A reversible fluorescence “ON–OFF–ON” sensor for sequential detection of F− and Cu2+ ions and its application as a molecular-scale logic device and security keypad lock

A new azoimine receptor, R₁, was synthesized by Schiff base condensation of 4-(4-butylphenyl) azophenol and 2,6-diaminopyridine and acts as a colorimetric and fluorometric chemosensor for F^? and also toward Cu²⁺ ions in aqueous environment. UV–Vis absorption and fluorescent emission spectra were employed to study the sensing process. Emission study was performed to examine the dual sensing ability of the obtained probe with sequential addition of F^? followed by Cu²⁺ and vice versa. The receptor is an efficient “ON–OFF” fluorescent probe for the fluoride ion. Also, R₁ + F^? operated as an “OFF–ON” fluorescent sensor for Cu²⁺ ions. Considering emission intensity and absorption wavelength for F^? and Cu²⁺ ions, a molecular system was developed with the ability to mimic the functions of XNOR logic gating on the molecular level. In addition, R₁ behaved as a molecular security keypad lock with F^? and Cu²⁺ inputs. The keypad lock operation is particularly important, as the output of the system depends not only on the proper combination but also on the order of input signals, creating the correct password that can be used to “open” this molecular keypad lock through strong fluorescence emission at 460?nm.     

Insights into the photophysics,protonation and Cu2+ ion coordination behaviour of anthracene-9,10-dione-based chemosensors

Carboxylic acid–diamine-based Cu²⁺ chromogenic sensors (3 and 4) exhibited colour switching from red to blue with good sensitivity and selectivity towards Cu²⁺ among other physiologically important alkali, alkaline earth and heavy metal ions. This colour-switching phenomenon arises due to selective deprotonation of aryl amine NH by Cu²⁺. Significantly, chemosensor 3 (λ_max 492 nm) shows multiple modes of complexation towards Cu²⁺. It is very much evident from the appearance of blue colour (λ_max 615 nm) at pH >7.0 and yellow colour (λ_max 465 nm) at pH < 4.0. In addition, chemosensor 3 exhibits a unique logic gate system that involves ‘INHIBIT’ and ‘TRANSFER’ logic gates.     

Sequential Logic Operations with a Molecular Keypad Lock with Four Inputs and Dual Fluorescence Outputs

A novel coumarin–rhodamine conjugate was prepared, and its metal binding properties were studied by UV/Vis and fluorescence spectroscopy. The conjugate serves as a ratiometric and highly selective fluorescent sensor for Hg²⁺ ions. Its metal‐responsive spectral properties were utilized to construct a molecular keypad lock with four inputs and dual fluorescence outputs. The complexity of this molecular logic network can greatly enhance the security level of this device.     

Benzothiazole-based chemosensor for CN− and Cu2+: multi-logic operations within a single molecule

2-Hydroxy-1-naphthaldehyde-based benzothiazole chemosensor (1) undergoes absorption and fluorescence changes with addition of CN^?  and Cu²⁺ ions. Addition of CN^?  ions results in the appearance of two new bands at 420 and 440 nm. However, Cu²⁺ addition causes decrease in absorption band at 370 nm up to 12 equiv., while addition of higher equiv. of Cu²⁺(～190 equiv.) results in the appearance of two new bands at 400 and 800 nm. Differential absorption changes observed with addition of Cu²⁺ and CN^?  ions results in the construction of ‘NOR’ and ‘INHIBIT’ logic gates at 370 and 440 nm, respectively.     

‘On-Off’ reversible switch for Fe and F mimicking XNOR logic function

A new pyrene-appended chemosensor based on thiacalix[4]arene of 1,3-alternate conformation has been synthesised which demonstrates selective optical recognition of Fe³⁺ and F⁻ in two contrasting modes. The chemosensor behaves as a bifunctional fluorescent switch which mimics the performance of an exclusive-NOR (XNOR) logic gate with chemical inputs of Fe³⁺ and F⁻ ions.     

Fluorescent probe mimicking multiple logic gates and a molecular keypad lock upon interaction with Hg2+ and bovine serum albumin

The output fluorescence exhibited by an intramolecular charge transfer fluorescent probe 1 providing different chemical inputs mimicked multiple logic gates. A molecular keypad lock security device authorizing password entries (logic memory) and capable of solving crossword puzzles has been constructed by computing the output emission of 1 upon chemical inputs of BSA and Hg(2+). Based on logic operations the devised fluorescent keypad lock could be unlocked upon entering a correct sequence of password, 'BHU'.     

Piperazine-based new sensor: selective ratiometric sensing of Fe3+, logic gate construction and cell imaging

Newly designed and synthesised chemosensor 1 selectively recognises Fe³⁺ ions in CHCl₃–MeOH (1:1, v/v) by showing ratiometric change in emission and green colouration of the solution under the exposure of UV light. The ensemble 1·Fe³⁺ selectively detects F^?  ions over other halides and the phenomenon is useful to construct combinatorial logic gate. Furthermore, the probe 1 can be used for in vitro detection of Fe³⁺ in human cervical cancer (HeLa) cells.     

Epoxy-based oligomer containing dithia-aza-based naphthylazobenzene pendant: a chemosensor for Hg2+ and Cu2+ ions

A simple epoxy-based oligomer 1 containing naphthylazobenzene-appended dithia-aza moieties was prepared. In UV–vis measurements, the proposed oligomer showed the ion-sensing ability to Hg²⁺ and Cu²⁺ ions. The discrimination between two differently responding Hg²⁺ and Cu²⁺ ions was also realised from ‘ON–OFF’ type fluorescence responses of 1.     

Naphthalene thiourea derivative based colorimetric and fluorescent dual chemosensor for F− and Cu2+/Hg2+ ions

A structurally simple (Z)-2-(naphthalen-2-ylmethylene)-N-phenylhydrazinecarbothioamide (R1) was used as a colorimetric and fluorescent sensor for both F^?  and Cu²⁺/Hg²⁺ ions. R1 selectively recognised F^?  ions as indicated by colour change from colourless to green. Fluorescence spectral data reveal that R1 is an excellent fluorescence chemosensor for Cu²⁺ ions. Finally, R1 was successfully applied to the bioimaging of Cu²⁺ ions in RAW 264.7 macrophage cells.     

A reversible dual-channel chemosensor for fluoride anion

A colorimetric and fluorescent fluoride probe bearing phenolic hydroxy and imine groups has been designed and synthesised. This receptor could visually and spectroscopically recognise F^?  with high selectivity over other anions. After the addition of fluoride ions to the solution of ([1,1′-biphenyl]-4,4′-diylbis (azanylylidene)) bis (methanylylidene)) bis (naphthalen-2-ol) (TY), since the deprotonation reaction occurred between the sensor and fluoride, the fluorescence intensity of the solution changed significantly. Furthermore, the quenched fluorescence caused by fluoride ions could be recovered upon the addition of calcium ions to this complex solution. This resulted in an ‘OFF-ON-OFF’ type sensing. In particular, an IMP logic gate has been proposed using the output obtained from the fluorescence studies. The fluorescence, UV-vis titration and ¹H NMR titration experiments indicated that the effects might occur via a combined process including hydrogen bond and deprotonation between the sensor and F^? .     

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.     

A selective fluorescent probe of Hg2+ based on triazole-linked 8-oxyquinoline calix[4]arene by click chemistry

Calixarene compound 1 with two 8-oxyquinoline subunits was synthesised using ‘click’ chemistry. Compound 1 shows strong fluorescence quenching by Hg²⁺ and lower pH. Using the fluorescence behaviour of 1 towards Hg²⁺ and lower pH, a NOR (not an OR) logic gate was established.     

A multichannel thiacalix[4]arene-based fluorescent chemosensor for Zn2+, F− ions and imaging of living cells

Abstract

The fluorescent sensor (3) based on the 1,3-alternate conformation of the thiacalix[4]arene bearing the coumarin fluorophore, appended via an imino group, has been synthesised. Sensing properties were evaluated in terms of a colorimetric and fluorescence sensor for Zn²⁺ and F^?. High selectivity and excellent sensitivity were exhibited, and ‘off-on’ optical behaviour in different media was observed. All changes were visible to the naked eye, whilst the presence of the Zn²⁺ and F^? induces fluorescence enhancement and the formation of a 1:1 complex with 3. In addition, 3 exhibits low cytotoxicity and good cell permeability and can readily be employed for assessing the change of intracellular levels of Zn²⁺ and F^?.     

Imidazo[1,2-a]pyridine-substituted coumarin as a selective ratiometric sensor for Cu2+ ion

A novel fluorescent chemosensor, (E)-7-(diethylamino)-3-((2-phenylimidazo[1,2-a]pyridin-3-ylimino)methyl)-2H-chromen-2-one 1a, has been synthesised and characterised. This chemosensor displayed an extreme selective fluorescence emission only with Cu²⁺ ion over all other metal ions examined. The Job’s plot experiment analysis suggested the binding ratio of the chemosensor 1a with Cu²⁺ was 1:1 metal-to-ligand ratio. The association constant for Cu²⁺ towards receptor 1a obtained from Benesi–Hildebrand plot was found to be 4.859 × 10³ M^?1 with a detection limit 4.6 × 10^?8 M. Fluorescence enhancement caused by Cu²⁺ binding with chemosensor 1a attributed to combinational effect of intramolecular charge transfer and chelation-enhanced fluorescence occurred at pH 8.0.     

Anthraquinone-modified calix[4]arene: click synthesis,selective calcium ion fluorescent chemosensor and INHIBIT logic gate

Novel anthraquinone-modified calix[4]arene was synthesized by click chemistry and exhibited selective fluorescent enhancement in the presence of Ca²⁺, which is attributed to photo-induced electron-transfer effect from the 1,2,3-triazole ring. The enhanced fluorescence was further quenched by F^?  ion. Thus, the potential Ca²⁺ and F^?  ion switched INHIBIT logic gate has been constructed.     

Development of solution‐dispersible hyperbranched conjugated polymer nanoparticles for Fe3+ fluorescent detection and their application in logic gate

Solution‐dispersible hyperbranched conjugated polymer nanoparticles (FT‐HBCPNs) consist of an intrinsic crosslinked rigid skeleton structure of both 9,9‐dihexyl‐fluorene and triphenylamine repeating units, and are synthesized via the miniemulsion Suzuki polymerization, and FT‐HBCPNs for highly selective and sensitive Fe³⁺ fluorescent detection and their application in logic gate at molecular level are successfully developed. FT‐HBCPNs with an average particle size of 10.6 nm can disperse in common organic solvents. FT‐HBCPNs show high selectivity and sensitivity for Fe³⁺ over other commonly co‐existent metal ions in THF solution with a detection limit of 3.65 × 10^?8 mol L^?1. Furthermore, homogeneous transparent thin films of FT‐HBCPNs developed by a simple spin‐coating method can be reversibly quenched by Fe³⁺ with a detection limit of 3.09 × 10^?7 mol L^?1. Using Fe³⁺ and EDTA as chemical inputs and the fluorescence intensity signal as outputs, FT‐HBCPNs films can be utilized as a logic gate at molecular level. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3694–3700     

Unique Fluorogenic Ratiometric Fluorescent Chemodosimeter for Rapid Sensing of CN− in Water

A new benzimidazole‐spiropyran conjugate chemosensor molecule ( BISP ) has been synthesized and characterized by ¹H NMR spectroscopy, mass spectrometry (ESI‐MS), and elemental analysis. The two isomeric forms ( BISP ? BIMC ) were shown to be highly selective and sensitive to CN^? among the ten anions studied in aqueous HEPES buffer, as shown by fluorescence and absorption spectroscopy and even by visual color changes, with a detection limit of 1.7 μM for BIMC . The reaction of CN^? with BIMC was monitored by ¹H NMR spectroscopy, high‐resolution mass spectrometry (HRMS), UV/Vis measurements, and fluorescence spectroscopy in HEPES buffer of pH 7.4. TDDFT calculations were performed in order to correlate the electronic properties of the chemosensor with its cyanide complex. Further, titration against thiophilic metal ions like Au³⁺, Cu²⁺, Ag⁺, and Hg²⁺ with [ BIMC‐CN ] in situ showed that it acts as a secondary recognition ensemble toward Au³⁺ and Cu²⁺ by switch‐on fluorescence. In addition, a reversible logic‐gate property of BIMC has been demonstrated through a feedback loop in the presence of CN^? and Au³⁺ ions, respectively. Furthermore, the use of BIMC to detect CN^? in live cells by fluorescence imaging has also been demonstrated. Notably, test strips based on BIMC were fabricated, which could serve as convenient and efficient CN^? test kits.     

Thiophene and diethylaminophenol-based “turn-on” fluorescence chemosensor for detection of Al3+ and F− in a near-perfect aqueous solution

A new fluorescent sensor 1, based on thiophene and diethylaminophenol moieties, has been synthesized and its binding capabilities for metal-ion and anion recognition were investigated. The sensor 1 showed ‘turn-on’ fluorescence in the presence of Al³⁺ and F^?. The sensing behaviors of 1 with Al³⁺ and F^? were studied by using photophysical experiments, ¹H NMR titration, and ESI-mass spectrometry analysis. The detection limits for the analysis of Al³⁺ and F^? were found to be 0.41 μM and 14.36 μM, respectively, which are below the WHO guidelines for drinking water (7.41 μM for Al³⁺ and 79 μM for F^?). Moreover, turn-on fluorescence of 1 toward Al³⁺ and F^? caused by intramolecular charge transfer (ICT) was well explained by density functional theory (DFT) calculations. Importantly, 1 could be used to detect Al³⁺ in the living cells.     

A rapid selective colorimetric and ‘On–Off’ fluorimetric sensor for detecting Cu2+ ions in aqueous media based on a simple bis-schiff-base derivative

A simple colorimetric and fluorimetric ‘On–Off’ sensor L (3,3′-dimethyl -[1,1′-biphenyl]-4,4′-diyl)bis(azanylylidene)bis(methanylylidene)bis(naphthalen-2-ol) for Cu²⁺ ions bearing o-tolidine substituents has been designed and synthesised, and exhibits significant fluorimetric and colorimetric response for Cu²⁺ in DMSO/H₂O (8:2, v/v) HEPES buffer (pH 7.2) solution. The detection limit of the sensor towards Cu²⁺ is 7.25 × 10^? 8 M and the association constant K_a of 9.86 × 10⁴ M^? 1 was determined. Furthermore, other anions, including Fe³⁺, Hg²⁺, Ag⁺, Ca²⁺, Co²⁺, Ni²⁺, Cd²⁺, Pb²⁺, Zn²⁺, Cr³⁺ and Mg²⁺ have almost no influence on the probe's behaviour. Test strips based on the sensor L were fabricated, which could act as convenient and efficient Cu²⁺ test kits.     

Three isomeric copper(II) coordination polymers based on a bis-triazole-bis-amide ligand: Assembly,structures, and luminescent properties

Three copper(II) isomers, [Cu(dtcd)(DNBA)₂]_n (1–3) (HDNBA = 3,5-dinitrobenzoic acid, dtcd = N,N-di(4H-1,2,4-triazole)cyclohexane-1,4-dicarboxamide), were synthesized in a one-pot reaction, and structurally characterized. Polymer 1 shows a 1-D single chain in which dtcd connect adjacent Cu²⁺ ions, while DNBA^? is monodentate. In 2, every two Cu²⁺ ions are linked by carboxylate of a DNBA^? in a chelate-bridging mode into a binuclear unit, which is further connected by dtcd ligands into a 1-D double chain. In 3, dtcd connect Cu²⁺ ions via triazole nitrogens to generate 1-D single chains, which are further extended into a 2-D network by the amide oxygens of a dtcb from an adjacent chain. The pH plays an important role in product distribution of 1–3. The coordination behaviors of dtcd and DNBA^? also influence the final structures. Luminescent properties of 1–3 have been investigated.