Spectroscopic Studies of Photochemical Reactions in Organic Solids. Photodimerization of p-Formylcinnamic Acid

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Abstract
Raman phonon spectroscopy and electronic absorption and emission spectroscopy have been used to study the mechanism of reaction and the role of electron–phonon coupling in determining the photoreactivity of p-formylcinnamic acid (p-FCA) in the crystalline state. Raman and infrared spectroscopy in the internal vibration region have been used to characterize the reactant p-FCA and the dimeric product t-3,t-4-bis(p-formylphenyl)-ν-1,c-2-cyclobutanedicarboxylic acid. Phonon spectroscopy reveals that the reaction proceeds principally by a heterogeneous mechanism though a homogeneous mechanism in the initial stage of short time domain can not be ruled out. The electronic spectroscopy suggests a strong electron–phonon coupling in the monomer crystal.