Evidence and mechanism of efficient thermally activated delayed fluorescence promoted by delocalized excited states.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 28508081.
- Also identified by DOI 10.1126/sciadv.1603282 and PMC identifier 5425233.
- Licence recorded as CC BY-NC.
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Abstract
The design of organic compounds with nearly no gap between the first excited singlet (S<sub>1</sub>) and triplet (T<sub>1</sub>) states has been demonstrated to result in an efficient spin-flip transition from the T<sub>1</sub> to S<sub>1</sub> state, that is, reverse intersystem crossing (RISC), and facilitate light emission as thermally activated delayed fluorescence (TADF). However, many TADF molecules have shown that a relatively appreciable energy difference between the S<sub>1</sub> and T<sub>1</sub> states (~0.2 eV) could also result in a high RISC rate. We revealed from a comprehensive study of optical properties of TADF molecules that the formation of delocalized states is the key to efficient RISC and identified a chemical template for these materials. In addition, simple structural confinement further enhances RISC by suppressing structural relaxation in the triplet states. Our findings aid in designing advanced organic molecules with a high rate of RISC and, thus, achieving the maximum theoretical electroluminescence efficiency in organic light-emitting diodes.