Ultrafast dynamics and relaxation pathways in Eu(III) complexes with fluorinated β–diketonate ligands

Abstract

A series of novel β-diketonate Eu3+ complexes with minor variations in the chemical structure of the diketone ligand were systematically studied. Six Eu3+ coordination compounds based on β-diketones, bearing linear perfluorinated substituents of various length (C1, C2, C3 and C6) and fixed pyrazole moiety were obtained. In addition, two water molecules, 1,10-phenanthroline or 4,7-diphenyl-1,10-phenanthroline as an ancillary ligand in compounds with fixed β-diketone ligand were used. Their photophysical properties were investigated by UV–Vis absorption and time-resolved femtosecond transient (fs-TA) absorption spectroscopy techniques. In this study, we investigate the impact of ancillary ligands and the fluorinated chain length of β-diketone ligands on the ultrafast relaxation processes that occur in the ligand environment. Relying on the ultrafast transient absorption measurements, it was demonstrated that the extension of fluorinated chains of β-diketone ligand leads to decrease of first excited singlet and triplet states relaxation rates. The compound with excessively long chain C6F13 exhibits the slowest relaxation of the triplet state T1.Besides, variation in the ancillary ligand alters the electronic energy transfer pathways in the whole complex. It was established, that introducing 4,7-diphenyl-1,10-phenanthroline (bath) instead of 1,10-phenanthroline (phen) dramatically changing the electronic energy transfer dynamics in the whole coordination compound. On the basis of the fs-TA measurements we conclude the bath ligand act as acceptor of electronic energy of diketone ligand in the excited state.