Physical properties of transition metal complexes in single‐molecule junctions

Abstract Transition metal possesses a unique d‐orbital electronic structure, which imparts a diverse range of physical and chemical properties. These properties render them significant in fields such as chemistry and materials science. The distinctive optical, electrical, and magnetic properties of these complexes can be attributed to the variations in the quantity of d‐orbital electrons, thereby influencing their spin and orbital characteristics. The d‐orbitals facilitate the formation of stable multidirectional bonds with ligands, resulting in a variety of geometric structures and rich coordination chemistry. These interactions result in variations in energy levels, thereby producing diverse electrical properties, including low attenuation coefficients, high rectification ratios, and unique multi‐channel transmission. Moreover, the unpaired electrons in the d‐orbitals can give rise to diverse magnetic behaviors, leading to magnetic effects such as spin‐related interfaces, switches, and magnetoresistance. This paves the way for extensive possibilities in the design and application of single‐molecule devices. This review elaborates on single‐molecule physical properties of transition metal complexes, including length attenuation, rectification, multi‐channel transmission, thermoelectric effect, and spin regulation, which are vital for the functionalization and regulation of molecular electronics. In addition, this review also explores the correlation between these physical properties and the electronic structure of transition metals, discussing the broad prospects of transition metal complexes in the fields of nanoelectronics, optoelectronics, and quantum technology.