Theoretical modeling of dynamics of photo-excited states in light-driven molecular rotary motors

PhD ceremony: Mr. A. Kazaryan, 16.15 uur, Academiegebouw, Broerstraat 5, Groningen

Title: Theoretical modeling of dynamics of photo-excited states in light-driven molecular rotary motors

Promotor(s): prof. M. Filatov

Faculty: Mathematics and Natural Sciences

The operation of synthetic light-driven rotary molecular motors is based on the photoisomerizationprocess. In photochemical studies one pursues an accurate description of potential energy surfaces(PES) of the ground S0 and excited S1 states. Commonly, one or several chemical bonds are brokenduring the photoreaction. If the multireference character arising in these cases is not properly takeninto account, this may lead to incorrect energy barriers and discontinuities of the PESs. To treat suchsituations in molecules of realistic size methods based on the ensemble density functional theory(DFT) can be used. We considered the practical implementation of ensemble DFT in the Restricted Ensemble-Referenced Kohn-Sham (REKS) method. An approach based on the ensemble representation of the S0 and S1 statesenergies termed the State-Averaged REKS method was developed to address both the ground S0 andthe excited S1 states of the molecules.The SA-REKS method was tested on model systems and subsequently applied to the study ofmolecular motors. The S0 and S1 states PESs were scanned and strongly pyramidalized conicalintersection (CI) structures were located. A hybrid SA-REKS/molecular dynamics study was carriedout. The preferable isomerization pathways of the reaction were pointed out. To facilitate the search ofCI structures and to estimate the relative transition probability at the avoided crossings thenonadiabatic coupling (NAC) matrix elements are needed. Using the SA-REKS method we calculatedthe NAC matrix elements and optimized the CI geometries in model systems. A good agreement with the corresponding ab initio results was found.