Blue Luminescent Organoaluminum Compounds: Al(CH3)2(dpa), Al2(CH3)5(dpa)2, Al4(O)2(CH3)6(dpa)2, and Al(pfap)3, dpa = Deprotonated Di-2-pyridylamine, pfap = Deprotonated 2-Pentafluoroanilinopyridine

The reactions of Al(CH 3 ) 3 with di-2-pyridylamine (dpaH) yielded a mononuclear zwitterion complex, Al(CH 3 ) 2 (dpa) ( 1 ), a dinuclear complex, Al 2 (CH 3 ) 5 (dpa) ( 2 ), and a tetranuclear complex, Al 4 (O) 2 (CH 3 ) 6 (dpa) 2 ( 3 ), depending on the stoichiometry and conditions of the reactions. The crystal structures of all three compounds were determined by single-crystal X-ray diffraction analyses. All three compounds emit an intense blue color in solution and the solid state at λ max = 475, 445, and 450 nm, respectively, when irradiated by an UV light. Molecular orbital calculations using ab initio methods (Gaussian 94) on dpa, dpaH, and compound 1 were performed which revealed that the aluminum ion in compounds 1 − 3 plays a key role in stabilizing the complexes and promoting the blue luminescence. The reaction of Al(CH 3 ) 3 with 2-pentafluoroanilinopyridine (pfapH) resulted in the formation of a mononuclear octahedral complex, Al(pfap) 3 ( 4 ). Variable-temperature and COSY 1 H NMR established that compound 4 is highly fluxional in solution due to a rapid interconversion of mer and fac isomers, with the mer isomer dominating at low temperature. The structure of the fac isomer of 4 was determined by X-ray diffraction. Compound 4 emits at λ max = 409 nm when irradiated by an UV light.