Synthesis and characterization of monomeric, oligomeric, and polymeric aluminum 8-hydroxyquinolines

We report the synthesis and characterization of monomeric, oligomeric, and polymeric aluminum 8-hydroxyquinolines. The new structures of aluminum quinolate are contrived for expanding the application of AlQ(3) in the area of solution process by modifying AlO3 structure for improving solution processibility and crystallization resistance. Oligomeric aluminum 8-hydroxyquinoline (OALQ) was obtained using methylaluminoxane (MAO) and 8-hydroxyquinoline (8-HQ). Polymeric aluminum 8-hydroxyquinoline (PALQ) consists of 8-HQ and a polymeric Al-O backbone, simply prepared by stoichiometrically reacting 8-hydroxyquinoline, pentaerythritol propoxylate, and triethyl aluminum in the presence of chloroform. The absorption and emission spectra of OALQ and PALQ bear a clear resemblance to those of AlQ(3), and the molecular orbitals of OALQ and PALQ are virtually identical to those of AlQ(3). In the SEM images of AlQ(3) and OALQ, cylindrical rods of >100 mu m in length and 5-10 mu m in diameter for AlQ(3) and 20-100 mu m in length and 1-5 mu m in diameter for OALQ were observed, respectively, The size of the cylindrical rods of OALQ decreased compared with that of AlQ(3). As for the image of PALQ, an amorphous phase with bulge spots (ca. 5 mu m) was observed. These microscope data correspond well to the X-ray powder pattern results. The chemical shifts (31.1, 57.0 ppm) and peak broadness of 27Al NMR of AlQ(3) and its DFT calculation results present that mer- and fac-AlQ(3) appear in equilibrium through pentacoordinated intermediates. With the combination of DFT optimization and NMR calculation, models of OALQ and PALQ, hexa-, penta-, and tetracoordinated structures, were proposed, which exist in polymeric Al-O backbone and with inter- and intracoordination of Al-O bonds.