Solvent- and Light-Sensitive AIEE-Active Azo Dye: From Spherical to 1D and 2D Assemblies

Fluorescent molecular assembly systems provide an exciting platform for creating stimuli-responsive nano- and microstructured materials with optical, electronic, and sensing functions. To understand the relationship between (i) the plausible molecular structures preferentially adopted depending on the solvent polarity (such as N,N-dimethylformamide [DMF], tetrahydrofuran [THF], and toluene), (ii) the resulting spectroscopic features, and (iii) self-assembled nano-, micro-, and macrostructures, we chose a sterically crowded triangular azo dye (3Bu) composed of a polar molecular core and three peripheral biphenyl wings. The chromophore changed the solution color from yellow to pink-red depending on the solvent polarity. In a yellow DMF solution, a considerable amount of the twisted azo form could be kept stable with the help of favorable intermolecular interactions with the solvent molecules. By varying the concentration of the DMF solution, the morphology of self-assembled structures was transformed from nanoparticles to micrometer-sized one-dimensional (1D) structures such as sticks and fibers. In a pink-red toluene solution, the periphery of the central ring became more planar. The resulting significant amount of the keto-hydrazone tautomer grew into micro- and millimeter-sized 1D structures. Interestingly, when THF-H2O (1:1) mixtures were stored at a low temperature, elongated fibers were stacked sideways and eventually developed into anisotropic two-dimensional (2D) sheets. Notably, subsequent exposure of visible-light-irradiated sphere samples to solvent vapor resulted in reversible fluorescence off↔on switching accompanied by morphological restoration. These findings suggest that rational selection of organic dyes, solvents, and light is important for developing reusable fluorescent materials.

Role of Solvent Polarity on Dispersion Quality and Stability of Functionalized Carbon Nanotubes

Dispersion of carbon nanotubes (CNT) in solvents and/or polymers is essential to reach the full potential of the CNTs in nanocomposite materials. Dispersion of CNTs is especially challenging due to the van-der-Waals attraction forces between the CNTs, which let them tend to re-bundle and/or re-aggregate. This paper presents a brief analysis of the quality and stability of functionalized multiwalled carbon nanotubes (fMWCNT) dispersion on polar solvents. A comparative study of functionalized CNT dispersion in water, methyl, and alcohol-based organic solvents has been carried out and the dispersion has been characterized by UV-VIS spectroscopy, electrochemical characterization such as cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Visual analysis of the dispersion has been investigated for up to 14 days to assess the dispersion’s stability. Based on the material characterization, it was observed that the degree of affinity fMWCNT with -COOH group highly depends on the polarity of the solvent, where the higher the polarity, the better the interaction of fMWCNT with solvents.

Synthesis of gold nano-mushrooms via solvent-controlled galvanic replacement to enhance phototherapeutic efficiency

In galvanic replacement, it was found that the solvent polarity had a significant effect on the formed nanostructure. Hollow-tailed Au nano-mushrooms were synthesized under co-solvent conditions and used in effective cancer phototherapy.

Polymeric Micelles: A Novel Approach towards Nano-Drug Delivery System

Nano delivery systems, polymeric micelles represent one of the most promising delivery platforms for therapeutic compounds. It has shown that a poorly soluble molecule which has high potency and remarkable toxicity can be encapsulated with the polymeric micelle. There are various poorly soluble drugs used in micellar preparations, mostly for their anti-cancer activity. Drugs in the inner core protect the drug from degradation and allow drug accumulation in the tumour site in the case of cancer treatment. Block copolymers are chosen based on the physicochemical characteristics of medicinal drugs. The amphiphilic block copolymer structure has both lipophilic and hydrophilic blocks, which enclose tiny hydrophobic molecules. It is a targeted drug delivery method because of its high effectiveness for drug retention in tissue, prevention of enzymes from degradation, and improvement of the cellular absorption mechanism. In an experimental environment, variations in temperature and solvent polarity stimulate copolymer micelle self-assembly. This is a thermodynamically guided procedure in which self-assembly happens by converting polymeric micelles. These aggregates go from a non-equilibrium to a thermodynamically equilibrium state, and they stay stable for a long time. The balance of thermodynamic and kinetic forces is critical in micelles self-assembly because the kinetic process predicts assembly behaviour and hierarchical structure. The purpose of this special issue is to provide an updated overview of micelles, a number of polymers and drugs commonly used in micellar preparation and their application.

Novel Metallochromic Hydrazone-Based Chemosensor Toward Colorimetric Paper Strip For Selective Detection Cu2+

A solid-state sensor was developed for the determination of copper ions (Cu2+) in aqueous media using tricyanofuranhydrazone as a spectroscopic probe and a paper sheet as the hosting strip. A new tricyanofuranhydrazone-based colorimetric chemosensor (TCFH) was synthesized for selective detection of Cu2+ in aqueous environments. The synthesis strategy of TCFH involved an azo-coupling process between the diazonium salt of 8-aminoquinoline and an active methyl-bearing tricyanofuran (TCF) heterocyclic moiety. The molecular structure of the prepared TCFH chemical sensor was verified with FT-IR, 1H and 13C NMR, as well as elemental analysis. Due to intramolecular charge transfer, TCFH chromophore demonstrated pronounced solvatochromism depending on the solvent polarity. Changes in both color and UV-vis absorption spectra demonstrated by the developed chemosensor proved that TCFH can be utilized to detect Cu2+ in the presence of other competing metallic cations and anions. The synthesized TCFH probe, which contains a hydrazone recognition moiety, demonstrates dramatic solvatochromic activity and high selectivity at the microlevel of copper ions with a color shift from yellow to purple. Mechanisms accounting for both metallochromic and solvatochromic activities were explored. Moreover, test strips of TCFH were successfully developed and applied for the detection of copper ions at different concentrations in aqueous media. The colorimetric properties of the prepared TCFH-immobilized paper strips were investigated by CIE Lab chromogenic parameters, colorimetric strength (K/S) and UV-Vis absorbance spectra. The metallochromic paper strip exhibited a detection limit at the ppm range. The best detection of Cu2+ was achieved in the pH range of 6.6-7.4 demonstrating an immediate color switch from yellow to purple relying on the total content of Cu2+. Scanning electron microscopy (SEM) was applied to characterize the deposition of tricyanofuranhydrazone onto the surface of the paper strip.

Controlling the Twisted Intramolecular Charge-Transfer Character of Pyrene Derivatives Through Solvent Polarity

Intramolecular charge transfer (ICT) plays a critical role in determining the photophysical properties of organic molecules, including their luminescence efficiencies. Twisted intramolecular charge transfer (TICT) is a process in which structural change accompanies ICT. Despite significant research, the relationship between TICT and solvent polarity, and its effects on photophysical properties, have been rarely investigated. Herein, we used time-resolved spectroscopy to study TICT in pyrene derivatives that are promising blue organic light emitting diode (OLED) emitter candidates; these derivatives show strong solvent-dependent charge-transfer (CT) behavior. Slight structural changes that do not affect excited state dynamics were observed in nonpolar solvents, while polar solvents were found to affect excited state dynamics and CT characteristics. The TICT behavior of these pyrene derivatives could be modulated through structural modification. Our study provides valuable guidelines for the control of optical properties, including the luminescence efficiencies of OLED emitters that show TICT characteristics.

Environment-Sensitive Fluorescent Labelling of Peptides by Luciferin Analogues

Environment-sensitive fluorophores are very valuable tools in the study of molecular and cellular processes. When used to label proteins and peptides, they allow for the monitoring of even small variations in the local microenvironment, thus acting as reporters of conformational variations and binding events. Luciferin and aminoluciferin, well known substrates of firefly luciferase, are environment-sensitive fluorophores with unusual and still-unexploited properties. Both fluorophores show strong solvatochromism. Moreover, luciferin fluorescence is influenced by pH and water abundance. These features allow to detect local variations of pH, solvent polarity and local water concentration, even when they occur simultaneously, by analyzing excitation and emission spectra. Here, we describe the characterization of (amino)luciferin-labeled derivatives of four bioactive peptides: the antimicrobial peptides GKY20 and ApoBL, the antitumor peptide p53pAnt and the integrin-binding peptide RGD. The two probes allowed for the study of the interaction of the peptides with model membranes, SDS micelles, lipopolysaccharide micelles and Escherichia coli cells. Kd values and binding stoichiometries for lipopolysaccharide were also determined. Aminoluciferin also proved to be very well-suited to confocal laser scanning microscopy. Overall, the characterization of the labeled peptides demonstrates that luciferin and aminoluciferin are previously neglected environment-sensitive labels with widespread potential applications in the study of proteins and peptides.

Estimating the Ground and Excited State Dipole Moments of Levofloxacin and Norfloxacin Drugs Using Solvatochromic Effects and Computational Work

Levofloxacin (LVF) and norfloxacin (NRF) are a group of fluoroquinolone antibiotics, broad spectrum used to treat various infections caused by many bacterial species. The drugs contain functional groups which control the type and degree of interaction with different solvents. In this research, the ground and excited state dipole moments of LVF and NRF drugs were estimated using solvatochromic effects and computational work. The dipole moments were estimated from absorption and emission spectra in polar and nonpolar solvents using Bakhshiev’s, Kawski–Chamma–Viallet, Lippert–Mataga, and Reichardt models. The results indicated the emission spectra are more strongly affected by solvent polarity than the absorption spectra. The calculated excited state dipole moment is larger than that of the ground state, indicating that the probe compounds are significantly more polarized in the excited state than in the ground state. From computational work, the HOMO-LUMO energy band gap, the dipole moments, electron charge density distribution, and oscillator strength were determined using the semiempirical MP6 method, DFT-B3LYP-6-31G, and DFT-B3LYP-3-21G employing Gaussian 09 software. In general, larger dipole moments were obtained by computation rather than from experiments due to the absence of solvent effects.