ABSTRACT
Herein, an aggregation-induced emission (AIE) active Schiff base (NHS) was synthesized by condensing naphthalimide hydrazide with salicylaldehyde. The non-fluorescent solution of NHS in DMSO turned to emissive NHS upon increasing the HEPES fraction in DMSO from 70 to 95%. The UV-Vis absorption and DLS studies supported the self-aggregation of NHS that restricted the intramolecular rotation and activated the ESIPT process. The blue fluorescence of AIE luminogen NHS in DMSO:HEPES (5:95, v/v, pH = 7.4) was examined by adding different metal ions (Al3+, Ca2+, Cd2+, Co2+, Cu2+, Cr2+, Fe2+, Fe3+, Hg2+, Mg2+, Mn2+, Ni2+, Pb2+ and Zn2+). NHS showed a selective fluorescence switch-off response for Cu2+ due to the chelation enhancement quenching effect (CHEQ). The quenching of NHS by Cu2+ was explored by using density functional theory (DFT) and Stern-Volmer plot. The practical utility of NHS was examined by quantitative and qualitative analysis of Cu2+ in real water samples.
ABSTRACT
An easy-to-prepare aggregation-induced emission enhancement (AIEE) active Schiff base NPY was synthesized by condensing vitamin B6 cofactor pyridoxal with 3-hydroxy-2-naphthoic hydrazide, and employed for the fluorescent sensing of pH and p-nitrophenol (p-NP). The AIEE phenomenon of NPY was investigated in mixed DMSO/H2O medium. The weakly yellow-fluorescent NPY (λem = 535 nm) in pure DMSO turned to a bright cyan-fluorescent NPY (λem = 490 nm) upon addition of poor solvent water. The DLS and SEM analyses supported the self-aggregation of NPY that restricted the intramolecular rotation and activated the excited state intramolecular proton transfer (ESIPT) process. The AIEE luminogen (AIEEgen) NPY containing 90% of water fraction (fwater) was employed for the fluorescent sensing of pH. AIEEgen NPY displays three distinct fluorescent pH windows: non-fluorescent below pH 3.0 and above pH 10.0, cyan fluorescent between pH 3.0 to 8.0, and yellow fluorescent between pH 8.0 to 10.0. AIEEgen NPY was also applied for the detection of nitroaromatics in HEPES buffer (10% DMSO, 10 mM, pH 7.0). The addition of p-NP selectively quenched the fluorescent intensity of AIEEgen NPY with an estimated detection limit of 1.73 µM. The analytical utility of AIEEgen NPY was examined by quantifying p-NP in different real water samples.
ABSTRACT
Schiff base 4-((E)-((E)-(2-hydroxybenzylidene)hydrazono)methyl)-5-(hydroxymethyl)-2-methylpyridin-3-ol (HSP) was synthesized by condensing vitamin B6 cofactor pyridoxal with salicylaldehyde hydrazone, and characterized by standard spectroscopic techniques (FT-IR, 1H NMR, 13C NMR, and ESI-MS). The solution of HSP in DMSO/HEPES (10 mM, pH = 7.4) mixed solvents with varying HEPES fractions (fw) from 0 to 95% showed aggregation-induced emission (AIE). The AIE active HSP in 95% HEPES gave intense fluorescent emission at 570 nm was employed for the detection of metal ions. The fluorescence of HSP was quenched upon adding Cu2+ and Fe2+ ions. The association constant (Ka) of the Schiff base HSP with Cu2+ and Fe2+ ions was estimated as 4.08 × 105 M-1 and 1.23 × 105 M-1, respectively by using the online analysis tool BindFit v0.5. The HSP showed the detection limit down to 1.75 µM and 1.89 µM for Cu2+ and Fe2+ ions, respectively. Further, the aggregates of HSP were applied to visualize latent fingerprints (LFPs) over a non-porous glass slide.
Subject(s)
Copper , Pyridoxal , Copper/analysis , Fluorescent Dyes/chemistry , HEPES , Ions , Optical Imaging , Schiff Bases/chemistry , Spectrometry, Fluorescence , Spectroscopy, Fourier Transform Infrared , Iron/analysisABSTRACT
An aggregation-induced emission (AIE) active Schiff base L was obtained by reacting pyridoxal and 2-hydroxy-1-naphthaldehyde with p-phenylenediamine in two simple steps. The colorimetric, UV/VIS and fluorescence studies of L revealed that the yellow emissive L (λem =540â nm, λex =450â nm) in pure DMSO turned to a red-emissive L, when the poor solvent fraction (HEPES buffer, 10â mM, pHâ 7.4) was increased above 50 % in DMSO. The SEM and DLS results indicated the formation of self-aggregates of L that restricted the intramolecular motion and promoted the excited state intramolecular proton transfer (ESIPT) process. The cations sensing ability of the AIEgen L was explored in HEPES buffer (5 % DMSO, 10â mM, pHâ 7.4), where Cu2+ selectively quenched the fluorescence at 608â nm due to the chelation-enhanced fluorescence quenching (CHEQ) effect with an estimated sensitivity limit of 0.9â µM. Subsequently, the inâ situ formed AIEgen L-Cu2+ complex was applied for the cascade detection of glutathione (GSH), cysteine (Cys) and homocysteine (Hcy). The decomplexation of Cu2+ from the AIEgen L-Cu2+ by GSH, Cys and Hcy restored the quenched fluorescence emission of AIEgen L at 608â nm. With this Cu2+ displacement approach, the concentration of Cys, Hcy and GSH can be detected down to 2.8â µM, 3.12â µM and 2.0â µM, respectively. The practical utility of AIEgen L and AIEgen L-Cu2+ was examined by monitoring the selective analytes in real environmental and biological samples, and also applied successfully for the cell imaging applications.