Isatin appended rhodamine scaffold as an efficient chemical tool to detect selectively Al3+.

5-methoxy isatin-appended rhodamine dye, (E)-3'-(diethylamino)-6'-(ethyl(methyl)amino)-2-((5-methoxy-2-oxoindolin-3-ylidene)amino)spiro[isoindoline-1,9'-xanthen]-3-one (L) has been designed, synthesized, and characterized by different spectroscopic techniques. The chemosensor L shows high sensitivity towards Al3+ ions without interference from other biologically important cations in DMSO/H2O (1/9, v/v) media. The Al3+-ion promoted ring opening of the rhodamine spirolactam ring in chemosensor L evokes a fluorescence turn-on response via chelation-enhanced fluorescence (CHEF) process. Its lowest detection limit for Al3+ is 2.2x10-8 M, and displays a significant color change from almost colorless to deep pink in the presence of Al3+. The titration results show a 1:1 complex formation between chemosensor L and Al3+. [ABSTRACT FROM AUTHOR]