Tuning of the excitation wavelength from UV to visible region in Eu3+-β-diketonate complexes: Comparison of theoretical and experimental photophysical properties

A novel class of efficient visible light sensitized antenna complexes of Eu(3+) based on the use of a series of highly conjugated β-diketonates, namely, 1-(1-phenyl)-3-(2-fluoryl) propanedione, 1-(2-naphthyl)-3-(2-fluoryl)propanedione, 1-(4-biphenyl)-3-(2-fluoryl) propanedione, and 2,2'-bis(di-p-tolylphosphino)-1,1'-binaphthyl oxide as an ancillary ligand has been designed, synthesized, characterized and their photophysical properties investigated. The coordination geometries of the typical Eu(3+) complexes were calculated using the Sparkle/PM3 model. Photophysical properties of europium complexes benefit from adequate protection of the metal by the rigid phosphine oxide ligand against non-radiative deactivation and efficient ligand-to-metal energy transfer exceeding 50% as compared to precursor samples. The replacement of the phenyl group with the naphthyl or biphenyl groups in the 3-position of the fluoryl based β-diketonate ligand remarkably extends the excitation window of the corresponding Eu(3+) complexes towards the visible region (up to 500 nm). The highly conjugated β-diketonate ligands sensitize efficiently the luminescence of Eu(3+) ions with quantum yields ranging from 19 to 43 % in the solid state, which is among the highest reported for a visible sensitized Eu(3+)complex. The theoretical quantum efficiencies from the Sparkle/PM3 structures are in good agreement with the experimental values, clearly attesting to the efficacy of the theoretical models.