Modulating luminescence spectra by controlling the π•••π stacking strength of the excimers of a new europium complex material

A new complex Eu(BTA)(3)(PBO) (1) (BTA=benzoyltrifluoroacetone, PBO=2-(2'-pyridy1)-benzoxazole) showing strong luminescence is designed and synthesized. Single-crystal X-ray diffraction has revealed that this new material crystallizes as mononnclear molecule with compact pi center dot center dot center dot pi stacking interaction. The material exhibits strong red emission dominated by the Eu3+ (D-5(0)-> F-7(2)) transition not only in solid state but also in doped film. A surprising spectral-shift has been observed both in the excitation and the absorption spectra from the dilute solution to powder samples. An excimer mechanism for this spectral-shift has been successfully proposed based on the X-ray structure, spectroscopy and calculation results. (C) 2015 Elsevier B.V. All rights reserved.