Ditriphenylenothiophene butterfly-shape liquid crystals. The influence of polyarene core topology on self-organization, fluorescence and photoconductivity.

Two series of regio-isomeric butterfly-shaped liquid crystalline systems, based on a ditriphenylenothiophene core (α/β-DTPT) equipped with eight peripheral long alkoxy chains, were synthesized in two steps by the Suzuki-Miyaura cross-coupling/Scholl cyclo-dehydrogenation reactions tandem from appropriate precursors. The influence of the core topology (i.e. positional isomerism) on the mesomorphism, gelling self-assembly, absorption and luminescence, and charge-transport properties of both sets of isomers was investigated and compared. The six fused π-conjugated molecules systematically display columnar hexagonal (Colhex) mesophases with β-fused ditriphenylenothiophene compounds (DTPTBn) showing more extended mesophase ranges and higher phase transition temperatures than their isomeric α-counterparts (DTPTAn). All ditriphenylenothiophenes also show strong aggregation behavior in organic solvents, and, in addition, good organic gelling abilities were found for the β-isomers. Interestingly too, high hole mobility rates greater than 10^-3 cm2 V^-1 s^-1 were measured for the β-isomers, which were about 10 times higher than those of the α-counterparts. Modeling of the molecular structures combined with DFT calculations showed that the β-isomers possess flatter and more extended π-conjugated cores than the slightly distorted α-isomers, and consequently were more prone to optimize π-π intermolecular interactions, in agreement with the high-temperature mesophases and high charge carrier mobilities observed for these isomers. Finally, both sets of compounds emit blue-purple light in solution and the emission is substantially redshifted when organized in films. DFT calculations of the HOMO-LUMO energy levels were also consistent with the optical measurements. This original molecular design and straightforward synthesis combination provides an efficient way to obtain novel π-extended organic, potentially semiconductor materials for further electronic device investigations. [ABSTRACT FROM AUTHOR]