Vapochromic Behavior Research Articles

Reversible colour/luminescence colour changes of tetracyanoruthenium(ii) complexes by sorption/desorption of water molecules in crystals

We report reversible vapochromic behaviour of tetracyanorutenium(ii) complexes by the sorption/desorption of water molecules in crystal.

Multifunctional Viologen-Derived Supramolecular Network with Photo/Vapochromic and Proton Conduction Properties.

A supramolecular network [H4bdcbpy(NO3)2·H2O] (H4bdcbpy = 1,1′-Bis(3,5-dicarboxybenzyl)-4,4′-bipyridinium) (1) was prepared by a zwitterionic viologen carboxylate ligand in hydrothermal synthesis conditions. The as-synthesized (1) has been well characterized by means of single-crystal/powder X-ray diffraction, elemental analysis, thermogravimetric analysis and infrared and UV-vis spectroscopy. This compound possesses a three-dimensional supramolecular structure, formed by the hydrogen bond and π–π interaction between the organic ligands. This compound shows photochromic properties under UV light, as well as vapochromic behavior upon exposure to volatile amines and ammonia, in which the electron transfer from electron-rich parts to the electron-deficient viologen unit gives rise to colored radicals. Moreover, the intensive intermolecular H-bonding networks in 1 endows it with a proton conductivity of 1.06 × 10−3 S cm−1 in water at 90 °C.

Halide Replacement Effect on Proton Conductivity and Vapochromic Luminescence of Pt(II) Complexes

Abstract A new vapochromic, proton-conductive Pt(II) complex, [PtBr(tpypyH)]Br2 ([1Br-H]Br, tpypy = 2,2′: 6′,2′′-terpyridine-4′,4′′′-pyridine) was synthesized to improve the proton conductivity and thermal stability of the Cl− analogue, [PtCl(tpypyH)]Cl2 ([1Cl-H]Cl). The effects of halide replacement on the photophysical properties of the complex differed in the solution and solid states; the metal-to-ligand charge transfer (MLCT) absorption band of [1Br-H]Br in the solution state appeared at a longer wavelength than that of [1Cl-H]Cl owing to the stronger π-donation of Br−. In contrast, the metal-metal-to-ligand charge transfer (MMLCT) emission of [1Br-H]Br appeared at a shorter wavelength than that of [1Cl-H]Cl, which is consistent with the longer Pt⋯Pt stacking distance in [1Br-H]Br. [1Br-H]Br exhibited relative humidity-dependent proton conductivity and water vapor induced vapochromic luminescence; the conductivity was comparably higher than that of [1Cl-H]Cl, but slightly lower in the high relative humidity (RH) region above 80%, likely due to the lower hydration number of [1Br-H]Br. HBr release from [1Br-H]Br occurred at a higher temperature than HCl release from [1Cl-H]Cl, suggesting the superior thermal stability of the HBr adduct. This study demonstrates the crucial role of halide anions in attenuating both the vapochromic and proton conduction behavior of Pt(II) complexes.

Meso-/Microscopic Single Particle Analyses of Vapochromic Solid-State Crystallization in [Pt(CN)2(H2dcbpy)

In this study, the vapochromic behavior of the platinum complex, [Pt(CN)2(H2dcbpy)], was investigated using super-resolution microscopy techniques, that is, structured illumination microscopy and confocal laser microscopy. In [Pt(CN)2(H2dcbpy)], the amorphous-to-crystal transition occurs under the influence of methanol vapor, and the meso-/microscopic solid-state crystallization processes of amorphous single particles can be directly traced by their phosphorescence changes. The time evolutions of three-dimensional vapochromic behaviors demonstrated that when the size of single particles exceeded 10 μm, vapochromism initially manifested along the direction of the position of the MeOH reservoir and that the vapor-induced crystallization initiated at the surface, and subsequently, the crystallization-induced voids enabled vapochromism to advance into the interior of the particles. The findings reported herein provide new insights into the mechanisms underlying solid-state crystallization processes, and a novel strategy to sense organic vapor molecules is proposed.

A novel conformationally adaptive macrocyclic tetramaleimide with flipping pyrene sidewalls

The synthesis, structure, and properties of pyrene-based conformationally adaptive macrocycles are described. This new type of conformationally adaptive macrocycle was constructed through Perkin reaction, followed by imidization. By changing the condensation partner as the linking unit, a family of conjugated macrocycles with different sizes of the cavity was synthesized, which provide a simple and modular synthetic strategy towards the conformationally adaptive macrocycles. Furthermore, the macrocycles provide two well-defined conformations through flipping pyrene subunit, which were unambiguously determined by single-crystal X-ray diffraction analysis. The conformational interconversion barrier was determined by density functional theory (DFT) calculations. This new macrocycle also demonstrated unique properties, such as vapochromic behavior and aggregation emission enhancement effect. Furthermore, we have also investigated the effect of the linker on the shape and photophysical properties of the resulting macrocyclic products.

Luminescent Soft Crystals That Exhibit Color Changes in Response to Vapor

It is well-known that square-planar Pt(II) complexes exhibit characteristic luminescence when the complex units are stacked with Pt···Pt short contacts. Such assembled systems have interesting properties that the luminescence color can change sensitively in response to the surroundings such as temperature, pressure, and vapor. Therefore, the Pt(II) complexes are attractive as flexible and ordered sensing materials called soft crystals. In this presentation, the latest topics of vapochromic Pt(II) complexes are introduced.1. Wide-range color tuning of luminescence based on the fine control of the Pt···Pt interactions.1) A series of assembled Pt(II) complexes comprising N-heterocyclic carbene and cyanide ligands was constructed using different substituent groups (Figure 1). All the complexes exhibited highly efficient photoluminescence with an emission quantum yield in the solid state at room temperature, originating from the triplet metal-metal-to ligand charge transfer (3MMLCT) state. Their emission colors cover the entire visible region from red to blue by changing the substituents. It is notable that blue 3MMLCT emission was realized firstly in this system. In addition, vapochromic response was observed based on the single-crystal-to-single-crystal transformation.2. Fast and stable vapochromic response induced through nanocrystal formation of a luminescent platinum(II) complex on periodic mesoporous organosilica.2) A hybrid vapoluminescent system exhibiting fast and repeatable response was constructed using periodic mesoporous organosilica with bipyridine moieties (Bpy-PMO) and a Pt(II) complex bearing a potentially luminescent 2-phenylpyridinato ligand. An intense red luminescence appeared when the Pt(II)-complex immobilized Bpy-PMO was exposed to methanol vapor and disappeared on exposure to pyridine vapor. The ON-OFF vapochromic behavior occurred repeatedly in a methanol/ pyridine/heating cycle. Interestingly, a rapid response was achieved in the second cycle and cycles thereafter. The unique vapoluminescence triggered by the unprecedented protodesilylation on exposure to protic solvent vapor at room temperature is attributable to Bpy-PMO being a giant ligand and an effective vapor condenser. Consequently, this hybrid system presents a new strategy for developing sensors using bulk powdery materials. 1) D. Saito et al., Angew. Chem. Int. Ed. 2020, 59, 18723–18730. 2) H. Matsukawa et al., Sci. Rep. 2019, 9:15151. Figure 1

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.

Structural Insights into the Vapochromic Behavior of Pt- and Pd-Based Compounds

Anionic complexes having vapochromic behavior are investigated: [K(H2O)][M(ppy)(CN)2], [K(H2O)][M(bzq)(CN)2], and [Li(H2O)n][Pt(bzq)(CN)2], where ppy = 2-phenylpyridinate, bzq = 7,8-benzoquinolate, and M = Pt(II) or Pd(II). These hydrated potassium/lithium salts exhibit a change in color upon being heated to 380 K, and they transform back into the original color upon absorption of water molecules from the environment. The challenging characterization of their structure in the vapochromic transition has been carried out by combining several experimental techniques, despite the availability of partially ordered and/or impure crystalline material. Room-temperature single-crystal and powder X-ray diffraction investigation revealed that [K(H2O)][Pt(ppy)(CN)2] crystallizes in the Pbca space group and is isostructural to [K(H2O)][Pd(ppy)(CN)2]. Variable-temperature powder X-ray diffraction allowed the color transition to be related to changes in the diffraction pattern and the decrease in sample crystallinity. Water loss, monitored by thermogravimetric analysis, occurs in two stages, well separated for potassium Pt compounds and strongly overlapped for potassium Pd compounds. The local structure of potassium compounds was monitored by in situ pair distribution function (PDF) measurements, which highlighted changes in the intermolecular distances due to a rearrangement of the crystal packing upon vapochromic transition. A reaction coordinate describing the structural changes was extracted for each compound by multivariate analysis applied to PDF data. It contributed to the study of the kinetics of the structural changes related to the vapochromic transition, revealing its dependence on the transition metal ion. Instead, the ligand influences the critical temperature, higher for ppy than for bzq, and the inclination of the molecular planes with respect to the unit cell planes, higher for bzq than for ppy. The first stage of water loss triggers a unit cell contraction, determined by the increase in the b axis length and the decrease in the a (for ppy) or c (for bzq) axis lengths. Consequent interplane distance variations and in-plane roto-translations weaken the π-stacking of the room-temperature structure and modify the distances and angles of Pt(II)/Pd(II) chains. The curve describing the intermolecular Pt(II)/Pd(II) distances as a function of temperature, validated by X-ray absorption spectroscopy, was found to reproduce the coordinate reaction determined by the model-free analysis.

Cooperative phenomenon of vapochromism and proton conduction of luminescent Pt(ii) complexes for the visualisation of proton conductivity.

The luminescent and proton conductive Pt(ii) complex [PtCl(tpy-o-py)]Cl and its HCl adduct [PtCl(tpy-o-pyH)]Cl2 (o-Pt and o-Pt·HCl, respectively; tpy-o-py = 2,2':6',2''-terpyridine-6',2'''-pyridine) were synthesised and their crystal structures, vapochromic behaviour, and proton conduction, were investigated and compared to those of the para isomers [PtCl(tpy-p-py)]Cl and [PtCl(tpy-p-pyH)]Cl2 (p-Pt and p-Pt·HCl, respectively; tpy-p-py = 2,2':6',2''-terpyridine-4',4'''-pyridine). X-ray structure analysis revealed that the intermolecular metallophilic (PtPt) interaction was negligible in o-Pt but effective in o-Pt·HCl. Reversible transformation between o-Pt and o-Pt·HCl coupled with significant colour and luminescence changes was achieved by four different external stimuli, namely: exposure of o-Pt to humid HCl gas to form o-Pt·HCl, heating, exposure to MeOH vapour, and finally drying in air to regenerate the original o-Pt. The intraligand π-π* orange emission observed for o-Pt exhibited negligible dependence on the relative humidity (RH). Conversely, o-Pt·HCl exhibited red metal-metal-to-ligand charge-transfer (MMLCT) phosphorescence at 725 nm, originating from effective intermolecular Pt-Pt interactions, and interesting vapochromic behaviour that was dependent on the RH. Notably, o-Pt·HCl presented higher conductivity than the p-Pt·HCl isomer at RH < 80%. This trend was reversed at RH values > 80%, probably owing to the second water-adsorption-induced transformation of p-Pt·HCl. The cooperative phenomenon between the proton conduction and vapochromic behaviour observed for both o-Pt·HCl and p-Pt·HCl should allow the visualisation of the proton-conducting pathway, without the need for a bulk electrode, via the absorption and emission colours at both macroscopic and microscopic levels.

Vapochromic behaviour of a nickel(II)-quinonoid complex with dimensional changes between 1D and higher.

The nickel(ii)-chloranilato complex {Ni(ca)(VM)2}n (H2ca = chloranilic acid, VM = coordinated vapour molecules, such as water) shows reversible vapochromism upon exposure to various vapours and subsequent drying by heating. In contrast to the Ni(ii)-quinonoid complex, [Ni(HLMe)2] (H2LMe = 4-methylamino-6-methyliminio-3-oxocyclohexa-1,4-dien-1-olate), which was reported to exhibit vapochromic spin-state switching between high and low spin states, the chloranilato complex does not change its spin state even after the removal of coordinated vapour molecules. X-ray absorption fine structure (XAFS) analysis revealed that the six-coordinate geometry of {Ni(ca)(VM)2}n was maintained even after the removal of vapour molecules, in contrast to the [Ni(HLMe)2] complex. The unique vapochromism that follows the dimensional change between 1D and higher is influenced by the relatively weaker ligand field of the chloranilate ligand.

Coordination-based vapochromic behavior of a luminescent Pt(ii) complex with potassium ions.

Vapochromic Pt(ii) complexes that exhibit color and luminescence changes induced by the presence of vapor molecules have drawn considerable attention because of their potential use as vapor sensors. Generally, the vapochromic responsiveness of Pt(ii)-based complexes is difficult to envisage, because a typical molecular design facilitates the stabilization of a vapor-adsorbed form through weak intermolecular interactions. Herein, we investigate the vapochromic behavior of a Pt(ii) complex with potassium ions, which act as vapor coordination sites, by strongly stabilizing the vapor-adsorbed form. Upon exposure to N,N-dimethylacetamide and N,N-dimethylformamide vapors, the complex exhibits crystal structural transformation with luminescence spectral changes. Crystal structural analysis indicates that the vapor molecules are coordinated to the potassium ions after vapor exposure. This study suggests the possibility of inducing Pt(ii)-based vapochromic responsiveness through establishing potassium-ion-based vapor coordination sites.

Water-vapochromic behavior of a mononuclear Pd(II) complex of piroxicam: A DFT and TD-DFT study

The vapochromic behavior of a mononuclear Pd(II) complex with piroxicam ligands (trans-[Pd(Pir)2] (Pir− is piroxicam anion)) in the presence of water vapor has been theoretically investigated using the time-dependent density functional theory (TD-DFT). The structure of Pd(II) complex interacting with different number of water molecules (n = 1–5) was optimized, separately. The electronic absorption spectra of the optimized structures were calculated using the TD-DFT method and the changes in the absorption spectrum of complex with the increase in the number of water molecules were followed. Comparison of the absorption spectrum of bare Pd(II) complex with those of its hydrated forms with different numbers of water molecules showed a considerable change in the region of 360–400 nm including the change in the intensity and peak position. The main electronic configurations of the intense absorption lines in the related absorption spectra were determined so that the molecular orbitals involved in these absorption lines were determined. The natural bonding orbital (NBO) analysis was performed to assign the NBOs contributing to these molecular orbitals and to see how the NBO composition of the involved molecular orbitals in the electron excitation change with the number of water molecules. It was observed that the change in the intensity and position of the inter- and intraligand π→π∗ transitions are responsible for the color change. Also, based on the NBO results, the contribution of the electronic transitions involving the Pd(II) ion in the color change of the complex was absent.

Macrocycle Co-Crystals Showing Vapochromism to Haloalkanes.

Organic co-crystal engineering is a promising method to make multifunctional materials. Here, the marriage of macrocyclic chemistry and co-crystal engineering provides a smart strategy to build vapochromic materials. The macrocycle co-crystals (MCCs) were constructed from π-electron rich pillar[5]arene (P5) and an electron-deficient pyromellitic diimide derivative (PDI) on a 10 g scale. MCCs of P5-PDI are in red owing to the formation of a charge-transfer (CT) complex. After solvent removal, a white crystalline solid with a new structure (P5-PDIα) is yielded, which exhibits selective vapochromic responses to volatile organic compounds (VOCs) of haloalkanes, accompanied by color changes from white to red or orange. Powder and single-crystal X-ray diffraction analyses reveal that the color changes are attributed to the vapor-triggered solid-state structural transformation to form CT co-crystals. Coating films of P5 and PDI on glass showed a visible vapochromic behavior with good reversibility.

Macrocycle Co‐Crystals Showing Vapochromism to Haloalkanes

AbstractOrganic co‐crystal engineering is a promising method to make multifunctional materials. Here, the marriage of macrocyclic chemistry and co‐crystal engineering provides a smart strategy to build vapochromic materials. The macrocycle co‐crystals (MCCs) were constructed from π‐electron rich pillar[5]arene (P5) and an electron‐deficient pyromellitic diimide derivative (PDI) on a 10 g scale. MCCs of P5‐PDI are in red owing to the formation of a charge‐transfer (CT) complex. After solvent removal, a white crystalline solid with a new structure (P5‐PDIα) is yielded, which exhibits selective vapochromic responses to volatile organic compounds (VOCs) of haloalkanes, accompanied by color changes from white to red or orange. Powder and single‐crystal X‐ray diffraction analyses reveal that the color changes are attributed to the vapor‐triggered solid‐state structural transformation to form CT co‐crystals. Coating films of P5 and PDI on glass showed a visible vapochromic behavior with good reversibility.

Sigmoidally hydrochromic molecular porous crystal with rotatable dendrons.

Vapochromic behaviour of porous crystals is beneficial for facile and rapid detection of gaseous molecules without electricity. Toward this end, tailored molecular designs have been established for metal–organic, covalent-bonded and hydrogen-bonded frameworks. Here, we explore the hydrochromic chemistry of a van der Waals (VDW) porous crystal. The VDW porous crystal VPC-1 is formed from a novel aromatic dendrimer having a dibenzophenazine core and multibranched carbazole dendrons. Although the constituent molecules are connected via VDW forces, VPC-1 maintains its structural integrity even after desolvation. VPC-1 exhibits reversible colour changes upon uptake/release of water molecules due to the charge transfer character of the constituent dendrimer. Detailed structural analyses reveal that the outermost carbazole units alone are mobile in the crystal and twist simultaneously in response to water vapour. Thermodynamic analysis suggests that the sigmoidal water sorption is induced by the affinity alternation of the pore surface from hydrophobic to hydrophilic.

Tri(pyridinyl)pyridine Viologen-Based Kagome Dual Coordination Polymer with Selective Chromic Response to Soft X-ray and Volatile Organic Amines.

The development of new responsive smart materials has been highly desirable in the recent decade due to growing demand in our daily life, and extended viologen-based coordination polymers are regarded as proper and promising candidates for stimuli-responsive study. A tri(pyridinyl)pyridine viologen-based Kagome dual (kgd) topological coordination polymer, [Mn3Cl4(tpptb)2]·Cl2·(H2O)2, (tpptb = N,N',N″-tri(3-carboxybenzyl)-2,4,6-tri(pyridinium-4-yl)pyridine; 1) has been solvothermally synthesized, which can selectively respond to soft X-ray Al-Kα (λ = 8.357 Å) irradiation but not to UV light and hard X-rays of λ < 1.5418 Å at room temperature. Appealingly, 1 is very sensitive and convenient for the visual detection of various volatile amine vapors, especially ethylamine vapors at a low concentration of 100 ppm, and the vapochromic sample can be recovered after exposure in the air at room temperature. The sequence of amines in vapochromism could be rationalized by combined consideration of vapor pressure, the molecular size, and electron-donor ability of various amine molecules as well as the void spaces of 1. In addition, 1 exhibits an obvious hydrochromic transformation upon heating in the air and an anhydrous atmosphere. Combined XPS and EPR confirmed that these physical and chemical stimuli can cause electron transfer from electron-rich groups to quaternary nitrogen atoms of the ligand to generate charge-separated radicals, leading to soft X-ray-induced photochromic and selective vapochromic behavior of 1. Such behavior indicates that it will become a convenient, recyclable, and practical multifunctional material for chemical and environmental sensing. These results provide an effective avenue for the rational design and synthesis of multifunctional chromic materials for potential use in sensing devices.

Understanding the vapochromic response of mixed copper(i) iodide/silver(i) Iodide nanoparticles toward dimethyl sulfide.

We report on the vapochromic behavior of a series of homo- and heterometallic copper(i) iodide/silver(i) iodide nanoparticles when exposed to dimethyl sulfide (DMS) vapor. These systems show remarkable colorimetric sensing behavior via emission color upon DMS exposure, shifting from pink to green emission. Kinetics measurements of CuI/AgI nanoparticle reactions with DMS show a significant rate increase with increasing Ag(i) content. However, luminescence spectroscopy and X-ray diffraction of the post-exposure samples with varying Ag(i) content reveal that the luminophore is identical in all cases and contains no Ag(i) ions. To rationalize the experimental observations and determine the vapochromic response mechanism, molecular dynamic calculations were performed on model (111) cation-terminated surfaces of copper iodide crystals doped with variable amounts of silver. Computational studies indicate that heterometallic Cu/Ag systems have a stronger binding affinity towards DMS vapor molecules than homometallic CuI and that embedding of the DMS molecules into the surface is the primary intermediate by which the vapochromic response occurs.

Vapochromic crystals: understanding vapochromism from the perspective of crystal engineering.

Vapochromic materials, which undergo colour and/or emission changes upon exposure to certain vapours or gases, have received increasing attention recently because of their wide range of applications in, e.g., chemical sensors, light-emitting diodes, and environmental monitors. Vapochromic crystals, as a specific kind of vapochromic materials, can be investigated from the perspective of crystal engineering to understand the mechanism of vapochromism. Moreover, understanding the vapochromism mechanism will be beneficial to design and prepare task-specific vapochromic crystals as one kind of low-cost 'electronic nose' to detect toxic gases or volatile organic compounds. This review provides important information in a broad scientific context to develop new vapochromic materials, which covers organometallic or coordination complexes and organic crystals, as well as the different mechanisms of the related vapochromic behaviour. In addition, recent examples of supramolecular vapochromic crystals and metal-organic-framework (MOFs) vapochromic crystals are introduced.

Unique vapochromism of a paddlewheel-type dirhodium complex accompanied by dynamic structural and phase transitions.

The one-dimensional coordination polymer [Rh2(HA)4]n (1G; HA = hexanoate) exhibits a drastic vapochromic color change from green to red upon exposure to pyridine (py) vapor. Heating the red discrete complex [Rh2(HA)4(py)2] (1R) at 338 K affords the purple discrete tetrarhodium complex [Rh2(HA)4(py)]2 (1P), which is an intermediate species in the vapochromic transformation of 1G to 1R. The obtained complexes 1G, 1R, and 1P differ not only in their color in the solid state, but also in their temperature-dependent phase transition properties.

Fast and stable vapochromic response induced through nanocrystal formation of a luminescent platinum(II) complex on periodic mesoporous organosilica

A hybrid vapoluminescent system exhibiting fast and repeatable response was constructed using periodic mesoporous organosilica with bipyridine moieties (BPy-PMO) and a Pt(II) complex bearing a potentially luminescent 2-phenylpyridinato (ppy) ligand. An intense red luminescence appeared when the Pt(II)-complex immobilised BPy-PMO was exposed to methanol vapour and disappeared on exposure to pyridine vapour. The ON-OFF vapochromic behaviour occurred repeatedly in a methanol/pyridine/heating cycle. Interestingly, a rapid response was achieved in the second cycle and cycles thereafter. Scanning and transmission electron microscopies (SEM/TEM), absorption and emission, and nuclear magnetic resonance spectroscopies, mass spectrometry, and powder X-ray diffraction indicated that methanol vapour induced Si-C cleavage and thus liberated [Pt(ppy)(bpy)]Cl (bpy = 2,2′-bipyridine) from the BPy-PMO framework. Furthermore, the self-assembling properties of the Pt(II) complex resulted in the formation of highly luminescent micro/nanocrystals that were homogeneously dispersed on the porous support. The unique vapoluminescence triggered by the unprecedented protodesilylation on exposure to protic solvent vapour at room temperature is attributable to BPy-PMO being a giant ligand and an effective vapour condenser. Consequently, this hybrid system presents a new strategy for developing sensors using bulk powdery materials.