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.