The room temperature solid state emission and excitation spectra of polycrystalline samples of cinnamic acids that photodimerize in the solid state have been recorded. The emissions are clearly not molecular and are likely associated with excimers. The potassium and ammonium complex salts of cinnamic acid were found to be unreactive to ultraviolet light. Room temperature emission spectra of polycrystalline samples of these salts reveal both molecular and excimeric emissions.