Azzaro Michael S, Le Aaron K, Wang Honghao, Roberts Sean T
Department of Chemistry , The University of Texas at Austin , Austin , Texas 78712 , United States.
J Phys Chem Lett. 2019 Sep 19;10(18):5602-5608. doi: 10.1021/acs.jpclett.9b02040. Epub 2019 Sep 6.
We examine CdSe NCs functionalized with the exciton-delocalizing ligand phenyldithiocarbamate (PDTC) using two-dimensional electronic spectroscopy (2DES). PDTC forms hybrid molecular orbitals with CdSe's valence band that relax hole spatial confinement and create potential for enhanced exciton migration in NC solids. We find PDTC broadens the intrinsic line width of individual NCs in solution by ∼30 meV, which we ascribe to modulation of NC band edge states by ligand motion. In PDTC-exchanged solids, photoexcited excitons are mobile and rapidly move to low-energy NC sites over ∼30 ps. We also find placing excitons into high-energy states can accelerate their rate of migration by over an order of magnitude, which we attribute to enhanced spatial delocalization of these states that improves inter-NC wave function overlap. Our work demonstrates that NC surface ligands can actively facilitate inter-NC energy transfer and highlights principles to consider when designing ligands for this application.
我们使用二维电子光谱（2DES）研究了用激子离域配体苯基二硫代氨基甲酸盐（PDTC）功能化的CdSe纳米晶体。PDTC与CdSe的价带形成混合分子轨道，从而缓解空穴的空间限制，并为纳米晶体固体中激子迁移的增强创造了潜力。我们发现，PDTC使溶液中单个纳米晶体的本征线宽拓宽了约30 meV，我们将其归因于配体运动对纳米晶体带边态的调制。在PDTC交换的固体中，光激发激子是可移动的，并在约30皮秒内迅速移动到低能量的纳米晶体位点。我们还发现，将激子置于高能态可以使其迁移速率加快一个数量级以上，我们将其归因于这些态的空间离域增强，从而改善了纳米晶体间的波函数重叠。我们的工作表明，纳米晶体表面配体可以积极促进纳米晶体间的能量转移，并突出了在设计用于此应用的配体时需要考虑的原则。
