Please join Yale Chemistry for a junior faculty candidate seminar with Diptarka Hait, Stanford Science Fellow at Stanford University.
Abstract: Electronic excitation of chemical systems leads to nonequilibrium configurations on excited state potential energy surfaces. The resulting ultrafast relaxation dynamics controls photophysical and photochemical properties but is challenging to computationally simulate. In this presentation, I will describe some recent theoretical efforts towards studying photorelaxation in radical ions, with relevance for both chemical physics and photocatalysis.
I will first describe the development of an orbital-optimized density functional theory (OO-DFT) approach for accurate and efficient modeling of electronic excitations. OO-DFT can quantitatively predict X-ray absorption spectra of both closed- and open-shell species without empirical adjustments. I will show the practical utility of OO-DFT through a collaborative study on the Jahn-Teller distortion dynamics of the methane cation, probed with attosecond soft X-ray pulses that excite the carbon 1s electrons. Time-resolved spectra from both experiment and theory demonstrate that symmetry breaking requires ~ 10 femtoseconds. Theory furthermore reveals how the shape of the hole orbital affects the X-ray absorption energy.
I will next discuss the potential utility of electrochemically accessible organic radical ions for photocatalysis. Excited states of radical anions (cations) have high energy electrons (low energy holes) that can permit strongly reducing (oxidizing) behavior. However, bimolecular redox catalysis in solution is only feasible if excited states of radical ions persist for at least a nanosecond. Using multireference perturbation theory, I show the existence of conical intersections enabling picosecond scale internal conversion from excited states to the ground state, for representative radical ions. Radical ion excited states thus appear unsuitable as bimolecular redox catalysts and alternate catalytic routes ought to be explored.
For more information on Diptarka Hait’s research: https://diptarkahait.com/
Faculty Host: Professor Victor Batista