A tridentate Schiff base probe L (2-NC5H4)C(H)=N(C6H4OH-2) was synthesized via a facile reaction. Probe L showed weak fluorescence emission that originated from intermolecular proton transfer in solution. With addition of Cu2+, the emission of L was quenched by the paramagnetic nature of Cu2+. However, after the solution of L and Cu2+ was refluxed, the emission presented a completely opposite result changing from fluorescent quenching to fluorescent enhancement. The fluorescent enhancement was attributed to a planar cis-structure of Cu2+ complex. Hence, a strategy for change of emission behavior of fluorescent probe L to Cu2+ was developed; a “turn on” mode of detection Cu2+ was realized in methanol solution. A simple refluxing made probe L work as a light-up fluorescent sensor for Cu2+ in methanol solution and gave improvement of sensitivity and selectivity in detection of Cu2+. When H2O was added into the solution of the Cu2+ complex, fluorescent enhancement increased and it can be used to detect water content in methanol.
A new anthraquinone derivative fluorescent probe (DPHA) was designed and synthesized for sequentially detecting aluminum ions and pyrophosphate (PPi) in a near-perfect aqueous medium with 0.4 % DMSO as a co-solvent. The DPHA probe displayed “turn-on” fluorescence sensing of Al 3+ at 575 nm, overcoming the interference of the other common cations through an apparent color variation from purple to light pink. Anthraquinone-derived conjugated skeleton and Schiff base-mediated multiple binding sites were responsible for the sensitive fluorescence response and selective recognition, respectively, thus producing a chelation-enhanced fluorescence effect. Furthermore, Job's plot analysis and high-resolution mass spectrometry (HRMS) studies supported the formation of a 1:1 ligand/metal complex for Al 3+ . The plausible binding mechanism was recognized by both experimentally and theoretically. The succeeding addition of PPi regenerated the original spectrum of DPHA and thus the strong affinity of Al 3+ to PPi. The in-situ formed DPHA-Al 3+ complex for selective identification of PPi by electrostatic interaction by drawing out Al 3+ and releasing the DPHA probe. Except for specific recognition of Al 3+ and PPi with corresponding low detection limits of 42.2 nM and 65.2 nM (S/N = 3). Owing to its good biocompatibility, DPHA also applied as a visual probe for monitoring Al 3+ ions and PPi in living cells and zebrafish, demonstrating its outstanding potential in biological work.
A simple ferrocene-based Schiff base (probe L ) exhibiting aggregation-induced emission ( AIE ) effect has been synthesized and investigated. The probe L showed selective detection for trivalent metal ions (Al 3+ , Cr 3+ and Fe 3+ ) over a range of monovalent and divalent metal ions in methanol via multi-channel of detection using colorimetry , fluorescence and electrochemistry . Upon binding with trivalent metal ions, color change from faint yellow to pink for Al 3+ , Cr 3+ and Fe 3+ was observed by the naked-eye, which was consistent with the change of UV–Vis absorption spectra. In addition, probe L showed a dramatic off-on fluorescence emission along with a large Stocks-shift of about 33 nm in the emission wavelength. The fluorescence enhancement with a blue shift may be attributed to the combined effect of rotation inhibition and an extended intramolecular charge transfer ( ICT ) mechanism. Moreover, electrochemical detection demonstrated that the oxidation potential difference between probe L and probe l -metal complexes was 0.028 V (Al 3+ ), 0.044 V (Cr 3+ ) and 0.015 V (Fe 3+ ), respectively, indicating that trivalent metal ions induced charge transfer from the ligand to the metal ( LMCT ) and reduced the electron density of ferrocene moiety. Therefore, Al 3+ , Cr 3+ and Fe 3+ can be selectively detected using multi-channel of detection techniques. Finally, 1 H NMR titration study confirmed that two molecules of probe L bind with one metal ion through the nitrogen atom and oxygen atom of the probe L .
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