Structural Transformation of the 2‐(p‐Aminophenyl)‐1‐hydroxyinden‐3‐ylmethyl Chromophore as a Photoremovable Protecting Group

Photoremovable protecting groups (PPGs) have attracted much attention not only in the field of organic synthesis but also in biology and materials science because of the spatiotemporally controlled release of various functional molecules upon photolysis. In this study, a new PPG, the 2‐(p‐aminophenyl)‐1‐hydroxyinden‐3‐ylmethyl (pAPHi) chromophore, is designed and synthesized for the efficient and fast release of functional molecules with high conversion yields. The photolysis of caged benzoic acid with the pAPHi chromophore in dimethyl sulfoxide released benzoic acid in 96 % yield, with a decomposition quantum yield of 13 %. A high quantum yield of 51 % was observed with the clean formation of benzoic acid (94 % yield) in methanol. Transient absorption spectroscopic analyses clarified the generation of an intermediate carbocation as well as its reactivity. Controlled release: A new photoremovable protecting group 2‐(p‐aminophenyl)‐1‐hydroxyinden‐3‐ylmethyl (pAPHi) is developed in this study. The photolysis of a model caged benzoic acid with the pAPHi chromophore releases benzoic acid in high chemical yield, high conversion, and high quantum yield. The structural transformation during the photolysis plays a key role in this clean uncaging reaction with high conversion efficiency.