Department of Chemistry and Biochemistry, University of Texas, Austin, TX 78712, USA.
Science. 2011 Dec 16;334(6062):1541-5. doi: 10.1126/science.1213986.
Multiple exciton generation (MEG) refers to the creation of two or more electron-hole pairs from the absorption of one photon. Although MEG holds great promise, it has proven challenging to implement, and questions remain about the underlying photo-physical dynamics in nanocrystalline as well as molecular media. Using the model system of pentacene/fullerene bilayers and femtosecond nonlinear spectroscopies, we directly observed the multiexciton (ME) state ensuing from singlet fission (a molecular manifestation of MEG) in pentacene. The data suggest that the state exists in coherent superposition with the singlet populated by optical excitation. We also found that multiple electron transfer from the ME state to the fullerene occurs on a subpicosecond time scale, which is one order of magnitude faster than that from the triplet exciton state.
多激子产生（MEG）是指通过吸收一个光子产生两个或更多的电子-空穴对。尽管 MEG 具有很大的潜力，但它的实现却极具挑战性，而且在纳米晶体和分子介质中，关于其潜在的光物理动力学仍存在一些问题。本研究使用并五苯/富勒烯双层模型体系和飞秒非线性光谱技术，直接观察到了由并五苯中单态裂变（MEG 的一种分子表现形式）产生的多激子（ME）态。数据表明，该态与由光激发产生的单态以相干叠加形式存在。我们还发现，从 ME 态到富勒烯的多个电子转移发生在亚皮秒时间尺度内，比从三重态激子态转移快一个数量级。
