Remarkable 980 nm circularly polarized luminescence from dinuclear Yb(iii) helicates with a D4 symmetry

Abstract

In this work, to develop strong near-infrared circularly polarized luminescent (NIR-CPL) emitters, a pair of ytterbium helicates, namely, [Yb₂(R-BTHP)₄]²⁻ and [Yb₂(S-BTHP)₄]²⁻, based on binaphthol-modified bis-β-diketones was synthesized. X-ray crystallography analysis confirms the formation of the homochiral quadruple-stranded dinuclear structure of the helicate. CPL spectroscopy measurements show that the helicates exhibit an exceptionally high luminescence dissymmetry factor (|g_lum|) of 0.81 at 980 nm, the highest value reported for Yb-CPL materials, as well as the largest near-infrared circularly polarized luminescence brightness (B_CPL, 821 M⁻¹ cm⁻¹). We proposed that the high g_lum value originates from the rigid and high symmetry of the helical structure, and the perfect eight-coordinated square antiprismatic configuration (8-SAPR) around the Yb³⁺ ion. This work offers an example for the design of chiral CPL-emitting lanthanide complexes with large g_lum values. In view of the 980 nm light localized at the biologically relative NIR emission window, the helicates reported herein show promising applications in biologically relevant sensors and 980 nm fiber lasers.