Boosting the sensitivity of pH responsible luminescent switches of polypyridyl ruthenium(II) complexes by structural design

A series of novel polypyridyl ruthenium(II) complexes with two 4,7-diphenyl-1,10-phenanthroline (dip) and one 2-phenyl-1H-imidazo[4,5-f][1,10]phenanthroline (pip) or its analogs have been designed to act as pH responsible luminescent switches through protonation of the imidazole-containing pip ligands in aqueous solution at room temperature. The complex containing methoxyl group showed an on–off ratio of 110 that is higher than any reported pH light switch. This extraordinary high sensitivity is attributed to both the higher LUMO energy level and the electronic donating property of methoxyl group.