Electronic energy transfer from triplet states of organic compounds to coordination compounds. Part 1.—Effects of spin-statistical factors on the efficiency of quenching by β-diketonato complexes of chromium(III)

Abstract

Quenching studies of triplet states of organic donors by chromium(III) complexes in benzene solution were carried out by nanosecond pulsed laser photolysis. Quenching of a series of well-characterized triplets by chromium(III)β-diketonates in benzene solution proceeds via electronic energy transfer. The quenching efficiency is associated with the energetically available doublet and quartet states of the central atom and the diffusion-controlled rate is modified by spin-statistical factors. Theoretical treatment of the quenching rates indicates that the free energy of activation for production of the distorted quartet states is at least five times higher than that for production of the undistorted doublet states. The transmission coefficient for energy transfer depends on the substituents in the ligands and increases as the nephelauxetic effect is enhanced.