PB~Tc$PPPYSKS OF DODCI

The solvent can exert significant in!-?uence on the pathways and rates of radiationless decay of the excited states of solute molecuIes. A major barrier to eIucidating such el3ects is the diversity of solute-solvent interactions which make it difficult to assign experimental observations to specific solvent properties. There exists, therefore, a great need for systematic experimental studies aimed at identifying the influence of a specific solvent property on a radiationless process. There are several classes of large organic molecules which are thought to undergo large conformational changes upon optical excitation, and these provide interesting systems for the study of solvent infiuences on the excited state decay, since one may hope to isolate the influence of solvent viscosity on the radiationless process. .&hong these, the cyanine dyes and other substituted polyeues have been studied intensively in recent years, both because of technologicai interest in them as laser and