Near-Infrared-Emitting Lanthanide(III)/Gallium(III) Metallacrowns with Appended Coumarins: Tuning the Sensitizer–Emitter Distance through the Linker

High Resolution Image Download MS PowerPoint Slide Near-infrared (NIR)-emitting trivalent lanthanides (Ln III ) are attractive for applications such as biological imaging and telecommunications. However, their sensitization remains challenging, particularly at excitation wavelengths corresponding to low energies. To address this challenge, a new coumarin-bearing isophthalate-based bridging ligand ( C-ip 2– ), in which the coumarin sensitizer is directly attached to the bridge, was synthesized. In the corresponding [Ln 2 Ga 8 (shi) 8 (C-ip) 4 ] 2– metallacrowns (MCs), the sensitization of the NIR-emitting Nd III, Er III, and Yb III cations was achieved upon excitation of appended coumarins in the visible range (λ exc = 435 nm). Compared to the previous generation of [Ln 2 Ga 8 (shi) 8 (C-mip) 4 ] 2– MCs, the coumarin antennas are about 5 Å closer to the Ln III emissive centers in this new series of [Ln 2 Ga 8 (shi) 8 (C-ip) 4 ] 2– MCs, resulting in an increase in the Q Ln L values by factors of 6.2, 9.4, and 2.7 for Nd III, Er III, and Yb III analogues, respectively. This allows the detection of their NIR emissions through tissue-mimicking phantoms of 1 mm thickness, validating the potential of this design for NIR imaging applications.