Synthesis of novel europium complexes and their photoluminescence properties

Two novel luminescent Eu(III) complexes with the formulas (NIP)Eu(DBM)31 and (ENIP)Eu(DBM)32 (NIP=2-(naphthalen-1-yl)-1H-imidazo [4,5-f] [1,10] phenanthroline, ENIP=1-ethyl-2-(naphthalen-1-yl)-1H-imidazo [4,5-f] [1,10] phenanthroline, DBM= dibenzoylmethanato) were successfully synthesized and characterized by IR and elemental analysis. The UV-vis absorption spectra and photoluminescence properties of the complexes were investigated, and the irradiation at the absorption band between 300–400 nm of europium complexes either in solution or in the solid state led to the emission of a sharp red band at ∼610 nm, a characteristic Eu3+ emission due to the transition of 5D0→7F2. Furthermore, the weak emission bands around 587 and 595 nm attributed to 5D0→7F0 and 5D0→7F1 transition were also displayed in the emission spectra. These results demonstrated that the Eu(III) ion was sensitized efficiently by the ligand and displayed photoluminescence with high intensity, narrow half-peak width, and monochromic light. The excited-state lifetimes of 1 and 2 were in the microsecond time scale, but the photoluminescence quantum yield of 2 (0.03) was two times higher than that of 1 (0.01) which should be attributed to the effect of the ethyl substituting in ENIP.