Eu3+-to-Cr3+ energy transfer for the improved Cr3+- characteristic near-infrared (NIR) phosphorescence in the Cr(III)-Eu(III)-Salen complex

Abstract

Through the self-assembling of Ln(OAc)3⋅6H2O (Ln = Eu or Tb) with the chromium(III)-complex precursor [Cr(L)Cl(H2O)] formed from the oxidation and the coordination reactions of CrCl2 and the Salen-type Schiff-base ligand H2L (N,N’-bis(3-methoxy-salicylidene)cyclohexane-1,2-diamine), two hetero-binuclear complexes [Cr(L)Cl(μ1-OAc)Ln(μ2-OAc)Cl(H2O)] (Ln = Eu, 1 or Tb, 2) were obtained, respectively. Moreover, attributing to effective Eu3+-to-Cr3+ energy transfer, the [Cr(L)Cl(μ1-OAc)Eu(μ2-OAc)Cl(H2O)] (1) exhibits the significantly improved Cr3+-characteristic near-infrared (NIR) phosphorescence in comparison to that of the Cr(III)-complex precursor [Cr(L)Cl(H2O)] or the [Cr(L)Cl(μ1-OAc)Tb(μ2-OAc)Cl(H2O)] (2).