Vapochromic Properties Research Articles

Multi-Stimuli Responsive Viologen-Imprinted Polyvinyl Alcohol and Tricarboxy Cellulose Nanocomposite Hydrogels.

Photochromic inks have shown disadvantages, such as poor durability and high cost. Self-healable hydrogels have shown photostability and durability. Herein, a viologen-based covalent polymer was printed onto a paper surface toward the development of a multi-stimuli responsive chromogenic sheet with thermochromic, photochromic, and vapochromic properties. Viologen polymer was created by polymerizing a dialdehyde-based viologen with a hydroxyl-bearing dihydrazide in an acidic aqueous medium. The viologen polymer was well immobilized as a colorimetric agent into a polyvinyl alcohol (PVA)/tricarboxy cellulose (TCC)-based self-healable hydrogel. The viologen/hydrogel nanocomposite films were applied onto a paper surface. The coloration measurements showed that when exposed to ultraviolet light, the orange layer printed on the paper surface switched to green. The photochromic film was used to develop anti-counterfeiting prints using the organic hydrogel composed of a PVA/TCC composite and a viologen polymer. Reversible photochromism with strong photostability was observed when the printed papers were exposed to UV irradiation. A detection limit was monitored in the range of 0.5-300 ppm for NH3(aq). The exposure to heat (70 °C) was found to reversibly initiate a colorimetric change.

Multistimuli Luminescence and Anthelmintic Activity of Zn(II) Complexes Based on 1H-Benzimidazole-2-yl Hydrazone Ligands

Three novel Zn(II) mononuclear complexes with the general formula ZnL2Cl2 (L = 2-(4-R-phenylmethylene)benzimidazol-2-hydrazines; R-H (1), R-CH3 (2), and R-OCH3 (3)) were synthesized and fully characterized by various means. These complexes demonstrate excitation-dependent emission, which is detected by a change in the emission color (from blue to green) upon an increase in the excitation wavelength. Moreover complex 1 shows reversible mechanochromic luminescence behavior due to the reversible loss of solvated methanol molecules upon the intense grinding of crystals. In addition, 1 exhibits vapochromic properties, which originate from the adsorption methanol vapor on the crystal surface. The strengthening of anthelmintic activity at the transition from free hydrazones to zinc-based complexes is shown.

Enhancing Vapochromic Properties of Platinum(II) Terpyridine Chloride Hexaflouro Phosphate in Terms of Sensitivity through Nanocrystalization for Fluorometric Detection of Acetonitrile Vapors

The vapochromic properties of [Pt(tpy)Cl](PF6) crystals in the presence of acetonitrile and its effect on the crystal structure as well as the fluorescence spectrum of this complex have already been studied in the past. We synthesized nanocrystals of this compound for the first time, and discussed different parameters and methods that affect nanocrystal structure modulation. The study demonstrates the vapochromic properties of the nanocrystals toward acetonitrile vapor by investigating the morphology and fluorescence spectra of the nanocrystals. Vapochromic studies were conducted on [Pt(tpy)Cl](PF6) nanocrystals for five cycles of absorption and desorption of acetonitrile, demonstrating shorter response times compared to regular bulk crystals.

Stimuli-Responsive Properties of a Zinc(II) Salen-Type Schiff-Base Complex and Vapochromic Detection of Volatile Organic Compounds.

This contribution reports, through a combined thermogravimetric analysis, differential scanning calorimetry, UV-vis, powder X-ray diffraction, and Rietveld refinement analysis, on the stimuli-responsive chromic properties of a substituted Zn(salmal) Schiff-base Lewis acidic complex with unique and distinct thermo- and vapochromic characteristics. The solid complex obtained in air or by evaporation of the solvent from their THF solutions shows a marked thermochromism associated with a phase transition, unusually triggered by the reversible desorption/adsorption of one lattice water molecule. In contrast, the anhydrous solid, achieved from THF solutions of the complex by evaporation of the solvent under anhydrous conditions, behaves very differently as it does not show any absorption of water or thermochromism and exhibits varied vapochromic properties. Detection of volatile organic compounds having Lewis basicity is demonstrated by using the anhydrous solid or the related cast films on glass or paper substrates. In both cases, a marked vapochromism is observed upon exposure to vapors of various volatile species and involves well-defined optical absorptions and naked-eye color changes, also allowing the discrimination of primary aliphatic amines. Vapochromic behavior with the formation of stable, stoichiometric adducts is also demonstrated for both the solid obtained in air and the anhydrous solid or for the related cast films after exposure to vapors of pyridine.

Achieving Simplified and Tunable Flexibility in Carborane-Based Emitters for Quantitative Vapochromic VOC Sensing.

Photoluminescence (PL) sensing of volatile organic compounds (VOCs) represents a convenient and economic detection method toward air pollutants. However, tetraphenylethylene (TPE)-based and recent carborane (Cb)-based sensors retained multiple sites that are responsive to VOC stimulation, making quantitative PL sensing rather challenging. Rendering the simplified and tunable flexibility in the PL sensors is key to achieve the quantitative target. In this work, we proposed a dimeric model of Cb-based emitters to deal with flexibility. Three emissive dibenzothiophene (DBT)-alkynylated carboranes (Cb-1/2/3) were designed and synthesized. Among them, Cb-3 contributed green and green-yellow emission in the crystals, as well as yellow and orange emission in the VOC-incorporated films, together unfolding its vapochromic properties. Crystallographic studies revealed that Cb-3 molecules were invariably dimerized in an interlocked fashion and the redshift in PL was caused by the successive through-space conjugation of DBT moieties. Theoretical calculations verified the thermodynamics stability of Cb-3 dimers and suggested that DBT could individually rotate different angles under the simulation of VOCs. Based on the above findings, we introduced DBT-alkynylated carboranes to detect the VOCs and established linear relationships between the photon energy at the PL maxima and the concentrations of benzene and tetrahydrofuran (THF) vapors. Aside from the successful implementation of quantitative vapochromic sensing, the fast response (6 s) and recovery (3∼5 s), as well as the good reusability, were also evidenced in the sensing of THF vapors.

MOFTextile: Metal‐organic frameworks nanosheets incorporated cotton textile for selective vapochromic sensing and capture of pyridine

Metal–organic frameworks (MOFs) improved several trends and are promising for industrial applications. However, current synthesis processes offer powder form, rendering their applications difficult. A simple solvothermal method offered an in situ growth of copper‐based MOFs, for example, CuBDC (BDC: benzene‐1,4‐dicarboxylic acid) into a cotton textile; the material was denoted as CuBDC@Textile. CuBDCTextile was used as a solid sensor and adsorbent for volatile organic compounds (VOCs). It exhibited good vapochromic properties that enabled a colorimetric detection of pyridine (Py) via naked eyes with high selectivity and good sensitivity. Adsorption of pyridine via pervaporation using CuBDC@Textile was recorded. CuBDCTextile is a flexible textile with a high adsorption capacity (137.9 mg g−1) toward pyridine. It offered dual functional: sensor probe and adsorbent. The synthesis of CuBDC@Textile and their excellent performance as a sensor and adsorbent are promising for further investigation of the “MOFs on textile materials” topic.

Theoretical study of the vapochromic properties of a mononuclear Pd(II) complex with piroxicam ligands for the detection of the vapor of several solvents

In this work, the vapochromic behavior of a mononuclear Pd(II) complex contains piroxicam ligands (trans-[Pd(Pir)2] where Pir− = piroxicam anion) is investigated in the presence of the vapor of twelve different solvents (H2O, CH3OH, CH3CH2OH, C6H5OH, CH2O, CH3CHO, CH3COCH3, DMF, CCl3H, CH3CN, CH3NO2, and DMSO), separately. For this purpose, the absorption spectrum of the complex when it is exposed to the vapor of each solvent is calculated using the time-dependent density functional theory (TD-DFT). The maximum number of vapor molecules which can be adsorbed by the complex is determined for each solvent. The interaction of the DMSO and C6H5OH molecules with the complex is stronger than that of the other solvent molecules. According to the calculated absorption spectra, the change of the color of the complex is observed for the vapors of the CH2O, CH3CHO, CH3COCH3, C6H5OH, and CH3NO2 solvents even in the presence of air humidity while the detection of the other solvent vapors is disturbed in the presence of water humidity. Based on the natural bonding orbital (NBO) calculations, the intra- and inter ligand π → π* transition is the main responsible for the color change of the complex in the presence of the selected solvent vapors. Also, the other electronic transitions such as π (ligand) → LP* (Pd), LP (Pd) → LP*(Pd), and the electron excitation from the π orbital of the adsorbed solvent molecules to the π* of the complex and vice versa, have some contributions in the color change of complex.

Vapochromism and Magnetochemical Switching of a Nickel(II) Paddlewheel Complex by Reversible NH3 Uptake and Release.

Reaction of [NiCl2(PnH)4] (1) (PnH=6‐tert‐butyl‐pyridazine‐3‐thione) with NiCl2 affords the binuclear paddlewheel (PW) complex [Ni2(Pn)4] (2). Diamagnetic complex 2 is the first example of a PW complex capable of reversibly binding and releasing NH3. The NH3 ligand in [Ni2(Pn)4(NH3)] (2⋅NH3) enforces major spectroscopic and magnetic susceptibility changes, thus displaying vapochromic properties (λ max(2)=532 nm, λ max(2⋅NH3)=518 nm) and magnetochemical switching (2: S=0; 2⋅NH3: S=1). Upon repeated adsorption/desorption cycles of NH3 the PW core remains intact. Compound 2 can be embedded into thin polyurethane films (2 P) under retention of its sensing abilities. Therefore, 2 qualifies as reversible optical probe for ammonia. The magnetochemical switching of 2 and 2⋅NH3 was studied in detail by SQUID measurements showing that in 2⋅NH3, solely the Ni atom coordinated the NH3 molecule is responsible for the paramagnetic behavior.

Vapochromism and Magnetochemical Switching of a Nickel(II) Paddlewheel Complex by Reversible NH 3 Uptake and Release

Vapochromism and Magnetochemical Switching of a Nickel(II) Paddlewheel Complex by Reversible NH ₃ Uptake and Release

Pagoda[5]arene with Large and Rigid Cavity for the Formation of 1∶2 Host–Guest Complexes and Acid/Base-Responsive Crystalline Vapochromic Properties

Pagoda[5]arene (P5), which is composed of five 2,6-dimethoxylanthracene (2,6-DMA) subunits bridged by methylene groups at 1,5 positions, was conveniently synthesized in 43% by trifluoroacetic acid ...

Robust Supramolecular Nano-Tunnels Built from Molecular Bricks*.

Herein we report a linear ionic molecule that assembles into a supramolecular nano-tunnel structure through synergy of trident-type ionic interactions and π-π stacking interactions. The nano-tunnel crystal exhibits anisotropic guest adsorption behavior. The material shows good thermal stability and undergoes multi-stage single-crystal-to-single-crystal phase transformations to a nonporous structure on heating. The material exhibits a remarkable chemical stability under both acidic and basic conditions, which is rarely observed in supramolecular organic frameworks and is often related to structures with designed hydrogen-bonding interactions. Because of the high polarity of the tunnels, this molecular crystal also shows a large CO2 -adsorption capacity while excluding other gases at ambient temperature, leading to high CO2 /CH4 selectivity. Aggregation-induced emission of the molecules gives the bulk crystals vapochromic properties.

Robust Supramolecular Nano‐Tunnels Built from Molecular Bricks**

AbstractHerein we report a linear ionic molecule that assembles into a supramolecular nano‐tunnel structure through synergy of trident‐type ionic interactions and π–π stacking interactions. The nano‐tunnel crystal exhibits anisotropic guest adsorption behavior. The material shows good thermal stability and undergoes multi‐stage single‐crystal‐to‐single‐crystal phase transformations to a nonporous structure on heating. The material exhibits a remarkable chemical stability under both acidic and basic conditions, which is rarely observed in supramolecular organic frameworks and is often related to structures with designed hydrogen‐bonding interactions. Because of the high polarity of the tunnels, this molecular crystal also shows a large CO2‐adsorption capacity while excluding other gases at ambient temperature, leading to high CO2/CH4 selectivity. Aggregation‐induced emission of the molecules gives the bulk crystals vapochromic properties.

Photoluminescent and vapochromic properties of the Mn(II)-doped (C6H11NH3)2PbBr4 layered organic–inorganic hybrid perovskite

By a wet-chemistry route we have been able to effectively dope the CHA2PbBr4 compound, a ferroelectric compound with photovoltaic effect, with different amounts of Mn2+ obtaining three pure compounds CHA2Pb1-xMnxBr4 with x = 0.05, 0.07 and 0.11. At room temperature the crystal structure of these new Mn-doped compounds present an orthorhombic symmetric with polar space group Cmc21, as in the case of the undoped compoud (x = 0). Very interestingly, the doped compounds exhibit a broad PL emissions at room temperature, with a maximum around 605 nm and a long PL lifetime (~0.55 ms), whose intensity increases further upon cooling. The observed PL emission is induced from an energy transfer from host semiconductor to the d-orbitals of Mn2+ cation. In addition, we have explored the capability of these materials to act as chemical sensors for volatile organic compounds and report the selective luminescence vapochromic response in this family of compounds. Therefore, the here presented Mn-doped CHA2Pb1-xMnxBr4 compounds belong to the scarce and desirable group of multifunctional materials, where not only ferroelectric and photovoltaic properties can coexist but also photoluminescence and vapochromic properties, rendering them extremely interesting for a large number of potential practical applications.

Solid-state spectroscopic properties of dinuclear cyclometalated Pt(II) complexes with different bridging ligands and anions

Crystal structures of dinuclear cyclometalated Pt(II) complexes with different bridging bis(diphenylphosphino)alkane ligands and counter anions have been compared, and solid-state emissions of crystallite powders and PMMA films doped with luminescent Pt(II) complexes have been investigated. Interestingly, mechanochromic and vapochromic properties are exhibited for solids of dinuclear cyclometalated Pt(II) complex (−)-1 bridged by bis(diphenylphosphino)methane (dppm), and multiple cycles have been repeated without any detectable degradation. However, no distinct stimuli-induced chromism can be observed with the naked eyes for solids of (−)-1 with other counter anions and PMMA films. In addition, with increasing the length of the bridging diphosphine ligand, green-solids without effective intramolecular Pt···Pt contacts have been obtained, and mechanochromic and vapochromic phenomena could not be detected.

Crystal Polymorphism-dependent Fluorescence of Fluoroarene-substituted Anthracene Derivatives

Abstract Fluorine-substituted 1-phenylanthracene derivatives were synthesized and their polymorphism-dependent fluorescence color change (B: blue and G: green) in the crystalline state was observed. For the green luminous crystals (G), a 1D linear π-π stacked structure of the anthracene rings and intermolecular Ar-F⋯H-Ar hydrogen bonding were observed. On the other hand, for the blue luminous crystals (B), weaker or no π-π stacked anthracene rings were observed. These crystallographic observations indicated the existence of the excimer emission and the monomer emission of the anthracene rings for the green (G) and blue (B) luminous crystals, respectively. Interestingly, thermal transformations of the green luminous crystals (G) to the blue luminous crystals (B) were observed. The mechanochromic and vapochromic properties of the obtained crystals were also evaluated.

Vapochromic Properties of Diethenylpyrrole with Naphthyl Tethers Induced by Formation of a Distorted Structure in the Solid State

We report a novel vapochromic compound composed of diethenylpyrrole and naphthyl tethers that does not include any rare metal. The compound shows a reversible fluorescence change upon exposure to t...

AIE Fluorescent Gelators with Thermo-, Mechano-, and Vapochromic Properties.

A series of aggregation-induced emission (AIE) fluorescent gelators (TPE-Cn -Chol) were synthesized by attaching tetraphenylethylene (TPE) to cholesterol through an alkyl chain. The properties of the gel, nano-/microaggregate, and condensed phases were studied carefully. TPE-Cn -Chol molecules form AIE fluorescent gels in acetone and in DMF. Their fluorescence can be reversibly switched between the "on" and "off" states by a gel-sol phase transition upon thermal treatment. The AIE properties of aggregated nano-/microstructures in acetone/water mixtures with different water fractions were studied by using fluorescence spectrometry and scanning electron microscopy (SEM). In different acetone/water mixtures, the TPE-Cn -Chol molecules formed different nano-/microaggregates, such as rodlike crystallites and spherical nanoparticles that showed different fluorescence colors. Finally, the condensed phase behavior of TPE-Cn -Chol was studied by using polarizing microscopy (POM), differential scanning calorimetry (DSC), fluorescence spectrometry, fluorescence optical microscopy, and wide-angle X ray scattering (WAXS). The clover-shaped TPE unit introduced into the rodlike cholesterol mesogen inhibits not only the formation of a liquid-crystal phase but also recrystallization upon cooling from the isotropic liquid phase. Very interestingly, TPE-Cn -Chol molecules in the condensed state change their fluorescence color under external stimuli, such as melting, grinding, and solvent fuming. The phase transition is the origin of these thermo-, mechano-, and vapochromic properties. These findings offer a simple and interesting platform for the creation of multistimuli-responsive fluorescent sensors.

Chemically Tunable Formation of Different Discrete, Oligomeric, and Polymeric Self-Assembled Structures from Digold Metallotweezers.

Digold metallotweezers whose complex supramolecular landscape is controlled by adding a series of metal cations are described. The metallotweezers have a strong tendency to form interesting supramolecular structures on addition of Tl+ , Ag+ , and Cu+ . The choice of the cation can be used to direct the formation of a designated molecular architecture. The addition of thallium facilitates the formation of a self-aggregated duplex structure in which the cation occupies the cavity of the dimer. The same type of structure is formed when Cu+ is added, and the resulting duplex inclusion complex shows interesting vapochromic properties. This copper-encapsulating system evolves in solution to a 1D helical supramolecular polymer showing multiple aurophilic and Au⋅⋅⋅Cu interactions, in which the copper cation is bound to several alkynyl ligands of the tweezer. The addition of a small amount of silver cations to the digold tweezer yields a similar type of inclusion dimer complex, but adding an excess of the cation produces new discrete molecules presumably exhibiting multiple Au⋅⋅⋅Au, Au⋅⋅⋅Ag, and Ag⋅⋅⋅Ag metallophilic interactions. The differences in the supramolecular structures formed are ascribed to the different tendencies of the metal cations to exhibit interactions with the gold atoms and to coordinate to the alkynyl ligands of the tweezer.

Controlling the canonical/zwitterionic balance through intramolecular proton transfer: a strategy for vapochromism

N-Substituted diamino-benzoquinone diimines featuring tunable aryl electron-withdrawing functions and vapochromic properties have been developed.

Highly selective vapochromic fluorescence of polycarbonate films Doped with an ICT‐Based solvatochromic probe

ABSTRACTThe vapochromic properties of a fluorescent 3‐[2‐(4‐nitrophenyl) ethenyl]‐1‐(2‐ethylhexyl)‐2‐methylindole (NPEMI‐E) characterized by intramolecular charge transfer (ICT) character, dispersed in polycarbonate (PC) films is reported. NPEMI‐E solvatochromism is investigated by means of experimental and computational methods. Fluorescent PC films containing 0.1 wt % of NPEMI‐E are prepared and exposed to saturated atmospheres of different volatile organic compounds (VOCs). NPEMI‐E/PC films show remarkable and reversible vapochromism when exposed to VOCs with high polarity index and favorable interaction with PC matrix such as CHCl3. Only minor variations in the emission wavelength are actually recorded for all other classes of VOCs investigated. The hue parameter is also used for the effective extraction of spectral information from digital color images without the need for wavelength discriminators. Overall, the present results support the use of NPEMI‐E/PC films for the cost‐effective detection of CHCl3 vapors. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 1171–1180