A novel piperazine-bis(rhodamine-B)-based chemosensor for highly sensitive and selective naked-eye detection of Cu2+ and its application as an INHIBIT logic device

We report the design and synthesis of a new piperazine-bis(rhodamine-B) (RB-P-RB)-based indicator for selective detection of Cu2+ ion. Optical sensing behavior toward various metal ions including alkali, alkaline earth and transition metal ions (Na+, K+, Ba2+, Mg2+, Ca2+, Zn2+, Cd2+, Mn2+, Co2+, Ni2+, Pb2+, Cu2+, Hg2+, and Ag+) were investigated by UV-vis and fluorescence spectroscopy in ethassnol solution. The indicator showed highly selective and sensitive colorimetric and “turn-on” fluorescence enhancement responses toward Cu2+ ion owing to the ring-opening structure of the rhodamine spirolactam. The significant change from colorless to pink upon the addition of Cu2+ could make it a suitable “naked-eye” indicator for Cu2+. Furthermore, a possible ring-opening mechanism (off-on) of the rhodamine spirolactam induced by Cu2+ binding is supported by Job plot, ESI-mass, FT-IR, and 1H NMR. More significantly, the probe displayed highly selective Cu2+-amplified absorption in the presence of Cu2+ ions. Finally, using Cu2+ and EDTA as inputs and the fluorescence emission intensity as output, an INHIBIT logic gate can be constructed at the molecular level.