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 quantum-dynamics tools successfully applied in ESIPT process studies, focusing on a critical comparison of their specific properties.
Highlights
Photochemistry of organic molecular systems is an extremely rich and exciting field of research, continuously growing and, pushing forward the frontiers of our understanding of light–matter interactions
PT reactions are typically challenging to be accurately studied with this protocol due to the large computational cost of multi-dimensional potential energy surface (PES) scans, on the one hand, and the critical role of the sequence of individual processes missed at this level, on the other hand
In which special precautions should be taken, is when excited-state intramolecular proton transfer (ESIPT) occurs within a dense manifold of electronic states, such as in situations in which a competition between various photochemical transformations is to be expected; in these cases, one may need to explicitly determine the relative efficiency of each channel, which usually requires the inclusion of nuclear-dynamic effects
Summary
Photochemistry of organic molecular systems is an extremely rich and exciting field of research, continuously growing and, pushing forward the frontiers of our understanding of light–matter interactions. The system undergoes further electronic relaxation—either radiative or nonradiative in nature In the former case, the characteristic strongly red-shifted fluorescence is nowadays regarded as the hallmark of ESIPT. In the context of the following discussion, it is important to underline a distinction between the ESIPT reaction investigated and similar processes, especially the proton-coupled electron transfer (PCET) reaction [23,24,25,26]. The latter phenomenon, often of nonadiabatic character, has a generally much more complex nature and may involve ground and excited-state reactions, such as intra- and intermolecular, concerted, and stepwise processes. D—proton donor; A—proton acceptor; GS—ground electronic state; ES—excited electronic state; blue arrow—initial photoabsorption; red arrow—Stokes-shifted fluorescence
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