Electron transfer singlet quenching and exciplexes in the photoreaction of substituted anthracenes with indole derivatives

A.I. NOVAIRA; C.D. BORSARELLI; J.J. COSA; C.M. PREVITALI

JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY

ELSEVIER SCIENCE SA

Lugar: Amsterdam; Año: 1998 vol. 115 p. 43 - 47

1010-6030

The effect of substituents on the singlet quenching and photoreaction of anthracene with indole derivatives was investigated in acetonitrile and n-heptane solutions at 298 K. The photoreaction proceeds by the quenching of the excited singlet of anthracene by the indoles. Bimolecular quenching rate constants in acetonitrile follow a Rehm-Weller type correlation. In the nonpolar solvent il-heptane, the rate constants are of the same order of magnitude than those in acetonitrile. However, methyl substitution at the N heteroatom of the indole greatly reduces the quenching in this solvent. In these cases, exciplex emission was observed. These differences in quenching capacity may be explained by a charge transfer interaction followed by proton transfer in the excited state, when it is available at the N-H bond. A nonreactive decay route and exciplex emission is operating in the case of the N-CH3 derivatives. Photobleaching quantum yields were also determined in heptane. The substitution by methyl or cyano groups at 9 and 10 positions on the anthracene ring decreases the reaction quantum efficiency.