Retraction: Hydrogen sulfate ion sensing in aqueous media based on a fused pyrimido benzothiazole derivative.

[This retracts the article DOI: 10.1039/C6RA01980C.].

Low-Molecular-Weight J-Aggregate Solid Red Emitter for Selective and Quantitative Detection of Cyanide.

A dimethylaniline (donor)-indanedione (acceptor) conjugate (sensor 1) with a very low molecular weight of 277 g mol-1 and intramolecular charge transfer (ICT) characteristics was synthesized. Sensor 1 shows weak ICT fluorescence in solution, but strong emission (Φ=16%) in the solid state owing to intramolecular and intermolecular C-H⋅⋅⋅O hydrogen bonds that inhibit the free rotation of the exocyclic C-C single bond. Compared to yellow emitter 1Y, which has a similar donor-acceptor structure, sensor 1 shows red fluorescence in the solid state owing to J-aggregate formation. The colorimetric and fluorometric responses of sensor 1 to cyanide in both solution and solid state are due to the nucleophilic addition of cyanide to the ß-conjugated carbon of the indanedione group, which prohibits ICT. Additionally, inexpensive portable paper-based test kits based on sensor 1 were easily prepared and could be used for fast and quantitative naked-eye cyanide detection in real time.

Intramolecular C-H⋠⋠⋠O Hydrogen-Bonded Solid Emitter as Colorimetric and Fluorometric Cyanide-Selective Chemodosimeter.

An indole-indanedione-based small molecule, compound 1Me, comprising an intramolecular C-H⋅⋅⋅O hydrogen-bond (H-bond) and with an intramolecular charge transfer (ICT) characteristic was prepared for the colorimetric and fluorometric detection of CN- . Compound 1Me is virtually nonfluorescent in solution but emits a strong yellow fluorescence in the solid state because of the intramolecular C-H⋅⋅⋅O H-bond, which inhibits the free rotation of the exocyclic C-C single bond of 1Me. The nucleophilic addition of CN- to the ß-conjugated carbon of the indanedione group of 1Me, which breaks the intramolecular C-H⋅⋅⋅O H-bond and blocks ICT, causes the colorimetric and fluorometric responses of 1Me to CN- . Furthermore, inexpensive and portable paper-based test kits containing 1Me could be used to rapidly and conveniently sense CN- using the naked eye in real time. The results provide a new strategy for designing colorimetric and fluorometric cyanide-selective sensors based on an intramolecular C-H⋅⋅⋅O hydrogen bonded solid emitter.

Rational Design of an ICT-Based Chemodosimeter with Aggregation-Induced Emission for Colorimetric and Ratiometric Fluorescent Detection of Cyanide in a Wide pH Range.

An alkoxy-substituted 1,3-indanedione-based chemodosimeter 1 with an aggregation-induced emission (AIE) characteristic was rationally designed and synthesized for the ultrasensitive and selective sensing of cyanide in a wide pH range of 3.0-12.0. The nucleophilic addition of cyanide to the ß-conjugated carbon of the 1,3-indanedione group obstructs intramolecular charge transfer (ICT) and causes a significant change in the absorption and fluorescence spectra, enabling colorimetric and ratiometric fluorescent detection of cyanide in a 90% aqueous solution. The cyanide-sensing mechanism is supported by single-crystal X-ray diffraction analysis, time-dependent density functional theory (TD-DFT) calculations, and 1H NMR titration experiments. Sensor 1 exhibits strong yellow fluorescence in the solid state due to the AIE effect, and the paper probes containing 1 can be conveniently used to sense cyanide by the naked eye. Furthermore, chemodosimeter 1 was successfully used for sensing cyanide in real environmental water samples.

Supramolecular super-helix formation via self-assembly of naphthalene diimide functionalised with bile acid derivatives.

The design of chiral chromophores that lead to self-assembly of higher order helical structures is a powerful tool to understand the hierarchical helical structures of molecules of nature. In this work, we present a self-assembled helical super-structure produced via facial stacking of a bile acid bolaamphiphile derivative with a naphthalene diimide core (NDI-DCA), driven by solvophobic effects in THF-H2O solvent mixtures. The chirality of the helical microstructure is directed by the multiple chiral centres in the precursor molecule. The chirality of the hierarchical assemblies was observed using circular dichroism (CD), Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) measurements. We propose that the NDI-DCA super-structures are formed via similar interactions and mechanisms to those observed in biological molecules such as proteins and DNA.

Proton Triggered Colorimetric and Fluorescence Response of a Novel Quinoxaline Compromising a Donor-Acceptor System.

Quinoxaline-based novel acid-responsive probe Q1 was designed on the basis of a conjugated donor-acceptor (D-A) subunit. Q1 shows colorimetric and fluorometric changes through protonation and deprotonation in dichloromethane. With the addition of the trifluoroacetic acid (TFA), UV-vis absorption spectral changes in peak intensity of Q1 was observed. Moreover, the appearance of a new peaks at 284 nm 434 nm in absorption spectra with the addition of TFA indicating protonation of quinoxaline nitrogen and form Q1.H⁺ and Q1.2H⁺. The emission spectra display appearance of new emission peak at 515 nm. The optical property variations were supported by time resolved fluorescence studies. The energy band gap was calculated by employing cyclic voltammetry and density functional calculations. Upon addition of triethylamine (TEA) the fluorescence emission spectral changes of Q1 are found to be reversible. Q1 shows color changes from blue to green in basic and acidic medium, respectively. The paper strip test was developed for making Q1 a colorimetric and fluorometric indicator.

The sensitivity of donor - acceptor charge transfer to molecular geometry in DAN - NDI based supramolecular flower-like self-assemblies.

A charge-transfer (CT) complex self-assembled from an electron acceptor (NDI-EA: naphthalene diimide with appended diamine) and an electron donor (DAN: phosphonic acid-appended dialkoxynapthalene) in aqueous medium. The aromatic core of the NDI and the structure of DAN1 were designed to optimize the dispersive interactions (π-π and van der Waals interactions) in the DAN1-NDI-EA self-assembly, while the amino groups of NDI also interact with the phosphonic acid of DAN1 via electrostatic forces. This arrangement prevented crystallization and favored the directional growth of 3D flower nanostructures. This molecular geometry that is necessary for charge transfer to occur was further evidenced by using a mismatching DAN2 structure. The flower-shaped assembly was visualized by scanning electron and transmission electron microscopy. The formation of the CT complex was determined by UV-vis and cyclic voltammetry and the photoinduced electron transfer to produce the radical ion pair was examined by femtosecond laser transient absorption spectroscopic measurements.

A pyrene based fluorescent turn-on chemosensor: aggregation-induced emission enhancement and application towards Fe3+ and Fe2+ recognition.

A pyrene-based probe bearing benzothiazole ionophore (Py-BTZ) was synthesised as a "turn-on" fluorescent chemosensor for the detection of Fe3+ and Fe2+ ions in CH3CN : H2O (1 : 1, v/v) solvent mixes. The chemosensor showed optical as well as colorimetric changes towards Fe3+ and Fe2+ ions along with a remarkable enhancement in fluorescence emission. The detection limit of Py-BTZ towards Fe3+ and Fe2+ ions was found to be 2.61 µM and 2.06 µM, respectively. The binding of Py-BTZ with Fe3+ and Fe2+ was determined by using FT-IR experiments. Interestingly, Py-BTZ shows aggregation induced emission enhancement (AIEE) properties in polar solvent mixes such as CH3CN : H2O (1 : 1, v/v).

Pyrene-Phosphonate Conjugate: Aggregation-Induced Enhanced Emission, and Selective Fe3+ Ions Sensing Properties.

A new pyrene-phosphonate colorimetric receptor 1 has been designed and synthesized in a one-step process via amide bond formation between pyrene butyric acid chloride and phosphonate-appended aniline. The pyrene-phosphonate receptor 1 showed aggregation-induced enhanced emission (AIEE) properties in water/acetonitrile (ACN) solutions. Dynamic light scattering (DLS) characterization revealed that the aggregates of receptor 1 at 80% water fraction have an average size of ≈142 nm. Field emission scanning electron microscopy (FE-SEM) analysis confirmed the formation of spherical aggregates upon solvent evaporation. The sensing properties of receptor 1 were investigated by UV-vis, fluorescence emission spectroscopy, and other optical methods. Among the tested metal ions, receptor 1 is capable of recognizing the Fe3+ ion selectively. The changes in spectral measurements were explained on the basis of complex formation. The composition of receptor 1 and Fe3+ ions was determined by using Job's plot and found to be 1:1. The receptor 1-Fe3+ complex showed a reversible UV-vis response in the presence of EDTA.