Rhodamine-Based Dual Chemosensor for Al3+ and Zn2+ Ions with Distinctly Separated Excitation and Emission Wavelengths

A rhodamine-based compound, 2-(2-((3-(tert-butyl)-2-hydroxybenzylidene)amino)ethyl)-3′-6′-bis(ethylamino)-2′,7′-dimethylspiro[indoline-1,9′-xanthen]-3-one, (HL-t-Bu), is reported here as a dual chemosensor for Zn2+ and Al3+ ions. This compound has been synthesized under mild conditions with high yield and characterized by elemental analysis and different standard spectroscopic methods. Its structure has been confirmed by single-crystal X-ray diffraction analysis. It acts as a fluorescent dual sensor for Zn2+ and Al3+ in 10 mM HEPES buffer in the methanol/water mixture (9:1, pH = 7.4) with well-separated excitation and emission wavelengths. The fluorescence intensity at 457 nm of HL-t-Bu increases by ∼7 folds in the presence of 1 equiv of Zn2+ when it is excited at 370 nm. With the excitation at 500 nm, the emission intensity of the probe at 550 nm increases massively (∼650 times) in the presence of 1 equiv of Al3+. No other metal has any significant effect on the enhancement of the emission intensity of t...