Kinetics and mechanism of intramolecular electron transfer in solution

Abstract

The picosecond pulse generated S_1,np state of 6-N-4-methylphenylamino-2-naphthalenesulphonic acid NN-dimethylamide (TNSDMA) decays by intramolecular electron transfer (i.e.t) faster than the appearance of the product, an equilibrium mixture of the charge-transfer, S_1,ct, and S_1,np states (temperature-independent ratio of 4–5), which decays at ca. 0.1 of the rate for the S_1,np state. In propan-1-ol, rates of “fast” i.e.t. processes vary with solvent cluster motion (1/τ₁, lowest dielectric relaxation rate) over a wide range of temperatures with log k linear in ⅔ log (1/η). Up to ca. –15 °C, “slow” i.e.t. processes probably vary in the same way, but at higher temperatures they are controlled by local group motion (1/τ₂, second lowest dielectric relaxation rate). A molecular model for the S_1,ct-state–methanol complex is presented.