Homogeneous acid catalysis of the trans—cis photoisomerization reaction of trans-3-(2-hydroxy- benzylidene)-4,5-dihydrofuran-2(3H)-one

The geometrical photoisomerization reaction of the title molecule ( trans -I) has been studied in methanol/water 90/10 wt.% mixtures containing sulphuric or hydrochloric acid. Quantum yields of the process, measured under acidic conditions in the range 0.095 N + ] trans -I as a function of pH, experimental quantum yields have been interpreted in the light of prototropic equilibria in the excited state. Mechanistic models are proposed which are able to fit results obtained in the investigated experimental conditions.