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

Abstract A new complex Eu(BTA) 3 (PBO) ( 1 ) (BTA=benzoyltrifluoroacetone, PBO=2-(2′-pyridyl)-benzoxazole) showing strong luminescence is designed and synthesized. Single-crystal X-ray diffraction has revealed that this new material crystallizes as mononuclear molecule with compact π∙∙∙π stacking interaction. The material exhibits strong red emission dominated by the Eu 3+ ( 5 D 0 → 7 F 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.