Quenching of rhodamine-beta fluorescence by metal ions

A series of metal ions has been tested for their quenching ability for the fluorescence of rhodamine B cation in water. The Stern-Volmer (SV) plots were found to be linear and the bimolecular quenching constants (kq) are in the order 109 M(-1)s(-1). The transition metal ions like Cr3+, Fe-2d, Co2+, Ni2+ and Cu2+ are efficient quenchers whereas Mn2+, Zn2+, Ba2+, Pb2+ are very poor quenchers. Various mechanisms like excited state charge transfer. heavy atom quenching, paramagnetic effect. resonance energy transfer etc. appear to be occurring parallely. in the fluorescence quenching process.