Synthesis and photophysical processes of 9-bromo-10-naphthalen-2-yl-anthracene

Article abstract of DOI:10.1016/j.saa.2006.04.015

A novel luminescent compound, 9-bromo-10-naphthalen-2-yl-anthracene (BNA) is synthesized by Suzuki Cross-coupling reaction of 9-bromo-anthracene and naphthalene-2-boronic acid. The structure is characterized by ¹H NMR, IR and UV-vis spectroscopy. The photophysical processes of 9-bromo-10-naphthalen-2-yl-anthracene have been carefully investigated by UV-vis absorption and fluorescence spectra. The results show that the compound emits blue and blue-violet light. The emission spectra exhibit obvious solvent effect. With the difference in polarity of solvents, The emission spectra is not only slightly blue shift with the increase of the solvent polarity but also change on the intensity of fluorescence at room temperature .The light emitting can be quenched by electron donor, N,N-dimethylaniline (DMA). On adding gradually DMA into the solution of BNA, the emission intensities of fluorescence are gradually decreased. The quenching effect follows the Stern-Volmer equation.

Full text of DOI:10.1016/j.saa.2006.04.015

Spectrochimica Acta Part A 66 (2007) 672–675
Synthesis and photophysical processes of
9-bromo-10-naphthalen-2-yl-anthracene
Zhiqiang Guo, Shuo Jin, Bo Liu∗
School of Chemistry and Chemical Engineering, Shanxi University, Taiyuan 030006, PR China
Received 22 December 2005; received in revised form 6 April 2006; accepted 14 April 2006
Abstract
A novel luminescent compound, 9-bromo-10-naphthalen-2-yl-anthracene (BNA) is synthesized by Suzuki Cross-coupling reaction of 9-bromo-
anthracene and naphthalene-2-boronic acid. The structure is characterized by 1H NMR, IR and UV–vis spectroscopy. The photophysical processes
of 9-bromo-10-naphthalen-2-yl-anthracene have been carefully investigated by UV–vis absorption and fluorescence spectra. The results show that
the compound emits blue and blue-violet light. The emission spectra exhibit obvious solvent effect. With the difference in polarity of solvents, The
emission spectra is not only slightly blue shift with the increase of the solvent polarity but also change on the intensity of fluorescence at room
temperature .The light emitting can be quenched by electron donor, N,N-dimethylaniline (DMA). On adding gradually DMA into the solution of
BNA, the emission intensities of fluorescence are gradually decreased. The quenching effect follows the Stern–Volmer equation.
© 2006 Elsevier B.V. All rights reserved.
Keywords: 9-Bromo-10-naphthalen-2-yl-anthracene; Interaction; N,N-dimethylaniline
1. Introduction
In this paper, we have synthesized a novel compound,
9-bromo-10-naphthalen-2-yl-anthracene from 9-bromo-anthra-
cene and naphthalene-2-boronic acid by Suzuki cross-coupling
reaction [4,5]. The photophysical properties are investigated,
the photoluminescence of BNA are examined in different
solvent. Moreover, the molecular interaction of BNA with
N,N-dimethylaniline (DMA) is investigated. It displays not
only a potential candidate as HIL materials for organic electro-
luminescent devices, but also an intermediate for luminescent
materials.
Organic electroluminescent (organic EL) devices [1] have
emerged as a propitious novel technology for the next gen-
eration of flat and thin panel displays, overcoming the draw-
backs of contemporary electronic displays, such as low power-
efficiency, narrow view angle, and a lack of brightness and
flexibility. Recent interest in developing practical EL devices for
long-term use with high power-efficiency is focused on those
with a multilayered structure which comprises hole-injecting,
hole-transporting, light-emitting, hole-blocking, and electron-
injecting layers between the indium–tin–oxide (ITO) electrode
and the cathode. A hole-injecting layer (HIL) has been used to
intermediate between the ITO electrode and a hole-transporting
layer (HTL) to demonstrate higher operational half-life com-
pared with that without HIL, several materials such as copper
phthalocyanine (CuPc) [2] and aryl-substituted tetraamine [3],
were reported for HIL materials. Among these, CuPc was intro-
duced by Kodak researchers and was a widely used material.
However, CuPc itself has strong absorption in a visible light
range so that the device containing it shows color fade, particu-
larly at a range of 550–700 nm, depending on the thickness.
2. Experimental
2.1. Materials and measurements
The reagents and chemicals for preparation of 9-bromo-
10-naphthalen-2-yl-anthracene were used as received unless
noted otherwise. Ethanol, acetonitrile, acetone, THF, dichloro-
methane, ethyl acetate, petroleum ether were purchased from
Beijing Chemical Plant and treated according to standard meth-
ods used before, which were all applied to measurement of the
lightemitting properties. The synthetic routes used are shown in
Scheme 1.
Melting points are determined on a Sanyo Gallenkamp
MPD350 melting point apparatus and uncorrected. The IR spec-
∗
Corresponding author.
1386-1425/$ – see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2006.04.015

Z. Guo et al. / Spectrochimica Acta Part A 66 (2007) 672–675
673
Scheme 1. The chemical structures of BNA in the study.
tra were determined on a PE-1700 IR spectrophotometer by dis-
persing samples in KBr disks. 1H NMR spectra are measured on
a Bruker ARX300 spectrometer with DCCl3 as solvent. UV–vis
and fluorescence spectra are obtained on a Shimadzu UV-265
spectrophotometer and Perkin-Elmer LS-50B spectrophotome-
ter, respectively. Both excitation and emission bands are set at
5 nm. All the experiments are carried out at 20 1 ◦C.
allowed to warm to room temperature, and was stirred for 8 h,
and adding HCl (1 N) at 0 ◦C. The mixture was extracted with
CH2Cl2, the organic layer was washed with hexane, Give a white
product. The yield is 70%, m.p. 267–268 ◦C.
2.2.3. Synthesis of 9-naphthalen-2-yl-anthracene
9-Bromo-anthracene (0.5 g) under a N2 atmosphere was
added to a stirred solution of the naphthalene-2-boronic acid
in DME/H2O and K2CO3 solution, the mixture was refluxed for
8 h, the reaction mixture was concentrated and extracted with
CH2Cl2. The crude product was purified by column chromatog-
2.2. Synthesis
2.2.1. Synthesis of 2-bromonaphalene
raphy (n-hexane), The yield is 92%. m.p. 213 ◦C. H NMR
1
Synthesis of 2-bromonaphthalene is prepared according to
Ref. [6]. The yield is 75%, m.p. 50–52 ◦C.
(DCCl3, ppm) δ: 8.56 (1H), 8.02–8.11 (4H), 7.91–7.96 (2H),
7.70–7.73 (2H), 7.57–7.62 (3H), 7.46–7.51 (2H), 7.32–7.37
(2H).
2.2.2. Synthesis of naphthalene-2-boronic acid
To a stirred solution of 2-bromonaphthalene (4.14 g,
0.02 mol) in dry THF (50 ml) was added dropwise a 2.5 M n-
pentane solution of t-butyllithium (9.6 ml, 0.024 mol) at −78 ◦C
under an argon atmosphere. After stirring for 1 h, the B(OMe)3
was added dropwise to the mixture at −78 ◦C, the mixture was
2.2.4. Synthesis of 9-bromo-10-naphthalen-2-yl-anthracene
Br2 (0.01 mol) was added to a stirred solution of 9-
naphthalen-2-yl-anthraceneinCCl4 (40 ml)at0 ◦C. Thesolution
was stirred at room temperature overnight. The reaction mixture

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was washed with 20% aqueous potassium hydroxide, saturated
aqueous sodium thiosulfate, and water, and the organic layer
was dried over anhydrous sodium sulfate and concentrates under
reduced pressure to leave a reside, which was reprecipitated with
hexane to give 9-bromo-10-naphthalen-2-yl-anthracene as a yel-
low solid. The yield is 65%, m.p. 171–173 ◦C. 1H NMR (DCCl3,
ppm) δ: 8.64–8.67 (2H), 8.02–8.08 (2H), 7.92 (2H), 7.52–7.69
(7H), 7.34 (2H). IR (KBr, cm−1): 1628, 1597, 1327, 1258,
1140, 1030, 927, 895, 856, 822, 758, 745, 669, 642, 621, 606,
and 478.
3. Results and discussion
3.1. Synthesis and characterization
Although this is a well-estabilished method for C–C bond
formation, but the contents of catalyst and reaction solvent have
a significant influence on the Suzuki cross-coupling reaction. It
has been found by experiment that the appropriate ratio of Pd
(OAc)2 to PPh3 is 1:4 (mol), which can successfully form the
reactive catalyst. And the ratio of DME to H2O is 9:1 (ml).
Fig. 2. Emission spectra of BNA solution in different solvents.
sion spectra of BNA are investigated in different solvents and
all results are showed in Figs. 2 and 3. It can be seen from
Figs. 2 and 3 that the emission spectra of BNA is not only slightly
blue shift with the increase of the solvent polarity but also change
on the intensity of fluorescence, and the emission intensity of
fluorescence are initially increased and then decreased with
the increase of the solvent polarity. Based on the experimental
facts and references, the following explanations can be given:
It is well known that BNA has greater ␲-system conjugation
and rigid configuration, so charge transfer between the conju-
gates system may be dramatically modified. Further research
toward a better understanding of this effect is currently in
progress.
3.2. UV–vis absorption and fluorescence emission spectrum
The UV–vis absorption and fluorescence emission spectra
of BNA in ethyl acetate are shown in Fig. 1. It can be seen from
Fig. 1 that the BNA has two maximum absorption, 265 and
376 nm, respectively. But the emission peak is only at 418 nm.
These phenomena can be attributed to its nuclear geometry
arrangement is different between in excitated state and in
ground state. Because the life of S1 electron state is longer
than the higher electron state, there is a possible remove before
emission.
3.4. Interactions of BNA with N,N-dimethylaniline
3.3. Solvent effects on photoluminescence
In order to go further into the fluorescence property of
BNA, the quenching process of BNA with N,N-dimethylaniline
(DMA) is also examined and shown in Fig. 4. DMA is a typical
electron donor [7,8]. The studies of interactions between BNA
The BNA has good solubility in common organic solvents,
such as dichloromethane, THF, ethyl acetate, etc. the emis-
Fig. 1. Absorption and emission spectra of BNA in ethyl acetate. Concentration
of BNA, 1.36 × 10−5 M.
Fig. 3. Emission spectra of BNA solution in different solvents.

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675
and DMA are helpful to understanding the photo-electronic
properties of BNA. When DMA is added to a solution of BNA
in ethyl acetate, the fluorescence of BNA is efficiently quenched
and the quenching process follows the Stern–Volmer equation,
FM0 /FM = 1 + Ksv[Q]. And shown in Fig. 5. The apparent
quenching coefficient, Ksv, is 1.94 × 104 M−1and no exciplex
emission spectra are observed.
4. Conclusions
In summary, 9-bromo-10-naphthalen-2-yl-anthracene was
synthesized from 9-bromo-anthracene by a straightforward way
of Pd-catalyzed Suzuki coupling with naphthalene-2-boronic
acid and subsequent halogenating reaction. The resulting com-
pounds have excellent solubility in common organic solvents.
The emission peak of BNA in ethyl acetate is at 418 nm. It
displays high photoluminescence quantum yields and is poten-
tial candidate as HIL materials for organic electroluminescent
devices.
Fig. 4. Fluorescence spectra of BNA at different concentration of DMA. Con-
centration of BNA, 1.36 × 10−5 M. Concentration of DMA (mol/L, M): (1)
0.00; (2) 7.89 × 10−6; (3) 2.10 × 10−5; (4) 3.42 × 10−5; (5) 4.73 × 10−5; (6)
6.05 × 10−5; (7) 8.68 × 10−5
.
Acknowledgement
Financial support from the National Natural Science Foun-
dation of China (No. 20372044) is gratefully acknowledged.
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Fig. 5. Dependence of FM0 /FM on concentration of DMA. Concentration of
BNA, 1.36 × 10−5 M.