Effects of cis–trans Conformation between Thiophene Rings on Conductance of Oligothiophenes

Oligothiophenes have been established as important πconjugated frameworks in organic electronics and molecular electronics.
Although oligothiophenes possess the rotational flexibility of thiophene rings,
the effects of cis−trans conformations on their electrical conductance have not
been investigated yet. To investigate the effects of cis−trans conformations
between thiophene rings on the conductance of oligothiophenes, we performed
first-principles transport calculations. The conductance of the cis-oligothiophene was calculated to be higher than that of trans-oligothiophene, because
the highest occupied molecular orbital was closer to the Fermi level of the gold
electrode in the cis isomer than the trans 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 cis−trans conformations. This study demonstrates that cis- and transconformations can affect the electrical properties of oligothiophene frameworks and can potentially be used to control the
electronic structure of long oligothiophene molecular wires.