We successfully demonstrate that metal–organic frameworks (MOFs) can be designed to be excited and emit within the biological diagnostic window (650–1450 nm). An isoreticular series of anionic rare earth MOFs with >fcu topology was synthesized using 10 different rare earth elements (Y3+, Eu3+, Gd3+, Tb3+, Dy3+, Ho3+, Er3+, Tm3+, Yb3+, Lu3+) and common linear ditopic ligands. Five different cationic dye molecules were incorporated into the MOFs via ion exchange. When LDS 750, which exhibits low-energy absorption in the range 450–770 nm, is loaded into an Yb3+-MOF, it can be used as an antenna to sensitize the near-infrared (NIR) emission of Yb3+ centred at 980 nm.
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