Reversible Quinoid-Diradical Inter-conversion in Single-Molecule Junctions.

Abstract

profound understanding of the reversible regulation mechanisms among multiple redox states of organic molecules is essential for further development of molecular switching devices. In this study, an oligo-aniline derived quinoidal molecular wire was designed and synthesized. The reversible inter-conversion processes between its initial (quinoidal) and protonated (diradical) states were comprehensively investigated with optical measurements, and the EPR experiments confirmed the formation of radical species upon protonation. The single-molecule charge transport properties were then investigated using scanning tunneling microscopy break junction (STM-BJ) technique. It was found that the molecular wire O-ANI can serve as a reversible molecular switching process with around 6.5-fold conductance variation through acid/base adjustments. Additionally, theoretical analyses elucidated the mechanism of the quinoidal-diradical inter-conversion. The enhanced comprehension of the reversible quinoidal-diradical inter-conversion at the single-molecule level provides new strategies for advancing the molecular switching materials and devices.