ISOMERIZATION OF DIPHENYL POLYENES .5. THE ORIGIN OF FLUORESCENCE OF 1,6-DIPHENYL-1,3,5-HEXATRIENE IN POLY(VINYL ALCOHOL) FILMS

The effect of temperature on the absorption and fluorescence spectra of 1,6-diphenyl-1,3,5-hexatriene (DPH) was investigated in three different polymer films: poly(vinyl chloride) (PVCh), poly(vinyl formal) (PVF) and poly(vinyl alcohol) (PVA) in the temperature range 296-423 K. Anomalous behaviour of the fluorescence intensity was observed only for DPH in non-heated PVA film. The intensity distribution in the fluorescence band of DPH in both non-heated and heated PVCh and PVF films was found to be independent of the excitation light wavelength, lambda(exc). The behaviour of DPH is similar in the PVA film heated to 423 K. For these samples, single exponential fluorescence decay was observed. The behaviour of non-heated DPH samples in PVA is quite different, the intensity distribution and the fluorescence band position depending strongly on lambda(exc) and the fluorescence decay being double exponential. It can be inferred that the fluorescence of DPH in a non-heated PVA sample consists of two components, the first originating from the all-trans conformer and the second from the ground-state s-cis conformer.