Laser flash photolysis study of photodehydroxylation phenomena of 9-phenylxanthen-9-ol and photobehavior of related intermediates. Enhanced electrophilicity of 9-phenylxanthenium cation singlet

摘要: In the course of 248-nm laser flash photolysis, solutions 9-phenylxanthen-9-ol (1) undergo homolytic and heterolytic photodehydroxylation, relative efficiency which depends strongly on solvent nature. Polar/hydroxylic solvents, particularly aqueous mixtures, cause copious formation 9-phenylxanthenium cation (2), ground, excited-state properties are conveniently studied by single- double-laser photolysis. 1:1 H{sub 2}O/MeCN, quantum yield carbenium ion generation is 0.4 {plus minus} 0.1; only 1 % photoheterolysis occurs through an adiabatic route. Surprisingly, in polar but nonhydroxylic solvents (e.g., acetonitrile 1,2-dichloroethane) also, photogenerated small sufficient yields to allow time-resolved spectroscopic detection study these relatively neutral inert media. nonpolar e.g., n-heptane benzene, photolysis dominated cleavage 9-phenxylxanthenyl radical (3). The short-lived triplets ({tau}{sub T} {<=} 0.3 {mu}s) also observed nonaqueous ({phi}{sub = 0.05 acetontrile). comparison weak, fast-decaying, doublet-doublet fluorescence 3 ({lambda}{sub max}{sup F} 590 nm, {tau}{sub 5 ns), singlet-singlet from 2 intense long-lived 550 25 nsmore » absence nucleophilic quenchers) almost nonquenchable oxygen (k{sub q} {times} 10{sup 8} M{sup {minus}1} s{sup {minus}1}). electrophilicity lowest excited singlet state 2, measured terms rate constants q}) bimolecular quenching anions lone-pair containing molecules, considerably more pronounced than that ground (that is, k{sub higher for several orders magnitude).« less