Gutiérrez-Meza Elizabeth, Malatesta Ravyn, Li Hongmo, Bargigia Ilaria, Srimath Kandada Ajay Ram, Valverde-Chávez David A, Kim Seong-Min, Li Hao, Stingelin Natalie, Tretiak Sergei, Bittner Eric R, Silva-Acuña Carlos
School of Chemistry and Biochemistry, Georgia Institute of Technology, 901 Atlantic Drive, Atlanta, GA 30332, USA.
School of Materials Science and Engineering, Georgia Institute of Technology, North Avenue, Atlanta, GA 30332, USA.
Sci Adv. 2021 Dec 10;7(50):eabi5197. doi: 10.1126/sciadv.abi5197.
Frenkel excitons are unequivocally responsible for the optical properties of organic semiconductors and are predicted to form bound exciton pairs (biexcitons). These are key intermediates, ubiquitous in many photophysical processes such as the exciton bimolecular annihilation dynamics in such systems. Because of their spectral ambiguity, there has been, to date, only scant direct evidence of bound biexcitons. By using nonlinear coherent spectroscopy, we identify here bound biexcitons in a model polymeric semiconductor. We find, unexpectedly, that excitons with interchain vibronic dispersion reveal intrachain biexciton correlations and vice versa. Moreover, using a Frenkel exciton model, we relate the biexciton binding energy to molecular parameters quantified by quantum chemistry, including the magnitude and sign of the exciton-exciton interaction the intersite hopping energies. Therefore, our work promises general insights into the many-body electronic structure in polymeric semiconductors and beyond, e.g., other excitonic systems such as organic semiconductor crystals, molecular aggregates, photosynthetic light-harvesting complexes, or DNA.
弗伦克尔激子无疑是有机半导体光学性质的成因，并且预计会形成束缚激子对（双激子）。这些是关键中间体，在许多光物理过程中普遍存在，比如此类系统中的激子双分子湮灭动力学。由于它们光谱的模糊性，迄今为止，仅有少量关于束缚双激子的直接证据。通过使用非线性相干光谱，我们在此处识别出一种模型聚合物半导体中的束缚双激子。我们意外地发现，具有链间振动子色散的激子显示出链内双激子相关性，反之亦然。此外，使用弗伦克尔激子模型，我们将双激子结合能与通过量子化学量化的分子参数联系起来，包括激子 - 激子相互作用的大小和符号以及位点间跳跃能。因此，我们的工作有望为聚合物半导体及其他体系（例如有机半导体晶体、分子聚集体、光合光捕获复合物或DNA等其他激子系统）的多体电子结构提供一般性见解。
