Size Matters: [2 + 2] Photoreactivity In Macro- and Microcrystalline Salts of 4‑Aminocinnamic Acid

• Published in: Crystal growth & design Vol. 18; no. 4; pp. 2510 - 2517
• Main Authors: d’Agostino, Simone, Boanini, Elisa, Braga, Dario, Grepioni, Fabrizia
• Format: Journal Article
• Language: English
• Published: American Chemical Society 04.04.2018
• ISSN: 1528-7483; 1528-7505
• DOI: 10.1021/acs.cgd.8b00109

The solid-state photoreactivity of 4-aminocinnamic acid (1) and molecular salts [1H]­ClO4 and [1H]­HSO4 has been investigated, and structural changes have been monitored by X-ray diffraction techniques and FTIR spectroscopy. While the parent compound 1 and its perchlorate salt [1H]­ClO4 are photoinert, irradiation of [1H]­HSO4 single crystals results in partial single-crystal to single-crystal (SCSC) [2 + 2] photodimerization, with formation of a {[1H]­HSO4}0.36·{[1 2H2]­[HSO4]2}0.64 solid solution. If crystalline powders of [1H]­HSO4 are irradiated, however, the formation of a monomer/dimer solid solution is followed by “extrusion” and recrystallization of both the phodimerization product [1 2H2]­HSO4 and unreacted [1H]­HSO4 as nonisomorphous crystal phases. The outcome of the UV irradiation of [1H]­HSO4, therefore, is influenced by the crystal size of the reacting monomer and changes dramatically if the irradiated sample is in the form of single macrocrystals or microcrystalline powder.