Anion binding and luminescent sensing using cationic ruthenium(II) aminopyridine complexes

The synthesis of a series of ruthenium(II) based anion sensors of the type [Ru(?⁶-C₆H₄MeCHMe₂)-Cl(L) ₂][BF₄] (2) is reported in which ligand L represents a series of substituted pyridinylmethyl-amine derivatives. The carbazole based ligand L³ exhibits a fluorescent intraligand charge-transfer (ILCT) state that is quenched by ligand-to-metal charge transfer (LMCT) upon coordination to ruthenium in the 1:1 complex [Ru(?⁶-C ₆H₄MeCHMe₂)Cl₂(L³)] (1c). The 1:2 complex 2c is fluorescent, however, and acts as a fluorescent anion sensor because of the mixing of an anion-dependent charge-transfer component into the excited state. The 1:2 complexes of type 2 all exhibit interesting low symmetry ¹H NMR spectra that also are a useful handle on anion complexation. The electronic structures of L³, 1c and 2c have been probed by time-dependent DFT calculations. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA,.