Microenvironmental effects on the photochemical and photophysical processes of long chain coumarin esters

The photochemical reactions and photophysics of long chain coumarin esters have been investigated. In dioxane-water (DX-H ₂O) solvent mixture, long chain 4-methyl-7-hydroxycoumarin hexadecanate and octadecanate form aggregates forced by the hydrophobic effect. The photochemical reactions of this two long chain coumarin esters gave exclusively anti-HT dimer in 75% and 90% yields respectively in dioxane-water(volume ratio 1 : 2) solvent mixture. The excimer formation and the acceleration of photochemical reaction were ascribed to the hydrophobic effect and the changes of microenvironment.