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

Journal Article · Wed Nov 22 00:00:00 EST 1989 · Journal of the American Chemical Society; (USA)

DOI:https://doi.org/10.1021/ja00206a014· OSTI ID:7075085

Minto, R E; Das, P K ^[1]

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1. Univ. of Notre Dame, IN (USA)

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} {<=} 0.3 {mu}s) are also observed in nonaqueous solvents ({phi}{sub T} = 0.05 in acetontrile). In comparison to the weak, fast-decaying, doublet-doublet fluorescence of 3 ({lambda}{sub max}{sup F} = 590 nm, {tau}{sub F} {<=} 5 ns), the singlet-singlet fluorescence from 2 is intense and long-lived ({lambda}{sub max}{sup F} = 550 nm, {tau}{sub F} = 25 ns in acetonitrile in the absence of nucleophilic quenchers) and is almost nonquenchable by oxygen (k{sub q} {<=} 5 {times} 10{sup 8} M{sup {minus}1} s{sup {minus}1}). The electrophilicity of the lowest excited singlet state of 2, measured in terms of rate constants (k{sub q}) of bimolecular quenching by anions and lone-pair containing molecules, is considerably more pronounced than that of the ground state (that is, k{sub q} are higher for the excited state by several orders of magnitude).

• OSTI ID: 7075085
• Journal Information: Journal of the American Chemical Society; (USA), Vol. 111:24; ISSN 0002-7863
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
PHENOLATES
PHOTOLYSIS
CHEMICAL BONDS
DATA ANALYSIS
EXPERIMENTAL DATA
MEASURING INSTRUMENTS
MEASURING METHODS
PHENOXY RADICALS
PHOTOCHEMISTRY
REACTION KINETICS
CHEMICAL REACTIONS
CHEMISTRY
DATA
DECOMPOSITION
INFORMATION
KINETICS
NUMERICAL DATA
PHOTOCHEMICAL REACTIONS
RADICALS
360100* - Metals &amp; Alloys
400500 - Photochemistry