Multilayers of Carbodithioate and Sulfide-Linked CdSeNanocrystals: Progressive Increase of Exciton Delocalization

Abstract

Multilayers of sulfur-based anchoring group linkers and CdSe nanocrystals (NCs) were realized on indium-tin oxide substrate via layer-by-layer alternation. The materials were investigated by UV–vis and Fourier transform infrared spectroscopy, photoluminescence, and photoconductivity. We found that the change of NC packing during multilayer build-up produces a progressive increase of exciton delocalization. In fact during multilayer deposition, the first excitonic peak of NCs shifts progressively toward longer wavelengths. We found a linear relation between the optical band gap shift (ΔEgn) and the inverse of the number of CdSe-NC layers (n) for n > 2, in particular, the decrease of its value for the infinite multilayer from one of the solution (2.10 eV) goes from 18 meV for the 1,2-ethylene-bis(dithiocarbamate) linker to 66 meV for sulfide dianions, corresponding to an apparent increase of the exciton radius of 0.20 and 0.85 nm, respectively.