Red-light responsive metastable-state photoacid

Abstract

Proton concentration is a important factor for various biological functions, and thus a method that allows spatial and temporal modulation of proton concentration with light has great potential in biomedical areas. Metastable-state photoacids (mPAHs) can reversibly produce a large proton concentration under visible light. For in vivo applications, the activating wavelength needs to be in the tissue penetration window (650–1350 nm). The commonly used approach for increasing the absorption wavelength based on donor-acceptor structure failed to yield an mPAH responding to a wavelength in this range. In this work, we developed a novel mPAH with a donor-acceptor-donor structure, which increases the absorption wavelength without deactivating the photoreaction. The mPAH reversibly released a proton under 660 and 700 nm light, and effectively transferred the proton to a weak base.