Long-Range Surface-Assisted Molecule-Molecule Hybridization

TL;DR

This study reveals how surface-mediated hybridization between magnesium phthalocyanines and a silver surface can extend over long distances, significantly altering their electronic structures and symmetries, with implications for molecule-based electronics.

Contribution

It demonstrates a long-range surface-assisted hybridization mechanism that modifies molecular electronic properties over distances greater than 3 nm.

Findings

Isolated MgPc molecules show degenerate LUMOs with four-fold symmetry.

Proximate MgPc molecules exhibit lifted LUMO degeneracy and reduced symmetry.

Hybridization involves molecule-surface and intermolecular interactions extending beyond 3 nm.

Abstract

Metalated phthalocyanines (Pc's) are robust and versatile molecular complexes, whose properties can be tuned by changing their functional groups and central metal atom. The electronic structure of magnesium Pc (MgPc) - structurally and electronically similar to chlorophyll - adsorbed on the Ag(100) surface is investigated by low-temperature scanning tunneling microscopy (STM) and spectroscopy (STS), non-contact atomic force microscopy (ncAFM) and density functional theory (DFT). Single, isolated MgPc's exhibit a flat, four-fold rotationally symmetric morphology, with doubly degenerate, partially populated (due to surface-to-molecule electron transfer) lowest unoccupied molecular orbitals (LUMOs). In contrast, MgPc's with neighbouring molecules in proximity undergo a lift of LUMOs degeneracy, with a near-Fermi local density of states with reduced two-fold rotational symmetry, indicative of a long-range attractive intermolecular interaction. The latter is assigned to a surface-mediated two-step electronic hybridization process. First, LUMOs interact with Ag(100) conduction electrons, forming hybrid molecule-surface orbitals with enhanced spatial extension. Then, these delocalized molecule-surface states further hybridize with those of neighbouring molecules. This work highlights how the electronic structure of molecular adsorbates - including orbital degeneracies and symmetries - can be significantly altered via surface-mediated intermolecular hybridization, over extended distances (beyond 3 nm), having important implications for prospects of molecule-based solid-state technologies.