Highly Fluorescent Group 13 Metal Complexes With Cyclic, Aromatic Hydroxamic Acid Ligands

The neutral complexes of two ligands based on the 1-oxo-2-hydroxy-isoquinoline motif with group 13 metals (Al, Ga, In) show bright blue-violet luminescence in organic solvents. The corresponding transition can be attributed to ligand-centered singlet emission, characterized by a small Stokes shifts of only a few nanometers combined with lifetimes in the range between 1 and 3 ns. The fluorescence efficiency is high, with quantum yields of up to 37% in benzene solution. The crystal structure of one of the indium(III) complexes (trigonal space group R3̅, a = b = 13.0384(15) Å, c = 32.870(8) Å, α = β = 90°, γ = 120°, V = 4839.3(14) Å3, Z = 6) shows a six-coordinate geometry around the indium center, which is close to trigonal-prismatic, with a twist angle between the two trigonal faces of 20.7°. Time-dependent density functional theory calculations (Al and Ga, B3LYP/6-31G(d); In, B3LYP/LANL2DZ) of the fac and mer isomers with one of the two ligands indicate that there is no clear preference for either one of the isomeric forms of the metal complexes. In addition, the metal centers do not have a significant influence on the electronic structure nor, as a consequence, on the predominant intraligand optical transitions.