Design, synthesis and photophysical properties of a hyperbranched conjugated polymer

The conjugated dendrimer, poly(3,5-bisvinylic)benzene HS1, was synthesized by two routes. Elementary analysis, FTIR, NMR and GPC spectra were used to characterize the dendrimer. HS1 has good solubility in common organic solvents although it does not contain long alkyl side chain. The photophysical properties in solution and net solid film are inspected. Absorption maxima were determined at 290 and 310 nm with a molar absorption coefficient in the order of 10(4), and the emission maxima were at 359 and 369 nm. The excitation spectrum is similar to that of the absorption. A minor image relationship existed between the absorption and emission spectra characteristic of the rigid structure of the polymer. The Stokes shift (70 nm) is large, which means the large difference in the energy level between the ground and singlet excited state. The fluorescence quantum yield is about 36%. The net film of HS1 has a broad emission at 446 nm. The marked difference between the solution and net solid film in photophysical properties suggested the large change in intermolecular interaction from solution to the solid film state. Molecular mechanical calculations are used to aid the design and simulation of the structure of HS1. In generation 1-2, the optimized geometry shows a relatively good planarity. While the torsion appeared at the interference of the branches in generation 3 and the optimized geometry feels a zeolite structure. The calculation result is used to explain the experimental observation. The good photophysical properties and processing ability could make HS1 an ideal candidate in electroluminecence device as a blue emitter. (C) 2000 Elsevier Science S.A. All rights reserved.