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The aim of this work is to investigate the observed STOKES shift for 1,3-bis(phenylethynyl)benzene (m22), for which the emission spectrum is different from tolane while the absorption spectrum is very similar. The explored hypothesis for such a difference is the presence of a conical intersection in the energy landscape of the m22 molecule. A diabatic linear vibronic coupling Hamiltonian model is proposed, with one or two dimensions, for the first two excited states and their conical intersection. A time-independent approach for finding the vibronic states is followed (diagonalization of the Hamiltonian). The results are completed by a time-dependent approach (wave packet propagation).

This report aims to review the developement of time-independent methods for the simulation of vibrationally-resolved electronic spectra. Key steps and approximations for the derivation of the electronic transition dipole moment are presented, highlighting the importance of Franck-Condon factors for the simulation. Issues and techniques for derivating them are presented in the simple case of one-dimensional harmonic oscillators, before exploring the issues the multi-dimensional problem. Finally, the aim of the incoming intership on the understanding of an unusual Stokes shift is presented.

Report

The project investigates the intersystem crossing in dimers of benzothioxanthiene imide and its dependance on the conformations of studied molecules. First step of the study is to compute potential energy surfaces by scanning along specific angles of the dimers. The spin-orbit coupling, responsible for the observed intersystem crossing from the first singlet excited state to triplet states, is then computed along with the energy differences between the involved states.

The relaxation dynamics of furanone and two other lactones has been studied through unbiased ab itinio molecular dynamics simulations, taking into account non-adiabatic transitions. First of all, the electronic relaxation dynamics of the experimentally bright excited state π → π* is compared for the three molecules. The main nuclear relaxation pathways are then identified as ring-puckering and ring-opening pathways. The character of involved states is investigated. Further relaxation of the main ring-opening pathway leads to chemical reactions as epoxydation, predicted in previous work, or CO elimination.