Computational photochemistry of organic molecular crystals
THEORETICAL CHEMISTRY AND COMPUTATIONAL MODELING
Duration: NanoX master Internship (8 months part-time in-lab immersion),
5 months full-time internship,
6 months full-time internship
Latest starting date: 03/01/2022
Localisation: LABORATOIRE DE CHIMIE ET PHYSIQUE QUANTIQUES, UNIVERSITÉ PAUL SABATIER, BÂT. 3R1b4, 118 ROUTE DE NARBONNE, 31062 TOULOUSE, FRANCE
This research master's degree project could be followed by a PhD
Understanding photoinduced processes in organic molecular crystals is central to the design of highly emissive materials such as organic light-emitting diodes, and multicolored photochromic materials with application for photoswitchable full-color displays and multifrequency three-dimensional optical memory media. However, the rationalization of the photochemical behavior is still poorly understood at the solid-state level because of the difficulty to model photochemical pathways in crystal environments. In particular, radiationless decay through conical intersections (CIs) is ubiquitous in photochemical processes. CIs not only provide critical structures acting as funnels for efficient non-radiative transitions between electronic states leading to the formation of photoproducts not reachable by thermal (ground-state) processes, but they are also at the origin of emission quenching depending on their accessibility on the excited-state potential energy surface. While computational photochemistry has been highly successful in studying various photochemical processes in the gas phase, in solution and even in complex biological environments, it has rarely been applied in the context of molecular crystals. This can mainly be explained by the lack of excited-state methodologies tailored for such periodic systems. Recently, embedding approaches based on the Ewald sum have been used in conjunction with excited-state electronic structure methods to model the localized excitations which characterize these materials.[6,7] During this internship, we aim at using different embedding schemes to study aggregation-induced emissions in different organic molecular crystals using either benzylideneimidazolinone or cinnamoyle pyrone derivatives. We will first use the point charge embedding (PCE) approach where only the Coulomb interactions are considered, using point charges, and nonelectrostatic interactions are neglected. Then, we will explore the possibility to increase the size of the quantum mechanical system to several chromophore units by using a cluster approach in combination with the PCE approach. Eventually, if time allows, we will use hybrid QM/QM’ electrostatic embedding schemes in order to account for the polarization of the environment. The purpose of these computational studies will be to rationalize the solid-state luminescence enhancement observed experimentally compared to the behavior in the gas phase or in solution.
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Areas of expertise:
THEORETICAL PHOTOCHEMISTRY, AGGREGATION-INDUCED EMISSION
Required skills for the internship:
QUANTUM CHEMISTRY, ELECTRONIC STRUCTURE METHODS