Generation of triarylamine radical cations through reaction of triarylamines with Cu(II) in acetonitrile. A kinetic investigation of the electron-transfer reaction.
Triphenylamine derivatives react with Cu(2+) in acetonitrile to give radical cations, which subsequently undergo dimerization to provide tetraphenylbenzidine derivatives. Kinetic aspects of radical cation formation were examined by stopped-flow spectrophotometry. A broad range of triphenylamine derivatives were studied, and the driving force for the electron-transfer reaction ranged from +3.67 to -8.56 kcal M(-1) with rate constants varying from 1.09 x 10(2) to 2.15 x 10(5) M(-1) s(-1) for these systems. Reorganization energy for the electron-transfer reaction was estimated using experimentally determined activation parameters. Fitting of the rate data to the Marcus equation using different values of the electronic coupling matrix element H(el) provided a good fit with H(el) = 100 cm(-1) suggesting that electron transfer in the TPA/Cu(2+) system conforms to the Marcus-type electron transfer. Furthermore, the high reorganization obtained from these studies is consistent with significant bond cleavage in the transition state, and a mechanism consistent with the experimental data is proposed.
Sreenath
Kesavapillai
K
Photosciences and Photonics, Chemical Sciences and Technology Division, National Institute for Interdisciplinary Science and Technology, Council of Scientific and Industrial Research, Trivandrum 695 019, India.
Suneesh
Chettiyam Veettil
CV
Gopidas
Karical R
KR
Flowers
Robert A
RA