Triplet reactivity of psoralens containing a benzo-fused furan ring: A laser flash photolysis study

Abstract

Abstract Laser flash photolysis (LFP) studies have been performed in order to investigate the triplet reactivity toward hydrogen and electron donors of the benzo-fused furan psoralens 3-ethoxycarbonyl-2 H -benzofuro[2,3-e]-1-benzopyran-2-one ( 1 ) and 3-ethoxycarbonyl-2 H -benzofuro[3,2-d]-1-benzopyran-2-one ( 2 ). Photolysis of the psoralens 1 and 2 results in the formation of the corresponding triplet excited state which is efficiently quenched by DABCO, triethylamine and phenols containing polar substituents. The reaction of the triplet state of 1 and 2 with electron donors (DABCO and triethylamine) leads to the formation of the corresponding anion radical whereas with phenols the corresponding aryloxyl radical was easily detected. Quenching rate constants for psoralen 2 are at least one order of magnitude greater than for 1 . The Hammett plot for the reaction of 1 and 2 with phenols yielded a reaction constant ρ of −1.88 ± 0.29 and −1.60 ± 0.21, respectively, which reflects the high electrophilicity of the carbonyl group of both psoralens.