Relaxation of Exciton Confinement in CdSe Quantum Dots by Modification with a Conjugated Dithiocarbamate Ligand
Relaxation of Exciton Confinement in CdSe Quantum Dots by Modification with a Conjugated Dithiocarbamate Ligand
复制标题
DOI：
10.1021/nn1007435
复制
发表时间：
2010-06-01
期刊：
影响因子：
17.1
通讯作者：
Weiss, Emily A.
中科院分区：
文献类型：
--
作者：
Frederick, Matthew T.;Weiss, Emily A.
苯基二硫代氨基甲酸酯（PTC）配体与液相胶体CdSe量子点（QDs）的配位使量子点的光学带隙E-g减小了220 meV。这些δ E-g值是通过化学修饰溶液相CdSe量子点表面实现的最大位移，并且在能量上超过一个数量级，是溶液相或固相中量子点实现的最大色移。与PTC配位后δ E-g的测量值对应于激子半径明显增加0.26 +/- 0.03 nm；在半径R = 1.1 ~ 1.9 nm范围内，激子离域与量子点的大小无关。密度泛函理论计算表明，PTC的最高占据分子轨道与QD的分子轨道接近共振，并且两者具有正确的交换电子密度的对称性（PTC是pi-供体，光激发QD是pi-受体）。因此，我们提出激子约束的弛豫是通过量子点的光激空穴离域到配体壳层中来实现的。
Coordination of phenyldithiocarbamate (PTC) ligands to solution-phase colloidal CdSe quantum dots (QDs) decreases the optical band gap, E-g, of the QDs by up to 220 meV. These values of Delta E-g are the largest shifts achieved by chemical modification of the surfaces of solution-phase CdSe QDs and are-by more than an order of magnitude in energy-the largest bathochromic shifts achieved for QDs in either the solution or solid phases. Measured values of Delta E-g, upon coordination to PTC correspond to an apparent increase in the excitonic radius of 0.26 +/- 0.03 nm; this excitonic delocalization is independent of the size of the QD for radii, R = 1.1-1.9 nm. Density functional theory calculations indicate that the highest occupied molecular orbital of PTC is near resonant with that of the QD, and that the two have correct symmetry to exchange electron density (PTC is a pi-donor, and the photoexcited QD is a pi-acceptor). We therefore propose that the relaxation of exciton confinement occurs through delocalization of the photoexcited hole of the QD into the ligand shell.