Influence of Peripheral Alkyl Groups on Junction Configurations in Single-Molecule Electronics

The addition of a lateral alkyl chain is a well-known strategy to reduce π-stacked ensembles of molecules in solution, with the intention to minimize the interactions between the molecules' backbones. In this paper, we study whether this concept generalizes to single-molecule junctions by using a combination of mechanically controllable break junction (MCBJ) measurements and clustering-based data analysis with two small series of model compounds decorated with various bulky groups. The systematic study suggests that introducing alkyl side chains also favors the formation of electrode-molecule configurations that are not observed in their absence, thereby inducing broadening of the conductance peak in the one-dimensional histograms. Thus, the introduction of alkyl chains in aromatic compounds for molecular electronics must be carefully designed and optimized for the specific purpose, balancing between increased solubility and the possibility of additional junction configurations.