RESUMO
Direct hybridization between the π-orbital of a conjugated molecule and metal electrodes is recognized as a new anchoring strategy to enhance the electrical conductance of single-molecule junctions. The anchor is expected to maintain direct hybridization between the conjugated molecule and the metal electrodes, and control the orientation of the molecule against the metal electrodes. However, fulfilling both requirements is difficult because multipodal anchors aiming at a robust contact with the electrodes often break the π-conjugation, thereby resulting in an inefficient carrier transport. Herein, a new tripodal anchor framework-a 7,7-diphenyl-7H-benzo[6,7]indeno[1,2-b]thiophene (PBIT) derivative-is developed. In this framework, π-conjugation is maintained in the molecular junction, and the tripodal structure makes the molecule stand upright on the metal electrode. Molecular conductance is measured by the break junction technique. A vector-based classification and first-principles transport calculations determine the single-molecule conductance of the tripodal-anchoring structure. The conductance of the PBIT-based molecule is higher than that of the tripodal anchor having sp3 carbon atoms in the carrier transport pathway. These results demonstrate that extending the π-conjugation to the tripodal leg is an effective strategy for enhancing the conductivities of single-molecule junctions.
RESUMO
The electrical properties of a single-molecule junction of spiropyran are investigated through the break junction (BJ) method, and the current-voltage (I-V) characteristics are switched from rectified to symmetric through mechanical stimulus. This phenomenon indicates isomerization from spiropyran to merocyanine. In addition, an increase in the conductance associated with isomerization is observed.
RESUMO
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 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 trans-conformations can affect the electrical properties of oligothiophene frameworks and can potentially be used to control the electronic structure of long oligothiophene molecular wires.