Observation of Biradical Spin Coupling through Hydrogen Bonds
Yang He, Na Li, Ivano E. Castelli, Ruoning Li, Yajie Zhang, Xue Zhang, Chao Li, Bing‐Wu Wang, Song Gao, Lian‐Mao Peng, Shimin Hou, Ziyong Shen, Jing‐Tao Lü, Kai Wu, Per Hedegård, Yongfeng Wang
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 ultralow 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⋯O hydrogen bonds, as elucidated from analysis combining density functional theory calculation and a modern version of valence bond theory.