Electron transfer in the photochemical reactions of phenothiazine with halomethanes

Photochemical transformations of phenothiazine (PTA) in solutions of halome thanes CHnX4-n (X = Cl, Br; n = 0, 1, 2) and in n-hexane-CHnX4-n mixtures u nder the irradiation with lambda = 337 and 365 nm were studied. The rate co nstants 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 t ransfer with the C-X bond cleavage in the radical anion fragment of the pri mary 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 trans fer corresponds to the Rehm-Weller empirical equation for a one-electron pr ocess and is satisfactorily described in terms of the theory of nonradiativ e electron transitions in the approximation of one quantum vibration.