Synthesis, Characterization And Fluorescence Properties Of The New Single-substituted Beta-diketone Pyridine Derivatives And Its Rare Earth Complexes

Luminescence lanthanide complexes have been used as catalysts, luminescent labels and gene probes,due to their peculiar properties: redox-active,,high quantum yields of the emission and large Stokes shift.The lanthanide complexes with-β-diketone-kind ligands be of high ability of UV-vis exicitation fluorescence,and the ligands make rare earth ions emit strong characteristic fluorescence by organic ligands' strong UV-vis absorbance and efficienct energy-transfer between the ligands and lanthanide ions.Therefore,designing and synthesizing novel pyridine-2,6-dicarboxylic derivatives,especiallyβ-diketone kind of compounds and their derivatives,is of great importance for searching and developing novel sensitizers for rare earth ions with pyridine-2,6-dicarboxylic acid as a starting material,and designing the structures of ligands is also a key point to discover new fluorescent sensitizers of rare-earth ions.β-Diketones are well known to have two forms,that is enol and keto forms.One of the most interesting properties is the conversion between the two forms,which was termed as keto-enol tautomerism.The enol form of pyridine mono-β-diketones are more stable than the keto form, and the tautomerism can be affected by various factors such as solvent polarity,substitution groups,PH values,and UV light irradiation.β-diketones possess a broad spectrum of useful and sometimes unique chemical properties,which make them extremely attractive as intermediates and are used widely in the chemistry of metallocomplexes.One novel pyridine mono-β-diketone named methyl 6-benzoylacetyl-2-pyridinecarboxylate(MBAP) were synthesized starting from pyridine-2,6-dicarboxylic through ester reaction and Claisen reaction.Condition of the Claisen reaction was optimized.Furthermore,in order to find and develope new organic fluorescence sensitizers,another list of novel mono-β-diketones: 6-benzoylacetyl-2-pyridinecarboxylic acid(BAPA),methyl 6-biphenyl acetyl-2-pyridinecarboxylate(MBP) and 6-biphenyl acetyl-2-pyridinecarboxylic acid(BAA) were synthesized successfully according to the design of molecule and the characteristic of organic fluorescence sensitizers.Besides,the lanthanide complexes of the four ligands were prepared. The structucres of complexes were deduced by EA and IR.Photoluminescence measurements indicate that the four ligands above can sensitize Eu(â…¢) and Tb(â…¢) ions to some extent;The ligand which has larger conjugate system is a better fluorescence sensitizer than the smaller conjugate system ligands;the effective energy transfer from the organic ligands(BAPA and BAA) to the central Tb(â…¢) ions occurs in the complexes,besides,strong and characteristic green emission appears due to the ⁵D_4- ⁷F₅ transitions of the 4f electrons of the central Tb(â…¢) ions. The synthesized Tb(â…¢) complexes are excellent green-emitters with electron-transporting groups,and would be considered as a candidate material for fabrication of organic light-emitting devices(OLEDs).