摘要:
In this study we report on the characterization of a series of pentacoordinate aluminum 8-hydroxyquinolines, AlQ(2)X (X = F, Cl, Br), composed of two 8-hydroxyquinoline (8-HQ) groups and one halogen ligand. These were prepared by reacting 8-hydroxyquinoline and dialkylaluminum halide stoichiometrically. The lambda(max)s of absorption and emission were in the range of 385-388 and 515-516 nm, respectively, which were similar to AlQ(3). The molar absorptivity of AlQ(2)X is similar regardless of the X group but emission efficiency of AlQ(2)X is 2-3 fold higher than that of AlQ(3) when X = F or Br, but not when X = Cl. This result can be attributed to decreased quenching of energy due to a less steric environment by reducing quinolinate content. The overall molecular orbital structures and the absorption spectra of AlQ(2)X and AlQ(3) are very similar due to a single quinolinate unit. The value of the potential difference of AlQ(2)Xs between anodic and cathodic waves (Delta E = 3.12 V) is close to the estimated HOMO-LUMO energy gap (the optical band gap, Delta E-optical similar to 1240/lambda(max)), 3.19 eV. Detailed optical and electrochemical properties of AlQ(2)X are discussed. (C) 2011 Elsevier B. V. All rights reserved.