Redox-Driven Antiaromaticity Enables Multistate Conductance in 1D Topological Insulators

Conjugated molecules with diradical character have emerged as promising building blocks for high-conductance single-molecule electronics because of their behavior as 1D topological insulators. However, the impact of antiaromaticity on these radical-based edge states has not been explored. Here, we introduce thiophene-based molecular wires that exhibit intrinsic diradical character in their ground state under ambient conditions and systematically investigate how their conductance responds to changes in aromaticity upon the oxidation of fluorene-based flanking moieties. Using scanning tunneling microscopy-based break junction (STM-BJ) techniques, we show that the conductance increases with molecular length in the neutral state, supporting one-dimensional topological behavior. We further examine the effect of oxidation on conductance through three complementary methods, revealing substantial conductance enhancements that we attribute to an increase in the antiaromatic character of the wires. Together, these findings establish a rational design strategy for highly conducting, electrochemically switchable molecular junctions, with implications for single-molecule electronics.