Luminescence Sensitization of Eu(III) Complexes with Aromatic Schiff Base and N,N'-Donor Heterocyclic Ligands: Synthesis, Luminescent Properties and Energy Transfer.

Five luminescent Eu(III)-4-fluoro-N-salicylideneaniline (Fsa) complexes with different N,N'- donor heterocyclic ligands (L) were synthesized (where L = 2,2'-bipyridine (bipy), 4,4'-dimethoxy-2,2'-bipyridine (dmbp), 1,10-phenanthroline (phen), 2,9-dimethyl-1,10-phenanthroline (neo) and 2,2'-biquinoline (biq)) and characterized by structural, thermal and spectroscopic analyses. The photophysical studies of the complexes viz. UV-Vis absorption spectra, emission spectra, lifetime decay curve, radiative, non-radiative transition rates and quantum yields were investigated. The photophysical properties indicated that fluorine substituted salicylideneaniline acts as a better sensitizer for Eu3+ ion after involvement of ancillary ligands which leads to efficient energy transfer resulted in bright red emission due to 5 D0  → 7 F2 transition. The highest overall quantum yield (32.78%) and sensitization efficiency (75.30%) of [Eu(Fsa)3 neo] showed that it is a potential candidate in optical field. Graphical Abstract Sensitization of europium(III)-Schiff base complexes by antenna effect.