An accurate and efficient calculation of phosphorescence (T1 to S0) decay rate is important by itself in the study of photophysical properties of phosphorescent molecules. A modeling of the T1 to S0 transition is also needed in the exploration of thermally activated delayed fluorescence (TADF), where phosphorescence decay competes with the reverse intersystem crossing (T1 to S1), thus affecting the overall TADF quantum efficiency. The phosphorescence decay rate is conveniently expressed using a sum-over-states (SOS) formula, but such SOS calculations can be expensive (a large number of excited states are needed) and inaccurate (if relevant higher-energy excited states are omitted from the summation). Alternatively, the phosphorescence decay rate can be efficiently computed within the quadratic response theory framework. Unfortunately, the latter is only available in the DALTON software package. In this presentation, we will report our implementation of the quadratic response theory approach for computing the phosphorescence decay rate within the Q-Chem software package, using time-dependent density functional theory (TDDFT) excited states or their Tamm-Dancoff variants. Calculation results on two test molecules (formaldehyde and naphthalene) will be presented.

Efficient calculation of the phosphorescence decay rate

ACS Spring Meeting 2021

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