Synthesis and characterization of tris(5,7-diphenyl-8-quinolinolato) aluminum(III), gallium(III), and indium(III) complexes: Effect of metal ions on the structural, photoluminescence, thermal and electrochemical properties

The 5,7-diphenyl-8-hydroxyquinoline (5,7-Phq) organic ligand was successfully synthesized via Suzuki cross-coupling reaction followed by synthesis of the novel organometallic complexes tris(5,7-diphenyl-8-quinolinolato) metal(III) [M(5,7-Phq)3; M = Al, Ga, or In]. All synthesized M(5,7-Phq)3 complexes were characterized using various analytical techniques. The molecular structure of In(5,7-Phq)3 was confirmed using single-crystal X-ray crystallography, which indicates that the three 5,7-Phq ligands are arranged in a meridional configuration around the central metal In3 + ion, and the complex is distorted from ideal octahedral geometry. There are no significant differences in the UV-visible absorption spectra of the com-plexes in the tetrahydrofuran (THF) solution and they are all red-shifted compared to that of the parent Mq3 ( M = Al3 +, Ga3 +, In3 +) compounds. The broad absorption band at around 417 nm is assignable to the pi-pi* transition. The synthesized M(5,7-Phq)3 complexes in the solution and in the solid-state show red -shifted emission compared to that of the parent unsubstituted compounds. The decrease in the solution and the solid-state emission efficiency and intensity from Al to In complexes is attributed to the heavy atom effect. Despite the electrochemical band gap energies (Egec ) of the complexes determined from cyclic voltammetry being in good agreement with those reported for the unsubstituted complexes, the optical band gap energies (Eopt g ) determined from the Tauc plot method are smaller. The results of the fluores-cence decay of the M(5,7-Phq)3 complexes both in CHCl3 solution and in solid state at 298 K show that the decays fit a bi-exponential model with two lifetimes (tau 1 and tau 2). The average values of fluorescence lifetimes of the complexes in CHCl3 are significantly greater than those of the complexes in the solid state.(c) 2023 Elsevier B.V. All rights reserved.

Automated summary

The 5,7-diphenyl-8-hydroxyquinoline (5,7-Phq) ligand was synthesized and used to form novel organometallic complexes tris(5,7-diphenyl-8-quinolinolato) metal(III) [M(5,7-Phq)3; M = Al, Ga, or In] through Suzuki cross-coupling reaction. The structures of the complexes were characterized and their optical properties were investigated. The synthesized complexes exhibited red-shifted absorption and emission compared to the parent compounds, and the emission efficiency decreased with increasing atomic weight of the metal ions.