Abstract
Noncomparative techniques for the measurement of the molar absorptivity of triplet-triplet absorption transitions, εT*, are reviewed. The methods covered include singlet depletion, total depletion, intensity variation (and its pulsed analog), partial saturation, and the so-called kinetic method. A critical analysis of the conceptual foundations of these varied approaches is performed. The fundamental equations of each technique are derived from a general three-state kinetic model of excitation and decay. From this unified approach it becomes very clear where assumptions are made in the traditional derivations of the methods. Additionally, one comparative method, that termed relative actinometry, is discussed, since it may be treated in a unimolecular fashion consistent with the above approach. The only major εT* method excluded from this review is that involving intermolecular energy transfer, a technique which has been thoroughly documented elsewhere.
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