POLARIZED SPECTRA OF A SERIES OF STILBAZOLIUM MEROCYANINES IN POLYVINYL-ALCOHOL FILMS

Polarized absorption, fluorescence and photoacoustic spectra of a series of stilbazolium merocyanines in stretched and unstretched polyvinylalcohol films were measured. Protonated dyes and free based are present in PVA films. The degree of orientation of the dye molecules depends on the substituents present in the molecule. The bulky t-butyl causes a decrease in the degree of orientation and prevents the formation of ground state complexes. In the excited state, the steric hindrance is less important and exciplexes are formed. Only ground state complexes and exciplexes fluoresce. The excitation of monomers is followed by effective thermal deactivation. Ground state complexes and exciplexes have different geometries. Axial deformation of PVA films favours excimer formation, but causes a partial dissociation of the ground state complexes.