Visible to Near-Infrared Light Activated Photoacids: Molecular Architecture for Chemical and Biological Applications

Abstract

Photoacid generators (PAGs) are compounds that generate acidic species upon light exposure, with functionalities that extend across various areas. For the past few years, PAGs have evolved from simple onium salts to complex structures, enhancing solubility, thermal stability, and spectral sensitivity. Structurally, they are designed with chromophores to absorb longer wavelengths, shifting their activation into the visible to near-infrared light spectrum. The classification of these PAGs includes photolysis, excited-state, and photoisomerized types, each with unique properties for light absorption and acid generation. Strategies for functional enhancement of these PAGs are summarized, such as introduction of electron-donating and withdrawing substituents, enlargement of the conjugated system, incorporation of D-π-A structures, and enhancement of two-photon absorption cross-sections. These strategies are essential for improving PAG performance in applications like photocatalysis, drug delivery, and photoacid therapy. Besides, the impediments to the practical utilization of PAGs across various domains are discussed as well.

Keywords: Photoacid generators, Long-wavelength excitation, Molecular design, Photoacid therapy