Triarylamines (TAAs) are widely used as outstanding donor and charge transport materials. Their pronounced donor character is expressed through their reversible electrochemistry of one one-electron oxidation per TAA unit leading to the formation of stable radical cations, a rarity for purely organic molecules. This renders them not only ideal candidates to study the phenomenon of mixed-valency but the presence of delocalized polarons makes them particularly interesting as future materials for molecular electronics or spintronics. Here we present the results of single-molecule conductance measurements on a series of oligo-triarylamines containing up to five triphenylamine subunits using the scanning tunneling microscope-based break junction (STM-BJ) technique. Special attention is paid to the conductance response of the parent neutral forms in the high-bias/resonant transport regime as well as the transport characteristics of the various accessible radical cationic species. The extent of charge and spin delocalization in solution is gauged through UV/Vis/NIR-spectroelectrochemistry as well as EPR spectroscopy and juxtaposed with the STM-BJ data to reveal new insight into their mechanism of charge-transport.

Charge transport through redox-active oligo-triarylamine molecular junctions

ACS Fall 2021

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