SPECTROSCOPIC PROPERTIES AND PHOTODIMERIZATION OF WATER-SOLUBLE POLY(VINYL ALCOHOL) MODIFIED WITH PENDANT (E)-2-[PARA-FORMYLSTYRYL]-3,4-DIMETHYL-THIAZOLIUM METHYL SULFATE GROUPS - POLYMER AND MODEL CHROMOPHORE STUDIES

Preliminary results are presented on the spectroscopic properties and photocross-linking behaviour of a novel water-soluble poly(vinyl alcohol) modified with pendant styrylthiazolium groups and are compared with those of the model chromophore, (E)-2-[p-formylstyryl]-3,4-dimethyl-thiazolium methane sulphate in aqueous media. Second-order derivative UV-visible absorption spectra of both the modified photopolymer and the chromophore at high concentrations (greater than 5 x 10(-5) M) shows the presence of long-wavelength aggregates or dimers in the ground state. Fluorescence analysis of both the photopolymer and the chromophore is also consistent with the presence of long-wavelength-emitting dimers at high concentrations. On dilution the dimer emission decreases in intensity but remains evident together with that of stronger excimer and monomer emissions. Microsecond flash photolysis gives strong transient absorptions in the regions 300-400 and 400-500 nm. The former have maxima at 315 and 360 nm with the maxima of the latter at 405 and 460 nm and are associated with trans-cis isomerization or possible cation species involved in the [2 + 2] photocyclization reaction. Fourier transform IR analysis of the irradiated chromophore provided substantial evidence for the loss of the trans vinyl group and the formation of a substituted cyclobutane product due to a [2 + 2] photocycloaddition reaction. In aqueous solution, only trans-cis isomerism could be observed.