Photochemistry of complex ions. IV. The role of quartet excited states in the photochemistry of chromium (III) complexes

Abstract

The photochemistry of Cr(III) complexes is reviewed with particular attention to those systems which exhibit a wavelength dependence of their photolytic behavior. For such cases, at least, it appears necessary to accept that, depending on the wavelength involved, different electronic states function as intermediates differently disposed to chemical reaction. It is proposed that the lifetime of quartet excited states may be longer than that expected from an absorption band area calculation, at least in the case of certain asymmetric complexes. Excited-state distortion is suggested to be potentially important in determining the relative importance of emission, photolytic, and radiationless deactivation processes and the rate of distortional relaxation, their relative temperature dependence. Some semiempirical rules are adduced which are useful in predicting which photolytic process will dominate, where more than one is possible.