Carbodithioate-containing oligo- and polythiophenes for nanocrystals' surface functionalization

Organic ligands containing the chelating carbodithioate group are excellent candidates for the surface functionalization of various semiconductor and metal nanoparticles or flat substrates. We provide a simple synthetic scheme for the preparation of a series of regioregular oligo- and polythiophenes containing this functional group. In the first step, 3-[4-(bromomethyl)phenyl]-2,5-dibromothiophene is coupled either to 3-n-octylthiophene or to 3,3-dioctyl-2,2':5',2-terthiophene, leading to quasisymmetric thiophene trimers or heptamers, respectively. In the second step, these oligomers are submitted to oxidative polymerization, and finally the carbodithioic acid function is introduced. This procedure can be generalized for the preparation of a large number of functional oligo- and polythiophenes by simply varying the chemical structure of the thiophene precursors used. We illustrate the grafting of these compounds on the surface of CdSe nanocrystals with the example of 4-thiophen-3-yldithiobenzoic acid. Spectroscopic studies of the resulting thiophene-functionalized nanocrystals reveal photoinduced charge transfer at the organic/inorganic interface.