Molecular Transients in Photoactive Heterocyclic Systems

by Sambit Kumar Das (Stockholm University)

Friday 11 Apr 2025, 09:00 → 12:00 Europe/Stockholm

FB54 (AlbaNova Main Building)

Abstract
The journey from light-induced excitation of a photoactive molecule to the formation of a stable photoproduct unfolds
through a sequence of complex transformations within the molecular system. These transformations are governed by
ultrafast processes and short-lived intermediates or transient species, which are crucial to the photoprocess. Studying
these intermediates is vital not only for understanding the fundamental light-matter interactions that underlie natural
optical phenomena but also for enabling the design of photochemical and photophysical reactions across diverse fields
of application. Optical spectroscopic methods are commonly used to gather experimental evidence of these phenomena.
Although these methods identify the intermediates based on their energy signatures, a proper characterization of the
electronic structure remains elusive.
This thesis delves into sophisticated quantum chemical frameworks, supported by multiple studies, to elucidate the
mechanism and architecture involved in characterizing the short-lived molecular transients. The studies addressed in the
thesis highlight the rich photochemistry of heterocyclic compounds through theoretical dynamical modeling and spectral
simulations. In the first part, the non-adiabatic effects in photoexcited thiopyridone are explored. A collective theoretical
and experimental investigation describes the molecular evolution during the ultrafast process and the observed variations
across its constitutional isomers. The possibility of formation of a molecular excimer is also explored. The second part
focuses on imidazole to simulate the electronic and structural changes that lead to proton transfer, with particular attention
given to the local effects that influence the overall characteristics.