Barford William
Department of Chemistry, Physical and Theoretical Chemistry Laboratory,University of Oxford, Oxford, OX1 3QZ, United Kingdom.
J Phys Chem Lett. 2023 Nov 9;14(44):9842-9847. doi: 10.1021/acs.jpclett.3c02435. Epub 2023 Oct 27.
A theory of singlet fission (SF) in carotenoid dimers is applied to explain the SF in lycopene H-aggregates observed after high-energy photoexcitation. The explanation proposed here is that a high energy, delocalized bright state first relaxes and localizes onto a single lycopene monomer. The high-energy intramonomer state then undergoes internal conversion to the 1 state. Once populated, the 1 state allows exothermic bimolecular singlet fission, while its internal conversion to the 2 state is symmetry forbidden. The simulation of SF predicts that the intramonomer triplet-pair state undergoes almost complete population transfer to the intermonomer singlet-pair state within 100 ps. Simultaneously, ZFS interactions begin to partially populate the intermonomer quintet triplet-pair state up to ca. 2 ns, after which hyperfine interactions thermally equilibrate the triplet-pair states, thus forming free single triplets within 50 ns.
一种关于类胡萝卜素二聚体中单线态裂变（SF）的理论被用于解释在高能光激发后观察到的番茄红素H聚集体中的SF现象。这里提出的解释是，一个高能、离域的亮态首先弛豫并定域到单个番茄红素单体上。然后，高能的单体内态经历内转换到1态。一旦被占据，1态允许放热的双分子单线态裂变，而其到2态的内转换在对称性上是禁阻的。SF的模拟预测，单体内三重态对态在100皮秒内几乎完全发生布居转移到单体间单线态对态。同时，零场分裂相互作用开始部分地使单体间五重态三重态对态布居，直至约2纳秒，在此之后超精细相互作用使三重态对态热平衡，从而在50纳秒内形成自由的单重态三重态。
