Spin-vibronic interaction induced reverse intersystem crossing: A case study with TXO-TPA and TXO-PhCz molecules

We highlight the important roles the direct spin–orbit (DSO) coupling, the spin-vibronic (SV) coupling, and the dielectric constant of the medium play on the reverse intersystem crossing (RISC) mechanism of TXO-TPA and TXO-PhCz molecules. To understand this complex phenomenon, we have calculated the...

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Veröffentlicht in:The Journal of chemical physics 2022-11, Vol.157 (17), p.174101-174101
Hauptverfasser: Karak, Pijush, Ruud, Kenneth, Chakrabarti, Swapan
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Sprache:eng
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Zusammenfassung:We highlight the important roles the direct spin–orbit (DSO) coupling, the spin-vibronic (SV) coupling, and the dielectric constant of the medium play on the reverse intersystem crossing (RISC) mechanism of TXO-TPA and TXO-PhCz molecules. To understand this complex phenomenon, we have calculated the RISC rate constant, kRISC, using a time-dependent correlation function-based method within the framework of second-order perturbation theory. Our computed kRISC in two different solvents, toluene and chloroform, suggests that in addition to the DSO, a dielectric medium-dependent SV mechanism may also have a significant impact on the net enhancement of the rate of RISC from the lowest triplet state to the first excited singlet state. Whereas we have found that kRISC of TXO-TPA is mostly determined by the DSO contribution independent of the choice of the solvent, the SV mechanism contributes more than 30% to the overall kRISC of TXO-PhCz in chloroform. In toluene, however, the SV mechanism is less important for the RISC process of TXO-PhCz. An analysis of mode-specific nonadiabatic coupling (NAC) between T2 and T1 of TXO-PhCz and TXO-TPA suggests that the NAC values in certain normal modes of TXO-PhCz are much higher than those of TXO-TPA, and it is more pronounced with chloroform as a solvent. The findings demonstrate the role of the solvent-assisted SV mechanism toward the net RISC rate constant, which in turn maximizes the efficiency of thermally activated delayed fluorescence.
ISSN:0021-9606
1089-7690
1089-7690
DOI:10.1063/5.0120068