Studies of relations between molecular structure and photochemical properties of spiro[indoline-2,3′-[1,4]oxazines]

Abstract

Photochromic reactions of 17 spiro[indolineoxazine] derivatives were investigated using nanosecond laser flash photolysis techniques. The substituent in the 2′-position of the oxazine moiety plays a decisive role in the formation of photoproducts. When the 2′-substituent is hydrogen, photoexcitation of spirooxazine only yielded long-lived photomerocyanine (PMC); however, with other substituents, a short-lived charge separation twisted species (CT) was formed as the predominant product. This observation is attributed to the steric hindrance effect of the substituent in the 2′-position of the oxazine moiety and methyl groups in the 1- and 3-positions of the indoline moiety. In addition, the substituent on nitrogen atom of the indoline moiety also affects the structural characteristics of the CT intermediate. The substituents in the 5-position of the indoline moiety and 9′-position of the naphthooxazine moiety affect the system mainly through electronic effects. A substituent effect on the λ_max of the absorption spectra of PMC is also observed. A potential energy surface is proposed to explain these substituent effects. The structural characteristics of PMC and CT intermediates are discussed.