Ru(II) complexes with N-heterocyclic carbene ligands or terpyridine analogues: synthesis, characterization, and electrochemical and proton-dependent spectrometric properties.

Four ruthenium(II) complexes, BPT, BPN, BPPT, and BPPN, have been prepared and characterized by (1)H NMR, (13)C NMR, high resolution mass spectrometry (HRMS), elemental analysis, and X-ray crystallography. All the complexes incorporate a pyridyl unit on the terpyridine-type or N-heterocyclic carbene (NHC) ligand and the pyridyl unit can be protonated upon addition of 1.0 M HCl in diethyl ether. The proton-dependent absorption and luminescence spectrum were measured in CH(3)CN. In the case of BPT, the λ(max)(abs) was moved by 10 nm from 490 nm to 500 nm after the addition of 12 equiv. of HCl and the intensity of the emission spectrum increased. In contrast, in the case of BPN, the λ(max)(abs) was red-shifted by 43 nm from 424 nm to 467 nm and the emission was dramatically quenched upon the addition of the equiv. of HCl. However, there were no noticeable changes in the λ(max)(abs) values of BPPT and BPPN even after the addition of the HCl to a solution of those complexes. Moreover, BPN has a selective sensing property for a proton among many cations.