Unusual photophysical switching in a Ru(II) diimine DNA probe caused by amide functionalisation

Whereas the complex Ru(phen)2Medpq]2+(phen=1,10-phenanthroline; Medpq=2-methyldipyrido3,2-f:2',3'-h]-quinoxaline) is luminescent in both aqueous and nonaqueous solutions, Ru(phen)2dpqa]2+(2-pentylamidodipyrido3,2-f:2',3'-h]-quinoxaline) does not emit in water but does so strongly in organic solvents or when bound to DNA--suggesting its use as a photochemical and photophysical probe for nucleic acids.