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 reflect variations in metal–molecule coupling and orbital alignment, leading to systematic modulation of charge-transport efficiency. Together, these results highlight anchoring-group chemistry as the primary design parameter governing metal–molecule coupling, surface assembly, and charge transport in molecular junctions. In this context, the antiaromatic Ni(II) norcorrole core serves as an electronic platform that provides intrinsically high conductance relative to aromatic analogues, while the anchoring groups determine the extent of conductance modulation and assembly behaviour. This distinction clarifies that antiaromaticity establishes a favourable electronic baseline, rather than acting as a unique driver of anchoring-dependent trends, and underscores the importance of anchoring chemistry for molecular device design.