A rhodamine-coumarin conjugate as a dual-channel dual-analyte probe with logic gate operation

• The designed probe was obtained using cheap, readily available starting materials. • The probe depicted distinct ‘naked-eye’ color changes for Cu 2+ and Ni 2+ ions. • It showed excellent FRET-based ratiometric emission response upon metal addition. • The probe could be applied as a dual-channel OR molecular logic gate. The ubiquity of Cu 2+ and Ni 2+ ions in the physiological and environmental samples impose a need to develop newer, easily synthesized molecules for their selective recognition. Special emphasis is given to absorption/emission based detection, specifically FRET-based ratiometric and colorimetric ‘naked-eye’ sensing due to their easy operability, accuracy and rapidity. The current study aimed to develop a readily synthesized coumarin-rhodamine FRET dyad as a fluorometric and colorimetric probe for simultaneous detection of Cu 2+ and Ni 2+ ions, exhibiting molecular logic gate function as well. It exhibited characteristic changes in its absorption spectrum as well as significant ratiometric response in its emission spectrum in the presence of metal ions. While Cu 2+ completely quenched the original fluorescence, Ni 2+ was able to only partially quench the same. There was also a slight distinction in the concomitant color changes observed for Cu 2+ (pale yellow to pink) and Ni 2+ (pale yellow to red) ions. The binding studies revealed 1:1 stoichiometry for both the metal-probe complexes. The binding was ascribed to the metal-assisted ring-opening of the spirolactam ring of rhodamine. The binding results were corroborated by theoretical studies. The dual-channel probe was applied as a molecular logic gate of the OR type, using both absorption and emission output signals.