Accurate treatment of charge-transfer excitations and thermally activated delayed fluorescence using the particle-particle random phase approximation
Rachel Al-Saadon, Ph.D. candidate
Weitao Yang, advisor
Friday, March 2, 2018 - 10:30am to 11:30am
Location: French Family Science Center 3225
Avery, Meg

Abstract: Thermally activated delayed fluorescence (TADF) is a mechanism that increases the electroluminescence efficiency in organic light emitting diodes by harnessing both singlet and triplet excitons. Delayed fluorescence is facilitated by a small energy difference between the first singlet and triplet excited states, which is minimized by spatial separation of the donor and acceptor moieties. The small energy splitting between the resultant charge-transfer (CT) excited states inherent in TADF molecules necessitates quantitative accuracy that is missed in time-dependent density functional due to the delocalization error present in standard density functional approximations for exchange-correlation energy. In my presentation I will focus on the excited state properties of organic molecules that exhibit TADF. Standard approaches that are used to mitigate the delocalization error will be reviewed and our results based on the particle-particle random phase approximation (pp-RPA) to the pairing matrix fluctuation will be introduced. Our pp-RPA approach to computing excitation energies is able to capture CT states and accurately reproduce excitation energies of TADF molecules. Qualitative characterization of excited states and interesting structural features of TADF molecules will be discussed as well.