The self-assembly of amphiphilic oligothiophenes: hydrogen bonding and poly(glutamate) complexation

The self-organization behavior of an amphiphilic sexithiophene bearing amide functionalities is studied and compared to that of a deriv. bearing an ester group at the same position. The introduction of hydrogen-bond interactions in assemblies of these pi-conjugated oligomers is found to affect the mol. organization both in protic media and in thin deposits on mica. The amphiphilic 2,2';5',2'';5'',2''';5''',2''''; 5'''',2'''''-sexithiophene-5,5'''''-dicarboxylic acid bis[(4,7,10,13,16-pentaoxaheptadecyl)amide] forms assemblies in n-butanol and water and partially aggregates in toluene. Spectroscopy reveals that the presence of a hydrogen-bonding moiety increases the thermal stability of the assemblies in n-butanol and even more in water soln. On mica surfaces, the formation of rod-like one-dimensional nano-structures is obsd. after deposition from toluene solns. In addn., transmission electron microscopy in combination with selected area electron diffraction shows that in water plate-like structures are formed built from parallel oriented stacks, with a pi-pi distance of 3.5 .ANG.. Comparison of these data to mol. modeling and quantum chem. calcns. is used to better understand the influence of the amide group on the stacking of these compds. The introduction of these H-bonding interactions leads to denser and more stable stacks. Furthermore, we show that a deriv. of the amide compd., bearing terminal ammonium groups, forms a complex with chiral polyanions in aq. media such that the sexithiophene segments are stacked in a meta-stable helical fashion with preferred handedness. We obsd. that poly(glutamate) and DNA generate a chiral sexithiophene assembly. In time the induced chirality disappears, which is explained by the meta-stability of the kinetically formed adduct. This constitutes one step forward towards the controlled formation of functional multi-component systems in aq. soln. [on SciFinder (R)