Substituted Aluminum and Zinc Quinolates with Blue-Shifted Absorbance/Luminescence Bands:  Synthesis and Spectroscopic, Photoluminescence, and Electroluminescence Characterization

Two novel lumophores based on aluminum and zinc metallo-8-hydroxyquinolates have been prepared as electroluminescent materials, and their absorbance, photoluminescence, and electroluminescence properties compared with unsubstituted versions of these same complexes. 8-Hydroxy-5-piperidinylquinolinesulfonamide (1) was synthesized in order to add an electron-withdrawing substituent at the 5-position in 8-hydroxyquinoline, increasing the solubility of the corresponding metal quinolate complexes in nonpolar solvents, and producing a blue-shift in the emission wavelength maximum, relative to complexes formed from the unsubstituted compound. The aluminum complex (Al(QS)3) and the zinc complex (Zn(QS)2) of 1 were compared with the aluminum and zinc complexes of unsubstituted 8-hydroxyquinoline (AlQ3 and ZnQ2), both as solutions and as pure thin films, or as poly(N-vinylcarbazole) (PVK) thin films doped with the metal quinolates. Ultraviolet photoelectron spectroscopy data are presented to assist in estimating the energies of the highest occupied molecular orbitals (HOMO) of AlQ3, ZnQ2, Al(QS)3, and Zn(QS)2. Electroluminescence data shows that ITO/Al(QS)3−PVK/aluminum and ITO/Zn(QS)2−PVK/aluminum devices exhibit good diode-like electrical behavior. Electroluminescence spectra mimic the photoluminescence spectra for all complexes.