Sensitized near-infrared emission of [Ln(hfac)4]- [Ln(III) = Nd, Yb, Er] via ruthenium counterions of 2,3,5,6-tetrakis-(2pyridyl)pyrazine

Abstract

The reaction of [Ru(tppz)2](PF6)2 with [Ln(hfac)3(H2O)2] [Ln(III) = Nd, Yb, Er] afforded three new 4d-4f heteronuclear metal ionic complexes: [Ru(tppz)2][Nd(hfac)4(H2O)]2 (1), and [Ru(tppz)2][Ln(hfac)4]2 [Ln(III) = Yb(2), Er(3)], where Ru(II) and Ln(III) are associated via electrostatic interactions and π-π stacking without direct metal-metal bonds. These complexes were characterized by single-crystal X-ray diffraction (SCXR), infrared (IR) spectroscopy, thermogravimetric analysis (TGA), and mass spectrometry (MS), and their photophysical properties were investigated through UV-Vis and solid-state fluorescence spectroscopy, complemented by Hirshfeld surface analysis. Among them, complex 1 exhibits efficient sensitization of Nd(III) NIR emission via a Förster-type energy transfer mechanism, with a luminescence lifetime of 1.24 µs. Complex 2 shows weaker Yb(III) emission, while no Er(III) emission is observed in 3. This work demonstrates that tppz-based ruthenium complexes can act as effective antenna units for sensitizing selected lanthanide ions, offering a strategy for tuning NIR luminescence in 4d-4f systems.