Photohydration reaction of 1-(1-naphthyl)buta-1,3-diynes

Abstract

Irradiation of 1-(1-naphthyl)buta-1,3-diynes (1)–(3) in aqueous sulphuric acid yields both type-A (4), (6), (8) and type-B (5), (7), (9) hydration products. The type A/B product ratio was 0.8–1 : 1 in neutral conditions, while the ratio increases as the acidity of the medium increases. The fluorescence of compounds (1) and (3) decreased but that of compound (2) was invariant with increasing acidity. The medium-acidity effect on the quantum yields of hydration, and azulene-quenching studies suggest that the singlet excited state yields both type-A and type-B photoadducts, while the triplet excited state yields only type-B photoadducts when R is an alkyl group.