Electron transfer in the photochemical reactions of phenothiazine with halomethanes

Abstract

Photochemical transformations of phenothiazine (PTA) in solutions of halomethanes CHnX4–n (X = Cl, Br; n = 0, 1, 2) and in n-hexane—CHnX4–n mixtures under the irradiation with λ = 337 and 365 nm were studied. The rate constants of quenching of PTA fluorescence with halomethanes (kq) are 4·105—1.3·1010 L mol–1 s–1. The process occurs due to electron transfer with the C—X bond cleavage in the radical anion fragment of the primary radical ion pair. This results in the formation of the stable radical cation salt (PTA·+X–). The plot of kqvs. free energy of electron transfer corresponds to the Rehm—Weller empirical equation for a one-electron process and is satisfactorily described in terms of the theory of nonradiative electron transitions in the approximation of one quantum vibration.