The Role of Long-Lived Excitons in the Dynamics of Strongly Coupled Molecular Polaritons
The Role of Long-Lived Excitons in the Dynamics of Strongly Coupled Molecular Polaritons
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DOI：
10.1021/acsphotonics.0c00895
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发表时间：
2020-08-19
期刊：
影响因子：
7
通讯作者：
Sfeir, Matthew Y.
中科院分区：
文献类型：
--
作者：
Liu, Bin;Menon, Vinod M.;Sfeir, Matthew Y.
在强耦合激子-极化系统中改变分子动力学的概念是光子学中的一个新兴课题，因为它有可能产生具有定制光物理性质的定制化学系统。然而，对于哪些类型的分子系统的动力学可以通过强耦合来改变，或者在什么条件下可以实现这些改变，目前还没有达成共识。这些悬而未决的问题源于激子-极化和局域激发态的寿命和转换动力学的持续不确定性，以及在时域中测量这种相互作用的适当方法。在这里，我们提供了一个框架来测量激子-极化子和多种单线态、三重态和多激子态之间的动态相互作用，使用一个模型分子自旋转换（单线态裂变）系统，该系统与光学微腔强耦合。除了通常的种群动力学外，微腔的瞬态光学测量还揭示了与激子-极化子跃迁能量和激子-光子耦合条件的瞬态变化有关的信息。这种方法可以确定在强耦合状态下修改分子动力学的主要实际限制，包括：(1)吸收到大量的“水库”状态，定义为暗激子（例如，三重态）和来自集体强耦合分子的暗态的简并流形，以及来自非耦合分子的所有激子，与极化激子状态相比；(2)从水库状态到腔极化激子的缓慢转换。由于储层状态和腔极性之间的弱相互作用，需要明智的设计考虑来实现改进的光物理动力学，需要使用具有长激发态寿命的分子系统或结构，以增强激子-光子耦合强度，这样就需要少量的分子。
The concept of modifying molecular dynamics in strongly coupled exciton-polariton systems is an emerging topic in photonics because of its potential to produce customized chemical systems with tailored photophysical properties. However, there is no consensus on the types of molecular systems whose dynamics can be modified using strong coupling or the conditions under which these modifications can be realized. These open questions stem from persistent uncertainties concerning the lifetime and conversion dynamics of exciton-polaritons and localized excited states, as well as the proper way to measure such interactions in the time domain. Here, we provide a framework for measuring dynamical interactions between exciton-polaritons and a diverse manifold of singlet, triplet, and multiexciton states, using a model molecular spin conversion (singlet fission) system that is strongly coupled to an optical microcavity. In addition to the usual population dynamics, transient optical measurements on microcavities reveal information pertaining to transient modifications of the exciton-polariton transition energies and exciton-photon coupling conditions. This approach allows to identify major practical limitations for modifying molecular dynamics in the strong coupling regime, including (1) absorption into the large number of "reservoir" states, defined as dark excitons (e.g., triplets) and the degenerate manifold of dark states from the collective strongly coupled molecules and all excitons from uncoupled molecules, compared to polariton states and (2) the slow conversion from reservoir states to cavity polaritons. As a consequence of weak interactions between reservoir states and cavity polaritons, judicious design considerations are required to achieve modified photophysical dynamics, necessitating the use of molecular systems with long excited-state lifetimes or architectures that enhance exciton-photon coupling strength such that a small number of molecules is required.