Functional Interfaces

The photophysics of the novel ruthenium dye [Ru(tmBiBzIm)(dppz)(tbbpy)]2+ (tmBiBzIm = 5,5′,6,6′-tetramethyl-2,2′-bibenzimidazole, dppz = dipyrido[3,2-a:2′,3,3′-c]phenazine, tbbpy = 4,4′-di-tert-butyl-2,2′-bipyridine) is investigated, which might be suitable as a model compound for intracellular DNA and pH sensors. The combination of three different bidentate ligands allows for controlling the photophysics by two distinct mechanisms: (i) protonation and deprotonation of the tmBiBzIm and (ii) hydrogen bonding to the phenazine nitrogens of the dppz ligand. As will be reported, deprotonation of the tmBiBzIm ligand causes a bathochromic shift of the metal-to-ligand charge-transfer transition, although the tmBiBzIm ligand itself does not directly contribute to the light absorption. Furthermore, tmBiBzIm deprotonation shortens the overall excited-state lifetime of the complex significantly. Although the protonation stage of the tmBiBzIm directly impacts the excited-state properties of the dye, the overall photoinduced dynamics is dominated by the dppz ligand. Consequently, addition of water to the solvent affects the excited-state relaxation pathway as known from, for example, [Ru(phen)2dppz]2+ (phen = 1,10-phenanthroline) complexes.