A highly selective fluorescence switch for Cu2+ and Fe3+ based on a new diarylethene with a triazole-linked rhodamine 6G unit

A new diarylethene compound with a triazole-linked rhodamine 6G unit attached to the imino group (1O) was designed and synthesized. According to the test results, the solution color and fluorescence color of diarylethene can be modulated by lights and metal ions. The solution color could change from colorless to light purple when irradiated with UV light. When Cu²⁺ was added to the diarylethene solution, the color of diarylethene solution became blue, the fluorescence color turned from dark to bright yellow. Although the solution color did not change by adding Fe³⁺, its fluorescence color varied from dark to yellow. Moreover, it was found that the complex ratio of the diarylethene to Cu²⁺ was 1:1 and the binding stoichiometry of the diarylethene to Fe³⁺ was also 1:1 based on the data of NMR, MS, and other experiments. Based on these findings, photochromic figure of the diarylethene with UV/Vis light, Cu²⁺ and Fe³⁺ was constructed. Furthermore, the logic circuit was designed by input signals (ultraviolet stimulus, visible light stimulus, Cu²⁺ (or Fe³⁺) and EDTA) and an output signal (fluorescent intensity at 566?nm (or 575?nm)).     

A multi-functional fluorescent sensor for Zn2+ and HSO4− based on a new diarylethene derivative

A new photochromic diarylethene derivative with a hydralazine unit was designed and synthesized. It was not only acted as a Zn²⁺ sensor with the fluorescent color change from dark blue to bright orange, but also acted as a fluorescent sensor for HSO₄^? with the fluorescent color change from dark blue to bright blue. Furthermore, the derivative also exhibits multi-addressable switching properties by the stimulations of lights and chemical reagents. Based on these characteristics, two combinational logic circuits were constructed with the emission intensity as the output signals, and the UV/vis lights, chemical species as the input signals.     

A multi-controllable selective fluorescent turn-on chemosensor for Al3+ and Zn2+ based on a new diarylethene with a 3-(4-methylphenyl)-1H-pyrazol-5-amine Schiff base group

A novel diarylethene containing a 3-(4-methylphenyl)-1H-pyrazol-5-amine was synthesized. Its multi-responsive properties induced by UV/Vis lights and metal ions were studied in detail by absorption and fluorescence emission spectroscopy. It showed excellent fluorescence sensing ability for Al³⁺ and Zn²⁺ with very low detection limit. In addition, based on the multi-responsive characteristics, a logic circuit was constructed by using both UV/Vis lights and chemical species stimuli as inputs and fluorescence intensity as outputs. Moreover, the diarylethene was successfully applied to effectively detect Al³⁺ and Zn²⁺ in actual water samples.     

Novel fluorescent probe bearing triarylimidazole and pyridine moieties for the rapid and naked-eye recognition of Cu2+

A new fluorescent probe (TPIP) bearing triarylimidazole and pyridine moieties was synthesized and applied to the detection of Cu²⁺ with high sensitivity and selectivity. Upon the addition of Cu²⁺, the probe displayed an apparent dual-channel signal change of the UV–Vis absorption and fluorescence spectra, and the obvious color change from bright blue to colorless under a UV lamp was discernable to the naked eye. The sensing mechanism of the probe towards Cu²⁺ was verified to be via complexation, and the binding reaction was rapidly complete within 30?s. Good linearity was observed between the probe and Cu²⁺, and the detection limit was calculated to be 1.96?×?10^?8?M. The reversibility of the probe was easily achieved by adding EDTA, which released the free probe with over 95% fluorescence recovery. Furthermore, the recognition of Cu²⁺ on TLC plates was realized, indicating the potential utility of the probe.     

Bifunctional probe for Cu2+/Al3+ based on a diarylethene with a 4, 5-[bis-(5-ethylacetate-yl)-2-thienyl]-1H-imidazole unit

A new asymmetric perfluordiarylethene (1O) was synthesized using 4, 5-[bis-(5-ethylacetate-yl)-2-thienyl]-1H-imidazole as a functional group. 1O exhibited favorable reversible cyclization and cycloreversion reactions upon alternating irradiation with UV and visible light. Both of its open- and closed-ring isomers were found to be highly selective towards Cu²⁺ with significant absorption and color changes, which could be used as a ‘naked-eye’ colorimetric sensor for Cu²⁺ detection. Upon exposure to acid, its fluorescence dramatically enhanced by 14-fold with a color change from dark to bright cyan due to the formation of the protonated compound. Moreover, 1O showed obvious fluorescence “turn-on” signal response towards Al³⁺, and the detection limit for Al³⁺ was determined to be 4.8 × 10^?9 mol L^?1. Based on the fluorescence signals of 1O, a combinational stimuli logic circuit were designed by using the fluorescence intensity as the output signal with the inputs of lights, Al³⁺ and EDTA. Finally, 1O could be used as a biological probe for detecting intracellular Al³⁺ in a physiological environmental.     

Synthesis of a new pyrene-devived fluorescent probe for the detection of Zn2+

A novel pyrene-based receptor bearing benzothiazole was synthesized as a good turn-on fluorescent sensor for the recognition of Zn²⁺. The probe showed an excellent selectivity for Zn²⁺over most other competing ions (eg, Cr³⁺, Li⁺, Cd²⁺, Al³⁺, Pb²⁺, Li⁺, Mg²⁺, Ag⁺, Ca²⁺, Ni²⁺, Mn²⁺, Fe³⁺, Hg²⁺, Ba²⁺, K⁺, Na⁺, Cu²⁺, Fe²⁺) in EtOH-HEPES (65:35, v/v, pH?=?7.20), which might be attributed to the photoinduced electron transfer (PET) mechanism. The formation of 1:1 stoichiometric PBZ-Zn²⁺ complex was determined based on the Job's plot, ¹H NMR titration and ESI-MS. The binding constant of the complex was 4.04?×?10⁴?M^?1 with a detection limit of 2.58?×?10^?7?M. The potential application of the PBZ in real water samples for recognizing Zn²⁺ was investigated. Bio-imaging study also revealed that PBZ could be applied to detecting Zn²⁺ in live cells. These results indicated that PBZ could be a favorable probe for Zn²⁺.     

A new fluorescence probe based on diarylethene with a benzothiazine unit for selective detection of Cd2+

A novel photochromic diarylethene derivative containing a benzothiazine unit has been synthesized. Its photochromism and fluorescent selectivity to metal ions were studied in detail in methanol solution. Under the stimulation of Cd²⁺ ions, the derivative showed a significant fluorescence enhancement and obvious red shift, accompanied by the fluorescent color changed from dark purple to bright blue. The 1: 1 stoichiometry between the derivative and Cd²⁺ was verified by titration experiments and high resolution mass spectrometry. In addition, a molecular logic circuit was designed with the emission intensity at 476?nm as output and the stimuli of Cd²⁺/EDTA and UV/vis as inputs.     

A multi-responsive diarylethene-rhodamine 6G derivative for sequential detection of Cr3+ and CO32−

A new unsymmetrical diarylethene derivative (1o) with rhodamine 6G as a functional group has been designed and synthesized. It displayed good physicochemical properties induced by lights and chemical stimuli. 1o could sensitively detect towards Cr³⁺ with a 1:1 stoichiometry, and exhibit an obviously fluorescence (from dark to light cyan) and color (from colorless to pink) changes during the recognition process. The limit of detection was determined to be 27?nM and 8.5?nM via UV/vis and fluorescence methods, respectively. More importantly, the resulting complex 1o-Cr³⁺ (1o') could be served as a potential fluorescent probe to selectively and sensitively recognize toward CO₃^2?, the limit of detection was determined to be 0.88?μM and 0.26?μM via UV/vis and fluorescence methods, respectively. Moreover, the quenching of fluorescence intensity can reach 95% due to the perfect FRET processes between the excited open-ring rhodamine 6G moiety and the closed-ring diarylethene unit.     

A highly selective diarylethene chemosensor for dual channel recognition of CN− and Zn2+ and its application

A novel diarylethene chemosensor comprising 3-aminobenzofuran-2-carboxamide Schiff base (1O) was synthesized and the photophysical and sensing behaviors of 1O were further investigated. Importantly, the introduction of electron-withdrawing group to 1O made the sensor an efficient tool for detection of toxic cyanide even in the presence of other plausible interfering anions including fluoride and acetate. In particular, addition of CN^? to 1O visibly changes the color from colorless to orange-red, which can be observed by the naked eye. Apart from this, it also exhibited an outstanding fluorometric sensing toward Zn²⁺ with high selectivity and sensitivity. Moreover, the remarkable spectral responses of the devised sensor prompted us to fabricate molecular logic circuit. Furthermore, the sensor was successfully applied to the detection of CN^? on test strips and silica coated microslides, and the methods were very simple to operate without resorting to any spectroscopic instrumentation. In addition, the 1O can also effectively detect CN^? and Zn²⁺ in actual water samples.     

A new Schiff-base as fluorescent chemosensor for selective detection of Cr3+: An experimental and theoretical study

A novel Schiff base fluorescent sensor N,N′-bis(salicylidene)-2,6-bis(4-aminophenyl)-4-phenylpyridine (P3) was synthesized through condensation of 2,6-bis(4-aminophenyl)-4-phenylpyridine and 2-hydroxybenzaldehyde. The obtained results from fluorescence analysis revealed that by excess of Cr³⁺ to P3, a remarkable increase was observed in the fluorescent intensity of the Schiff base at 663?nm with the ratio of CH₃CN/H₂O (95/5%), even though the other cations would likely have no impact on the fluorescence intensity. The cause of this trend might be ascribed to the formation of a 1:1 stoichiometric P3-Cr³⁺ complex, confirmed by Job's plot, which is resulted in preventing the photo-induced electron transfer (PET) process. From fluorescence titration, the association constant K_a was gained 2.28?×?10⁵?M^?1 and the limit of detection (LOD) was determined to be 1.3?×?10^?7?M. Furthermore, the optimized structure together with the electronic spectra of the proposed complex was determined by DFT and TDDFT calculations.     

A highly selective colorimetric sensor for Hg2+ based on a copper (II) complex of thiosemicarbazone in aqueous solutions

By applying an indirect strategy, a new copper (Ⅱ) complex of a thiosemicarbazone L has been successfully developed as a colorimetric chemosensor for the sensitive detection of mercury (Ⅱ) ions. In the presence of copper (Ⅱ) ions, the colorless solution of L became yellow; however, upon the addition of traces of mercury (Ⅱ) ions, the yellow color faded to colorless immediately. Other ions, including Fe3+ , Ag+ , Ca2+ , Zn2+ , Pb2+ , Cd2+ , Ni2+ , Co2+ , Cr3+ and Mg2+ had a negligible influence on the probe behavior. The detection limits were 5.0×10 -6 M and 3.0×10 -7 M of Hg2+ using the visual color changes and UV-vis changes respectively. Test strips based on Cu-L were fabricated, which could act as a convenient and efficient Hg2+ test kits.     

A fluorescent sensor for Al3+ based on a photochromic diarylethene with a hydrazinobenzothiazole Schiff base unit

A new fluorescent turn-on chemosensor for Al³⁺ based on a diarylethene unit was designed and synthesized. Photochromism, fluorescence switch, and metal ion recognition behaviors of this diarylethene derivative were investigated by absorption and fluorescence emission spectra. It shows an outstanding fluorometric sensing ability toward Al³⁺ ion, and the detection limit was measured to be 9.3 × 10^?8 mol L^?1 via fluorescence methods. Based on these interesting properties, a combinational logic circuit was constructed successfully.     

Novel multi-responsive fluorescence switch for Hg2+ and UV/vis lights based on diarylethene-rhodamine derivative

A new multi-responsive fluorescent switch DTE-Pip-Rho 1O has been designed and synthesized in this study. For this molecule, the reactive site of spirolactam ring is far away from the diarylethene unit through the intramolecular piperazine. It exhibited high selectivity and sensitivity to Hg²⁺ in addition to obvious color change (colorless-pink) and fluorescence “off-on” (dark-orange) during this process. It is believed that the color change is due to Hg²⁺-assisted hydrolysis of rhodamine hydrazide. Therefore, the new molecule can be used as colorimentric and fluorescent chemosensor for Hg²⁺ with high selectivity. The detection limits of absorbance and fluorescence for Hg²⁺ were calculated to be 1.15?μM and 1.16?μM, respectively. The resulting DTE-Pip-Rho 1O-Hg²⁺ could also function as a reversible fluorescence photo-switch in response to UV/vis light owing to FRET mechanism. Moreover, it has been demonstrated that the photo-switchable system displayed excellent fatigue resistance and remarkable anti-photobleaching capability.     

A highly sensitive and selective fluorescent probe for Fe3+ containing two rhodamine B and thiocarbonyl moieties and its application to live cell imaging

A novel turn-on rhodamine B-based fluorescent chemosensor (RBCS) was designed and synthesized by reacting N-(rhodamine B)lactam-1,2-ethylenediamine and carbon disulfide. Upon addition of Fe³⁺ in EtOH/H₂O solution (2:1, v/v, HEPES buffer, 0.6?mM, pH 7.20), the RBCS displayed a significant fluorescence enhancement at 582?nm and a dramatic color change from colorless to pink, which can be detected by the naked eye. Significantly, the RBCS exhibited a highly selective and sensitive ability toward Fe³⁺. The detection limit of the probe was 2.05?×?10^?7?M. Job's plot indicated the formation of 1:1 complex between the RBCS and Fe³⁺. Moreover, the practical use of the RBCS is demonstrated by its application in the detection of Fe³⁺ in HeLa cells.     

Solvent-dependent chromogenic sensing for Cu and fluorogenic sensing for Zn and Al: a multifunctional chemosensor with dual-mode

A new multifunctional chemosensor 1 was synthesized and characterized by spectroscopic tools along with a single crystal X-ray crystallography. It can exhibit selective recognition responses toward Cu²⁺, Zn²⁺ and Al³⁺ in different solvent systems with bimodal methods (colorimetric and fluorescence). This sensor 1 detected Cu²⁺ ions through a distinct color change from colorless to yellow in aqueous solution. Interestingly, the receptor 1 was found to be reversible by EDTA. The detection limit (11 μM) of 1 for Cu²⁺ is much lower than WHO guideline (30 μM) in drinking water. In addition, the sensor 1 showed significant fluorescence enhancements in the presence of Zn²⁺ ion and Al³⁺ ion in two different organic solvents (DMF and MeCN), respectively. The binding modes of the three complexes were determined to be a 1:1 complexation stoichiometry through Job plot, ESI-mass spectrometry analysis, and ¹H NMR titration.     

Chromenone-rhodamine conjugate for naked eye detection of Al3+ and Hg2+ ions in semi aqueous medium

Chromenone-rhodamine conjugate 1 has been synthesized and its metal ion binding properties have been studied in CH₃CN/water (3:1, v/v; 10 mM HEPES buffer; pH = 6.85). Compound 1 senses multiple metal ions such as Al³⁺ and Hg²⁺ by exhibiting turn on fluorescence and color change (colorless to pink). Al³⁺ and Hg²⁺ ions have been distinguished with the aid of tetrabutylammonium iodide (TBAI). While in the presence of I^? the pink color of the 1.Hg²⁺ complex was completely discharged; under identical conditions the pink color of 1.Al³⁺ complex was retained.     

A coumarin based highly selective fluorescent chemosensor for sequential recognition of Cu2+ and PPi

In this study, we have successfully synthesized a new coumarin based fluorescent chemosensor 1, in which tren and quinolone are introduced as receptors for sequential recognition of Cu²⁺ and PPi. The structure of chemosensor 1 was characterized by ¹H NMR, ¹³C NMR and ESI-HR-MS. Sensor 1 showed an obvious “on-off” fluorescence quenching response toward Cu²⁺, and the quenching efficiency reached a maximum of 99.6% with the addition of 20 equiv. of Cu²⁺. The 1-Cu²⁺ complex showed an “off-on” fluorescence enhancement response toward PPi over many competitive anions, especially HPO₄^2? and H₂PO₄^?. The detection limit of sensor 1 was 1.9?×?10^?6?M to Cu²⁺ and 5.96?×?10^?8?M to PPi. In addition, sensor 1 showed a 1:1 binding stoichiometry to Cu²⁺ and sensor 1-Cu²⁺ showed a 2: 1 binding stoichiometry to PPi in CH₃CN/HEPES buffer medium (9:1 v/v, pH?=?7.4). The stable pH range of sensor 1 to Cu²⁺ and 1-Cu²⁺ to PPi was from 4 to 8.     

A pyrene-based dual chemosensor for colorimetric detection of Cu2+ and fluorescent detection of Fe3+

A pyrene based chemosensor was designed and synthesized. The pyrene fluorophore was connected with a pyridine unit through a Schiff base structure to give the sensor (L). L was tested with a variety of metal ions and exhibited high colorimetric selectivities for Cu²⁺ and Fe³⁺ over other ions. Upon binding with Cu²⁺ or Fe³⁺, L showed an obvious optical color change from colorless to pink for Cu²⁺ or orange for Fe³⁺ over a wide pH range from 3 to 12. Moreover, the fluorescence of L at 370 nm decreased sharply after bonding with Fe³⁺, while other metal ions including Cu²⁺ had no apparent interference. Thus, using such single chemosensor, Cu²⁺ and Fe³⁺ can be detected independently with high selectivity and sensitivity. The limits of detection toward Cu²⁺ and Fe³⁺ were 8.5 and 2.0 μM, respectively. DFT calculation results also proved the formation of stable coordination complexes and the phenomenon of fluorescence quenching by Fe³⁺. Furthermore, L was also successfully used as a bioimaging reagent for detection of Fe³⁺ in living cells.     

Interaction of a Schiff-base fluorescent sensor with Al3+: experimental and computational studies

A fluorescent Al³⁺ chemo-sensor, 1-phenyl-3-methyl-5-hydroxypyrazole-4-acetone-(3′,4′-dimethylpyrrole-2′-formyl) hydrazone (L), has been synthesized and characterized. L can detect Al³⁺ in ethanol solution with a significant fluorescence enhancement of a turn-on ratio over 155-fold due to the formation of a 1?:?1 complex which is based on the molar ratio between L and Al³⁺ ions, and the 1?:?1 stoichiometric complexation can be obtained from density functional theory calculations. No significant interference of other metal ions such as Na⁺, K⁺, Mg²⁺, Ca²⁺, Ni²⁺, Zn²⁺, Cd²⁺, Co²⁺, Cu²⁺, Fe³⁺, Cr³⁺, Pb²⁺, and Ag⁺ was found. The detection limit for Al³⁺ was 5?×?10^?9?M in ethanol.     

A ratiometric fluorescent probe for zinc ions based on the quinoline fluorophore

A ratiometric fluorescent zinc probe 1 of carboxamidoquinoline with a carboxylic acid group was designed and synthesised. Probe 1 exhibits high selectivity for sensing Zn²⁺; about a 13-fold increase in fluorescence emission intensity and an 82?nm red-shift of fluorescence emission are observed upon binding Zn²⁺ in EtOH/H₂O (1?:?1, V/V) solution. The ratiometric fluorescence response is attributed to the 1?:?1 complex formation between probe 1 and Zn²⁺ which has been utilised as the basis for the selective detection of Zn²⁺. The analytical performance characteristics of the proposed Zn²⁺-sensitive probe were investigated. The linear response range covers a concentration range of Zn²⁺ from 2.0?×?10^?6 to 5.0?×?10^?5?mol?L^?1 and the detection limit is 2.7?×?10^?7?mol?L^?1. The determination of Zn²⁺ in both tap and river water samples shows satisfactory results.