Computational screening of multi-resonance thermally activated delayed fluorescence (MR-TADF) molecules for lasing application

Abstract

Multi-resonance thermally activated delayed fluorescence (MR-TADF) molecules charactering large emission oscillator strengths, effective reverse intersystem crossing (RISC), and narrow emission spectral width, have great potential as laser materials. We propose a molecular descriptor for quick screening MR-TADF molecules as laser candidate materials, A = ${\Delta E}_{\text{ST}}{\sigma }_{\text{eff}}^{\text{net},\text{opt}}$, namely, the product of singlet-triplet energy gap and the optical pumping net stimulated emission cross section. These quantities can be calculated by combining quantum chemistry package Gaussian and our own MOMAP program. Through extensive computations benchmarked with existing experiments, we suggest that A value should be larger than 0.311 ⨉ 10⁻¹⁷ cm² eV for promising lasing molecules. We virtually designed 119 molecules with MR-TADF property, and based on our theoretical protocol by considering descriptor A, we are able to select 10 molecules as lasing molecules. We then further screen out 2 molecules through analyzing the spectral overlap, indicating that only eight molecules are prospective candidates for laser materials. Particularly, we find that ADBNA-Me-BPy molecule possesses large radiative decay rate and large reverse intersystem crossing rate, 1.90 × 10⁶ s⁻¹ and 1.01 × 10⁸ s⁻¹, respectively, implying a low lasing threshold, promising for electrically pumped lasing.