A ruthenium(II) complex with environment-responsive dual emission and its application in the detection of cysteine/homocysteine

A ruthenium polypyridine complex [Ru(phen)(2)(IPBA)](PF6)(2) (complex 1) (IPBA = 4-(1H-imidazo[4,5-f]-[1,9]phenanthroline-2-yl)benzaldehyde), which displays environment-responsive dual emissive properties, was designed and synthesized. In aprotic solvent, such as DMSO, DMF or CH3CN, the complex emits strong cyan light. When in protic solvent, it emits orange light. Similarly, the response of the complex to homocysteine and cysteine (Hcy/Cys) also shows obvious solvent dependence. TDDFT calculations reveal that the protonation of imidazole nitrogen in protic solution is responsible for the luminescent red shift. Hence, the complex could be used to detect Hcy/Cys in aprotic solvent, as well as in protic solvent.