Design, synthesis and photophysical properties of a hyperbranched conjugated polymer
Introduction
Conjugated polymers [1] have emerged as viable electronic materials for numerous applications [2]. In particular, the current activities in the development of light-emitting diode (LED)-based conjugated polymers [3], [4], [5] have attracted much attention. Various new conjugated polymers have been designed and synthesized, for efficient light emission or charge transfer [6], [7], [8], [9], [10].
So far, the majority of work on polymers LEDs has been focused on linear one-dimensional polymer. Although a few of two-dimensional conjugated polymer, such as hyperbranched conjugated polymer have been reported to exhibit comparable charge transferring and processing properties to their linear counterparts, [11], [12], [13] two-dimensional conjugated polymeric light materials have been less discussed in the literature [14].
Dendrimers, including hyperbranched polymers, differ from conventional linear polymers in two critical ways. First, they are constructed from ABn required for hyperbranched structure the monomers rather than the standard AB monomers which produce linear polymers. Secondly, they are often synthesized in an interative fashion. The combination of these two features leads to a non-linear, stepwise synthetic growth wherein the number of monomer units incorporated in each of the successive interation roughly doubles (AB2) or triples (AB3) the existing branches. The novel structure of dendrimers is expected to produce unique properties [15], [16], [17].
Accordingly, conjugated dendrimers may be certain superior color tunabilty, charge transferring efficiency and processing properties than conventional linear emitting polymers. Therefore, we designed and synthesized various hyperbranched-conjugated polymers for potential materials applications.
In this report, we report on the synthesis and photophysical properties of a model compound, poly(3,5-bisvinylicbenzene) (HS1).
Section snippets
Experimental
The methods for preparing of the HS1 are outlined in Fig. 1. In route 1, tribromidemethylbenzene was condensated under the organic strong base. Route 2 is a Wittig reaction. Both are characterized by a low yield and a lower molecular weight. Especially for the route 2, the molecular weight is so small that oligomers were produced. So we only give results from route 1. The polymer structure shown is consistent with the element analysis and the spectroscopic date including 1H-NMR, 13C-NMR and
Results and discussion
It is very interesting to find that the polymer has a good solubility in chloroform, dichloromethane, THF, ethyl acetate etc, although the polymer contains no long alkyl chain. Good solubility has also been found for other hyperbranched conjugated polymers [17]. This unique properties may be attributed to their weak intermolecular interaction and low solvation energy.
The optical properties of this novel polymer are of primary interest to us. The photophysical data were listed in Table 1 and the
Acknowledgements
This project is supported by National Science Foundation of China (Nos 29992530 and 29873060) and A Key program of CAS (KJ97T-05-02).
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