265 NM LASER FLASH PHOTOLYSIS OF SOME ORTHO‐SUBSTITUTED ANILIDES AND RELATED N‐FORMYLKYNURENINE DERIVATIVES

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Abstract
Abstract— The physical and chemical properties of the triplet state of eight ortho‐substituted anilides including N‐formylkynurenine (FK), the major trp UV‐photooxidation product and a remarkable photodynamic agent, have been investigated using both pulse radiolysis and 265 nm laser flash photolysis techniques. The molar extinction coefficient, the intersystem‐crossing quantum yield and the oscillator strength of the T1→Tn absorption band (Λmax˜ 450 nm) have been determined. It is shown that anilides having n,π* triplets readily react with most solvents whereas those having π,π* triplets slowly react with alcohols. In both cases, the semi‐reduced species are formed. In water, the formation of the semi‐reduced. species most probably involves the first excited singlet state. The triplet state properties of the FK derivatives (i.e. ortho‐substituted anilides having a side chain bearing charged groups such as carboxylic or amino groups) are strongly modified by the ionization state of the charged side chain. In the case of the FK derivatives possessing an uncharged amino group, quenching of the triplet state occurs via a fast reversible electron transfer reaction from the NH2 to the triplet anilide.