The synthesis of dendritic β-diketonato ligands and their europium complexes

Two kinds of dendritic beta-diketonato ligands (1a,1b and 2a-2c) which contain a dibenzoylmethane (dbm) core and poly(aryl ether) dendron, have been synthesized by a convergent strategy. The attachment point of the dendron to dbm is found to play an important role in the preparation of europium(III) complexes. Reaction of the beta-diketonato ligands 2a-2c, which bear a dendron substituted on the phenyl group of dbm, with EuCl3 center dot 6H(2)O gives the first- to third-generation dendritic europium(III) complexes in good yields, while europium(III) complexes could not be formed with beta-diketonato ligands 1a and 1b, which have dendrons attached to the 2-position of dbm. The resulting dendritic europium(III) complexes were characterized by elemental analysis and MALDI-TOF mass spectrometry, and further confirmed by luminescence measurements. Incorporation of 1,10-phenanthroline as the second ligand in these dendritic (beta-diketonato)europium(III) complexes gives new dendritic europium(III) complexes with enhanced luminescence intensity. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheirn, Germany, 2007).