Subpicosecond Exciton Dynamics in Polyfluorene Films from Experiment and Microscopic Theory
Subpicosecond Exciton Dynamics in Polyfluorene Films from Experiment and Microscopic Theory
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DOI：
10.1021/acs.jpcc.5b00680
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发表时间：
2015-05-07
影响因子：
3.7
通讯作者：
Galbraith, Ian
中科院分区：
文献类型：
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作者：
Denis, Jean-Chrisophe;Schumacher, Stefan;Galbraith, Ian
有机材料中的电子能量转移(EET)是控制许多过程效率的关键机制，包括自然和人工光合作用中的光收集天线、有机太阳能电池和生物系统。在本文中，我们用超快光致发光实验和理论模拟研究了典型的共轭聚合物聚荧烯固态薄膜中的EET。我们通过观察光致发光的去偏振来观察EET在680+/-300fs的时间尺度上发生的情况。通过定义125,000个同时包含空间无序和能量无序的发色团，建立了一个独立的、可预测的微观理论模型，该模型适用于旋涂薄膜。该模型使用非相干Forster跳跃模型，在没有任何拟合参数的情况下，预测了含时激子动力学。用改进的共振线偶极子模型计算了生色团之间的电子耦合。在不需要更高能级相互作用的情况下，我们发现该模型与实验观察到的EET引起的680+/-300fs退极化基本一致。这使得我们得出结论，只要能很好地捕捉到相关的微观参数，我们就可以用传统的共振能量转移很好地描述聚荧烯中的飞秒EET。这一发现的含义是，在某些情况下，偶极-偶极共振能量转移完全足以描述超快EET，而不需要调用强或中等耦合机制。
Electronic energy transfer (EET) in organic materials is a key mechanism that controls the efficiency of many processes, including light harvesting antennas in natural and artificial photosynthesis, organic solar cells, and biological systems. In this paper we have examined EET in solid-state thin-films of polyfluorene, a prototypical conjugated polymer, with ultrafast photoluminescence experiments and theoretical modeling. We observe EET occurring on a 680 +/- 300 fs time scale by looking at the depolarisation of photoluminescence. An independent, predictive microscopic theoretical model is built by defining 125 000 chromophores containing both spatial and energetic disorder appropriate for a spin coated thin film. The model predicts time-dependent exciton dynamics, without any fitting parameters, using the incoherent Forster-type hopping model. Electronic coupling between the chromophores is calculated by an improved version of the usual line dipole model for resonant energy transfer. Without the need for higher level interactions, we find that the model is in general agreement with the experimentally observed 680 +/- 300 fs depolarisation caused by EET. This leads us to conclude that femtosecond EET in polyfluorene can be described well by conventional resonant energy transfer, as long as the relevant microscopic parameters are well captured. The implications of this finding are that dipole-dipole resonant energy transfer can in some circumstances be fully adequate to describe ultrafast EET without needing to invoke strong or intermediate coupling mechanisms.