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An azo armed Schiff base chemosensor was synthesized based on a naphthalene fluorophore, which transduces greenish-yellow emission by complexing with Al3+. It emits greenish-yellow fluorescence through restricted C＝N isomerization, chelation-enhanced fluorescence, and the photo-induced electron transfer mechanism. The clear visible transformation of the achromatic ligand to a chromatic ligand by the 1 : 1 complexation with Al3+ is substantiated by ESI-MS spectra. 1H NMR, 13C NMR, and FTIR spectroscopies are used to characterize the HL. The selectivity of the HL for Al3+ in the presence of other metal ions was investigated through absorbance and fluorescence spectroscopies. The average lifetimes of HL and L–Al3+ have been evaluated using a time-resolved photoluminescence experiment to explore the sensing mechanism. The Al3+ sensing mechanism was also established by density functional theory calculations. A reversibility experiment was performed, demonstrating that Al3+ binding to HL is reversible. The pH variation on luminescence affirms that the HL can survive in physiological pH. Finally, the lower limit of detection of 5.4 × 10−7 and a good response in a cytotoxicity and cell imaging study confirm the usability of the ligand as an indelible signature of an effective biosensor for target Al3+. [ABSTRACT FROM AUTHOR]

The high absorption coefficient, fluorescence quantum yield, photo stability and relatively long wavelengths of rhodamine dye have expanded its applicability as a promising fluorescent probe. In the present investigation, two dyes, namely rhodamine and azobenzene, have been conjugated for the detection of Al3+ in aqueous ethanol. The turn on fluorescence response of chemosensor L towards Al3+ is attributed to the inhibited PET (photo-induced electron transfer) and CHEF (chelation enhanced fluorescence) process along with the spirolactam (non-fluorescent) to ring-opened amide (fluorescent) process. The presence of the PET and CHEF process was corroborated by time-resolved photoluminescence study and the spirolactam ring opening was confirmed by 13C NMR and infrared spectroscopy. In the presence of Al3+, the opened spirolactam ring forms a 1 : 1 binding complex with the metal, which is supported by its high binding constant (Ka = 7.033 × 103 M−1). The limit of detection (LOD) and limit of quantification (LOQ) values are found to be 1.1 × 10−7 M and 3.6 × 10−7 M, respectively. The reversible recognition of Al3+ was also proved in the presence of Na2EDTA by both UV-Vis and fluorometric titration. The sensing behaviour of the chemosensor towards Al3+ was supported by DFT/TDDFT calculations. [ABSTRACT FROM AUTHOR]

Cost-effective and highly sensitive biocompatible probes for the detection of Al3+ have tremendously important practical applications. Herein, we report for the first time, the hydrazinopyrimidine based Al3+ chemosensor L (1-[(4,6-dimethyl-pyrimidin-2-yl)-hydrazonomethyl]-naphthalen-2-ol) prepared by the condensation of 2-hydroxy-1-naphthaldehyde and 4,6-dimethyl-2-hydrazino-pyrimidine. Our as-synthesized chemosensor L (Φ = 0.0066) shows ∼15 fold fluorescence enhancement in the presence of Al3+ (Φ = 0.0955, Ka = 1.9 × 104 M−1) via chelation enhanced fluorescence (CHEF), excited state intramolecular proton transfer (ESIPT), and inhibited photo-induced electron transfer (PET) phenomena. The limit of detection (LOD) and limit of quantification (LOQ) were estimated to be 2.78 μM and 9.27 μM, respectively. Furthermore, for the first time, a hydrazino pyrimidine based ‘INHIBIT’ molecular logic gate for Al3+ was successfully developed using the fluorescence properties of L. The experimental sensing mechanisms of L for Al3+ were corroborated by theoretical calculations. Biocompatibility and good water-solubility properties of a pyrimidine moiety of L inspired us to investigate Al3+ imaging in human embryonic kidney cell lines, HEK293, and the results for practical applications are highly promising. [ABSTRACT FROM AUTHOR]

Proper fusion of fluorescence mechanisms in a single fluorophore unit is highly desirable to obtain better sensitivity, as well as selectivity towards a particular metal ion. In this regard, a Zn2+ chemosensor exhibiting strong fluorescence through synergistic CHEF-PET-ESIPT fluorescence mechanism has not received substantial deployment. This type of chemosensor provides an ample avenue to detect metal ions with a large stokes shift and are useful in living cell imaging study. Herein, we report an unparalleled Zn2+ chemosensor (L) based on these three types of fluorescence mechanisms by condensing 2,6-diformyl-4-methylphenol and 2-hydrazinyl-4,6-dimethylpyrimidine. All the three types of mechanism were experimentally verified by UV-Vis, fluorescence and time resolved photoluminescence (TRPL) spectroscopic evaluation. The sensor L and Zn2+ formed a 1 : 1 ratio complex demonstrating a high binding constant value (Ka = 4.812 × 105 M−1) and L showed clear discrimination from the Cd2+ ion. The limit of detection (LOD) and limit of quantification (LOQ) were calculated to be 9.727 × 10−7 (M) and 3.24 × 10−6 (M), respectively. We have also shown that cell imaging can be performed using L without many cytotoxicity concerns. [ABSTRACT FROM AUTHOR]

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]

An azo armed Schiff base chemosensor was synthesized based on a naphthalene fluorophore, which transduces greenish-yellow emission by complexing with Al3+. It emits greenish-yellow fluorescence through restricted C＝N isomerization, chelation-enhanced fluorescence, and the photo-induced electron transfer mechanism. The clear visible transformation of the achromatic ligand to a chromatic ligand by the 1 : 1 complexation with Al3+ is substantiated by ESI-MS spectra. 1H NMR, 13C NMR, and FTIR spectroscopies are used to characterize the HL. The selectivity of the HL for Al3+ in the presence of other metal ions was investigated through absorbance and fluorescence spectroscopies. The average lifetimes of HL and L–Al3+ have been evaluated using a time-resolved photoluminescence experiment to explore the sensing mechanism. The Al3+ sensing mechanism was also established by density functional theory calculations. A reversibility experiment was performed, demonstrating that Al3+ binding to HL is reversible. The pH variation on luminescence affirms that the HL can survive in physiological pH. Finally, the lower limit of detection of 5.4 × 10−7 and a good response in a cytotoxicity and cell imaging study confirm the usability of the ligand as an indelible signature of an effective biosensor for target Al3+. [ABSTRACT FROM AUTHOR]