Electron transfer in the photochemical reactions of phenothiazine with halomethanes

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 lambda = 337 and 365 nm were studied. The rate constants of quenching of PTA fluorescence with halomethanes (k(q)) are 4 (.) 10(5)-1.3 (.) 10(10) 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 kq vs. 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.