Does the photochemical conversion of colchicine into lumicolchicines involve triplet transients? A solvent dependence study

beta- and gamma -lumicolchicines are photoproducts formed by the cycloisome rization of the tropolone ring of colchicine (COL) alkaloids, The mechanism of the photoconversion, suggested to involve the tripler state, is examine d here by studying the effect of the solvent polarity on the lumicolchicine photoisomer ratio. Tripler COL, detected by laser hash photolysis, is quen ched by oxygen, but not by trans-stilbene or 1-methylnaphtalene. Neither th e quantum yield of conversion of COL nor the photoproduct ratio was altered by the presence of oxygen, Likewise, energy transfer to COL front triplet acetone produced by either isobutanal/horseradish peroxidase system or tetr amethyldioxetane thermolysis failed to provoke photoreaction of COL, Our da ta argue against the intermediacy of a COL tripler state in the photoisomer ization and stress on the role of specific solvent-solute interactions in d etermining the partitioning of excited singlet state into the beta- and gam ma -isomer formation.