Up-Conversion Intersystem Crossing Rates in Organic Emitters for Thermally Activated Delayed Fluorescence: Impact of the Nature of Singlet vs Triplet Excited States

The rates for up-conversion intersystem crossing (UISC) from the T1 state to the S1 state are calculated for a series of organic emitters with an emphasis on thermally activated delayed fluorescence (TADF) materials. Both the spin–orbit coupling and the energy difference between the S1 and T1 states (ΔEST) are evaluated, at the density functional theory (DFT) and time-dependent DFT levels. The calculated UISC rates and ΔEST values are found to be in good agreement with available experimental data. Our results underline that small ΔEST values and sizable spin–orbit coupling matrix elements have to be simultaneously realized in order to facilitate UISC and ultimately TADF. Importantly, the spatial separation of…

• NR
  National Research Foundation of Korea

  Award: 2015R1D1A1A01061487
• KA
  King Abdullah University of Science and Technology