Uppala Veera Venkata Shravan, Dones Lassalle Christian Y, Kelm Jennica E, Camp Andrew M, Ter Horst Marc A, Esker Alan R, Dempsey Jillian L, Madsen Louis A
Department of Chemistry and Macromolecules Innovation Institute, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, United States.
Department of Chemistry, University of North Carolina, Chapel Hill, North Carolina 27599-3290, United States.
ACS Nano. 2025 Aug 5;19(30):27246-27258. doi: 10.1021/acsnano.5c03943. Epub 2025 Jul 22.
Semiconductor quantum dots (QDs) show promise for various applications, including biological imaging and photovoltaics. QDs are typically stabilized by surface-bound ligands, which exhibit a dynamic binding equilibrium. This study combines nuclear magnetic resonance (NMR) spectroscopy and diffusometry to quantify the populations and kinetics of oleic acid (OAH) ligand binding to PbS QD surfaces. In addition to quantifying ligand population fractions in bound and free states, our analysis reveals the existence of a third ligand state, which we hypothesize to be the weak coordination of the OAH at (100) sites through the acidic headgroup (-COOH). Thus, bound ligands exist in two subpopulations: weakly bound OAH on (100) facets and strongly bound oleate (OA) on (111) facets. Through variations in temperature and concentration, we assess the changes in ligand populations in different states and determine the energetics of their exchange equilibria. Additionally, using dynamic NMR spectroscopy, we quantify rapid exchange rates (0.09-2 ms) between weakly bound and free OAH ligands as a function of OAH titration concentration and temperature. These findings highlight the complexity of ligand binding mechanisms and enable strategies for precisely tuning QD surface properties, with significant implications for the innovation of next-generation optoelectronic materials.
半导体量子点（QDs）在包括生物成像和光伏在内的各种应用中显示出前景。量子点通常由表面结合的配体稳定，这些配体表现出动态结合平衡。本研究结合核磁共振（NMR）光谱和扩散测量法来量化油酸（OAH）配体与硫化铅量子点表面结合的数量和动力学。除了量化结合态和游离态的配体数量分数外，我们的分析还揭示了第三种配体状态的存在，我们假设这是OAH通过酸性头基（-COOH）在（100）位点的弱配位。因此，结合的配体存在于两个亚群中：（100）晶面上的弱结合OAH和（111）晶面上的强结合油酸根（OA）。通过温度和浓度的变化，我们评估了不同状态下配体数量的变化，并确定了它们交换平衡的能量学。此外，使用动态核磁共振光谱，我们量化了弱结合和游离OAH配体之间的快速交换速率（0.09 - 2毫秒），作为OAH滴定浓度和温度的函数。这些发现突出了配体结合机制的复杂性，并为精确调节量子点表面性质提供了策略，对下一代光电子材料的创新具有重要意义。
