ISOMERIZATION OF DIPHENYL POLYENES .6. PROPERTIES OF 1,8-DIPHENYL-1,3,5,7-OCTATETRAENE FLUORESCENCE IN POLY(VINYL ALCOHOL) AND OTHER POLYMER-FILMS

Absorption, fluorescence and emission anisotropy spectra of 1,8-diphenyl-1,3,5,7-octatetraene (DPO) in non-heated and heated poly(vinyl alcohol) (PVA) films were measured at 296 and 87 K. Similar spectra to those of DPO in PVA heated to 423 K were observed for DPO in polymer films: poly(vinyl chloride) (PVCh), poly(vinyl formal) (PVF) and ethylacetate (EtA). Unusual photophysical properties of DPO fluorescence occur only in non-heated PVA. These are the increase in the absorbance and quantum yield at temperatures above 358 K and the change in the emission anisotropy, r, due to softening or stiffening of the PVA film. For DPO in PVCh and EtA, high values of r, close to 0.4, are observed (0.391 and 0.389, respectively), thus manifesting the stiffening of the microenvironment around the DPO molecule in these polymers. In the case of DPO in non-heated PVA film, strong temperature dependence of the intensity distribution in the fluorescence band and double exponential emission decay are observed. This proves that the fluorescence originates from two conformers: all-trans and s-cis.