Synthesis and photophysical processes of a novel 1,10-phenanthroline-containing p-conjugated chromophores and Zn(II) chelated complex

Article abstract of DOI:10.1016/j.saa.2006.06.009

A novel 1,10-phenanthroline-containing p-conjugated chromophore, 3,8-di-(1-naphthyl)-1,10-phenanthroline, was synthesized by Suzuki reaction and its chelated complex was prepared. The UV-visible spectroscopy and photoluminescent (PL) properties were investigated. The results show that when the solution of the complex in THF located in low concentration range (<10^-6 mol/L), the fluorescence emission exhibit only one emission band and the excimer is formed with gradual increase in concentration of the complex. The emission spectra of the complex show obvious solvent effect. In addition, the intermolecular action between the complex and fullerene (C₆₀) were investigated. The fluorescence intensity of the complex is decreased and the maximal emission obvious red-shifted with the increasing of the concentration of C₆₀, which suggests that the strong interactions between the complex and C₆₀ happen in the excited state.

Full text of DOI:10.1016/j.saa.2006.06.009

Spectrochimica Acta Part A 66 (2007) 1204–1207
Synthesis and photophysical processes of a novel
1,10-phenanthroline-containing p-conjugated
chromophores and Zn(II) chelated complex
Caihong Zhang, Liheng Feng, Zhaobin Chen∗
School of Chemistry and Chemical Engineering, Shanxi University, Taiyuan 030006, PR China
Received 16 January 2006; received in revised form 29 May 2006; accepted 19 June 2006
Abstract
A novel 1,10-phenanthroline-containing p-conjugated chromophore, 3,8-di-(1-naphthyl)-1,10-phenanthroline, was synthesized by Suzuki reac-
tion and its chelated complex was prepared. The UV–visible spectroscopy and photoluminescent (PL) properties were investigated. The results
show that when the solution of the complex in THF located in low concentration range (<10−6 mol/L), the fluorescence emission exhibit only one
emission band and the excimer is formed with gradual increase in concentration of the complex. The emission spectra of the complex show obvious
solvent effect. In addition, the intermolecular action between the complex and fullerene (C60) were investigated. The fluorescence intensity of the
complex is decreased and the maximal emission obvious red-shifted with the increasing of the concentration of C60, which suggests that the strong
interactions between the complex and C60 happen in the excited state.
© 2006 Elsevier B.V. All rights reserved.
Keywords: 1,10-Phenanthroline; Suzuki reaction; Photoluminescence; Fullerene
1. Introduction
region, bright light-emission and good electro- and photo-active
properties [10–14]. The disubstituted 1,10-phenanthroline-
containing p-conjugated chromophore with electron donors are
multifunctional ligands for construction of effective organic
light-emitting materials [15]. With the above considerations in
mind, a novel ligand based on 1,10-phenanthroline incorpo-
rating naphthalene groups was designed and synthesized by
Suzuki reaction of 3,8-dibromo-1,10-phenanthroline with 1-
naphthylbronic acid and a corresponding Zn(II) luminescent
complex has also been prepared. The photophysical processes
of the complex were investigated carefully. The formation of
excimer in different concentration, the photoluminescence (PL)
properties of the complex in different solvents and the molecular
interaction of the complex with fullerene (C60) was investigated.
We forecast it will be a quality luminescent material. Further
research toward the photochemical and photophysical properties
is currently in progress.
The search for organic metal compounds (OMC) with novel
luminescence and photoelectric properties is a thriving subject
undergoing rapid development [1–3]. The widespread interest
stems from their potential applications in diverse areas such as
light-emitting diodes (LEDs) [4,5], organic photovoltaic cells
[6], chemosensor [7] and molecular probes [8]. The first organic
LEDs were fabricated by Tang and Van Slyke by using OMC,
8-hydroxyquinoline aluminum (Alq3), as emitting material in
EL devices [9]. In order to modulate the emitted colors and
to increase luminescence efficiencies, the development of new
organic metal luminescence compounds have received con-
siderable attention. Along with Alq3, other metallic chelates
and transient metal complexes have been used as the emitting
materials in organic light-emitting diodes (OLEDs). 1,10-
Phenanthroline has a rigid framework and it possesses a superb
ability to coordinate a large number of metal ions, which show
potential for technological applications, due to their high charge
transfer mobility, strong absorption in the ultraviolet spectral
2. Experimental
2.1. Synthesis
∗
The targeted compound was synthesized according to
Scheme 1. The basic strategies employed for synthesizing
Corresponding author. Tel.: +86 351 7011492; fax: +86 351 7011688.
E-mail address: zchen@sxu.edu.cn (Z. Chen).
1386-1425/$ – see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2006.06.009

C. Zhang et al. / Spectrochimica Acta Part A 66 (2007) 1204–1207
1205
Scheme 1. The synthetic routes of the complex.
3,8-di-(1-naphthyl)-1,10-phenanthroline were based on Pd-cat-
alyzed Suzuki reactions between 3,8-dibromo-1,10-phenan-
throline and 1-naphthylbronic acid [16]. 3,8-Dibromo-1,10-
phenanthroline and 1-naphthaleneboronic acid were synthesized
according to the literature procedure [17,18]. The 1-bromo-
naphthalene was converted to corresponding boronic acids in
21–75% yields [19]. The Suzuki coupling reactions of aryl
bromide with boronic acids were carried out under an argon
atmosphere with Na2CO3 as a base in toluene–water (2:1) in
the presence of Pd(OAC)2 and P(Ph)3 (52–70% yields). The
Zn(II) chelating complexes was obtained in high yields from
the reaction between 3,8-di-(1-naphthyl)-1,10-phenanthroline
and Zn(II) chloride (89–93%). FAB/MS supports the conclu-
sions that the Zn(II) complexes is generated from the 2:1
complexation of 3,8-di-(1-naphthyl)-1,10-phenanthroline with
Zn(II).
Both excitation and emission bands were set at 5 nm. All the
experiments were carried out at 20 1 ◦C.
3. Results and discussion
3.1. Absorption and fluorescence excitation and emission
spectrum
The peak positions of the absorption spectra of the complex in
different solvents are similar, without an obvious change. The
UV–vis absorption spectra of the complex in tetrahydrofuran
(THF) were shown in Fig. 1 The UV–vis absorption spectra of
the complex show absorption peak (λab) around 240 and 275 nm,
which can be attributed to the naphthalene and phenanthroline
*
rings and the ␲–␲ transition of the conjugation backbone.
In addition to the intense absorptions, there was a shoulder
at 320 nm in UV–vis absorption spectra, which is assigned to
Zn(II) and ligand charge transition. The fluorescence excitation
and emission spectra of the complex in THF were shown in
Fig. 2. The photoluminescent (PL) excitation spectra are dis-
played maximum (λex,max) at 320 nm. The complex emits blue
and blue-green light with emission maximum (λf,max) at 360 nm
with using excitation wavelengths at 320 nm.
2.2. Materials and instruments
The reagents and chemicals for preparation of the complex
were used as received unless noted otherwise. Ethanol, ace-
tonitrile, acetone, THF, toluene, benzene were purchased from
Beijing Chemical Plant and treated according to standard meth-
ods used before, which were all applied to measurement of the
light-emitting properties.
The UV–vis absorption spectra and fluorescence spectra
were obtained on a Shimadzu UV-265 spectrophotometer and
Shimadzu RF-540 spectrofluorothotometer, respectively. Lumi-
nescencespectrometerwaswithaxenonlampasthelightsource.
3.2. Concentration effects on photoluminescence and
formation of excimer
The fluorescence spectra of the complex was measured in
THF solution and shown in Fig. 3. It can be seen when concentra-

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C. Zhang et al. / Spectrochimica Acta Part A 66 (2007) 1204–1207
Fig. 4. The emission spectra of the complex in different solvents. Solvents are
cyclohexane, toluene, ethylacetate, tetrahydrofuran, chloroform and ethanol.
Fig. 1. Absorption spectra of the complex in THF.
tion of the complex is in low concentration 1.35 × 10−6 mol/L,
the maximal fluorescence emission is at 360 nm which exhibits
only one emission band and its spectrum as ‘1’ shown. On
progressiveincreaseinconcentrationofthecomplex, thefluores-
cence of the complex is quenched efficiently. At the same time,
a new emission band appeared at the relatively longer wave-
length 470 nm. The emission intensity of the new band increase
with an increase in the concentration of the complex and the
spectra all pass an isostilbic point 415 nm. Evidently, the new
emission band can be attributed to the excimer formed between
the complex molecules [20].
3.3. Solvent effects on photoluminescence
The emission spectra of the complex in different solvents,
including cyclohexane, toluene, ethylacetate, tetrahydrofuran,
chloroform and ethanol were showed in Fig. 4. It can be seen
from Fig. 4 that with the increase of the solvents polarity in non-
protonic solvent, the emission spectra of the complex are red
shift from 335 to 365 nm. It is well known that the red shift of
emission spectra of chromophore with the increase of the sol-
vents polarity due to the dipole–dipole interaction of the excited
state.
Fig. 2. The fluorescence excitation and emission spectrum of the complex.
The large blue shift is observed when the surrounding
medium is a protic solvent such as ethanol. From Fig. 4, it can
be seen that there is no the corresponding red shift relationship
in emission spectra in ethanol, the maximal emission shifts to
345 nm and the emission band is broader than in non-protonic
solvents. This may be attributed to metal-to-ligand charge trans-
fer in excited states in protic solvent [21].
3.4. Interaction between the complex and fullerene (C60)
Many investigations show that C60 is a good electron
acceptor. It possesses a wide range of physical and chemical
properties. One of the most remarkable properties of C60 is to
induce efficiently a rapid charge separation and a further slow
charge recombination [22]. In the experiment, the interactions of
the complex with C60 were examined. The results were shown in
Fig. 3. Fluorescence spectra of the complex and its excimer. Concentration
of the complex (mol/L): (1) 1.35 × 10−6; (2) 2.70 × 10−6; (3) 4.05 × 10−6
;
(4) 5.40 × 10−6; (5) 8.10 × 10−6; (6) 1.21 × 10−5; (7) 2.42 × 10−5; (8)
4.84 × 10−5
.

C. Zhang et al. / Spectrochimica Acta Part A 66 (2007) 1204–1207
1207
of the complex to C60 competes with the radiative emission of
the complex [23].
4. Conclusion
A new organic metal compound, 3,8-di-(1-naphthyl)-
1,10-phenanthroline and its Zn(II) chelated complex were
successfully synthesized and the photoluminescent (PL) prop-
erties were investigated. The excimer is formed with gradual
increase in concentration of the complex. The emission spec-
tra of the complex show obvious solvent effect. In addition, the
strong interactions between the complex and C60 happen in the
excited state.
Acknowledgements
Fig. 5. Fluorescence spectra of the complex at different concentration of
C
60. Concentration of the complex, 1.35 × 10−6 mol/L. Concentration of C60
The present work was supported by the Science Foundation
of Taiyuan City of China; Laboratory of Organic Solid, Chi-
nese Academy of Sciences and The Returned Student Science
Foundation of Shanxi Province of China.
(mol/L): (1) 0.00; (2) 1.39 × 10−6; (3) 2.78 × 10−6; (4) 4.17 × 10−6; (5)
5.56 × 10−6; (6) 7.65 × 10−6; (7) 9.73 × 10−6; (8) 1.25 × 10−5
.
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