Physical Properties of Excited States: A General Method for Measuring Triplet—Triplet Extinction Coefficients, Singlet—Triplet Intersystem Crossing Efficiencies, and Related Parameters

Abstract

The quantitative measurement of the various radiative and nonradiative deactivations of electronically excited states is the main purpose behind studies of photophysics and photochemistry. This objective is far from being achieved for any molecule. In this article we describe a general method for measuring two important photophysical parameters, molar extinction coefficients of triplet excited states, ϵT, and quantum yields of formation of lowest triplet, ΦT. Tabulations of all the triplet extinctions and singlet-triplet intersystem crossing efficiencies that have been thus measured to date are also given. A knowledge of these constants allows one to determine a variety of other parameters describing electronically excited molecules and their degradation, for instance: molar extinction coefficients of first excited singlet states, quantum yields of internal conversion, rate constants of intersystem crossing S1 → T1? internal conversion S1 → S0, or triplet-triplet annihilation.