Applications of photothermal beam deflection calorimetry to organic photochemistry

Photothermal beam deflection calorimetry (PDC) measures the time-dependent heat release that follows optical excitation of a sample. From these measurements, parameters such as reaction enthalpies and rates can be determined. In this work, it is shown that this method can be conveniently applied to the measurement of intersystem crossing quantum yields, triplet energies and photochemical reaction enthalpy changes in a variety of organic molecules. In general, PDC signals are linear with excitation energy and sample concentration. Also, the rates and enthalpies derived from these measurements show good agreement with literature values. In certain cases, a non-linear response of the signal with respect to the excitation energy is observed. This appears to be the result of multiphoton absorption by the sample. Comparison of PDC with complementary photothermal methods, such as photoacoustic calorimetry and thermal lens calorimetry, is discussed.