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A novel fluorescent chemosensor based on a rhodamine derivative (L) was designed, synthesized, and used as a selective Al+3 ion sensor. Upon addition of Al3+ to an aqueous-acetonitrile solution of L, the development of a strong fluorescence signal by a chelation-enhanced fluorescence (CHEF) process was observed with an attractive glowing orange emission. This sensor shows high selectivity towards Al3+ ions in the presence of other competing metal ions. The fluorescence quantum yield of L–Al3+ (Φf = 0.30) was found to be very high compared to the bare ligand. The limit of detection (LOD) of Al3+ ions was calculated to be 2 × 10−8 M by fluorescence titration. The 1 : 1 binding stoichiometry of the metal complex was established by combined UV-vis, fluorescence and TOF-MS spectroscopy. [ABSTRACT FROM AUTHOR]

A new chelating ligand [4-methyl-2,6-bis-(pyridin-2-yl-hydrazonomethyl)-phenol] (1) was prepared by the condensation of 2-hydrazinylpyridine with 2,6-diformyl-p-cresol. Compound 1 exhibits weak fluorescence due to intramolecular photoinduced electron transfer (PET). The sensor (1) demonstrates Zn2+-specific emission enhancement due to the “PET off” process through a 1 : 1 binding mode with the metal ion. The fluorescence quantum yield of chemosensor 1 is only 0.020, and it increases more than 14-fold (0.280) in the presence of one equivalent of the zinc ion. Interestingly, the introduction of other metal ions causes the fluorescence intensity to remain either unchanged or weakened except for Cd2+. The new sensor showed ‘naked-eye’ detection of Zn2+ ions: a color change of the solution from colorless to yellow. Ratiometric displacement of Cd2+ ions from the complex by Zn2+ ions supports the formation of a more stable sensor–Zn2+ complex over the sensor–Cd2+ complex. The experimental findings have been correlated with theoretical results using the B3LYP functional and 6-31G (d, p), LANL2DZ basis set for Cd2+ (2) and Zn2+ (3) complexes, respectively, by the Density Functional Theory (DFT) method. Moreover, the ability of probe 1 to sense Zn2+ within human melanoma cancer cells has been explored, and the Zn2+-probing process in living cells was found to be reversible with zinc chelator solution of N,N,N,N-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) or EDTA. [ABSTRACT FROM AUTHOR]

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]

Abstract: A novel rhodamine-based chemosensor, 3′,6′-bis(diethylamino)-2-((2,7-dimethoxy-9H-fluoren-9-ylidene)amino)spiro[isoindoline-1,9′-xanthen]-3-one (1) for aluminum ion, was designed and synthesized. Compound 1 is an orange colored, weak fluorescent compound which was synthesized via one-step facile reaction of rhodamine B hydrazide with 2,7-dimethoxy-9H-fluoren-9-one in MeOH. When Al3+ salt was added in methanol:water (30:70, v/v) solution then spirolactum ring of 1 was opened. The absorbance and fluorescence of the mixed solution were increased dramatically because of the opening of the lactum ring. Thus, signal transduction occurred via reversible CHEF (chelation-enhanced fluorescence) mechanism in the range 580–584nm. [Copyright &y& Elsevier]