论文标题
类胡萝卜素的光激发状态动力和单线裂变
Photoexcited state dynamics and singlet fission in carotenoids
论文作者
论文摘要
我们描述了对类胡萝卜素神经孢子激发态的动态模拟，其光激发在“明亮”（名义上是$ 1^1b_u^+$）状态之后。我们在$π$缀合的电子的UV模型上采用自适应TDMRG方法，并使用Ehrenfest运动方程式来模拟耦合的核动力学。为了说明名义$ 1^1b_u^+$和$ 2^1A_G^ - $状态在Franck-Condon Point的相对能量顺序中的实验和理论不确定性，我们考虑两个参数集。在这两种情况下，都有从“明亮”状态到“黑暗”单线三重态状态的超快内部转换。通过计算瞬态吸收，我们直接连接从预测到实验性可观察物。对于直接$ 1^1b_u^+$至$ 2^1a_g^ - $内部转换的情况，我们表明CA的主要过渡。 2 eV，接近但能量低于$ t_1 $至$ t_1^*$过渡，可以归因于$ 2^1a_g^ - $ s_1 $的$ 2^1a_g^ - $。此外，我们证明它是负责此过渡的$ 2^1A_G^ - $状态的电荷转移激子组成部分，而不是其三重态组件。接下来，我们将讨论“明亮”至“黑暗”状态内部转换的微观机制，强调这是通过两种状态的激子组成部分发生的。最后，我们描述了一种机制，通过该机制，“黑暗”状态的强大结合的内部三胞胎可能会经历链间的放热分离。我们预测，只有在分子在其基态中扭曲的情况下，这才有可能。在我们的同伴论文中解释了此处描述的计算的基础计算方法，即$ \ textIt {使用密度矩阵重新归一化组技术对类胡萝卜素光激发状态的动态模拟} $，D。Manawadu，D。J. Valentine和W. Barford，W。Barford，W。Barford，$ \ textit {j。化学西奥。 comp。} $（2023）。
We describe our dynamical simulations of the excited states of the carotenoid, neurosporene, following its photoexcitation into the 'bright' (nominally $1^1B_u^+$) state. We employ the adaptive tDMRG method on the UV model of $π$-conjugated electrons and use the Ehrenfest equations of motion to simulate the coupled nuclei dynamics. To account for the experimental and theoretical uncertainty in the relative energetic ordering of the nominal $1^1B_u^+$ and $2^1A_g^-$ states at the Franck-Condon point, we consider two parameter sets. In both cases there is ultrafast internal conversion from the 'bright' state to a 'dark' singlet triplet-pair state. We make a direct connection from our predictions to experimental observables by calculating the transient absorption. For the case of direct $1^1B_u^+$ to $2^1A_g^-$ internal conversion, we show that the dominant transition at ca. 2 eV, being close to but lower in energy than the $T_1$ to $T_1^*$ transition, can be attributed to the $2^1A_g^-$ component of $S_1$. Moreover, we show that it is the charge-transfer exciton component of the $2^1A_g^-$ state that is responsible for this transition, and not its triplet-pair component. We next discuss the microscopic mechanism of 'bright' to 'dark' state internal conversion, emphasising that this occurs via the exciton components of both states. Finally, we describe a mechanism whereby the strongly bound intrachain triplet-pairs of the 'dark' state may undergo interchain exothermic dissociation. We predict that this is only possible if the molecules are twisted in their ground states. The computational methodology underlying the calculations described here is explained in our companion paper, $\textit{Dynamical simulations of carotenoid photoexcited states using density matrix renormalization group techniques}$, D. Manawadu, D. J. Valentine, and W. Barford, $\textit{J. Chem. Theo. Comp.}$ (2023).
