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

• Published in: Journal of the American Chemical Society 1989-11, Vol.111 (24), p.8858-8866
• Main Authors: Minto, Robert E, Das, Paritosh K
• Format: Article
• Language: English
• Subjects: 360100 - Metals & Alloys; 400500 - Photochemistry; CHEMICAL BONDS; CHEMICAL REACTIONS; CHEMISTRY; DATA; DATA ANALYSIS; DECOMPOSITION; Exact sciences and technology; EXPERIMENTAL DATA; General and physical chemistry; INFORMATION; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; KINETICS; MATERIALS SCIENCE; MEASURING INSTRUMENTS; MEASURING METHODS; NUMERICAL DATA; PHENOLATES; PHENOXY RADICALS; PHOTOCHEMICAL REACTIONS; PHOTOCHEMISTRY; PHOTOLYSIS; Physical chemistry of induced reactions (with radiations, particles and ultrasonics); RADICALS; REACTION KINETICS
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja00206a014

In the course of 248-nm laser flash photolysis, solutions of 9-phenylxanthen-9-ol (1) undergo homolytic and heterolytic photodehydroxylation, the relative efficiency of which depends strongly on the solvent nature. Polar/hydroxylic solvents, particularly aqueous mixtures, cause copious formation of 9-phenylxanthenium cation (2), the ground, and excited-state properties of which are conveniently studied by single- and double-laser flash photolysis. In 1:1 H{sub 2}O/MeCN, the quantum yield of carbenium ion generation is 0.4 {plus minus} 0.1; only 1 % of photoheterolysis occurs through an adiabatic route. Surprisingly, in polar but nonhydroxylic solvents (e.g., acetonitrile and 1,2-dichloroethane) also, the cation is photogenerated in small but sufficient yields to allow time-resolved spectroscopic detection and study in these relatively neutral and inert media. In relatively nonpolar solvents, e.g., n-heptane and benzene, the photolysis of 1 is dominated by homolytic cleavage to 9-phenxylxanthenyl radical (3). The short-lived triplets of 1 ({tau}{sub T} {