Higher-energy triplet-pair states in polyenes and their role in intramolecular singlet fission
Higher-energy triplet-pair states in polyenes and their role in intramolecular singlet fission
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DOI：
10.1103/physrevb.102.125107
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发表时间：
2020-09-08
影响因子：
3.7
通讯作者：
Barford, W.
中科院分区：
文献类型：
--
作者：
Valentine, D. J.;Manawadu, D.;Barford, W.
探测能量超过亮态 (1(1)B(u)(+)/S-2) 能带边缘的扩展多烯系统，通过单线态裂变生成三线态。该过程不被认为涉及 2(1)A(g)(-)/S-1 态，表明其他态也发挥了作用。使用 Pariser-Parr-Pople-Peiierls 哈密顿量的密度矩阵重正化群 (DMRG) 计算，我们研究了可能参与单线态裂变的候选态。我们发现松弛的 1(1)B(u)(-) 和 3(1)A(g)(-) 单重态和 1(5)A(g)(-) 五重态位于 S-2 态下方。 1(1)B(u)(-)、3(1)A(g)(-)和1(5)A(g)(-)态都被认为具有三重态对特征，这通过我们对键二聚化、自旋-自旋相关性和波函数与三重态产物重叠的计算得到证实。因此，我们表明存在一族单重态激发（即2(1)A(g)(-)、1(1)B(u)(-)、3(1)A(g)(-)，...），由三重态对和电子空穴特征组成，它们基本上是相同的激发，但具有不同的质心能量。该族中能量最低的成员，2(1)A(g)(-) 态，不能发生单线态裂变。但较高能量的成员（例如 3(1)A(g)(-)）态，由于其动能增加和电子晶格弛豫减少，可以在某些链长度下发生单线态裂变。
Probing extended polyene systems with energy in excess of the bright state (1(1)B(u)(+)/S-2) band edge generates triplets via singlet fission. This process is not thought to involve the 2(1)A(g)(-)/S-1 state, suggesting that other states play a role. Using density matrix renormalization group (DMRG) calculations of the Pariser-Parr-Pople-Peierls Hamiltonian, we investigate candidate states that could be involved in singlet fission. We find that the relaxed 1(1)B(u)(-) and 3(1)A(g)(-) singlet states and 1(5)A(g)(-) quintet state lie below the S-2 state. The 1(1)B(u)(-), 3(1)A(g)(-) and 1(5)A(g)(-) states are all thought to have triplet-pair character, which is confirmed by our calculations of bond dimerization, spin-spin correlation, and wave function overlap with products of triplet states. We thus show that there is a family of singlet excitations (i.e., 2(1)A(g)(-), 1(1)B(u)(-), 3(1)A(g)(-), ...), composed of both triplet-pair and electron-hole character, which are fundamentally the same excitation, but have different center-of-mass energies. The lowest energy member of this family, the 2(1)A(g)(-) state, cannot undergo singlet fission. But higher-energy members (e.g., the 3(1)A(g)(-)) state, owing to their increased kinetic energy and reduced electron-lattice relaxation, can undergo singlet fission for certain chain lengths.