2-Iminophenol ligands and their Boron Complexes: Coordination-Controlled Photophysical Duality

This Viewpoint aims at providing a concise overview of the photophysical properties of recent examples of 2-iminophenol ligands, sometimes referred to as anils and their corresponding boron complexes, boranils, formed upon boron coordination in the N'̂'O chelating site. Due to the presence of a strong internal hydrogen bond, anil derivatives are prone to display excited-state intramolecular proton transfer (ESIPT) processes, which can induce thermochromic and photochromic properties, due to the presence of an isomerizable imine moiety. While these motions of the molecular scaffold of anils are inevitably detrimental for solution-state fluorescence, aggregation-induced emission behavior has been evidenced in confined media, leading to fluorescent nanoaggregates. Coordination to trivalent boron ion drastically modifies the optical properties, by rigidifying the molecular backbones, enabling environment-sensitive intense fluorescence in both solution and solid states.