**Modern Theoretical Approaches to Modeling the Excited-State Intramolecular Proton Transfer: An Overview**

**Joanna Jankowska 1,\* and Andrzej L. Sobolewski 2**


**\*** Correspondence: jjankowska@chem.uw.edu.pl

**Abstract:** The excited-state intramolecular proton transfer (ESIPT) phenomenon is nowadays widely acknowledged to play a crucial role in many photobiological and photochemical processes. It is an extremely fast transformation, often taking place at sub-100 fs timescales. While its experimental characterization can be highly challenging, a rich manifold of theoretical approaches at different levels is nowadays available to support and guide experimental investigations. In this perspective, we summarize the state-of-the-art quantum-chemical methods, as well as molecular- and quantumdynamics tools successfully applied in ESIPT process studies, focusing on a critical comparison of their specific properties.

**Keywords:** excited-state intramolecular proton transfer; photochemistry; photobiology; quantum chemistry; molecular dynamics; ultrafast processes
