Theoretical and experimental investigation of UV-Vis absorption spectrum in a Eu(3+) based complex for luminescent downshifting applications

摘要

The adduct between Tris[3-(trifluoromethylhydroxymethilene)-d-camphorate] europium(III) and 4,4'-Bis(N, N-dimethylamino) benzophenone (EABP) presents an absorption band in the visible region that the neat reagents do not display, making this system interesting as an antenna system devoted to an efficient absorption in the visible region. The UV-Vis spectroscopic properties of the reagents and the adduct have been determined by a combined experimental and theoretical investigation. The equilibrium constant of the adduct formation has been determined. The theoretical investigation, carried out in the framework of density functional theory and its time-dependent extension by using the PBE1PBE and B3-LYP hybrid functionals, allowed to nicely reproduce the features of the experimental spectra of the neat reagents and of the mixture and to propose an interpretation at the molecular level of the observed appearance of the absorption band for the adduct in the visible region: It originates from the redshift of the S-0 -> S-1 transition observed in EABP-essentially deriving from the pi HOMO -> pi*LUMO excitation-due to the energy stabilization of the LUMO of EABP consequent to the electrostatic interaction between the Eu3+ ion and EABP in the adduct.