Mesophase Tuning in Discotic Dimers π-Conjugated Ionic Liquid Crystals through Supramolecular Interactions and the Thermal History

pi-Conjugated ionic liquid crystals are a very interesting class of salts where the coupling of ionic and electronic functions with the anisotropy typical of liquid crystals may give rise to materials with advanced bulk properties. Defect-free active thin films obtainable by simple mesophase self-assembly of these materials may be exploited in a number of different electro-optical devices. Here we show that the rich mesomorphism of the thienoviologen salts 4,4'-(2,2'-bithiophene-5,5'-diyl)bis(1-alkylpyridinium), which includes smectic, columnar, and nematic phases, significantly depends on the counterion type and the length of the promesogenic alkyl chains, highlighting the delicate balance among ion/ion, pi-pi stacking, and hydrophobic interactions. These salts show notable fluorescence properties in the bulk, strongly dependent on the self-assembling.