Solution-processable Yb/Er 2D-layered metallorganic frameworks with high NIR-emission quantum yields

Abstract

Here we report on solution-processable homo- and hetero-metallic Yb³⁺, Er³⁺ and Gd³⁺ lanthanide 2D-layered metallorganic frameworks with the chlorocyananilate linker (ClCNAn²⁻, the dianion of 2-chloro-5-cyano-3,6-dihydroxybenzoquinone) showing long-lived emission in the near-infrared (NIR) spectral region after efficient ligand photosensitization. In these compounds the nature of the lanthanide ion determines the in-plane structural arrangement of the 2D layers, giving rise to peculiar porous networks. The investigated compounds, which are synthesized in high yields through a rapid one-pot procedure, show strong luminescence upon ligand excitation in a broad visible range with unusually long-lived emission for Er³⁺ (∼10 μs), either in the bulk crystalline state, in solution, or in crystalline films dropcast from solution. The remarkable sensitization properties of the ligand provide NIR emission total quantum yields as high as 15.6% for Yb³⁺ and 0.16% for Er³⁺ in DMSO-d⁶, which are the highest so far reported for coordination compounds. Efficient Yb-to-Er energy transfer is observed in the heterometallic derivative, which is maintained in all the studied material phases. The remarkable optical performance, the high thermal stability, the facile synthesis and the suitability for solution processing make these materials particularly promising for integration in photonic devices working in the NIR.