Anchoring-Group-Controlled Self-Assembly and Charge Transport in Antiaromatic Molecular Systems

Abstract

Antiaromatic π-systems with 4n electrons are predicted to exhibit narrow frontier orbital gaps and enhanced charge-transport characteristics, but experimental studies at the single-molecule level have been limited by their intrinsic instability. Here, we investigate a chemically stable Ni(II) norcorrole (Ni(nor)) functionalized with thiol, pyridyl, and carboxyl anchoring groups using scanning tunnelling microscopy (STM) and single-molecule break-junction (BJ) measurements. STM imaging revealed distinct anchoring-group-dependent assemblies on the surface: thiol derivatives formed upright self-assembled monolayers, carboxylic acid derivatives produced one-dimensional supramolecular chains stabilised by intermolecular hydrogen bonding, whereas pyridyl derivatives did not form ordered structures on Au(111). These anchoring-dependent assemblies modulate molecular coupling and charge-transport efficiency, yielding conductance values of ~10⁻³ G₀ for thiol, ~10⁻⁴ G₀ for pyridyl, and ~10⁻⁶ G₀ for carboxyl anchoring. Together, these results demonstrate a strategy for device design that harnesses antiaromaticity while controlling self-assembly and charge transport through anchoring chemistry, providing design principles for functional molecular electronic components.