, Bull. Chem. Soc. Jpn 58 (1985)
731.
The novel coumarin derivative, BMC, containing an
electron-transporting moiety was synthesized, and the reaction
mechanism was also discussed. Its structure was studied both
experimentally and theoretically. Both the absorption and
emission spectra of BMC were blue-shifted with respect to
those of coumarin because of the electron-withdrawing
substitute and steric hindrance. The HOMO and LUMO levels
of BMC were deduced and the LUMO energy of BMC was
elevated by introducing the electron-withdrawing moiety.
ˇ
[10] I. Novak, B. Kovac, J. Electron. Spectrosc. 113 (2000) 9.
[11] B.M. Krasovitskii, in: B.M. Krasovitskii, B.M. Bolotin (Eds.), Organic
Luminescent Materials, VCH, Weinheim, 1988 (Chapter 7).
[12] F. Gao, H.-R. Li, Y.-Y. Yang, Dyes Pigm. 47 (2000) 231.
[13] B. Bangar Raju, B. Eliasson, J. Photochem. Photobiol. A: Chem. 116
(1998) 135.
[14] C.W. Tang, S.A. VanSlyke, C.H. Chen, J. Appl. Phys. 65 (1989) 3610.
[15] J. Kido, K. Hongawa, K. Okuyama, K. Nagai, Appl. Phys. Lett. 64 (1994)
815.
[16] C.C. Wu, J.C. Sturm, R.A. Register, J. Tian, E.P. Dana, M.E. Thompson,
IEEE Tans. Electron Devices 44 (1997) 1269.
5. Supplementary material
[17] T. Mori, K. Obata, K. Imaizumi, T. Mizutani, Appl. Phys. Lett. 69 (1996)
3309.
The crystallographic data (excluding structure factors) of
BMC has been deposited with the Cambridge Crystallographic
Center as supplementary publication no. CCDC-286841.
[18] Y. Hamada, H. Kanno, T. Sano, H. Fujii, Y. Nishio, H. Takahashi,
T. Usuki, K. Shibata, Appl. Phys. Lett. 72 (1998) 1939.
[19] H.P. Zheng, R.F. Zhang, F. Wu, W.J. Tian, J.C. Shen, Synth. Met. 100
(1999) 291–295.
Acknowledgements
[20] S.A. Swanson, G.M. Wallraff, J.P. Chen, W.J. Zhang, L.D. Bozano,
K.R. Carter, J.R. Salem, R. Villa, J.C. Scott, Chem. Mater. 15 (2003)
2305.
This work was supported by ‘Qing Lan’ talent engineering
funds (QL-06-01A) of the Lanzhou Jiaotong University.
[21] S.H. Ahn, M. Czae, E.R. Kim, H. Lee, S.H. Han, J. Noh, M. Hara,
Macromolecules 34 (2001) 2522.
[22] J.T. Gupton, F.A. Hicks, S.Q. Smith, A.D. Main, S.A. Petrich,
D.R. Wilkinson, J.A. Sikorski, A.R. Katritzky, Tetrahedron 49 (1993)
10205.
References
[23] F.M. Liu, Z.F. Zhang, Y.T. Liu, S.X. Kong, Y.Z. Chen, Chin. J. Org.
Chem. 20 (2000) 499.
[1] R. O’Kennedy, in: R.D. Thornes (Ed.), Coumarins. Biology, Applications
and Mode of Action, Wiley, Chichester, 1997.