Electron Spin Resonance at the Single‐Molecule Scale

Abstract

Abstract Electron spin resonance (ESR) is a widely employed spectroscopic technique for studying systems with unpaired electron spins, such as molecular radicals. Typically, many billions of spins are required to get a detectable ESR signal, which is subject to extensive ensemble averaging. Downscaling ESR to a single molecule allows studying the signatures of each individual molecule separately, applicable to biomolecules in their native environment, for example. Single‐molecule ESR offers several novel research avenues, such as in quantum sensing with a single molecule. Over the last decades, four different single‐molecule ESR approaches have been developed, which rely on either optically detected magnetic resonance or scanning‐probe microscopy. An introduction into these four approaches including their deployment in pioneering works will be provided.