A new photometric method for directly determining molar absorptivity–quantum yield products of excited states: application to triplet C60

A new method is presented for calibrating excited state absorption strengths in terms of absolute densities of excited sample molecules. Beam-imaging photometry measures the profiles of an excitation laser pulse and a collinear probing beam. From these data plus the ground state absorptivity and the induced absorbance at the probing wavelength, one calculates the product of excited state molar absorptivity and formation quantum yield. This photometric method involves no comparison to reference samples. Measurements on the triplet state absorptivity of C60 agree closely with recent reports based on comparative methods, suggesting the validity of both approaches.