A quantitative description of photoluminescence efficiency of a carbazole-based thermally activated delayed fluorescence emitter

Abstract

A reliable quantitative description of photoluminescence efficiency is crucial for designing and developing new-type thermally activated delayed fluorescence (TADF) emitters. In this contribution, we computed the conversion and decay rates of a novel TADF-active molecule, 2-(9H-carbazol-9-yl)-thianthrene-5,5,10,10-tetraoxide (CZ-TTR), involving the lowest singlet excited S₁ state and triplet excited T₁ state. The efficiency of total fluorescence containing prompt fluorescence and delayed fluorescence was obtained correspondingly. The present results reveal that the rate of reverse intersystem crossing from T₁ to S₁ is calculated to be slightly larger than the radiative and non-radiative decay rates of the S₁ state at 300 K temperature, thus resulting in an occurrence of delayed fluorescence. Additionally, the total fluorescence efficiency is estimated to be 54.5%, which agrees very well with the photoluminescence quantum yield of 56.7% observed experimentally. It is also found that the dominant charge transfer characteristics in the S₁ and T₁ states produce a small energy difference between the two states, and consequently an efficient reverse intersystem crossing process and a high fluorescence efficiency.