Recent progress on the excited-state multiple proton transfer process in organic molecules

In contrast to the widely reported excited-state single proton-transfer, excited-state multiple proton transfer (ESMPT) containing two or more intra- or inter-molecular proton transfers has greatly expanded the research scope of the excited-state proton transfers. In recent decades, ESMPT-active organic molecules have attracted much attention owing to their unique photophysical properties, such as large magnitude Stokes shifts and dual emission. These photophysical properties facilitate the application of the organic molecules in organic solid-state lasers, fluorescent probes and sensors, and molecular switches. Herein, we introduce the fundamentals of the ESMPT and review the recent advances in different types of ESMPTs in organic molecules. Finally, we present our conclusions and the future development prospects of the ESMPT in organic molecules.