OPTICAL-SPECTRA AND EXCITATIONS IN PHENYLENE VINYLENE OLIGOMERS

Experimental results of optical absorption spectra, photoluminescence spectra due to singlet exciton emission and photoinduced absorption sp ectra due to triplet-triplet transitions of triplet excitons for sever al oligomers of poly(p-phenylene vinylene) are reported. From the red- shift of the peaks with increasing chain length, the effective conjuga tion length for long-chain precursor-route samples of the polymer are estimated to be about 10 to 17 repeat units. Theoretical studies, usin g the valence-effective Hamilotonian (VEH) technique, of the effects o f ring torsions upon the electronic properties are also reported. Comp arison between absorption and luminescence spectra in solution and in the solid state shows a blue-shift for the solution spectra; this is m odelled in terms of a greater degree of ring torsion for these oligome rs in solution.