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(eta(6)-C6H4MeCHMe2)- Cl(L)(2)][BF4] (2) is reported in which ligand L represents a series of substituted pyridinyhriethyl-arnine derivatives. 'flie carbazole based ligand L-3 exhibits a fluorescent intraligand chargetransfer (ILCT) state that is quenched by ligand-to-metal charge transfer (LMCT) upon coordination to ruthenium in the 1:1 complex [Ru(eta(6)-C6H4MeCHMe2)Cl-2(L-3)] (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 H-1 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.