Synthesis and optical properties of a gallium(III) bis(8-quinolyl)amide complex

Complexes of main group elements represent a promising but underexplored approach in the development of earth-abundant alternatives to precious metal complex photosensitizers. We herein report the synthesis, structural characterization and optical spectroscopy, supported by DFT and TD-DFT calculations, of a cationic gallium(III) complex, [Ga(BQA)₂]PF₆, expanding the relatively underexplored field of luminophores based on main group elements. Although [Ga(BQA)₂]PF₆ exhibits favorable ligand-based CT absorptions in the visible spectrum, it is only weakly fluorescent and apparently does not undergo intersystem crossing to access the triplet excited state manifold. Computational studies suggest that these unfavorable excited state properties arise from a large singlet-triplet splitting, and accessibility to the central atom by solvent. Our results reinforce recent reports on the need to sterically protect the central element to obtain photoactive earth-abundant metal complexes, extending the concept to main-group complexes where the central element is not electronically involved in the excited state.