Copper(I) complexes with thermal activated delayed fluorescence (TADF) have attracted considerable attention for the development of emissive materials in organic light-emitting devices. However, many emissive Cu I complexes are cationic emitters and cannot be vacuum-sublimed, a process used for device fabrication. This has limited their applications in devices. In this work we have developed a series of emissive charge-There is a growing interest in the development of earth-abundant luminescent transition-metal complexes for a wide range of applications, including dye-sensitized solar cells, [1] oxygen sensors, [2] and organic light-emitting devices (OLEDs). [3] Although many luminescent precious-metal complexes have been demonstrated to show promising applications, [4] the exploration of earth-abundant luminescent transition-metal complexes for related applications would be highly desirable because of their sustainability. The much-less-explored first-row luminescent transition-metal complexes in comparison with second-and third-row complexes can be attributed to the presence of the low-lying nonradiative deactivating ligand-field excited state and nonradiative ligand reorganization deactivation processes, which could quench the emissive excited states.Copper(I) complexes have received considerable attention because of their closed-shell electronic configurations and their relatively small singlet-triplet splitting, which lead to their welldocumented thermal-activated delayed fluorescence (TADF). [5] Emission materials with TADF properties are of particular interest for OLED emissive materials as these materials are capable of harvesting both singlet and triplet excitons, which may improve the overall efficiency of the devices. Luminescent Cu I diimine complexes, such as those with sterically bulky ligands, for example, 2,9-dimethyl-1,10-phenanthroline (Me 2 phen), are an important class of luminescent Cu I complexes. The presence of sterically bulky substituents is essential for maintaining the emissive nature of these complexes as they can significantly [a] ] through the incorporation of a strong π-accepting anionic isocyanoborate ligand. All the complexes have been structurally characterized and their photophysical properties have been studied.