13C-CPMAS and other solid-state NMR methods have been applied to monitor the solid-state
reactions of trans-cinnamic acid derivatives, which are the pioneer and model compounds in the field of
topochemistry previously studied by X-ray diffraction, AFM, and vibrational spectroscopy. Single-crystal
X-ray analyses of photoirradiated R-trans-cinnamic acid where the monomers are arranged in a head-totail
manner have revealed the formation of a centrosymmetric R-truxillic acid photodimer. For a