Novel solvatochromic and halochromic sulfahydrazone molecular switch

Green and sustainable smart wooden system integrated with cellulose nanowhiskers-supported polyvinyl alcohol and anthocyanin biomolecules to monitor food freshness

Smart packaging materials have been used to protect human health from environmental hazards by sending real-time colorimetric signals for changes in the food packaging environment. However, the colorimetric material sensors use synthetic sensor dyes, which are toxic, expensive, non-biodegradable, and difficult to prepare. Herein, a simple strategy is presented for the development of an environmentally-friendly halochromic wood able to change color upon exposure to spoilage of food. A combination of anthocyanin (Ac)/aluminum (Al) mordant (Ac/Al) nanoparticles and cellulose nanowhiskers (CNW)-reinforced polyvinyl alcohol (PVA) was infiltrated into a delignified wood to produce a translucent wood with halochromic properties. CNW were employed as reinforcement agent to improve the mechanical performance of PVA. Additionally, CNW function as a dispersing agent to prevent agglomeration of Ac/Al nanoparticles. The diameters of CNW are in the range of 12-19 nm, whereas Ac/Al particles showed diameters of 9-22 nm. The smart wood changed color from purplish to colorless when exposed to food spoilage. A hypsochromic change from 539 nm to 370 nm was shown by the anthocyanin receptor when the spoilage level of food increased. This could be attributed to the pH-driven molecular switching of anthocyanin, leading to charge delocalization.

Sulfonamides as Optical Chemosensors

Sulfonamides are auspicious chemosensors which are capable to bind with ionic species through various ways like complexation, charge transfer, proton transfer etc. and produce a detection signal in the form of an optical change either in visible or UV-light and for electronic as well as fluorimetric spectra. Sulfonamides have gained much attention of analytical chemists these days as these are inexpensive, robust, green in nature and some what sensitive and selective to many anionic and cationic species. Due to their promising versatility in sensing properties, these are under great consideration in forensic, environmental, analytical and biochemistry laboratories. This review narrates how sulfonamides are being used to optically sense ionic species.

Modification of wood lignin and integration with multifunctional polyester nanocomposite

A simple strategy was introduced to develop fluorescent wood with the ability to alter its color when exposed to both visible and ultraviolet lights. Injecting a combination of europium and dysprosium doped aluminate (EDA; 7-12 nm) nanoparticles and polyester resin (PET) into a lignin-modified wood (LMW) produced a translucent smart wooden window with fluorescence and afterglow emission properties. In order to prevent formation of aggregates and improve the preparation process of transparent woods, EDA must be properly disseminated in the polyester matrix. We analyzed the fluorescent wood samples using a variety of spectroscopic and microscopic methods, including energy-dispersive X-ray (EDX), scanning electron microscopy (SEM), photoluminescence spectra, and hardness tests. We found that the photoluminescent woods had an excitation peak at 365 nm and emission peaks at 437 nm and 517 nm. The translucent luminous woods showed rapid and reversible emission response to ultraviolet light. Fluorescence emission was detected for samples with lower EDA content, and afterglow emission was detected for wood samples with higher EDA content. Increases in EDA content were associated with improvements in water resistance and ultraviolet radiation protection in the EDA@PET-infiltrated wood.

Development of toxic gas sensor from anthocyanin-embedded polycaprolactone-co-polylactic acid nanofibrous mat

The colorless ammonia gas has been a significant intermediate in the industrial sector. However, prolonged exposure to ammonia causes harmful effects to organs or even death. Herein, an environmentally friendly solid-state ammonia sensor was developed utilizing colorimetric polycaprolactone-co-polylactic acid nanofibrous membrane. Pomegranate (Punica granatum L.) peel contains anthocyanin (ACN) as a naturally occurring spectroscopic probe. A mordant (potassium aluminum sulfate) is used to immobilize the anthocyanin direct dyestuff inside nanofibers, generating mordant/anthocyanin (M/ACN) coordinated complex nanoparticles. When exposed to ammonia, the color change of anthocyanin-encapsulated polycaprolactone-co-polylactic acid nanofibrous membrane from purple to transparent was examined by absorbance spectra and CIE Lab color parameters. With a quick colorimetric shift, the polycaprolactone-co-polylactic acid fabric exhibits a detection limit of 5-150 mg/L. The absorbance spectra showed a hypsochromic shift when exposed to ammonia, displaying an absorption shift from 559 nm to 391 nm with an isosbestic point of 448 nm. Scanning electron microscopy (SEM) images revealed that the polycaprolactone-co-polylactic acid nanofibers had a diameter of 75-125 nm, whereas transmission electron microscopy (TEM) images revealed that M/ACN nanoparticles exhibited diameters of 10-20 nm.

Development of photoluminescent viscose fibers integrated with polymer containing lanthanide-doped phosphor

Smart clothing refers to textiles that can sense an external stimulus by changing their physical properties such as colorimetric and fluorescent fabrics. The pad-dry-curing coloration approach was used to apply a luminous and hydrophobic composite coating onto cellulose-based materials. This novel method includes incorporating phosphor nanoparticles made from lanthanide-doped strontium aluminum oxide (LSAO) into room temperature vulcanizing silicone rubber (RTV). The LSAO nano-sized particles (3-8 nm) must be mixed evenly throughout RTV without aggregation to allow for the formation of a colorless layer onto viscose surface. Pad-dry-curing the film onto viscose cloth worked well at room temperature. The contact angles of the luminous fibers enhanced from 138.6° to 158.2° as the LSAO ratio increased. The antimicrobial and ultraviolet (UV) protection of the LSAO-finished viscose were investigated. The transparent fluorescent film on viscose surface was excited at 367 nm to display an emission peak at 518 nm. According to CIE Lab coordinates and luminescence analyses, the fluorescent viscose fibers showed various colors, including white under visible light, intense green beneath UV device, and greenish-yellow under darkness. The comfort properties of the LSAO-finished viscose were assessed by measuring their bend length and permeability to air. Transmission electron microscopic analysis of LSAO nanoparticles was explored. Energy dispersive x-ray, x-ray fluorescence, and scanning electron microscopy were utilized to describe the spectroscopic outcomes of the treated textiles. The colorfastness of the LSAO-finished viscose fabrics was examined. The coated fabrics exhibited a non-fatigable reversible luminous photochromism in response to UV illumination. RESEARCH HIGHLIGHTS: Multifunctional LSAO@RTV nanocomposite was pad-dry-cured onto viscose textile. Photochromism to green under UV light and greenish-yellow in the dark was detected. Efficient antimicrobial, UV protective, and superhydrophobic activity were observed. The antimicrobial properties were maintained for 24 washing cycles. Pad-dry-cured viscose showed good comfortability and photostability.

Green preparation of electrically conductive solution blow spun nanofibers from recycled polyethylene terephthalate via plasma-assisted oxidation-reduction

Simple and green strategy was described for the development of multifunctional polyester nanofibers (PNFs). Solution blow spinning (SBS) technology was applied to in situ immobilize nanocomposites of polyaniline (PANi) and silver nanoparticles (AgNPs) into plasma-treated polyester nanoscaled fibers prepared. The polyester nanofibers were prepared from recycled polyethylene terephthalate waste, which was exposed plasma-curing and a REDOX reaction in the presence of AgNO₃, aniline, and CH₃COONH₄. Plasma-catalyzed oxidative polymerization of aniline to polyaniline together with a reductive process of Ag⁺ to silver nanoparticles led to their enduring insoluble dispersion into the surface of polyester nanofibers. By taking the advantage of the PANi oxidation, AgNPs were precipitated from an aqueous medium of AgNPs. The morphological properties were investigated by various analytical techniques. The polyester fiber diameter was determined in the range of 450-650 nm. In addition, transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were utilized to examine AgNPs, demonstrating diameters of 4-20 nm. The plasma-uncured AgNPs/PANi immobilized nanofibrous film displayed weak absorption bands at 399 nm and 403 nm upon increasing the concentration of AgNPs. On the other hand, the plasma-cured AgNPs/PANi immobilized nanofibers displayed strong absorption bands at 526 nm and 568 nm upon increasing the concentration of AgNPs. The AgNP-induced antimicrobial performance and the PANi-induced electrically conductivity were explored. The prepared PNFs showed high UV protection.

Development of photoluminescent artificial nacre-like nanocomposite from polyester resin and graphene oxide

Long-lasting phosphorescent nacre-like material was simply prepared from a nanocomposite of inorganic and organic materials. Low molecular weight unsaturated polyester (PET), graphene oxide (GO), and nanoparticles of rare-earth activated aluminate pigment were used in the preparation process of an organic/inorganic hybrid nanocomposite. Using methylethylketone peroxide (MEKP) as a hardener, we were able to develop a fluid solution that hardens within minutes at room temperature. Covalent and hydrogen bonds were introduced between the polyester resin and graphene oxide nanosheets. The interface interactions of those bonds resulted in toughness, excellent tensile strength, and high durability. The produced nacre substrates demonstrated long-persistent and reversible luminescence. The excitation of the produced nacre substrates at 365 nm resulted in a 524 nm emission. After being exposed to UV light, the photoluminescent nacre substrates became green. The increased superhydrophobic activity of the produced nacre substrates was achieved without affecting their physico-mechanical properties.

A novel three-position molecular switch based on the transformations of a cyano-substituted pyrrol-2-one derivative

A new nitrile-rich heterocycle showing a reversible naked-eye response to basic and nucleophilic agents as well as to temperature was characterized.

Synthesis, characterization, and self-assembly of fluorescent fluorine-containing liquid crystals

S_N Ar has been used to synthesize various functionalized derivatives of pentafluorobenzenes which are highly specific at the para position; and consequently are ideal for building calamitic (rod-like) liquid crystalline molecular systems. Here, we display the effectiveness of S_N Ar chemistry as a convenient method toward the synthesis of fluorescent liquid crystalline perfluorinated comprising ethers and thioethers in excellent yields and high purity. In the current work, we describe the synthesis, self-assembly, and mesogenic properties of new perfluorinated para-terphenyls bearing various para-substituted alkoxy and thioalkoxy chains. The terphenyl core was prepared using Cu(I) (or Cu(I)/phenanthroline)-catalyzed decarboxylative carbon-carbon (or carbon-oxygen [sulfur]) cross-coupling from the analogous aromatic iodide and fluorobenzoate potassium salt. The molecular structures of the prepared perfluorinated terphenyls were demonstrated with ¹ H, ¹³ C, and ¹⁹ F NMR, as well as FT-IR and X-ray crystallography. The liquid crystalline properties and mesogenic phases were characterized with differential scanning calorimetry and high-resolution polarized optical microscope. Both UV-visible absorbance and emission spectra demonstrated solvatochromism. Supramolecular self-assembly of the generated perfluorinated para-terphenyls was monitored by van der Waals and π-π stacking interaction forces. The creation of nanofibrous architectures was monitored by scanning electron microscopy.

Synthesis and characterization of novel fluoroterphenyls: self-assembly of low-molecular-weight fluorescent organogel

Nucleophilic aromatic substitution has been highly para selective on a range of functionalized pentafluorobenzenes. Here, we demonstrate the utility of nucleophilic aromatic substitution chemistry for the preparation of fluorinated fluorescent low-molecular-weight organogels. The molecular design, synthesis and photophysical performance of a new class of thermoreversible and fluorescent low-molecular-weight organogels from para-alkoxy-functionalized fluorinated terphenyls are described. Both CuI-catalyzed decarboxylative cross-coupling and nucleophilic aromatic substitution chemistry were used for the preparation of those highly fluorinated gelators in high yields and excellent purity via simple filtration, from the corresponding potassium fluorobenzoate salts and aryl iodides. Various fluorinated symmetrical and asymmetrical para terphenyls were prepared with various para terminal alkoxy tails. Those fluorinated terphenyls were characterized using X-ray crystallography, differential scanning calorimetry, Fourier-transform infrared spectroscopy, as well as ¹ H, ¹³ C, and ¹⁹ F nuclear magnetic resonance. UV-visible light absorbance and emission spectra of those new materials displayed a solvatochromic and solvatofluorochromic behaviour, respectively. Self-assembly of the produced fluorinated terphenyls occurred via cooperative π-π stacking and van der Waals interactions, which resulted in gelating various organic solvents. Scanning electron microscopy displayed the formation of fibre-like nanostructures. The cytotoxicity of some selected fluorinated symmetrical and asymmetrical para terphenyls was explored.

Synthesis and characterization of novel tricyanofuran hydrazone probe: solvatochromism, density-functional theory calculation and selective fluorescence, and colorimetric determination of iron (III)

A tricyanofuran hydrazone (TCFH) spectroscopic probe was produced to visually recognize Fe(III) ions in aqueous environments. The synthesis was started by reacting tricyanofuran with 4-aminophenol diazonium chloride. All the synthesized compounds were characterized by spectroscopic analyses. TCFH showed distinctive solvatochromic behaviour in various organic polar solvents due to intramolecular charge transfer. Its behaviour towards sensing Fe(III) was studied using ultraviolet-visible spectrophotometry. The sensing behaviours of the proposed probe for other metal ions, namely Co(II), Cr(III), Mg(II), Pb(II), Cd(II), Ba(II), Hg(II), Mn(II), Ni(II), Cu(II), Zn(II), Ca(II), Al(III), Na(I) and K(I), were also investigated, but no spectral changes were observed, indicating the probe's potential use as a highly selective and Fe(III)-sensitive colorimetric and fluorescent chemical sensor. The TCFH probe using EtOH/H₂ O (5:1; v/v) served as a colorimetric and fluorescent chemosensor for identification of Fe(III) by the naked eye owing to both its high sensitivity and selectivity towards Fe(III) compared with the other examined metal ions. The proposed TCFH probe can therefore be utilized as an effective spectroscopic sensor for Fe(III). Both colorimetric and fluorescence recognition of the analyte depended on the concentration of Fe(III) ions and was accomplished at a pH of 7. A rapid colour change from yellow to red occurred when an aqueous solution of Fe(III) ions was added. The intensity of the colour increased at higher Fe(III) concentrations. Cyclic voltammetry measurements in the dimethylformamide solvent indicated a nonreversible redox potential. This study also explained the possible mechanisms for both solvatochromism and the detection of Fe(III) through TCFH-Fe(III) complex formation. The binding constant of the generated TCFH-Fe(III) complex was explored. Computational modelling was conducted to explain the deprotonation-triggered changes that occur in the photophysical properties of TCFH dyes.

Design and fabrication of green and sustainable vapochromic cellulose fibers embedded with natural anthocyanin for detection of toxic ammonia

Exposure to colorless ammonia gas may lead to damage in human organs or even death. Herein, we describe facile fabrication of an environmentally-friendly, portable, reversible, and sensitive solid-state colorimetric cellulose (Cell)/anthocyanin (Anth) vapochromic sensor that exhibits instant visual color change to both gaseous and aqueous phases of ammonia. The naturally occurring anthocyanin can be easily extracted from the red-cabbage plant and applied as a direct dyestuff onto viscose fibers in the presence of potassium aluminum sulfate as mordant to generate nanoparticles of mordant/anthocyanin coordinated complex. Thus, upon exposure to aqueous ammonia, an instant color change of the smart (Cell-Anth) diagnostic assays, from purple to colorless, was noted and quantitatively probed via both CIE Lab coordinates and UV-Vis spectral measurements. Importantly, the fabricated (Cell-Anth) viscose fabric showed rapid responses, fraction of second, with a good limit of detection (LOD) in the range of 200-1200 mg L^-1. This receptor also demonstrated ratiometric changes in the UV-Vis absorbance spectra, giving a hypsochromic shift from 611 to 375 nm upon increasing the total content of ammonia in an aqueous media. The morphologies of Cell-Anth fabrics as well as particle size of the generated mordant/dye complex on the fabric surface have been characterized by transmission electron microscopic (TEM), scan electron microscopy (SEM), energy-dispersive X-ray patterns (EDX) and Fourier-transform infrared spectroscopic (FT-IR). The comfortability of the dyed cellulose fibers was also investigated in terms of their bend length, air-permeability and colorfastness properties. Significantly, the present study offers a promising onsite vapochromic device that enables detection of ammonia in either aqueous or gas phase in various environments and products.

Simple Development of Novel Reversible Colorimetric Thermometer Using Urea Organogel Embedded with Thermochromic Hydrazone Chromophore

Thermochromic urea (U) organogel immobilized with a thermochromic tricyanofuran hydrazone (TCFH) chromophore was developed. Thermochromic TCFH chromophore bearing two nitro functional groups on a hydrazone recognition unit was synthesized via an azo-coupling reaction of tricyanofuran (TCF) heterocyclic moiety containing an active methyl group with the diazonium chloride salt of 2,4-dinitroaniline comprising two strongly electron-withdrawing nitro groups. The molecular structure of both intermediates and TCFH dye were characterized by several analytical methods, including 1H NMR, 13C NMR, IR, mass spectroscopy (MS), and elemental analysis. The thermochromic responsiveness could be attributed to the charge delocalization of TCFH as well as to the presence of an intramolecular charge transfer. The generated organogel displayed a thermoreversible sol–gel transition associated with color change. The origin of the monitored thermochromism is a conformational change of the tricyanofuran hydrazone backbone due to the temperature-driven deprotonation–protonation reversible process. The prepared urea–tricyanofuran hydrazone (UTCFH) thermometer acted as a diagnostic tool providing an instant color change between yellow, orange, red and purple upon changing the temperature of the UTCFH organogel in dimethyl sulfoxide (DMSO). This color change was proportionally correlated with increasing the temperature from 44 to 63 °C. The UTCFH organogel composed of urea and push-π-pull hydrazone type tricyanofuran chromophore immobilized physically in the urea organogel was found to function as a temperature-driven chromic thermometer. This chromogenic UTCFH organogel in DMSO displayed a phase transition at 41–48 °C. The morphological properties of the gel internal fibrous nanostructure (80–120 nm) were monitored by scanning electron microscopy (SEM). The colorimetric measurements were monitored by UV–Vis absorption spectroscopy. The chromogenic thermometer demonstrated a good reversibility without fatigue. The mechanism accounting for thermochromism of UTCFH organogel is proposed.

Textile dyeing industry: environmental impacts and remediation

Color is a major attraction component of any fabric regardless of how admirable its constitution. Industrial production and utilization of synthetic dyestuffs for textile dyeing have consequently become a gigantic industry today. Synthetic dyestuffs have introduced a broad range of colorfastness and bright hues. Nonetheless, their toxic character has become a reason of serious concern to the environment. Usage of synthetic dyestuffs has adverse impacts on all forms of life. Existence of naphthol, vat dyestuffs, nitrates, acetic acid, soaping chemicals, enzymatic substrates, chromium-based materials, and heavy metals as well as other dyeing auxiliaries, makes the textile dyeing water effluent extremely toxic. Other hazardous chemicals include formaldehyde-based color fixing auxiliaries, chlorine-based stain removers, hydrocarbon-based softeners, and other non-biodegradable dyeing auxiliaries. The colloidal material existing alongside commercial colorants and oily froth raises the turbidity resulting in bad appearance and unpleasant odor of water. Furthermore, such turbidity will block the diffusion of sunlight required for the process of photosynthesis which in turn is interfering with marine life. This effluent may also result in clogging the pores of the soil leading to loss of soil productivity. Therefore, it has been critical for innovations, environmentally friendly remediation technologies, and alternative eco-systems to be explored for textile dyeing industry. Different eco-systems have been explored such as biocolors, natural mordants, and supercritical carbon-dioxide assisted waterless dyeing. Herein, we explore the different types of dyeing processes, water consumption, pollution, treatment, and exploration of eco-systems in textile dyeing industry.

Optical Recognition of Ammonia and Amine Vapor Using "Turn-on" Fluorescent Chitosan Nanoparticles Imprinted on Cellulose Strips

A practical fluorescent test dipstick for an efficient recognition of ammonia and amines vapors was developed. The prepared testing strip was based on a composite of molecularly imprinted chitosan nanoparticles, supported on cellulose paper assay, with artificial fluorescent receptor sites for ammonia/amines recognition in aqueous and gaseous phases. A modified chitosan nanoparticles containing fluorescein molecules, were successfully prepared and employed on cellulose paper strip creating fluorescent cellulose (FL-Cell) to act as "turn-on" fluorescent sensor for sensing and determining ammonia and organic amine vapor. We employed chitosan nanoparticles that had fluorescein incorporated as the fluorescent probe molecule, with a readout limit achieved for aqueous ammonia as low as 280 ppm at room temperature and atmospheric pressure. The sensor responded linearly relying on the aqueous ammonia concentration in the range of 0.13-280 ppm. The chromogenic fluorescent cellulose platform response depended on the acid-base characteristic effects of the fluorescein probe. The protonated form of fluorescein molecules immobilized within the chitosan nanoparticles were in a nanoenvironment demonstrating only weak fluorescence. When binding to ammonia/amine vapor, the fluorescein active sites were deprotonated and exhibited higher "turned-on" fluorescence as a result of exposure to those alkaline species. The simple fabrication and abovementioned characteristics of such fluorescent chitosan nanoparticles are such that they should be applicable for monitoring of ammonia/amines in either aqueous or vapor states. We studied the distribution of the fluorescent chitosan onto paper sheets fabricated from bleached bagasse pulp and coated with two different thicknesses of a fluorescent nanochitosan and blank nanochitosan solutions. A thin fluorescent nanochitosan layer was created on the surface of cellulose strips using an applicator. Its distribution was assessed by scanning electron microscopic (SEM) and transmission electron microscopic (TEM) analysis as well as Fourier-transform infrared spectroscopic (FT-IR) measurements. The mechanical properties were also tested. The exploitation of this "turn-on" fluorescence sensor invented platform should be amenable to different situations where determination of ammonia/amine vapor or aqueous solution is required.

Synthesis, Solvatochromic Performance, pH Sensing, Dyeing Ability, and Antimicrobial Activity of Novel Hydrazone Dyestuffs

New tricyanofuran intramolecular charge transfer dyes comprising the hydrazone group were prepared and fully characterized in order to study their possible solvatochromism, dyeing ability, and antimicrobial activity. The preparation of the hydrazone dyes was achieved in relatively good yields starting from different aromatic amines. The hydrazone functional group was presented via the azo-coupling reaction of the tricyanofuran compound by the properly substituted diazonium chloride. Chemical structures of the prepared hydrazones were confirmed via nuclear magnetic resonance spectroscopy (1H- and 13C-NMR), Fourier-transform infrared spectroscopy (FT-IR), and elemental analysis (C, H, and N). The UV-visible absorption spectra of the produced sensor colorants displayed interesting solvatochromism in solvents with a different polarity, which was found to be affected by the substituents bonded to the aromatic hydrazone moiety. The pH molecular switching was investigated through tuning the intramolecular charge transfer stimulated by the reversible deprotonation/protonation process in acetonitrile solution showing color change from yellow to purple. The produced disperse dyestuffs were employed for dyeing polyester fibers to introduce acceptable color strength and colorfastness properties. Moreover, the dyes verified a weak to moderate antimicrobial activity against some selected pathogens, including S. aureus, E. coli, and Candida albicans.