On the structural and electronic properties of N-heterotriangulene derivatives on metal surfaces: the role of bridging units in tuning molecule-substrate interactions.

Abstract

N-Heterotriangulene (N-HTA) derivatives are promising building blocks for organic electronic devices, owing to their tunable electronic and optical properties. However, the role of the intramolecular bridging moiety in governing molecule-substrate interaction, adsorption geometry, electronic structure and surface mobility on coinage metals has remained largely unexplored. Here, we systematically investigate a series of N-HTA derivatives with different bridging units adsorbed on coinage metal surfaces. Most species adopt a weakly physisorbed state, governed by dispersion interactions through the aromatic π-system, with negligible energy corrugation upon translation and rotation, suggesting weak lateral confinement of the adsorbed molecules on the surface. The sulfur-bridged TPA-S3 stands out as an exception, exhibiting pronounced adsorption energy minima, interfacial charge redistribution, and hybridization between metal d-states and molecular orbitals-indicative of a partially chemisorbed state. These findings establish clear structure-property relationships for adsorption of N-HTA derivatives on coinage metals and provide a rational basis for the design of functional molecular assemblies on surfaces.