Synthesis and photoluminescent properties of 7-N,N-diphenylamino-3- benzoheterocyclic coumarin derivatives

Article abstract of DOI:10.1007/s11164-012-0755-y

Two new 7-N,N-diphenylamino-3-benzoheterocyclic coumarin derivatives containing electron-transporting benzotriazolyl or benzoxazolyl moiety, 3-(1-benzotriazole)-7-N,N-diphenylaminocoumarin (BTDC) and 3-(2-benzoxazole)-7- N,N-diphenylaminocoumarin (BODC),

Full text of DOI:10.1007/s11164-012-0755-y

Res Chem Intermed (2013) 39:2259–2266
DOI 10.1007/s11164-012-0755-y
Synthesis and photoluminescent properties
of 7-N,N-diphenylamino-3- benzoheterocyclic coumarin
derivatives
•
Tianzhi Yu Ming Zhao Aiwen Li Yuling Zhao
•
•
•
•
Hui Zhang Duowang Fan
Received: 9 June 2012 / Accepted: 30 July 2012 / Published online: 18 August 2012
Ó Springer Science+Business Media B.V. 2012
Abstract Two new 7-N,N-diphenylamino-3-benzoheterocyclic coumarin deriva-
tives containing electron-transporting benzotriazolyl or benzoxazolyl moiety,
3-(1-benzotriazole)-7-N,N-diphenylaminocoumarin (BTDC) and 3-(2-benzoxaz-
ole)-7-N,N-diphenylaminocoumarin (BODC), were synthesized and characterized
1
by element analysis, H NMR and FT-IR spectra. The UV–vis and fluorescence
spectra of these coumarin derivatives were investigated. The results show that
BTDC and BODC exhibit strong blue and red emissions, respectively, under
ultraviolet light excitation. The relationships between the chemical structure and the
fluorescence characteristics of the 7-N,N-diphenylamino-3-benzoheterocyclic cou-
marin derivatives are discussed. It was found that the coumarin derivative will
become a high-efficiency emitting material when an amino group is attached in
7-position of the coumarin ring, and 7- strong electron donors can improve the
ability of the intramolecular charge transfer of the coumarin molecules.
Keywords Synthesis Á 7-N,N-diphenylaminocoumarin derivative Á Benzotriazole Á
Benzoxazole Á Photoluminescence
Introduction
Coumarins are an important class of naturally occurring and synthetic compounds,
which have been extensively investigated for electronic and photonic applications
T. Yu (&) Á M. Zhao Á A. Li Á H. Zhang Á D. Fan
Key Laboratory of Opto-Electronic Technology and Intelligent Control (Ministry of Education),
Lanzhou Jiaotong University, Lanzhou 730070, China
e-mail: yutianzhi@hotmail.com
M. Zhao Á A. Li Á Y. Zhao
School of Chemical and Biological Engineering, Lanzhou Jiaotong University,
Lanzhou 730070, China
123

2260
T. Yu et al.
[1–5], such as fluorescence probe, charge-transfer agents, solar energy collectors, and
nonlinear optical properties, due to their characteristics of high emission yield, excellent
photo-stability, extended spectral range, good solubility, and their relative ease of
synthesis.Asemittingmaterials,theirfluorescentwavelengthandfluorescencequantum
yield strongly depend on the property and the position of the substituent and also on the
rigidity of the molecule.
Highly efficient organic dyes often have a push–pull structure, which is composed of
an electron-donating (D) unit, conjugated bridge (p) linker and electron-accepting
(A) unit. The introduction of both an electron-donating substituent and an electron-
accepting substituent to a core of the p system can also modulate the light-harvesting
properties of the organic dyes [6–8]. The molecules with D-p-A structures are
considered to be one of the most promising types of organic dyes, and have attracted
intensive attention because of their great potential applications as electroactive and
photoactive materials in molecular electronics, such as biochemical fluorescent
technology [9], nonlinear optics [10], organic light-emitting diodes (OLEDs) [11] and
photovoltaic cells [6–8, 12]. Among donor groups, triphenylamine and its derivatives
have been widely used as sensitizers and have promising properties in the development
of organic dyes, because the triphenylamine unit suppresses the aggregation of the dye
due to its nonplanar structure. Moreover, triphenylamine derivatives were often used as
light-emitting materials and hole transport materials due to their high hole mobility,
solubility and the formation of amorphous film [13]. In order to achieve charge
generating materials and charge transporting materials, many researchers have
introduced several kinds of substituents in the rings of triphenylamine to improve the
solubilityofthecompounds. Thiscannotonlyenhancethemolecularconjugatedsystem
but also effectively improve the hole mobility, the thermal stability and the resin
compatibility [14–16].
In this communication, two new coumarin derivatives, 3-(1-benzotriazole)-7-
N,N-diphenylaminocoumarin (BTDC) and 3-(2-benzoxazole)-7-N,N-diphenylami-
nocoumarin (BODC), were synthesized by introducing a diphenylamino group at
7-position of the coumarin ring as electron donor and a benzotriazole or a
benzoxazole as electron acceptor. The chemical structures of 3,7-disubstituted
coumarin derivatives in the present study are shown in Scheme 1. Their UV–vis
absorption and photoluminescent (PL) properties were investigated. The substituent
effects of the electron donors and the electron acceptors on the photoluminescent
properties of the compounds are discussed.
N
N
N
N
N
N
N
O
O
N
O
O
N
O
O
N
O
BODC
BTDC
DABTC-1
Scheme 1 Molecular structures of 3,7-disubstituted coumarin derivatives in the present study
123

Synthesis and photoluminescent properties
2261
Experimental
Materials and methods
3-methoxybenzenamine from Acros Organics, 1H-benzotriazole (BTA) and boron
tribromide from Aldrich were used without further purification. Bronze power,
18-crown-6, triethylamine (TEA), piperidine, chloroacetonitrile, iodobenzene,
o-aminophenol, diphenylether and phosphorus oxychloride were analytical grade
reagents from Tanjin Fuchen Chemical Reagent Factory. 7-N,N-diethylamino-3-
(benzotriazol-1-yl)coumarin (DABTC-1) was synthesized according to the methods
previously described [11].
IR spectra (400–4,000 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 measured on an Elemental Vario-EL automatic
elemental analysis instrument. Melting points were measured by using an X-4
microscopic melting point apparatus made by Beijing Taike Instrument, and the
thermometer was uncorrected. UV–vis absorption and fluorescence spectra were
recorded on a Shimadzu UV-2550 spectrometer and on a Perkin Elmer LS-55
spectrometer, respectively.
Synthesis and characterization of BTDC and BODC
The synthetic routes were shown in Scheme 2. The intermediate, 2-(1H-
benzotriazol-1-yl)acetonitrile, was obtained as previously described [11]. BTDC
I
OCH3
OH
OCH3
OH
CHO
H2N
BBr3
POCl3
DMF
N
N
N
Cu, K2CO3, 18-C-6
diphenylether, 24 h
CH2Cl2
O
OH
O
N
N
N
N
Piperdine
Anhydrous alcohol
N
N
+
N
CHO
N
CN
BTDC
COOH
O
O
N
NH2
+ NCCH2COOC2H5
HO
OH
CHO
O
N
+
N
n-butyl alcohol
BODC
Scheme 2 Synthetic routes of BTDC and BODC
123

2262
T. Yu et al.
and BODC were synthesized according to the methods previously described in [11]
and [17], respectively.
4-(diphenylamino)-2-hydroxybenzaldehyde
4-(diphenylamino)-2-hydroxybenzaldehyde were obtained by two steps according
to the method reported by Swanson et al. [16, 18].
Amounts of 7.468 g (0.06 mol) of 3-methoxybenzenamine, 28.494 g (0.14 mol)
of iodobenzene, 14.99 g (0.24 mol) of copper powder, 0.440 g (1.6 mmol) of
18-crown-6 and 64.16 g (0.46 mol) of anhydrous potassium carbonate in 250 mL of
diphenylether were placed into a 500-mL three -necked round-bottom flask. The
reaction mixture was refluxed with stirring for 72 h under nitrogen atmosphere. The
solids were removed by filtration and the solvents were removed by vacuum
distillation. The crude was purified by chromatography on silica gel using ethyl
acetate/petroleum ether (1:10, v/v) as the eluent, and 9.35 g of brown oil was
3-methoxytriphenylamine (yield 56 %). 1H NMR (500 MHz, CDCl3, d, ppm):
6.85–7.31 (m, 11H, Ar–H), 6.62–6.66 (m, 2H, Ar–H), 6.53 (d, J = 7.2 Hz, 1H,
Ar–H), 3.71 (s, 3H, OCH3).
Next, 5 g (0.018 mol) of 3-methoxytriphenylamine was dissolved in dry CH2Cl2
(50 mL). 9 g (0.036 mol) of BBr3 was added dropwise into the solution at -78 °C.
The reaction mixture was further stirred overnight. Saturated aqueous Na2CO3
(100 mL) was added to quench the reaction. The organic layer was separated. The
aqueous layer was extracted with CH2Cl2 (3 9 50 mL). The combined extracts
were washed with water and dried over anhydrous MgSO4. After filtering, the
filtrate was evaporated to dryness under reduced pressure. The crude product was
purified by chromatography on silica gel using ethyl acetate/petroleum ether (1:5,
v/v) as the eluent to give 3-Hydroxytriphenylamine as absinthe-green solid (3.5 g,
73.76 %). m.p.: 98–100 °C. 1H NMR (500 MHz, CDCl3, d, ppm): 7.27–7.23
(m, 4H, Ar–H), 7.11–7.09 (m, 5H, Ar–H), 7.07–7.01 (m, 2H, Ar–H), 6.66–6.63
(d, J = 8.2 Hz, 1H, Ar–H), 6.52 (t, J = 1.8 Hz, 1H, Ar–H), 6.47–6.45 (d, J =
8.1 Hz, 1H, Ar–H), 4.61 (s, 1H).
A solution of POCl3 (4.700 g, 30.7 mmol) in DMF (20 mL) was cooled at 0 °C.
3-Hydroxytriphenylamine (4.000 g, 15.33 mmol) was dissolved in another portion
of DMF (20 mL). The POCl3 solution was then added dropwise into 3-Hydroxy-
triphenylamine solution at 0 °C. The reaction mixture was reacted for 2 h and then
hydrolyzed with water (40 mL) for 6 h. The crude product was extracted with
CH2Cl2 (3 9 100 mL). The combined extracts were washed with water and dried
over anhydrous MgSO4. After filtering, the filtrate was evaporated to dryness under
reduced pressure, and purified by chromatography on silica gel using ethyl acetate/
petroleum ether (1:4, v/v) as the eluent to give 4-(diphenylamino)-2-hydroxybenz-
aldehyde (3.29 g, 74.3 %). m.p.: 128–130 °C. 1H NMR (500 MHz, CDCl3, d, ppm):
11.40 (s, 1H, –CHO), 9.58 (s, 1H, Ar–OH), 7.34 (m, 4H, Ar–H), 7.25 (d, J =
8.5 Hz, 1H, Ar–H), 7.25–7.18 (m, 6H, Ar–H), 6.45 (d, J = 8.5 Hz, 1H, Ar–H), 6.34
(d, J = 1.6 Hz, 1H, Ar–H).
123

Synthesis and photoluminescent properties
2263
3-(1-benzotriazole)-7-N,N-diphenylaminocoumarin (BTDC)
Under nitrogen atomosphere, 4-(diphenylamino)-2-hydroxybenzaldehyde (2.000 g,
6.91 mmol) and 2-(1H-benzotriazol-1-yl)acetonitrile (1.093 g, 6.91 mmol) was dis-
solved in 30 mL of anhydrous ethanol, and treated with piperidine (0.1 mL) at room
temperature. The reaction mixture was refluxed with stirring for 50 h, and then acidized
with hydrochloric acid (3.5 %) for 8 h. Ammonia was added to neutralize the acidity.
The solution was extracted with CH2Cl2 (3 9 25 mL) and then dried over anhydrous
MgSO4. After filtering, the filtrate was evaporated to dryness under reduced pressure,
and purified by chromatography on silica gel using ethyl acetate/petroleum ether (1:10,
v/v) as the eluent to give BTDC as solid (0.8 g, 26.9 %). m.p.: 210–212 °C. 1H NMR
(500 MHz, CDCl3, d, ppm): 6.38 (s, 1H, Ar–H), 6.5–6.7(m, 12H, Ar–H), 6.95 (s, 1H,
Ar–H), 7.1 (m, 2H, Ar–H), 7.25 (m, 2H, Ar–H). 13C NMR (100 MHz, CDCl3, d, ppm):
162.2, 150.8, 145.4, 141.1, 140.3, 132.1, 129.5, 127.3, 123.2, 122.6, 119.3, 118.2, 116.5,
113.0. IR(KBr pelletcm-1):3,031 (Ar–CH), 1,733 (C=O, lactone), 1,660 (C=C), 1,502,
1,457, 1,338, 1,253, 1,247, 1,164, 746. Anal. Calc. for C27H18N4O2 (%): C, 75.34; H,
4.21; N, 13.02. Found: C, 75. 41; H, 4.18; N, 12.95.
3-(2-benzoxazole)-7-N,N-diphenylaminocoumarin (BODC)
Under nitrogen atomosphere, a mixture of 4-(diphenylamino)-2-hydroxybenzaldehyde
(2.000 g, 6.91 mmol), o-aminophenol (0.754 g, 6.91 mmol), benzoic acid (0.400 g,
3.09 mmol) and ethyl cyanoacetate (0.785 g, 6.91 mmol) was dissolved in 50 mL of
1-butanol. The mixture solution was refluxed for 12 h at 80 °C, and then 100 mL NaOH
(2 %) was added to the mixture solution and stirred vigorously for 4 h at 80 °C. The
mixture solution was extracted with CH2Cl2 (3 9 100 mL). The combined organic
layer was washed with water and dried over anhydrous MgSO4. After filtering, the
filtrate was evaporated to dryness under reduced pressure, and purified by chromatog-
raphy on silica gel using ethyl acetate/petroleum ether (1:3, v/v) as the eluent to give
BODC (1.2 g, 40.3 %). m.p: 216–218 °C. 1H NMR (500 MHz, CDCl3, d, ppm): 6.8 (s,
1H, Ar–H), 7.21-7.50 (m, 12H, Ar–H), 7.60–7.80 (m, 4H, Ar–H), 8.14 (s, 1H, Ar–H).
13C NMR (100 MHz, CDCl3, d, ppm): 162.1, 152.3, 151.2, 150.0, 146.1, 141.2, 140.5,
129.5, 127.6, 125.0, 123.6, 122.6, 119.1, 116.7, 113.0. IR (KBr pellet, cm-1): 3,013
(Ar–CH), 1,737 (C=O, lactone), 1,653 (C=C), 1,626, 1,591, 1,328, 1,236, 1,238, 1,164,
1,155,1,096,746.Anal. Calc. forC28H18N2O3 (%):C,78.13;H, 4.21;N,6.51. Found:C,
78. 32; H, 4.16; N, 6.47.
Results and discussion
Absorption of BTDC and BODC
UV–vis absorption spectra of BTDC, BODC and DABTC-1 in dilute chloroform
solutions are given in Fig. 1. It is shown that the absorption spectrum of BTDC
exhibits absorptions at 228 and 284 nm. From the structures of BTDC and
DABTC-1, they all have an electron-withdrawing benzotriazolyl moiety at
123

2264
T. Yu et al.
DABTC-1
BODC
BTDC
1.0
0.8
0.6
0.4
0.2
0.0
200
300
400
500
600
Wavelength (nm)
Fig. 1 UV–vis absorption spectra of the compounds in dilute chloroform solutions (C = 3.0 9
10-5 mol/L)
3-position of coumarin ring, but BTDC has an electron-pushing diphenylamino
group at 7-position of the coumarin ring, while DABTC-1 has an electron-pushing
diethylamino group at 7-position. Due to the p–p conjugation effect, the electron
density of the nitrogen atom in the diphenylamino group is smaller than that in the
diethylamino group, and the electron-pushing power of the diphenylamine group is
weaker than that of the diethylamino group. Compared with BTDC, the absorption
bands of DABTC-1 were bathochromically shifted, in which the absorption bands
were at 253 and 414 nm. This suggests that the molecular conjugation degree of
DABTC-1 is larger than that of BTDC due to the strong electron-pushing power of
the diethylamino group.
As shown in Fig. 1, the absorption spectrum of BODC gives four absorption bands
which locate at 228, 289, 358 and 520 nm. Compared with BTDC, except that two
shorter absorption bands at 228 and 289 nm were present in the absorption spectrum of
BODC, an important feature of the absorption spectra of BODC is that two absorption
bands were observed at 358 and 520 nm, which were absent in the spectrum of
BTDC. From the structures of BTDC and BODC, it can be seen that they have the same
electron-pushing diphenylamine group at 7-position of the coumarin ring and
different electron-withdrawing groups at 3-position. BTDC possesses an electron-
withdrawing benzotriazolyl moiety at 3-position of the coumarin ring, while BODC has
an electron-withdrawing benzoxazolyl group. From the maximum absorption band at
284 nm for BTDC and 520 nm for BODC, it is deduced that the electron-withdrawing
power of benzotriazole is larger than that of benzoxazole, and the molecular
conjugation degree of BODC is larger than that of BTDC.
Photoluminescence of BTDC and BODC
Figure 2 shows the photoluminescent spectra of BTDC, BODC and DABTC-1 in
dilute chloroform solutions. It is clear that BTDC and DABTC-1 exhibit bright blue
123

Synthesis and photoluminescent properties
2265
emissions in dilute solutions, and the emission peaks of them locate at around 420
and 447 nm, respectively. The emission peak of DABTC-1 was red-shifted by about
27 nm compared with that of BTDC due to the larger conjugation of molecule in
DABTC-1.
As shown in Fig. 2, the compound BODC shows bright red emission with a peak
at 630 nm in dilute solution. Compared with BTDC, the emission maximum peak of
BODC was red-shifted by about 210 nm due to the larger conjugation of molecules
in BODC.
From the above photoluminescent characteristics of the three compounds, it is
further indicated that the electron-pushing power of the diphenylamine group is
weaker than that of the diethylamino group and the electron-withdrawing power of
benzotriazole is larger than that of benzoxazole.
In addition, the fluorescence quantum yields of BTDC and BODC in chloroform
solutions were calculated according to the method described by Kaholek et al. [19]
with anthracene as a standard (UF = 0.25 [19]). In the research, the UF,BTDC and
UF,BODC are 0.38 and 0.46, respectively. The fluorescence quantum yields of BTDC
and BODC in chloroform solutions are less than that of DABTC-1in chloroform
solution [11].
Conclusions
Two new 3,7-disubstituted coumarin derivatives, 3-(1-benzotriazole)-7-N,N-diphe-
nylaminocoumarin (BTDC) and 3-(2-benzoxazole)-7-N,N-diphenylaminocoumarin
(BODC), were successfully synthesized and characterized. All synthesized com-
pounds are fluorescent in solutions: BTDC exhibits bright blue emission with the
peak at 420 nm and BODC emits bright red light with the peak at 630 nm.
DABTC-1
BTDC
1.0
BODC
0.8
0.6
0.4
0.2
0.0
400
500
600
700
800
Wavelength (nm)
Fig. 2 Photoluminescent spectra of the compounds in dilute chloroform solutions (C = 3.0 9
10-5 mol/L, kex,BTDC = 284 nm, kex,DABTC = 414 nm and kex,BODC = 520 nm)
123

2266
T. Yu et al.
Acknowledgments This work was financially supported by the National Natural Science Foundation of
China (Grant 61166003) and the Natural Science Foundation of Gansu Province (1010RJZA060), and
also supported by the Program for Changjiang Scholars and Innovative Research Team in University
(IRT0629).
References
1. R.P. Haugland, M.T.Z. Spence, I.D. Johnson, Handbook of fluorescent probes and research chem-
icals, 6th edn. (Molecular Probes, Eugene, 1996)
2. H. Schwander, P. Hendrix, in Ullmann’s encyclopedia of industrial chemistry, vol. A11, 5th edn., ed.
by Y.S. Yamamoto (VCH, Weinheim, 1988), p. 280
3. O.S. Wolfbeis, E. Koller, P. Hochmuth, Bull. Chem. Soc. Jpn. 58, 731–734 (1985)
4. U. Tripathy, P.B. Bisht, J. Chem. Phys. 125, 144502–144509 (2006)
´
5. S.L. Gilat, A. Adronov, J.M.J. Frechet, Angew. Chem. Int. Ed. 38, 1422–1427 (1999)
6. H. Imahori, T. Umeyama, S. Ito, Acc. Chem. Res. 42, 1809–1818 (2009)
´
´
7. S. Franco, J. Garin, N.M. De Baroja, R. Perez-Tejada, J. Orduna, Y.H. Yu, M. Lira-Cantu, Org. Lett.
14, 752–755 (2012)
8. S.P. Singh, M.S. Roy, K.R. Justin Thomas, S. Balaiah, K. Bhanuprakash, G.D. Sharma, J. Phys.
Chem. C 116, 5941–5950 (2012)
9. G.S. Jiao, L.H. Thoresen, K. Burgess, J. Am. Chem. Soc. 125, 14668–14669 (2003)
10. K. Staub, G.A. Levina, S. Barlow, T.C. Kowalczyk, H.S. Lackritz, M. Barzoukas, A. Fortd, S.R.
Marder, J. Mater. Chem. 13, 825–833 (2003)
11. T.Z. Yu, P. Zhang, Y.L. Zhao, H. Zhang, J. Meng, D.W. Fan, L.L. Chen, Y.Q. Qiu, Org. Electron. 11,
41–49 (2010)
12. Z.J. Ning, Q. Zhang, W.J. Wu, H.C. Pei, B. Liu, H. Tian, J. Org. Chem. 73, 3791–3797 (2008)
13. Q. Xu, H.Z. Chen, M. Wang, J. Funct. Mater. 36, 1659–1663 (2005)
14. Y. Imai, M. Ishida, M.A. Kakimoto, High Perform. Polym. 15, 281–290 (2003)
15. C. Lambent, G. Noll, Synth. Met. 139, 57–62 (2003)
16. 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, 2305–2312 (2003)
17. Y.L. Zhao, T.Z. Yu, Y.Z. Wu, H. Zhang, D.W. Fan, Z.W. Gan, L.L. Yang, X.Q. Han, Y.M. Zhang, J.
Fluoresc. 22, 631–638 (2012)
18. C.T. Chen, C.L. Chiang, Y.C. Lin, L.H. Chan, C.H. Huang, Z.W. Tsai, C.T. Chen, Org. Lett. 5,
1261–1264 (2003)
ˇ
19. M. Kaholek, P. Hrdlovic, J. Photochem. Photobiol. A Chem. 127, 45–55 (1999)
123