Recent Progress in Isomerization‐Based Photoacids

Photoacids harness light to enable precise, on‐demand proton transfer and Brønsted/Lewis acid release, laying the foundation for mimicking biological processes and unlocking novel chemical functions. Classical subfamilies—photolytic and excited‐state photoacids—are valued for their high quantum yields and ease of modification. The emergence of isomerization‐based photoacids has expanded this toolbox, offering unique mechanisms for reversible or irreversible light‐controlled modulation of acidity. Built upon diverse photoisomerizable scaffolds such as diarylethenes and spiropyrans, these systems allow fine‐tuning of p K a , activation wavelengths, and quantum yields, supporting integration into catalysis, supramolecular assembly, and bioresponsive platforms. This review systematically highlights recent advances in isomerization‐based photoacids, critically examines their advantages and limitations, and provides guidelines for the rational design and application of photoisomerizable acids in future biological and materials science applications.