Dalton
Transactions
Cite this: Dalton Trans., 2011, 40, 8510
COMMUNICATION
Photo- and electroluminescence in thin films of covalently bonded
azomethin–zinc/SiO2 hybrid materials†
Chenyang Wei, Peng Jiang, Weimin Huang, Qianjun He, Xiangzhi Cui and Jianlin Shi*
Received 15th April 2011, Accepted 8th June 2011
DOI: 10.1039/c1dt10669d
We report the design and chemical synthesis of covalently
bonded azomethin–zinc/SiO2 hybrid transparent thin films
with photoluminescent and electroluminescent emissions in
condensed solid state by a sol-gel approach.
organic–inorganic hybrid materials that combine the advantages
of both organic molecules and an inorganic matrix have received
great interest nowadays. The sol–gel method has been proven to
be a suitable approach for the preparation of hybrid materials. Its
low-temperature chemical processing and mild conditions allow
many organic moieties, which are susceptible to high-temperature
degradation, to be incorporated into an inorganic network. It also
has the advantage of easy preparation of transparent films by
the solution-process, such as spin-coating or ink-printing, which
means the products can be fabricated with large areas and desired
patterns, rather than the processing difficulties encountered in
vacuum-deposition.
Because of the inherent properties of the silica matrix, a variety
of hybrid thin films with organic molecules chemically bonded
to the silica-based backbone have been reported in the field of
optical application.12 We reported a covalently bonded AlQ3/SiO2
hybrid material SiAlQ with strong blue light emission by a sol–gel
approach,13,14 which makes AlQ3 solution-processable and chemi-
cally stable. However, the photoluminescence quenching occurred
in the high concentration region of alkoxysilicon-modified AlQ3.
To avoid this, a high content of SiO2 in the hybrid material has
to be adopted, which, unfortunately, leads to very poor electrical
conductivity. Comparatively, the electron-transporting mobility
of zinc complexes has been reported to be higher than that of
AlQ3,15 and together with their interesting fluorescent properties
reported,16 a solution-processable hybrid with zinc complexes
as the light emission medium may be a potential candidate for
OLEDs.
Since azomethin–zinc complexes were reported for the first
time as potential OLED materials by Hamada et al. in 1993,11
much work has been reported around it, almost all of which was
about small complex molecules.15,17,18 In this report, a covalently
bonded azomethin–zinc/SiO2 (SiAM-Zn) hybrid material with
photo- and electroluminescence in the condensed solid state was
designed and synthesized by a sol–gel approach. Compared to
small azomethin–zinc complexes, the sol–gel derived covalently
bonded hybrid complex material has the advantages of high
solution-processability and thermal stability.
To make such a hybrid material mentioned above, the func-
tionalized sol–gel precursor (SiAM) was prepared by reacting the
amidine groups of 3-aminopropyltriethoxysilane (APTES) with
the aldehyde groups of salicylaldehyde at a molar ratio of 1:1
in ethanol at 78.4 ◦C by refluxing for 48 h as shown in step 1
in Scheme 1. The GC-MS spectra of the reaction solution are
Since the first organic light-emitting diode (OLED) was reported
by Tang and Vanslyke in 1987,1 OLEDs based on organic materials
have attracted extensive interest due to their high luminescent
efficiency, low power consumption, large viewing angle and
wide range of emissive colors. The operation of OLEDs is
based on the combination of electrons and holes injected from
the electrodes in the organic light emitting layer. A variety of
small organic molecules,2 dendrimers,3 oligomers,4 conjugated
polymers,5 dye doped polymers,6 metal complex molecules and
metal complex polymers7 for OLEDs have been synthesized and
investigated. To achieve full color displays, three primary colors,
red, green and blue are required. Especially, among various
emitting materials, performance of the reported blue electrolu-
minescent materials is usually still inferior to those of green or red
materials. Meanwhile, the blue luminescent materials are the most
important materials for the development of full-color OLEDs
because a blue luminescence can be converted to other color
luminescence through the “color changing medium” technology.8
So far, many blue electroluminescent materials have been re-
ported, such as oxadiazoles,9 distyrylarylenes,10 metal complexes,11
spirobifluorenes,2 oligoquinolines,4 and oligofluorenes,5 etc.
One of the biggest obstacles for the industrialization of OLED
is its high cost and size limitation resulting from its vacuum sput-
tering processes in depositing light emitting and/or hole/electron
injection film layers for OLED device fabrication. Therefore, great
efforts have been made to make the film layer solution-processable.
The grafting of light-emitting small molecules onto selected
polymers has been one of the most common choices. Alternatively,
State Key Lab of High Performance Ceramics and Superfine Microstructure,
Shanghai Institute of Ceramics, Chinese Academy of Science, Shang-
hai, 200050, People’s Republic of China. E-mail: jlshi@sunm.shcnc.ac.cn;
Fax: +86 21 5241 3122
† Electronic supplementary information (ESI) available: GC-MS spectra
of SiAM, the photo image of the solution and the spin-coated film of
SiAM-Zn, X-ray diffraction pattern of the hybrid film of SiAM-Zn,
schematic drawings of OLEDs, the OLED device with SiAM-Zn as LEL
in electroluminescent emission measurement, sectional SEM image of
the OLED device, electroluminous intensity vs voltage and current with
SiAM-Zn as LEL, and voltage vs current with SiAM as LEL. See DOI:
10.1039/c1dt10669d
8510 | Dalton Trans., 2011, 40, 8510–8512
This journal is
The Royal Society of Chemistry 2011
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