论文标题
多烯中较高的能量三胞胎态及其在分子内单线裂变中的作用
Higher energy triplet-pair states in polyenes and their role in intramolecular singlet fission
论文作者
论文摘要
探测具有超过明亮状态（$ 1^1b_u^+$/$ s_2 $）的扩展多烯系统，带有单线裂变会生成三重态。人们认为此过程不涉及$ 2^1a_g^ - $/$ s_1 $状态，这表明其他状态发挥作用。使用密度矩阵重质化组（DMRG）计算，对Pariser-Parr-Pople-Peierls Hamiltonian进行了研究，我们研究了可能参与单裂裂变的候选状态。我们发现放松的$ 1^1b_u^ - $，$ 3^1a_g^ - $ singlet状态和$ 1^5a_g^ - $五重五个状态位于$ s_2 $状态下。 $ 1^1b_u^ - $，$ 3^1a_g^ - $和$ 1^5a_g^ - $状态都被认为具有三重态 - 三重性字符，这是通过我们对债券二聚体，自旋旋转相关性和波浪函数与三重态产品的计算确认的。因此，我们表明，有一系列单元激动（即$ 2^1a_g^ - $，$ 1^1b_u^ - $，$ 3^1a_g^ - $，$ \ cdots $），由三胞胎pair和电子孔组成，基本上是相同的激发，但具有不同的中心含量。这个家族的最低能量成员，$ 2^1a_g^ - $ state无法进行单身裂变。但是，由于其动能的增加和电子静态放松的减少，高能量成员（例如$ 3^1a_g^ - $）状态可以在某些链长的长度上进行单重裂变。
Probing extended polyene systems with energy in excess of the bright state ($1^1B_u^+$/$S_2$) band edge generates triplets via singlet fission. This process is not thought to involve the $2^1A_g^-$/$S_1$ state, suggesting that other states play a role. Using density matrix renormalisation 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 $1^1B_u^-$, and $3^1A_g^-$ singlet states and $1^5A_g^-$ quintet state lie below the $S_2$ state. The $1^1B_u^-$, $3^1A_g^-$ and $1^5A_g^-$ states are all thought to have triplet-triplet character, which is confirmed by our calculations of bond dimerization, spin-spin correlation and wavefunction overlap with products of triplet states. We thus show that there is a family of singlet excitations(i.e., $2^1A_g^-$, $1^1B_u^-$, $3^1A_g^-$, $\cdots$), 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 $2^1A_g^-$ state, cannot undergo singlet fission. But higher energy members (e.g., the $3^1A_g^-$) state, owing to their increased kinetic energy and reduced electron-lattice relaxation, can undergo singlet fission for certain chain lengths.
