jp072407x_si_001.pdf (11.94 MB)
Download fileDifferences in Cross-Link Chemistry between Rigid and Flexible Dithiol Molecules Revealed by Optical Studies of CdTe Quantum Dots
journal contribution
posted on 2007-08-02, 00:00 authored by R. Koole, B. Luigjes, M. Tachiya, R. Pool, T. J. H. Vlugt, C. de Mello Donegá, A. Meijerink, D. VanmaekelberghThe cross-link chemistry of CdTe quantum dots (QDs) in solution is studied for different types of aliphatic
(flexible) and aromatic (rigid) dithiol linker molecules. A remarkable difference in the cross-linking efficiency
is observed: the rigid dithiols are shown to form aggregates at much lower concentrations. Qualitative and
quantitative information on the formation of aggregates is obtained from cryogenic transmission electron
microscopy (cryo-TEM) images and photoluminescence decay measurements. The luminescence decay curves
are analyzed with a model for energy transfer to neighboring QDs in aggregates. The analysis shows that the
cross-linking efficiency is 4 times higher for the rigid dithiols than for the flexible dithiols. The difference is
attributed to the formation of loops for the flexible dithiols by attaching with both thiol groups to the same
nanocrystal surface (preventing cross-linking), whereas the rigid aromatic dithiols cannot form loops and the
second thiol group is oriented away from the surface (enabling cross-linking). The difference in conformation
between flexible and rigid dithiols is confirmed by studies on the red-shift in the optical absorption spectra
due to capping exchange of amines by monothiols or dithiols and by molecular simulations.