Department of Chemistry and Center for Atomic, Molecular and Optical Sciences and Technologies, Indian Institute of Technology Tirupati, Tirupati, AP 517619, India.
J Phys Chem A. 2023 Apr 20;127(15):3347-3355. doi: 10.1021/acs.jpca.2c08937. Epub 2023 Apr 4.
Small singlet-triplet gap (Δ) and large spin-orbit coupling (SOC) between the low-lying excited spin singlet and triplet states greatly promote the intersystem crossing (ISC) and reverse intersystem crossing (RISC) processes that are keys to harvest the triplet population. The electronic structure of a molecule, which strongly depends on its geometry, governs the ISC/RISC. Herein, we have studied visible-light-absorbing freebase corrole and its electron donor/acceptor functional derivatives to explore and understand the effect of homo/hetero meso-substitution in the modulation of corrole photophysical characteristics using time-dependent density functional theory implementing optimally tuned range-separated hybrid. Dimethylaniline and pentafluorophenyl are considered as the representative donor and acceptor functional groups, respectively. Solvent effects are accounted for using a polarizable continuum model with the dichloromethane dielectric. Calculations reproduce the experimentally measured 0-0 energies for some of the functional corroles studied here. Importantly, results reveal that both the homo- and hetero-substituted corroles including the unsubstituted one show substantial ISC rates (∼10 s) that are comparable to the fluorescence rates (∼10 s). On the other hand, while homo-substituted corroles exhibit modest RISC rates (∼10 - 10 s), hetero-substituted ones show relatively lower RISC rates (∼10 - 10 s). These results together suggest that both homo- and hetero-substituted corroles could act as triplet photosensitizers, which is also evident from some experimental reports on modest singlet oxygen quantum yield. Calculated rates are analyzed with respect to the variation of Δ and SOC, and their dependence on the molecular electronic structure was evaluated in detail. The research findings reported in this study will add to understanding rich photophysical properties of functional corroles and also aid in devising molecular-level design strategies for developing heavy-atom free functional corroles or related macrocycles for applications in lighting, photocatalysis, photodynamic therapy, etc.
小的单线态-三线态能隙 (Δ) 和大的自旋轨道耦合 (SOC) 有利于低能激发单线态和三线态之间的系间窜越 (ISC) 和反向系间窜越 (RISC) 过程，这些过程是收集三线态的关键。分子的电子结构强烈依赖于其几何形状，从而控制 ISC/RISC。在此，我们研究了可见光吸收的游离基卟啉及其电子给体/受体功能衍生物，以探索和理解同/杂中位取代对卟啉光物理特性的调制作用，使用时间相关密度泛函理论实施最佳调谐的范围分离混合。二甲苯胺和五氟苯基分别被认为是代表性的供体和受体官能团。使用具有二氯甲烷介电常数的极化连续体模型来考虑溶剂效应。计算结果再现了一些研究中的功能卟啉的实验测量的 0-0 能量。重要的是，结果表明，包括未取代的卟啉在内的同/杂取代卟啉都表现出相当大的 ISC 速率 (∼10 s)，与荧光速率 (∼10 s) 相当。另一方面，虽然同取代卟啉表现出适度的 RISC 速率 (∼10 - 10 s)，但杂取代卟啉表现出相对较低的 RISC 速率 (∼10 - 10 s)。这些结果表明，同/杂取代卟啉都可以作为三重态光敏剂，这也从一些关于适度单线态氧量子产率的实验报告中得到证实。计算速率与 Δ 和 SOC 的变化有关，并详细评估了它们对分子电子结构的依赖性。本研究报告的研究结果将有助于理解功能卟啉丰富的光物理特性，并有助于设计无重金属功能卟啉或相关大环的分子水平设计策略，以应用于照明、光催化、光动力疗法等领域。
