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Indium tin oxide (ITO) is an attractive substrate for single-molecule electronics since it is transparent while maintaining electrical conductivity. Although it has been used before as a contacting electrode in single-molecule electrical studies, these studies have been limited to the use of carboxylic acid terminal groups for binding molecular wires to the ITO substrates. There is thus the need to investigate other anchoring groups with potential for binding effectively to ITO. With this aim, we have investigated the single-molecule conductance of a series of eight tolane or “tolane-like” molecular wires with a variety of surface binding groups. We first used gold–molecule–gold junctions to identify promising targets for ITO selectivity. We then assessed the propensity and selectivity of carboxylic acid, cyanoacrylic acid, and pyridinium-squarate to bind to ITO and promote the formation of molecular heterojunctions. We found that pyridinium squarate zwitterions display excellent selectivity for binding to ITO over gold surfaces, with contact resistivity comparable to that of carboxylic acids. These single-molecule experiments are complemented by surface chemical characterization with X-ray photoelectron spectroscopy, quartz crystal microbalance, contact angle determination, and nanolithography using an atomic force miscroscope. Finally, we report the first density-functional theory calculations involving ITO electrodes to model charge transport through ITO–molecule–gold heterojunctions., This work was supported by EPSRC under Grants EP/M005046/1 (Single-Molecule Photo-Spintronics, Liverpool), EP/M029522/1 (Single Molecule Plasmoelectronics, Liverpool), EP/M029204/1 (Single Molecule Plasmoelectronics, Durham), EP/N017188/1, EP/M014452/1, EP/P027156/1, and EP/N03337X/1. Support from the European Commission is provided by the FET Open project 767187 – QuIET. A.V. acknowledges funding from the Royal Society (URF\R1\191241) and thanks Dr. Richard J. Brooke and Prof. Walther Schwarzacher for assistance in developing the Python script used for data processing. I.J.P. would like to thank Vivien Walter for his help with coding some of the data analysis procedures. S.S. thanks the Leverhulme Trust for funding (Early Career Fellowship ECF-2018-375). H.S. thanks UKRI for funding (Future Leaders Fellowship MR/S015329/2). S.M. and P.C. acknowledge financial assistance from Ministerio de Ciencia e Innovación from Spain and fondos FEDER in the framework of projects MAT2016-78257-R and PID2019-105881RB-I00 and support from Gobierno de Aragón through the grant numbers LMP33-18 and E31_20R with European Social Fund (Construyendo Europa desde Aragón).

We studied the electrical conductance of single-molecule junctions formed from molecular wires with four anchor groups. Three tetraphenyl-aza-BODIPYs with four or two thiomethyl anchor groups were synthesized, and their single-molecule conductance was measured using break-junction-STM. Using DFT based calculations these compounds were shown to display a combination of a high and low conductance, depending on the molecule's connectivity in the junction. A scissor correction is employed to obtain the corrected HOMO-LUMO gaps and a tight binding model (TBM) is used to highlight the role of transport through the pi system of the tetraphenyl-aza-BODIPY central unit. The three higher-conductance geometries follow the sequence 3 > 4 > 2, which demonstrates that their conductances are correlated with the number of anchors.