Koole Rolf, Schapotschnikow Philipp, Donegá Celso de Mello, Vlugt Thijs J H, Meijerink Andries
Condensed Matter and Interfaces, Debye Institute, Utrecht University, Utrecht, The Netherlands.
ACS Nano. 2008 Aug;2(8):1703-14. doi: 10.1021/nn8003247.
The exchange kinetics of native ligands that passivate CdSe quantum dots (hexadecylamine (HDA), trioctylphosphine oxide (TOPO), and trioctylphosphine (TOP)) by thiols is followed in situ. This is realized by measuring, in real-time, the decrease in emission intensity of the QDs upon addition of hexanethiol (HT) which quenches the emission. The effect of adding an excess of native ligands prior to thiol addition on the capping exchange is studied to provide insight in the bond strength and exchange kinetics of the individual surfactants. Temperature-dependent measurements reveal faster kinetics with increasing temperature. A kinetic model to describe the time-dependent measurements is introduced, taking into account the equilibrium between native ligands before thiol addition and describing the evolution of surface coverage by all ligands over time. The model allows us to extract the quenching rate for a single thiol ligand (0.004 ns(-1)) as well as exchange rates, equilibrium constants, activation energies, and changes in Gibbs free energy for replacement of the different native surfactants by HT. The analysis reveals that the substitution half-time of HDA by HT (72 s) is much shorter than for TOP (5 h) or TOPO (2.5 h) under the same conditions. The temperature dependence of the kinetics shows that the activation energy for exchange of HDA/TOPO by hexanethiol (1.6 kJ/mol) is much smaller than for TOP (20.9 kJ/mol).
通过原位跟踪巯基对钝化CdSe量子点的天然配体（十六胺（HDA）、三辛基氧化膦（TOPO）和三辛基膦（TOP））的交换动力学。这是通过实时测量添加己硫醇（HT）后量子点发射强度的降低来实现的，己硫醇会淬灭发射。研究了在添加巯基之前添加过量天然配体对封端交换的影响，以深入了解各个表面活性剂的键强度和交换动力学。温度依赖性测量表明，随着温度升高，动力学更快。引入了一个描述时间依赖性测量的动力学模型，该模型考虑了添加巯基之前天然配体之间的平衡，并描述了所有配体表面覆盖率随时间的变化。该模型使我们能够提取单个巯基配体的淬灭速率（0.004 ns(-1)）以及交换速率、平衡常数、活化能，以及用HT取代不同天然表面活性剂时吉布斯自由能的变化。分析表明，在相同条件下，HT取代HDA的半衰期（72 s）比TOP（5 h）或TOPO（2.5 h）短得多。己硫醇交换HDA/TOPO的动力学温度依赖性表明，其活化能（1.6 kJ/mol）比TOP（20.9 kJ/mol）小得多。
