Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, USA.
J Am Chem Soc. 2011 Jul 6;133(26):10146-54. doi: 10.1021/ja2010237. Epub 2011 Jun 13.
Transient absorption (TA) spectroscopy of solution-phase mixtures of colloidal CdS quantum dots (QDs) with acid-derivatized viologen molecules, N-[1-heptyl],N'-[3-carboxypropyl]-4,4'-bipyridinium dihexafluorophosphate (V(2+)), indicates electron transfer occurs from the conduction band of the QD to the LUMO of V(2+) after photoexcitation of a band-edge exciton in the QD. Analysis of the magnitude of the ground state bleach of the QD as a function of the molar ratio QD:V(2+) yields the QD-ligand adsorption constant, K(a) (4.4 × 10(4) M(-1)) for V(2+) ligands adsorbed in geometries conducive to electron transfer. The value of K(a), together with the measured rates of (i) formation of the V(+•) electron transfer product and (ii) recovery of the ground state bleach of the QD, enables determination of the intrinsic rate constant for charge separation, k(CS,int) ~ 1.7 × 10(10) s(-1), the rate for a single QD-V(2+) donor-acceptor pair. This analysis confirms previous reports that the number of ligands adsorbed to each QD is well-described by a Poisson distribution. This is the first report where the QD-ligand charge transfer and binding equilibria are quantitatively investigated simultaneously with a single technique.
胶体 CdS 量子点 (QD) 与酸衍生的紫精分子，N-[1-庚基]，N'-[3-羧基丙基]-4,4'-联吡啶二六氟磷酸酯 (V(2+)) 在溶液相混合物的瞬态吸收 (TA) 光谱表明，在 QD 的带边激子光激发后，电子从 QD 的导带转移到 V(2+)的 LUMO。分析 QD 的基态漂白程度作为 QD:V(2+)摩尔比的函数，可以得到 V(2+)配体在有利于电子转移的几何结构中吸附的 QD-配体吸附常数 K(a)（4.4×10(4) M(-1)）。K(a)的值，以及测量的 (i) V(+•)电子转移产物的形成速率和 (ii) QD 的基态漂白的恢复速率，使我们能够确定电荷分离的固有速率常数 k(CS,int)~1.7×10(10) s(-1)，这是单个 QD-V(2+)给体-受体对的速率。该分析证实了先前的报告，即每个 QD 吸附的配体数量很好地符合泊松分布。这是首次使用单一技术同时定量研究 QD-配体电荷转移和结合平衡的报告。
