Self-Assembly of -Conjugated Amphiphiles: Free Standing, Ordered Sheets with Enhanced Mobility

Oligo(p-phenylenevinylenes) (OPVs) with amphiphilic character are synthesized and their self-assembly characteristics studied. Careful studies point at two morphologically different states of assemblies, with one being two dimensional sheets and the other as rolled tubes. This is also the first time that self-assembled sheets are achieved for OPVs. Morphological and photo-physical studies reveal a unique aggregate to aggregate transition between rolled tubes and two dimensional sheets, which is outlined as a more thermodynamic aggregate. The thermodynamic aggregate (2D sheet) is better ordered and consists of chromophores that are better excitonically coupled. The mobilities of these aggregates are also studied for a field effect transistor device and as expected sheets supersede rolled tubes by a couple of orders. More interestingly, the mobility values obtained for the well ordered chromophores in sheets is three orders higher than any other self-assembled OPV previously reported. It is hypothesized that the better interactions enforced by the amphiphilic design and the resultant supramolecular organization is a prime factor for such a remarkable rise in mobilities.