Scientific Reports ( IF 3.8 ) Pub Date : 2024-01-08 , DOI: 10.1038/s41598-023-50860-4
Takao Tsuneda 1, 2 , Tetsuya Taketsugu 1, 3
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The feasibility of singlet fission (SF) in organic photosensitizers is investigated through spin-flip long-range corrected time-dependent density functional theory. This study focuses on four major organic photosensitizer molecules: benzophenone, boron-dipyrromethene, methylene blue, and rose bengal. Calculations demonstrate that all these molecules possess moderate \(\pi\)-stacking energies and closely-lying singlet (S) and quintet (triplet–triplet, TT) excitations, satisfying the essential conditions for SF: (1) Near-degenerate low-lying S and (TT) excitations with a significant S–T energy gap, and (2) Moderate \(\pi\)-stacking energy of chromophores, slightly higher than solvation energy, enabling dissociation for triplet-state chromophore generation. Moreover, based on the El-Sayed rule, intersystem crossing is found to simultaneously proceed at very slow rates in all these photosensitizers. This is attributed to the fact that the lowest singlet excitation of the monomers partly involves \(n\pi ^*\) transitions alongside the main \(\pi \pi ^*\) transitions. The proposed mechanisms are strongly substantiated by comparisons with experimental studies.
中文翻译:
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单线态裂变引发有机光敏化
通过自旋翻转长程校正的时间相关密度泛函理论研究了单线态裂变(SF)在有机光敏剂中的可行性。这项研究重点关注四种主要的有机光敏剂分子:二苯甲酮、硼二吡咯亚甲基、亚甲蓝和玫瑰红。计算表明,所有这些分子都具有中等的\(\pi\)堆积能和紧密的单重态 (S) 和五重态 (三重态-三重态,TT) 激发,满足 SF 的基本条件: (1) 近简并低- 具有显着 S-T 能隙的 S 和 (TT )激发,以及 (2) 中等的生色团堆积能,略高于溶剂化能,能够解离产生三重态生色团。此外,根据埃尔赛义德规则,发现所有这些光敏剂中的系间穿越同时以非常慢的速率进行。这是由于单体的最低单线态激发部分涉及\(n\pi ^*\)跃迁以及主要的\(\pi \pi ^*\)跃迁。通过与实验研究的比较,所提出的机制得到了强有力的证实。