Department of Chemistry, University of Calcutta, 92 A. P. C. Road, Kolkata 700009, West Bengal, India.
Hylleraas Centre for Quantum Molecular Sciences, Department of Chemistry, University of Tromsø-The Arctic University of Norway, 9037 Tromsø, Norway.
J Chem Phys. 2022 Nov 7;157(17):174101. doi: 10.1063/5.0120068.
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, k, using a time-dependent correlation function-based method within the framework of second-order perturbation theory. Our computed k 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 k 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 k 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 T and T 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.
我们强调了直接自旋轨道（DSO）耦合、自旋-声子（SV）耦合以及介质介电常数在 TXO-TPA 和 TXO-PhCz 分子的反向系间窜越（RISC）机制中所起的重要作用。为了理解这一复杂现象，我们使用基于时变相关函数的二阶微扰理论方法计算了 RISC 速率常数 k。我们在两种不同溶剂（甲苯和氯仿）中计算的 k 表明，除了 DSO 之外，介电常数相关的 SV 机制也可能对从最低三重态到第一激发单线态的 RISC 速率的净增强产生重大影响。虽然我们发现 TXO-TPA 的 k 主要由 DSO 贡献决定，与溶剂的选择无关，但 SV 机制对 TXO-PhCz 在氯仿中的总 k 的贡献超过 30%。然而，在甲苯中，SV 机制对 TXO-PhCz 的 RISC 过程不太重要。对 TXO-PhCz 和 TXO-TPA 的 T 和 T 之间的模式特定非绝热耦合（NAC）的分析表明，TXO-PhCz 的某些正常模式中的 NAC 值比 TXO-TPA 高得多，并且在使用氯仿作为溶剂时更为明显。这些发现表明了溶剂辅助的 SV 机制对净 RISC 速率常数的作用，这反过来又最大限度地提高了热激活延迟荧光的效率。
