Effects of - Conformation between Thiophene Rings on Conductance of Oligothiophenes.

Oligothiophenes have been established as important π-conjugated frameworks in organic electronics and molecular electronics. Although oligothiophenes possess the rotational flexibility of thiophene rings, the effects of - conformations on their electrical conductance have not been investigated yet. To investigate the effects of - conformations between thiophene rings on the conductance of oligothiophenes, we performed first-principles transport calculations. The conductance of the oligothiophene was calculated to be higher than that of -oligothiophene, because the highest occupied molecular orbital was closer to the Fermi level of the gold electrode in the isomer than the isomer. This prediction was confirmed through mechanically controllable break junction measurements and fitting of the current-voltage characteristics for the newly synthesized, insulated oligothiophenes with controlled - conformations. This study demonstrates that - and -conformations can affect the electrical properties of oligothiophene frameworks and can potentially be used to control the electronic structure of long oligothiophene molecular wires.