NIR-emitting ytterbium complexes with a large Stokes shift for detection of sulfide

Four new NIR-emitting ytterbium complexes Ln(L)(HL) and K[Ln(L)2](H2O)n (Ln = Yb, Lu; L = 2-tosylaminobenzaldehyde-4-azidomethylbenzoylhydrazone (L1) and 2-tosylamino-5-bromobenzaldehyde-4-azidomethylbenzoylhydrazone (L2)) were obtained and characterized, and 6 crystal structures of Yb(L1)(HL1), Lu(L2)(HL2), Lu(L2)(HL2)(n-Hex) (n-Hex = n-Hexane), K[Lu(L1)2](H2O), {KYb(L1)2(H2O)2(THF)}2 and K[Yb(L2)2](THF) were determined. Rational design yielded complexes with intense NIR emission, a Stokes shift of 500 nm (16 100 cm−1), and sensitivity towards the S2− anion. The complexes could penetrate cells, and showed low toxicity.