Synthesis, structure, phase controlled colour tuning of dinuclear Pr(III) and Tb(III) complexes with fluorinated β-diketone and heterocyclic Lewis base as UV light converters

Abstract

Heteroleptic homo dinuclear complexes, [Pr(fod)3(μ-bpp)Pr(fod)3] and [Tb(fod)3(μ-bpp)Tb(fod)3] (fod is the anion of 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione (Hfod) and bpp is 2,3-bis(2-pyridyl)pyrazine) have been synthesized and thoroughly characterized. The 1H NMR spectra of the complexes are consistent with the dinuclear complex formation. In the absorption spectra, the 3P2 ← 3H4, 3P1 + 1I6 ← 3H4 and 1D2 ← 3H4 transitions of Pr(III) complex show considerable sensitivity towards the host medium and prominent stark splitting of these transitions is observed in chloroform and dichloromethane. The effect of phase change on photophysical properties of Pr(III) and Tb(III) complexes is investigated by observing the steady state and time resolved fluorescence spectra of the solid complexes, their solutions and PMMA doped thin hybrid films. Intense emission is observed for the PMMA doped hybrid materials of the complexes. In the case of [Pr(fod)3(μ-bpp)Pr(fod)3] complex doped PMMA, additional emission peaks are observed from the high energy excited states (3P2, 1I6, 3P1 and 3P0), indicating that the PMMA facilitates emission from the higher emitting levels. The emitting colour of Pr(III) complex shows phase dependence with the emission of blue and purple light in the solutions, orange in solid state and in the case of PMMA doped hybrid films at a doping concentration of 5 % and 10 %, the Commission Internationale de l'Eclairage (CIE) colour coordinates are in the white region x = 0.351, y = 0.377 and light blue region x = 0.313, y = 0.319, respectively. Intense green light emission is observed for the terbium complex in all media. The semiempirical theoretical tool of Sparkle/PM7 has been used for obtaining the geometry of the complexes.