Steady-State and Time-Resolved Studies on Photoinduced Interaction of Phenothiazine and 10-Methylphenothiazine with Chloroalkanes

Phenothiazine and 10-methylphenothiazine have been found to form weak complexes with the chloroalkanes, such as CCl4 and CHCl3, both in the ground and excited singlet states as investigated by spectrophotometric and fluorimetric techniques. Steady-state and time-resolved fluorescence quenching experiments indicate that the strength of interaction of the excited singlet (S1) state of the phenothiazines with the chloroalkanes increases as the reduction potentials of the latter become less negative or the oxidation potentials of the phenothiazines become less positive. These results indicate that the electron-transfer or charge-transfer type of interaction is operative in these systems. In less polar solvents, such as cyclohexane and ethyl acetate, weak exciplex formation between the S1 state of the phenothiazines and the chloroalkanes has been observed, whereas in a more polar solvent, such as acetonitrile, direct electron transfer takes place from the S1 state of the phenothiazines to the chloroalkanes, leading to dissociation of the C−X bond of chloroalkanes. Picosecond flash photolysis studies carried out on these systems showed the presence of the cation radical of the phenothiazines and support the photoinduced charge separation and other processes proposed.