Photocontrolled proton transfer in solution and polymers using a novel photoacid with strong C–H acidity

Abstract

Over the past few years, metastable-state photoacids (mPAHs) have been used to control various chemical, material and biological processes using visible light. In this work, a novel mPAH with strong C–H acidity was studied. The pK_a of its photoacidic state was experimentally determined and compared to a commonly used mPAH. The photoacid showed low dark acidity and a large pK_a change when irradiated by visible-light. The pK_a for the photoinduced C–H acidity is 4.8 units lower than that for the O–H acidity in the dark. These features together with its easy preparation make it promising for the development of photoresponsive materials based on proton transfer. Proton transfer between the photoacid and proton acceptors with different pK_as in solutions and polymer films was studied. The photoacid showed superior properties in polymer films compared to a commonly used mPAH. Photochromic films with various color changes were demonstrated as an example of potential application.