Observation of biradical spin coupling through hydrogen bonds

TL;DR

This study demonstrates that hydrogen bonds can mediate antiferromagnetic spin coupling between radical pairs of retinoic acid molecules on gold surfaces, with measurable exchange energies, using advanced microscopy and theoretical analysis.

Contribution

It provides direct experimental evidence and theoretical explanation of hydrogen-bond-mediated spin coupling in organic radical pairs.

Findings

Antiferromagnetic coupling observed between radicals.

Exchange energies range from 0.1 to 1.0 meV.

Hydrogen bonds facilitate the spin interaction.

Abstract

Investigation of intermolecular electron spin interaction is of fundamental importance in both science and technology.Here, radical pairs of all-trans retinoic acid molecules on Au(111) are created using an ultra-low temperature scanning tunneling microscope. Antiferromagnetic coupling between two radicals is identified by magnetic-field dependent spectroscopy.The measured exchange energies are from 0.1 to 1.0 meV. The biradical spin coupling is mediated through O-H$\cdots$O hydrogen bonds, as elucidated from analysis combining density functional theory calculation and a modern version of valence bond theory.