Photochromic fulgides and spirooxazines: mechanism and substituent effect on photoreactions

摘要

Abstract Molecular design, synthesis and photochromic properties of spirooxazines and fulgides are described. In the case of fulgides, the change of the substituents may lead to different photochromic properties and different photoreactions of this kind of compounds. In photochromic process of pyrryl-substituted fulgides, the excited singlet state is the main species, but the excited triplet state is also involved. However, no excited triplet state has been observed in cydization of aryl-substituted .fulgides. In the case of spirooxazines, the substituents at 2'-position have great effect on the formation of photoproduct and on the mechanism of photoreaction. The increase of steric hindrance of the 2'-position substituent gives rise to the decrease of the quantum yield for the formation of photochromic merocyanine (PMC) and the increase of the relative quantum yield for the charge separated twist intermediate (CT).