Time-Dependent Photodimerization of α-trans-Cinnamic Acid Studied by Photocalorimetry and NMR Spectroscopy

The time course of photochemical solid-state reactions is routinely monitored by using spectroscopic methods such as NMR or IR spectroscopies, but is comparatively less investigated with thermal methods. In this work, a combination of thermal methods (thermogravimetric analysis and differential scanning calorimetry) was applied together with irradiation with UV light to quantify the conversion and monitor the progress of a well-known photochemical reaction, the [2 + 2] dimerization of trans-cinnamic acid, and the results are compared with the conversion determined by using ¹H NMR spectroscopy. The conversion was correlated with thermodynamic parameters for the reactant such as molar enthalpy, entropy, and melting temperature.