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.

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).

Fabrication of diverse nano-architectures through the self-assembly of a naphthalene diimide derivative bearing four carbamates

We found that naphthalene diimide (W2) bearing four carbamates bonds can organise various well-defined self-assembled nanostructures driven by π–π interaction and carbamate H-bonding.

Spermine-directed supramolecular self-assembly of water-soluble AIE-active tetraphenylethylene: nanobelt, nanosheet, globular and nanotubular structures

Tetrasulfonate-tetraphenylethylene (Su-TPE) is non-emissive in water and upon addition of a good solvent such as THF (f_THF = 95%) it displays strong fluorescence emission with a quantum yield of 6.33%.

Synthesis and Liquid Crystalline Properties of Unsymmetrically Substituted Naphthalenediimides with a Polar Headgroup: Effect of Amide Hydrogen Bonding and Alkyl Chain Length

A series of new unsymmetrically substituted naphthalenediimide (NDI) moieties NDI-1 to NDI-6 were synthesized. The structures of these compounds were confirmed by means of FT-IR, 1H NMR, 13C NMR, ESI-mass and HRMS spectroscopic measurements. UV/Vis and fluorescence spectroscopy were employed to investigate the photophysical properties of the prepared compounds in solution and in the solid state. Using the onset of UV/Vis absorption, the optical band gaps were calculated. Cyclic voltammetry measurements were performed to study the electrochemical behavior and to calculate the LUMO energy levels. The thermal properties of NDI derivatives were studied by differential scanning calorimetry. The mesomorphic birefringent behavior of the NDI derivatives was investigated with polarizing optical microscopy. Among all of the studied NDI derivatives, only NDI-1, NDI-2, and NDI-3 showed liquid crystalline texture, owing to the presence of an amide linkage for H-bonding along with aromatic moieties for π-π-stacking.

Cover Feature: Synthesis and Liquid Crystalline Properties of Unsymmetrically Substituted Naphthalenediimides with a Polar Headgroup: Effect of Amide Hydrogen Bonding and Alkyl Chain Length (ChemistryOpen 1/2018)

The Cover Feature illustrates the outstanding liquid‐crystalline properties of unsymmetrically substituted naphthalenediimides through amide hydrogen bonding and hydrophobic interactions along with p—p stacking. More information can be found in the Full Paper by N. V. Ghule et al. on page 61 in Issue 1, 2018 (DOI: 10.1002/open.201700151).

Effect of Amide Hydrogen Bonding Interaction on Supramolecular Self-Assembly of Naphthalene Diimide Amphiphiles with Aggregation Induced Emission

In the present work, two new naphthalene diimide (NDI) amphiphiles, NDI-N and NDI-NA, were successfully synthesized and employed to investigate their self-assembly and optical properties. For NDI-NA, which contains an amide group, aggregation-induced emission enhancement (AIEE) was demonstrated in the presence of various ratios of methylcyclohexane (MCH) in chloroform, which led to the visual color changes. This new amide-containing NDI-NA amphiphile formed nanobelt structures in chloroform/MCH (10:90, v/v) and microcup-like morphologies in chloroform/MCH (5:95, v/v). The closure of these microcups led to the formation of vesicles and microcapsules. The structural morphologies gained from the solvophobic control of NDI-NA were confirmed by various complementary techniques such as infrared spectroscopy, X-ray diffraction, and scanning and transmission electron microscopy. In the absence of the amide moiety in NDI-N, no self-assembly was observed, indicating the fundamental role of H-bonding in the self-association process.

Photomodulation of fluoride ion binding through anion-π interactions using a photoswitchable azobenzene system

The discovery of photoswitchable azobenzene-systems that undergo trans-to-cis photoisomerisation was a milestone in supramolecular chemistry. Such photoswitches have possible applications in data storage, stimuli responsive delivery systems, and molecular machines due to fast and selective switching. However, the light induced cis isomer of azobenzene is rather unstable and reverts thermally and photochemically to the thermodynamically stable trans configuration. We report, for the first time, controlled photoswitching of an azo-naphthalenediimide (azo-NDI) which can be achieved upon binding of fluoride ions through anion-π interaction. This NDI-F-NDI "sandwich" stabilises the cis configuration through the generation of an NDI(•-) radical anion, and a dianionic, NDI(2-) species that becomes unusually stable in the cis form. The sandwiched cis form reverts to the trans form only upon decomplexation of F(-). A model pollutant was successfully degraded using the photogenerated NDI-F-NDI sandwich. This opens a wide range of applications in molecular and supramolecular nanotechnology.

The fluorescence detection of autophagosomes in live cells under starvation using core-substituted naphthalenediimide probes

We developed NDI-C probe for the analysis of the autophagosomes in live cells. A new flow cytometric method was also developed for the analysis of cell population on the basis of intracellular pH.

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

The receptor 3-cyano-4-imino-2-methylthio-4H-pyrimido[2,1-b][1,3]benzothiazole (SVK-1) was employed for the selective sensing of HSO₄⁻ ions in aqueous media.

Controlled chiral supramolecular assemblies of water soluble achiral porphyrins induced by chiral counterions

A controlled handed chiral supramolecular assembly of achiral porphyrins induced by chirald- andl-arginine (Arg) in water.