PHOTOCHEMICAL CONVERSION OF POLYPHENYLENEVINYLENE

The light-assisted conversion of the soluble polyelectrolyte precursor polymer containing. a tetrahydrothiophenium group to poly(p-phenylenevinylene) (PPV) is studied. Optical absorption measurements and spectrally resolved photoluminescence show that irradiation under vacuum at 293 K with ultraviolet light (hnu less-than-or-equal-to 6.2 eV) leads to partially converted PPV. Nevertheless under these conditions extension of the pi-conjugated system is hindered by a so far unidentified photochemical reaction. In contrast we found that fully converted PPV is obtained if the cast film is heated at 120-degrees-C in the dark and subsequently UV-irradiated at the same temperature. The onset of optical absorption of the obtained material is E0 almost-equal-to 2.44 eV and the energy of the 0-0 radiative transition, measured at 77 K, is E0-0 almost-equal-to 2.35 eV as compared with E0 = 2.34-2.44 eV and E0-0 almost-equal-to 2.33 eV for the thermally converted PPV.