Solvent Effects on the Photochromism of 2-Hydroxychalcones

Abstract

Photochemical reaction of some 2-hydroxychalcone derivatives into colored flavylium ions was studied in various solvents. 4'- Amino derivatives revealed high quantum yields for coloration (φ_F 0.2-0.3) in the presence of 5 mM trifluoroacetic acid in toluene or tetrahydrofuran, while acetic acid, water, and some alcohols as solvent appeared to depress the reaction. A simpler reaction scheme has been proposed involving photochemical trans- cis isomerization followed by acid- catalyzed cyclization into cyclic hemiacetals and subsequent dehydration to give flavylium ions.