Probing Ultrastrong Through-Space Electronic Coupling in Donor-Acceptor Systems at the Single-Molecule Level

Through-space donor-acceptor (TSDA) interactions have recently emerged as a new paradigm for charge transfer and transport in organic semiconductors. However, the intrinsic D-A coupling strength and charge transport properties at the molecular level remain unexplored in comparison to established through-bond channels. Here, we employ a variety of single-molecule techniques to directly probe TSDA charge transport characteristics in a series of strategically designed face-to-face D-A systems, revealing that optimized spatial proximity and electronic complementarity yield conductance values up to ∼0.19 G₀, comparable to the best-performing through-bond molecular wires. Flicker noise analysis, current-voltage characterization, and mechanical stretching measurements confirm robust electronic and mechanical coupling, while theoretical calculations and photophysical studies identify through-space transmission as the prevailing mechanism. These findings establish non-covalent TSDA coupling as an efficient charge-transport channel and provide new molecular-level insight for the design of D-A systems in organic electronics and optoelectronics.