Steady state and laser photolysis studies of keto-enol tautomerizations in 2-alkyl-1,3-diketones having five-membered rings in acetonitrile: Temporal UV-A sunscreen

Abstract

Abstract Keto-enol tautomerization in 2-alkyl-1,3-diketons having five-membered rings was studied using steady state and laser flash photolysis techniques in solution. The alkyl keto-diketones undergo photoinduced tautomerization mainly in the triplet state to the enol in acetonitrile. The alkyl enol-diketones, thus formed, undergo thermal tautomerization to the original keto forms in a few days. The alkyl enol-diketones show fast internal conversion from the excited singlet state to the ground state without yielding the corresponding isomeric forms (rotamer). Based on the computation for state energies of the keto, enol and isomer forms, a schematic energy diagram for the tautomerization was drawn.