Energy transfer and spatial scrambling of an exciton in a conjugated dendrimer
Energy transfer and spatial scrambling of an exciton in a conjugated dendrimer
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共轭树枝状聚合物中激子的能量转移和空间扰乱
DOI：
10.1039/c8cp05852k
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发表时间：
2018
影响因子：
3.3
通讯作者：
Fernandez-Alberti, S.
中科院分区：
文献类型：
--
作者：
Ondarse-Alvarez, D.;Oldani, N.;Roitberg, A. E.;Kleiman, V.;Tretiak, S.;Fernandez-Alberti, S.
多发色分子的光激发诱导了一系列分子内电子能量的驰豫和再分配路径，最终导致超快激子在单个生色团单元上的自陷。我们研究了发生在苯乙叉树枝状大分子上的光诱导过程，该树枝状大分子由九个等价的线性生色团单元或分支组成。分支之间的间位取代键破坏了共轭，导致了它们之间的弱耦合和局域激发。我们的非绝热激发态分子动力学模拟表明，激子在超快内转换到最低激发态的过程中伴随着激子的内→外分支间迁移，这是由于与能量等价的共轭链段相关的熵偏差所致。电子能量在生色团单元之间的重新分配通过几种可能的途径发生，在这些途径中可以区分通键输运和穿过空间的激子跳跃机制。此外，三键激发与电子跃迁密度的局域化相吻合，表明分子内能量再分配是一个电子和振动能量协同转移的过程。
Photoexcitation of multichromophoric light harvesting molecules induces a number of intramolecular electronic energy relaxation and redistribution pathways that can ultimately lead to ultrafast exciton self-trapping on a single chromophore unit. We investigate the photoinduced processes that take place on a phenylene-ethynylene dendrimer, consisting of nine equivalent linear chromophore units or branches. meta-Substituted links between branches break the conjugation giving rise to weak couplings between them and to localized excitations. Our nonadiabatic excited-state molecular dynamics simulations reveal that the ultrafast internal conversion process to the lowest excited state is accompanied by an inner → outer inter-branch migration of the exciton due to the entropic bias associated with energetically equivalent conjugated segments. The electronic energy redistribution among chromophore units occurs through several possible pathways in which through-bond transport and through-space exciton hopping mechanisms can be distinguished. Besides, triple bond excitations coincide with the localization of the electronic transition densities, suggesting that the intramolecular energy redistribution is a concerted electronic and vibrational energy transfer process.