Photochemistry and photophysics of metal-metal bonded dinuclear transition metal complexes

Transition metal complexes (TMCs) play a crucial role in a wide range of light-mediated processes across chemical, material, and physical systems, attracting significant attention from both experimental and theoretical perspectives. Within this realm, there has been extensive exploration into the photochemistry and photophysics of dinuclear TMCs featuring metal-metal bonded interactions in electronically ground or excited states, owing to their well-defined electronic and vibrational configurations. This review begins with a general overview of the family of quadruple-bonded dinuclear TMCs, aiming to delineate the key similarities and differences in photophysical properties compared to mononuclear TMCs. Various case studies covering emerging research themes are outlined, encompassing electronic structure, luminescence emission, and the excited state dynamics associated with metal -to-ligand charge transfer (MLCT). Additionally, special attention is given to aspects related to the fundamental mechanism of vibronic coupling that underpins interstate conservation in some representative diplatinum complexes. Finally, we offer a brief outlook on future research directions, with a particular emphasis on investigating vibronic coupling to shed light on the absence of MLCT emission often observed in quadruple-bonded dinuclear TMCs. This perspective aims to provide insights into molecular design principles for optimizing photophysical properties and enhancing their practical applicability.