Dipyridophenazine complexes of Ru(II): Versatile optical sensors for small and large molecules

Bis(phenanthroline)dipyridophenazineruthenium(II), [(Ru(phen) ₂dppz]²⁺, exhibits unusual optical properties compared to other derivatives of [Ru(bpy)₃]²⁺. [Ru(phen) ₂dppz]²⁺ does not exhibit photoluminescence in water, but does emit brightly at approximately 610 nm in the presence of nonaqueous solvents or hydrated polymers like DNA and Nafion. We have observed this "light switch" effect upon binding [Ru(phen)₂dppz] ²⁺ to a protein with a hydrophobic pocket (chymotrypsin), suggesting that we may be able to develop optical probes of protein tertiary structure. We have also prepared derivatives of [Ru(phen)₂dppz]²⁺ that have ancillary ligands other than phenanthroline, and find that these molecules change color upon exposure to small molecules; the environmental parameters we have been able to assess so far include Lewis acidity, the nature of hydrated counterions, polarity, and hydrogen-based donation ability.