Vapochromic Behavior Research Articles

Efficient Molecular Array Control and Vapochromic Behavior Changes by Positional Isomer‐Dependent Molecular Building Blocks (Advanced Optical Materials 28/2024)

Efficient Molecular Array Control and Vapochromic Behavior Changes by Positional Isomer‐Dependent Molecular Building Blocks (Advanced Optical Materials 28/2024)

Efficient Molecular Array Control and Vapochromic Behavior Changes by Positional Isomer‐Dependent Molecular Building Blocks

AbstractStructurally flexible organic porous molecular arrays are promising for the development of vapochromic materials with superior detection performance. Exploring the photophysical control of vapochromic materials using these molecular arrays is important for the design of new vapochromic materials. However, difficulties arise in the formation and control of organic porous molecular arrays owing to weak and less‐oriented noncovalent forces and their tendency to arrange into energetically preferred high‐density configurations. Herein, an efficient strategy is presented to control molecular arrays by manipulating the shapes of donor–acceptor–donor system‐based molecular building blocks using positional isomerism and report on the correlation between controlled molecular arrays and vapochromic behavior. Depending on their shape (Z‐shaped, quasi‐Z‐shaped, or linear shape), the building blocks formed different molecular arrays that controlled the intermolecular interactions and void volumes. This led to differences in the final microstructural morphologies. Consequently, they exhibited different vapochromic behaviors, and an in‐depth understanding of the correlation between the molecular arrays and vapochromism/vapofluorochromism is obtained.

Cucurbit[7]Uril‐Based Self‐Assembled Supramolecular Complex with Reversible Multistimuli‐Responsive Chromic Behavior and Controllable Fluorescence

AbstractMultistimuli‐responsive color‐changing materials have potential applications in areas such as chemical sensing and anti‐counterfeiting. In this work, a fluoro‐phenyl‐acetyl‐substituted viologen derivative (FPAV·Cl2) is synthesized, which can form a supramolecular inclusion complex with cucurbit[7]uril (Q[7]) via self‐assembly. Significantly, the resulting inclusion complex FPAV2+@Q[7] in the solid‐state exhibits visual color changes in response to multiple external stimuli including light, heat, and vapors of ammonia and organic amines. The electron spin resonance (ESR) and ultraviolet–visible (UV–vis) spectra analysis reveals that the photochromic, thermochromic, and vapochromic behavior of FPAV2+@Q[7] is due to the generation of FPAV+• free radicals resulting from electron transfer. Furthermore, in the solid‐state, FPAV2+@Q[7] shows controllable fluorescence regulated by its chromic process. Based on the multi stimuli‐responsive color‐changes and fluorescence properties of FPAV2+@Q[7], its practical applications in erasable inkless printing, multiple anti‐counterfeiting processes, visible ammonia/organic amines detection, and information encryption are demonstrated. The supramolecular strategy of encapsulating viologen derivatives into macrocycles provides a general method for fabricating multi stimuli‐responsive chromic materials with multiple practical applications.

Macrocycle‐Based Charge Transfer Cocrystals with Dynamically Reversible Chiral Self‐Sorting Display Chain Length‐Selective Vapochromism to Alkyl Ketones

AbstractChirality‐driven self‐sorting plays an essential role in controlling the biofunction of biosystems, such as the chiral double‐helix structure of DNA from self‐recognition by hydrogen bonding. However, achieving precise control over the chiral self‐sorted structures and their functional properties for the bioinspired supramolecular systems still remains a challenge, not to mention realizing dynamically reversible regulation. Herein, we report an unprecedented saucer[4]arene‐based charge transfer (CT) cocrystal system with dynamically reversible chiral self‐sorting synergistically induced by chiral triangular macrocycle and organic vapors. It displays efficient chain length‐selective vapochromism toward alkyl ketones due to precise modulation of optical properties by vapor‐induced diverse structural transformations. Experimental and theoretical studies reveal that the unique vapochromic behavior is mainly attributed to the formation of homo‐ or heterochiral self‐sorted assemblies with different alkyl ketone guests, which differ dramatically in solid‐state superstructures and CT interactions, thus influencing their optical properties. This work highlights the essential role of chiral self‐sorting in controlling the functional properties of synthetic supramolecular systems, and the rarely seen controllable chiral self‐sorting at the solid‐vapor interface deepens the understanding of efficient vapochromic sensors.

Macrocycle-Based Charge Transfer Cocrystals with Dynamically Reversible Chiral Self-Sorting Display Chain Length-Selective Vapochromism to Alkyl Ketones.

Chirality-driven self-sorting plays an essential role in controlling the biofunction of biosystems, such as the chiral double-helix structure of DNA from self-recognition by hydrogen bonding. However, achieving precise control over the chiral self-sorted structures and their functional properties for the bioinspired supramolecular systems still remains a challenge, not to mention realizing dynamically reversible regulation. Herein, we report an unprecedented saucer[4]arene-based charge transfer (CT) cocrystal system with dynamically reversible chiral self-sorting synergistically induced by chiral triangular macrocycle and organic vapors. It displays efficient chain length-selective vapochromism toward alkyl ketones due to precise modulation of optical properties by vapor-induced diverse structural transformations. Experimental and theoretical studies reveal that the unique vapochromic behavior is mainly attributed to the formation of homo- or heterochiral self-sorted assemblies with different alkyl ketone guests, which differ dramatically in solid-state superstructures and CT interactions, thus influencing their optical properties. This work highlights the essential role of chiral self-sorting in controlling the functional properties of synthetic supramolecular systems, and the rarely seen controllable chiral self-sorting at the solid-vapor interface deepens the understanding of efficient vapochromic sensors.

Heteroleptic Cu(I) complex with vapochromism and its application as electrochromic material

Heteroleptic Cu(I) complex with vapochromism and its application as electrochromic material

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.

Separation of cyclohexanol from cyclohexanol/cyclohexene mixtures by crystals of pillar[6]arene containing three benzoquinone units.

Here, we develop a new absorbent for efficient separation of cyclohexanol (CHA-ol) and cyclohexene (CHA-ene) by using crystals of pillar[6]arene with three benzoquinone units (P3QA). P3QA crystals are found to show remarkable selectivity for CHA-ol in 50 : 50 (v/v) CHA-ol : CHA-ene mixtures with a purity of 95.2%, along with vapochromic behavior.

Vapochromic separation of toluene and pyridine azeotropes using adaptive macrocycle co-crystals.

The separation of toluene (Tol) and pyridine (Py) azeotropes is significant in the chemical industry. Herein, we present a new method for the energy-efficient separation of Tol and Py using pillar[5]arene-based adaptive macrocycle co-crystals (MCCs) that can selectively separate Py from a Py/Tol equimolar mixture with 99.2% purity, accompanied by vapochromic behavior from white to yellow.

Grinding-induced supramolecular charge-transfer assemblies with switchable vapochromism toward haloalkane isomers

Synthetic macrocycles have proved to be of great application value in functional charge-transfer systems in the solid state in recent years. Here we show a switchable on-off type vapochromic system toward 1-/2-bromoalkane isomers by constructing solid-state charge-transfer complexes between electron-rich perethylated pillar[5]arene and electron-deficient aromatic acceptors including 4-nitrobenzonitrile and 1,4-dinitrobenzene. These charge-transfer complexes with different colors show opposite color changes upon exposure to the vapors of 1-bromoalkanes (fading) and 2-bromoalkanes (deepening). Single-crystal structures incorporating X-ray powder diffraction and spectral analyses demonstrate that this on-off type vapochromic behavior is mainly attributed to the destruction (off) and reconstruction (on) of the charge-transfer interactions between perethylated pillar[5]arene and the acceptors, for which the competitive host-guest binding of 1-bromoalkanes and the solid-state structural transformation triggered by 2-bromoalkanes are respectively responsible. This work provides a simple colorimetric method for distinguishing positional isomers with similar physical and chemical properties.

Tailoring the extrinsic porosity of a vapochromic metal–organic polyhedron for rapid VOC detection

Metal-organic polyhedra (MOPs) are intrinsically porous building blocks for the bottom-up construction of hierarchically porous materials. Herein, we report the syntheses of unprecedented solvato- and vapochromic MOP (DGIST-8) nanocrystals and aerogels, each exhibiting a different permanent porosity. Notably, the DGIST-8 aerogels with combined micro-, meso-, and macropores underwent unprecedented color changes perceivable to the naked eye after exposure to volatile organic compounds in both liquid and vapor phases. The key to achieving rapid and reversible vapochromic behavior involves a well-preserved high surface area that ensures the enhanced diffusion of solvent molecules due to the combined presence of micro-, meso- and macropores. The design principles of the vapochromic MOP aerogels disclosed in this report facilitate the use of MOPs as a new type of sensing material.

Separation of Cyclohexanone and Cyclohexanol by Adaptive Pillar[5]arene Cocrystals Accompanied by Vapochromic Behavior.

The separation of cyclohexanone (CHA-one) and cyclohexanol (CHA-ol) mixtures is of great importance in the chemical industry. Current technology exploits multiple steps of energy-intensive rectification due to their close boiling points. Herein, we report a new and energy-efficient adsorptive separation method employing binary adaptive macrocycle cocrystals (MCCs) built with π-electron-rich pillar[5]arene (P5) and an electron-deficient naphthalenediimide derivative (NDI) that can selectively separate CHA-one from an equimolar CHA-one/CHA-ol mixture with >99% purity. Intriguingly, this adsorptive separation process is accompanied by vapochromic behavior from pink to dark brown. Single-crystal and powder X-ray diffraction analyses reveal that the adsorptive selectivity and vapochromic property are derived from the CHA-one vapor inside the cocrystal lattice voids triggering solid-state structural transformations to yield charge-transfer (CT) cocrystals. Moreover, the reversible transformations make the cocrystalline materials highly recyclable.

Triggering the Vapochromic Behavior in C60 via the Supramolecular Wrapping of st-PMMA

Understanding the physicochemical modulation of functional molecules is the primary step in exploring novel stimuli-responsive materials, and preventing the π-π stacking configuration of π-conjugated molecules has been an effective strategy of vapochromic material development, such as of nanoporous frameworks. Nevertheless, the more complicated synthetic strategy should in fact be applied in many circumstances. In this study, we explore a facile supramolecular strategy where the commodity plastic, syndiotactic-poly(methyl methacrylate) (st-PMMA), is utilized to wrap C60 to form the inclusion complex. The structural characterization revealed that C60s in the st-PMMA supramolecular helix had a lower coordination number (CN = 2) compared to the face-centered-cubic packing of pure C60s (CN = 12). Since the st-PMMA/C60 helical complex has structural flexibility, the π-π stacking structure of C60 was further interrupted by the intercalation of toluene vapors, and the complete isolation of C60 in the complex induced the desired vapochromic behavior. Furthermore, the aromatic interaction between C60 and aromatic solvent vapors enabled the st-PMMA/C60 inclusion complex to selectively encapsulate chlorobenzene, toluene, etc., and induce the color change. The st-PMMA/C60 inclusion complex exhibited a transparent film of sufficient structural integrity such that it can still induce a reversible color change after several cycles. As a result, a new strategy has been discovered for the development of novel vapochromic materials via host-guest chemistry.

Substituent Effect on Stimuli-Responsive Donor–Acceptor Framework-Based 2-Thiohydantoins for Monitoring Nonanal Vapors

Tuning the π-conjugation and varying the functional units can improve the response behavior with superior sensitivity and selectivity. Herein, we report on five novel donor–acceptor (D–A) molecular ensembles developed through C5 substitution on 2-thiohydantoin (2TH) with π-conjugation having different electron-donating groups. The structure–property relationships were investigated by single-crystal X-ray diffraction (SC-XRD) analysis, photophysical, electrochemical, and computational studies. The structural influence of 2TH derivatives on surface interactions with volatile organic compounds (VOCs) were analyzed by binding affinities, kinetics, and other intrinsic parameters (work function, surface photovoltages (SPVs), and response and recovery times). N,N-diMeAPh-2TH exhibits mechanochromic and vapochromic behavior, shows red-shifted emission at ∼554 nm upon exposure to nonanal vapors with a visual color change from orange-red to brown, and shows vivid color variations with different VOCs. N,N-diMeAPh-2TH shows reversible vapochromic behavior as well. Ph-2TH, 4-OMePh-2TH, and 2,4-diOMePh-2TH exhibit n-type behavior with the greater SPV response achieved for Ph-2TH (90%), but good recovery (58%) in SPV in 439 s is observed in the case of 2,4-diOMePh-2TH. In contrast, 3,4-diOMePh-2TH and N,N-diMeAPh-2TH exhibit p-type behavior toward nonanal vapors with a high SPV response obtained for N,N-diMeAPh-2TH (94%) within 293 s as well as recovery (87%) in surface PVT in 692 s. The results demonstrate that electron-donating substituents −N(CH3)2 can improve sensing performance by increasing electron density, whereas steric hindrance on the phenyl unit can modulate sensing performance.

Vapochromic behaviour of a gold(I)-lead(II) complex as a VOC sensor.

The reaction among [Au2Ag2(C6F5)4(OEt2)2]n, PbCl2 and terpyridine leads to the polymeric complex [{Au(C6F5)2}2{Pb(terpy)}]n (1). Its crystal structure reveals potential voids close to the lead centres large enough to hold different molecules. The availability of these free sites allows complex 1 to act as a VOC sensor. Thus, when 1 is exposed to different solvent vapours such as acetonitrile, toluene or THF, variations in its solid appearance and its photophysical properties are observed as a consequence of the formation of the new polymorphs [{Au(C6F5)2}2{Pb(terpy)(CH3CN)2}]n (2), [{Au(C6F5)2}2{Pb(terpy)}]n·Tol (3) and [{Au(C6F5)2}2{Pb(terpy)(THF)}]n·THF (4). Each polymorph displays a different emission energy depending on its structure and the presence of metallophilic interactions. In addition, the reversible solvent molecule exchange allows the tuning of the luminescence emissions in the greenish yellow-red range. DFT and TD-DFT calculations were performed to explain the origin of the luminescence of all these complexes.

Chloroform-selective vapochromic behavior based on crystal-state host–guest complexation of an organic cage

Crystalline DHTA-cage shows vapochromic response to chloroform selectively over dichloromethane or tetrachloromethane, realizing the discrimination between molecules with similar structures.

Mechanical and Thermal ON–OFF Switching of the Vapochromic Behavior of a Luminescent Polymorphic Pt(II) Complex

Vapochromic materials that exhibit color/luminescence changes induced by vapor exposure have attracted considerable attention. Herein, we report the grinding- and heating-induced ON-OFF switching of the vapochromic behavior of [Pt(ppyCl2)(Clacac)] (1; ppyCl2 = 2-(3-chlorophenyl)-4-chloropyridinato, Clacac = 3-chloroacetylacetonato). 1 formed yellow and orange polymorphs (1-Y and 1-O), and 1-Y could be converted to 1-Og, which showed a very similar crystal structure but with a broadened X-ray diffraction pattern compared with that of 1-O. Moreover, 1-Og can be reversibly transformed into 1-O via heating and grinding. Notably, 1-Og underwent a N,N-dimethylacetamide vapor-induced transformation to 1-Y, whereas 1-O did not undergo such a transformation. These results indicate the ON-OFF switching of vapochromic behavior induced via grinding and heating. This finding will be beneficial for developing intelligent molecular devices.

Host‐Guest Properties of a Trigonal Iminoboronate Ester Cage Self‐Assembled from Hexahydroxytriphenylene

AbstractThe self‐assembly of 1,3‐diaminopropane (DAP), 2‐formylphenylboronic acid (FPBA) and 2,3,6,7,10,11‐hexahydroxytriphenylene (HHTP) into a trigonal‐prismatic molecular cage through reversible iminoboronate ester motifs is reported. The organic cage generates solvates with acetonitrile and nitrobenzene, exhibiting vapochromic behavior. Single‐crystal X‐ray diffraction analysis evidenced the inclusion of nitrobenzene within the cage cavity. The resulting host‐guest complex is stabilized by donor‐acceptor‐donor interactions between the nitrobenzene guest and the π electron‐rich HHTP units of the cage.

Multistimuli-Responsive Properties of Aggregated Isocyanide Cycloplatinated(II) Complexes

Here, we describe the neutral cyclometalated tert-butylisocyanide PtII complexes, [Pt(C∧N)Cl(CNBut)] 1, the double salts [Pt(C∧N)(CNBut)2][Pt(C∧N)Cl2] 2, and the cationic complexes [Pt(C∧N)(CNBut)2]ClO43 [C∧N = difluorophenylpyridine (dfppy, a), 4-(2-pyridyl)benzaldehyde (ppy-CHO, b)]. A comparative study of the pseudopolymorphs 1a, 1a·CHCl3, 1b, 1b·0.5Toluene, 1b·0.5PhF, and 3a·0.25CH2Cl2 reveals strong aggregation through Pt···Pt and/or π···π stacking interactions to give a variety of distinctive one-dimensional (1D) infinite chains, which modulate the photoluminescent properties. This intermolecular long-range aggregate formation is the main origin of the photoluminescent behavior of 1a and 1b complexes, which exhibit highly sensitive and reversible responses to multiple external stimuli including different volatile organic compounds (VOCs), solvents, temperatures, and pressures, with distinct color and phosphorescent color switching from green to red. Furthermore, complex 1b undergoes supramolecular self-assembly via Pt···Pt and/or π···π interactions into a polymer thin polystyrene (PS) film 10 wt % in response to toluene vapors, and 3a exhibits vapochromic and vapoluminescent behavior. Theoretical simulations on the dimer, trimer, and tetramer models of 1a and 1b have been carried out to get insight into the photophysical properties in the aggregated solid state.

Multistimuli-Responsive Squaraine Dyad Exhibiting Concentration-Controlled Vapochromic Luminescence.

Stimuli-responsive organic materials with controllable luminescence are of enormous importance because of their potential applications in sensing, data security, and display devices. In this study, a multistimuli-responsive squaraine dyad (SQ-d) composed of two rigid squaraine moieties and a flexible ethylene linker was rationally designed and synthesized. SQ-d exhibits polymorphic luminescence, which can be reversibly switched by various external stimuli, including solvent vapor exposure, heat, and shear force. Unexpectedly, the weakly luminescent phase (O1) of SQ-d exhibits concentration-controlled vapochromic behavior. Film O1 can convert to a highly green-emissive phase (G1) under a low concentration of CHCl3 vapor and convert to a highly yellow-emissive phase (Y) under a high concentration of CHCl3 vapor; these originate from two distinct crystallization-induced emission enhancement processes. To the best of our knowledge, this is the first investigation of the effect of vapor concentration on the phase transitions of organic vapochromic luminophores. By analyzing the single-crystal structures and photophysical properties of SQ-d, we concluded that the green and yellow emissions probably originated from a zigzag stacking mode and an H-type π-π stacking mode, respectively. Finally, two prototypes based on SQ-d for applications in information encryption and vapor sensing were successfully demonstrated.