Differentiate bisulfite from sulfite by a new cycloruthenated 2-(2-thienyl)pyridine complex in pure water

A newly designed water-soluble cycloruthenated complex Ru(bpy)2(pthb)+ (1) involving thienyl and benzo[e]indolium block was successfully used as a colorimetric chemo-sensor for sulfites in aqueous system, whose absorption band can extend to 1000 nm. It is interesting that the solution color changes of 1 in pure water are quite different upon the addition of HSO3- and SO32-, respectively. The apparent solution color changes displayed that 1 can be used to distinguish HSO3- from SO32- in pure water by naked eyes.182