Abstract: In this paper, Cu2+ fluorescence enhancement probe RA based on rhodamine B have been synthesized. It was discovered that the fluorescence intensity of RA increased with the addition of Cu2+ in acetonitrile/water (1/1, V/V) solution, the maximum absorption wavelength was 548 nm. The maximum emission wavelength was 571 nm. Addition of a Cu2+ ion lead to an obvious color change to pink as well as significantly enhanced fluorescence, while other common metal ions such as Na+, K+, Mg2+, Ca2+, Mn2+, Cd2+, Cr3+, Co2+, Ni2+, Ag+, Pb2+, Zn2+, Fe3+, Hg2+ induced no or much smaller color/fluorescent spectral changes. The selective fluorescence enhancement of RA attributed to the spirolactam ring being opened upon the addition of Cu2+ to RA, and a highly delocalized conjugated structure of RA was formed. The sensor was useful for measuring Cu2+ at concentrations ranging from 6.5×10-8 to 2.9×10-6 mol?L-1 with a detection limit of 5.0×10-8 mol?L-1. The recognition of Cu2+ was not reversible, and compound RA was pH-insensitive Cu2+ fluorescent probe, which would detect Cu2+ effectively in a relatively wide range of pH (pH=4.1—10.5) including the significant physiological region.

Key words: Fluorescent probe, Cu2+, Selectivity, pH