The 5,7-diphenyl-8-hydroxyquinoline (5,7-Phq) ligand was successfully synthesized via Suzuki cross-coupling reaction before the synthesis of the tris(5,7-diphenyl-8- quinolinolato) metal(III) [M(5,7-Phq)3; M = Al, Ga, or In] complexes. In addition, tris(5,7- dibromo-8-quinolinolato) metal(III), M(5,7-Brq)3 complexes were successfully synthesized. All the synthesized complexes were characterized using a variety of analytical techniques. The molecular structures of the 5,7-Phq ligand and the In(5,7-Phq)3 complex were confirmed using single-crystal X-ray crystallography. The X-ray structure of the In complex indicates that the three 5,7-Phq ligands are arranged in a meridional configuration about the central metal In3+ ion, and the complex is distorted from ideal octahedral geometry. The effect of the central metal ion on the structural, photoluminescence, thermal, and electrochemical properties of the synthesized complexes has been investigated. Moreover, the influence of the substituents (phenyl group or bromine atom) on the photophysical properties of the complexes was investigated. It is found that the electronic nature of the substituent is the main reason for the redshift or blueshift of the maximum wavelength of UV-visible absorption and emission compared to that of the parent unsubstituted Mq3. The FT-IR spectroscopic analysis confirms the formation of the complexes through the existence of the stretching vibrations of the M‒ O, and M‒N bonds in the spectra. The TGA and DSC results show that the complexes are thermally stable, degrade in several stages, and decompose at higher temperatures than the unsubstituted Mq3 compounds. The decrease in the relative fluorescence efficiency from Al to Ga and In complexes is attributed to the heavy atom effect. The band gap energies (𝐸𝑔 𝑜𝑝𝑡) determined from the Tauc plot method are smaller in both series of complexes than those determined from cyclic voltammetry. The structural analysis of the obtained M(5,7-Brq)3 nanomaterials using the physical vapor deposition method shows that the products are flower and grass-like crystals dominated by nanotubes or nanosheets, while the obtained M(5,7-Phq)3 nanomaterials using the surfactant-assisted microemulsion method, the anti-solvent diffusion method, and the extremely facile solution method are spherical-like or rod-like crystals. The difference in the nanomaterials produced by different fabrication methods may be related to the different growth mechanisms. The FT-IR spectra reveal that no significant bonding change occurs in molecules after the nanofabrication process. The PL spectra show that the PL intensity of M(5,7-Phq)3 microstructures is significantly higher than that of bulk material thin films due to the high crystallinity and large surface area. The PL decay curves show that the microstructured M(5,7-Phq)3 thin films have a lower average lifetime than those of bulk material thin films. The results show that the decays fit a bi-exponential model with two lifetimes (τ1 and τ2). The PL microscopy images of the synthesized micro- and nanostructures confirm the green luminescence of the products when illuminated under light (Ex = 490-500 nm, YFPHQ filter) and show optical waveguiding property. These micro- and nanostructures are promising materials for optoelectronic nanodevices.