Luminescence Switching Properties Research Articles

Stimuli-Responsive Properties on a Bisbenzofuropyrazine Core: Mechanochromism and Concentration-Controlled Vapochromism.

Stimulus-responsive organic materials with luminescence switching properties have attracted considerable attention for their practical applications in sensing, security, and display devices. In this paper, bent-type bisbenzofuropyrazine derivatives, Bent-H and Bent-sBu, with good solubilities were synthesized, and their physical and optical properties were investigated in detail. Bent-H gave three crystalline polymorphs, and they showed different luminescence properties depending on their crystal packing structures. In addition, Bent-H exhibited mechanochromic luminescence in spite of its rigid skeleton. Bent-sBu exhibited unique concentration-dependent vapochromic luminescence. Ground Bent-sBu was converted to blue-emissive, green-emissive, and green-emissive high-viscosity solution states at low, moderate, and high concentrations of CHCl3 vapor, respectively. This finding represents a concentration-dependent multi-phase transition with an organic solvent, which is of potent interest for application in sensing systems.

Dual Monomeric Inorganic Units Constructed Bright Emissive Zero-Dimensional Antimony Chlorides with Solvent-Induced Reversible Structural Transition.

A5M2X11 and A3M2X9 families (A = monovalent organic cation; M = trivalent metal; X = halogen) are receiving increasing attention because of their combination of easy solution processability and superior ferroelectricity properties. However, synthesizing highly efficient A5M2X11 and A3M2X9-type fluorophores with multiple monomeric inorganic units and achieving their structural interconversion remains challenging. Here, we report two novel zero-dimensional (0D) antimony halides, (C10H16N)5Sb2Cl11·C2H3N (1) and (C10H16N)3Sb2Cl9 (2), which not only contain two distinct [SbXn]3-n units but also have excellent orange (590 nm) and yellow-green emission (540 nm) with high PLQY of 17.7% and 31.5%, respectively. Interestingly, a reversible structural conversion could be triggered by acetonitrile steam stimulation, accompanied by luminescence switching properties. This work not only enriches the structure of hybrid Sb-based halides but also provides the possibility of well-known A5M2X11 and A3M2X9 families as structural transformation materials.

The two-stepwise luminescent switching properties of triple-stimuli-responsive platinum(II) complexes bearing 4,4′-bis(2-phenylethynyl)-2,2′-bipyridine ligand

Three new square-planar platinum(II) complexes, Pt(PhC≡CbpyC≡CPh)(C≡CC6H4-X-2)2 [PhC≡CbpyC≡CPh = 4,4′-bis(2-phenylethynyl)-2,2′-bipyridine; X = F(1), Cl(2), and Br(3)] were synthesized and characterized. Upon exposure of the ground sample to volatile organic compound (VOC) vapors, a series of metastable structures of three complexes, including yellow solvent-free species 2 and 3, orange species 1, 2·ClCH2CH2Cl and 3·ClCH2CH2Cl, red species 1·1.5(CHCl3), 2·½(CH2Cl2), 2·½(ClCH2CH2Cl), 3·½(Toluene), and 3·½(ClCH2CH2Cl) were isolated. All three complexes exhibit vapor-, thermo-, and mechanical-grinding-triggered triple-stimuli-responsive luminescent switching properties. More interestingly, upon exposure to ClCH2CH2Cl vapor, the red species 2·½(CH2Cl2) or 3·½(Toluene) undergo an unusual time-dependent two-stepwise luminescent switching process and convert to the orange species 2·ClCH2CH2Cl or 3·ClCH2CH2Cl via intermediate 2·½(ClCH2CH2Cl) or 3·½(ClCH2CH2Cl). Furthermore, 1·1.5(CHCl3) also displays a two-stepwise thermoluminescent property and is transformed into orange species 1via intermediate 1·⅛(CHCl3). Furthermore, both 2 and 3 present the irreversible vapochromic and vapoluminescent properties as the yellow and orange species could not be converted to each other or transformed to the red species by absorbing the corresponding VOC vapors. Systematic studies revealed that the vapor-, thermo-, and mechanical-grinding-triggered triple-stimuli-responsive luminescence switching properties of 1–3 are due to the structural conversion and resultant changes of the lowest-energy excited states. The crystal structure, 1H NMR, luminescence spectra and PXRD measurements demonstrate that the two-stepwise luminescent switching behavior of complexes are associated with the stacking structure of species with same kind and different amount of solvent molecule. The irreversible vapoluminescent property of 2 and 3 are most likely due to the closed stacking of species which prevent the inserting of solvent molecules into the crystal lattice. In addition, complexes 1–3 have good application prospects in the visual identification of CHCl3, CH3CN and 1,2-dichloroethane vapors.

Facile development of novel photochromic luminescent composite fiber for anticounterfeiting and wearable UV detector

Photo-responsive fibers with persistent luminescence and reversible color switching properties are highly in demand owing to their potential application in information security, camouflage, optical sensors, and anticounterfeiting. Herein, a facile strategy to develop novel photochromic luminescent fiber (PLF) via a wet-spinning process was presented. The resulting fiber is composed of rare-earth luminescent phosphors SrAl2O4: Eu2+, Dy3+ (SAO) and Y2O2S: Eu3+, Mg2+, Ti4+ (YOS) as the luminescence sources, photochromic yellow microcapsules (PYM) as the reversible photochromic materials, and the matrix is polyacrylonitrile (PAN). The as-prepared fiber emits unique yellow luminescence with long afterglow under ultraviolet (UV) light. Furthermore, the fiber shows a quick and reversible color response to UV stimulation. Benefiting from the excellent reversible photochromic behavior, and persistent luminescence, the photochromic luminescent fiber can be adopted in various applications such as smart textiles, anticounterfeiting, and wearable UV detection devices.

The triple-stimuli-responsive luminescence switching properties and application of a square-planar platinum(II) complex

A new square-planar platinum (II) complex, Pt(Me3SiC≡CbpyC≡CSiMe3)(CCC6H4–Me-4)2 (1) was synthesized and characterized. This complex has a series of metastable structures, including seven orange solvated species, red 1·½(ClCH2CH2Cl), dark-brown 1B, black 1·¼(CH2Cl2) and 1·½(CH3OH), red-brown 1H and solvent-free amorphous 1G. Among them, 1B, 1H, 1G, 1·¼(CH2Cl2) and 1·½(CH3OH) display the long-wavelength NIR luminescence with emission beyond 900 nm. Complex 1 exhibits interesting triple-stimuli-responsive luminescence switching properties. First, 1 shows the reversible vapochromic and vapoluminescence properties between different metastable structures. Upon heating, all species of 1 change to a same solvent-free sample 1H, which emits the NIR luminescence peaked at 988 nm and can be reversibly converted back to the original species by exposure to specific VOC vapor. Furthermore, 1 also shows reversible mechanoluminescence property that all species of 1 will change to a brown amorphous 1G after grinding with its emission wavelength peaked at 954 nm. Systematic studies revealed that the vapor-, thermo-, and mechanical-grinding-triggered triple-stimuli-responsive luminescence switching property of 1 is due to the structural conversion and resultant changes of the lowest-energy excited states. Interestingly, the stacking structure and solvated molecule can influence the responses of metastable structures of 1 to heating or mechanical grinding. In addition, complex 1 can be used for visual recognition of CH3CN and 1,2-dichloroethane vapors as well as the development of simple rewritable data recording device.

Vapor-, thermo-, and mechanical-grinding-triggered tri-stimuli-responsive luminescence switching of cycloplatinated(II) complex bearing 8-quinolinol derivatives

Four novel cycloplatinated(II) complexes, Pt(ppy)(L1) (1), Pt(ppy)(L2) (2), Pt(ppy)(L3) (3) and Pt(ppy)(L4) (4) based on 5-[2-(4-substituent-phenyl)ethynyl]-8-quinolinol ligands {substituent = H (L1), Me(L2), Et(L3), t-Bu(L4)} were synthesized and characterized. Complex 4 has three main pseudopolymorphs, including orange 4·CH3CH2OH, red 4R, and dark-brown 4·½(CCl4). Complex 4 exhibits interesting tri-stimuli-responsive luminescence switching properties. Upon exposure to different VOC vapors, three pseudopolymorphs display unusual irreversible vapoluminescence that 4R and 4·½ (CCl4) can be exchanged with each other and be irreversibly converted to 4·CH3CH2OH. Furthermore, 4·½(CCl4) shows reversible thermochromic luminescence behaviour and can be reversibly converted to 4R upon heating. No detectable change in color and luminescence of 4·CH3CH2OH and 4R can be found during the heating process, although 4·CH3CH2OH lost its solvent and changed to desolvated 4O. In addition, 4·CH3CH2OH, and 4·½ (CCl4) also show the mechanoluminescent property that both of them will be converted to the same red amorphous 4G peaked at 742 nm after grinding. Systematic studies revealed that the tri-stimuli-responsive luminescence switching property of 4 is due to the structural conversion and resultant changes of the lowest-energy excited states. In contrast, complexes 1–3 have not any luminescent switching property. The reason is most likely due to the compact stacking structures of them which prevent their structural conversion triggered by external stimuli.

Electroluminochromic Materials and Devices Based on Metal Complexes.

Electroluminochromism (ELC) refers to an interesting phenomenon exhibited by a material whose luminescent properties can be reversibly modulated under an electrical stimulus. Such a luminescence-switching property has been widely used in various organic optoelectronic devices because it can simultaneously detect electrical and optical signals. Metal complexes are the promising candidates for ELC materials due to their sensitivity to an electrical stimulus. Herein, recent progress on electroluminochromic materials and devices based on various metal complexes has been summarized. Meanwhile, the applications of these complexes in data recording and security protection have also been discussed. Finally, a brief conclusion and outlook are presented, pointing out that the development of electroluminochromic metal complexes with excellent performance is important because they play a vital role in future intelligent optoelectronic devices.

Synthesis, structure and dual-stimulus-responsive luminescence switching of a new platinum(II) complex based on 3-trimethylsilylethynyl-1,10-phenanthroline

A new diimine-platinum(II) complex, Pt(PhenC≡CSiMe3)(C≡C-C6H4-3-F)2 (1) based on 3-trimethylsilylethynyl-1,10-phenanthroline (PhenC≡CSiMe3), was synthesized and characterized. Two solvated crystals, 1·1/2(ClCH2CH2Cl) and 1·CHCl3 exhibited dual-stimulus-responsive color and luminescence switching behaviors triggered by heating or mechanical grinding. Upon heating, the color and luminescence of both complexes were changed to red with luminescence red-shifting to 656 for 1·1/2(ClCH2CH2Cl) and 691 nm for 1·CHCl3, corresponding to the thermo-triggered luminescence red-shifts of 112–142 nm and 156–189 nm, respectively. The different heated samples confirm that the original stacking structure can accurately affect the luminescence switching properties of luminescent switching materials. Under the mechanical grinding, both complexes were converted to the same red amorphous product with red emission peaked at 702 nm. Interestingly, once exposure to ClCH2CH2Cl or CHCl3 vapor, the heated and ground samples could be thoroughly reverted to crystalline 1·1/2(ClCH2CH2Cl) and 1·CHCl3. Such reversible thermo- and mechanical-grinding-triggered luminescence switching properties of the complexes are attributed to the interconversions of the lowest energy excited states between metal-to-ligand charge transfer (MLCT) and metal-metal-to-ligand charge transfer (MMLCT) transitions during the heating/grinding-vapor absorbing processes. Furthermore, 1·CHCl3 was successfully used for rewritable data recording.

Photophysics and luminescence switching properties of a series of photochromic styrylbenzene-terpyridine conjugate: Experimental and DFT/TD-DFT investigation

Joint experimental and computational investigation have been carried out in this work with regard to photophysical and photo-isomerization behavior of a series of photochromic terpyridine derivatives covalently coupled with styrylbenzene unit. Several electron-donating and electron-accepting groups were incorporated in the compound, tpy-pvp-X (X = H, Me, Cl, NO2, and Ph) to tune their photophysical as well photo-isomerization behaviors. All the compounds underwent trans-to-cis isomerization upon interaction with UV light with substantial changes in their absorption and luminescence spectra. Reversal of cis to trans forms were also achieved upon interacting with visible light. Trans-to-cis isomerization leads quenching of luminescence, while backward cis-to-trans isomerization gives rise to restoration of the original luminescence. Thus, "on-off" and "off-on" emission switching was made possible upon alternate interaction of the compounds with UV and visible light. Interestingly, the photochromic and photo-isomerization behaviors of the compounds are strongly influenced by the presence of acid. Detailed kinetic and thermodynamic aspects of the photo-isomerization process were also addressed in this study.

Facile and Equipment-Free Data Encryption and Decryption by Self-Encrypting Pt(II) Complex.

Luminescence switching materials are vital to various data security-related techniques, including data encryption-decryption. Here, we report a family of pseudopolymorphs based on a diimine-platinum(II) complex, Pt(Me3SiC≡CbpyC≡CSiMe3)(C≡CC6H4Br-3)2 (1), and systematically studied the influence of stacking modes on luminescence switching behaviors. Upon exposure to heat or tetrahydrofuran vapor, these pseudopolymorphs exhibit unusual stacking mode-intervened luminescence switching (SMILS) property that non-columnar and quasi-columnar pseudopolymorphs undergo single- and multi-step conversion processes, respectively, to the same non-columnar products. Systematic studies revealed that the unique SMILS behavior is caused by the existence of stable intermediate products as well as different conversion processes of pseudopolymorphs with distinct stacking modes. Such a new property leads to the self-encryption function of 1, which is very important for improving the existing data encryption-decryption technique. On this basis, we developed a facile, reusable, equipment-free technique with 1 as the only starting material and realized data encryption-decryption successfully.

Synthesis of hollow and aggregated CeO2:Sm3+ microspheres and their redox-responsive luminescence

Hollow and aggregated microspheres of an Sm3+-doped CeO2 phosphor material were synthesized by liquid processes using organic materials as a template and a structure-directing agent, respectively The microstructure of both the microspheres obtained were characterized as their crystallite size and specific surface area because they were comprised of CeO2:Sm3+ nanocrystals approximately 20 nm in size. The microspheres showed orange luminescence due to electronic transitions of the Sm3+ ions upon excitation with ultraviolet light. The luminescence intensity was decreased when the microspheres were treated with an aqueous l(+)-ascorbic acid solution as a reductant. The intensity was then recovered by treating the microspheres with an H2O2 solution as an oxidant. Such the redox-responsive luminescence switching is promising for sensing applications if the sensitivity can be controlled well. The relationship between the structural features of the microspheres and the luminescence switching property was then examined in detail.

Luminescence switching property of cycloplatinated(II) complexes bearing 2-phenylpyridine derivatives and the application for data security storage

Four novel cycloplatinated(II) complexes, Pt(ppy)(acac-C6H4I-4) (1), Pt(ppy)(acac-C6H4t-Bu-4) (2), Pt[dF(CF3)ppy](acac-C6H4I-4) (3) and Pt[dF(CF3)ppy](acac-C6H4t-Bu-4) (4) based on either 2-phenylpyridine (ppy) or 2-(2,4-difluorophenyl)-5-(trifluoromethyl)pyridine [dF(CF3)ppy] ligands were synthesized and characterized. Complex 4 has two isomers with different color and luminescence. Yellow-green 4G emits a green luminescence whereas orange 4O exhibits red luminescence. Complexes 1, 2 and 4G display mechanoluminescence with the luminescence red-shift in a range of ca. 94–135 nm. Whereas 3 and 4O exhibit no response to mechanical grinding. Systematic studies on crystal structure, TGA, luminescence spectra, and PXRD demonstrate that the mechanoluminescence of 1 and 2 is due to the formation of π-π interactions, whereas, the mechanism for 4G is the destruction of F⋯F interactions during mechanical grinding. All complexes exhibit concentration-dependent luminescence switching behaviour in CHCl3 solution. Extremely large red-shifts of their luminescence spectra suggest the formation of aggregates via PtPt interaction in high concentration solutions. Moreover, 4O don't respond to ethanol vapor, but its ground species can be converted to 4G upon exposure to ethanol vapor. Based on this unique property, a simple device was developed using 4O as starting material and successfully demonstrated potential for data security storage.

Reversible luminescence switching and non-destructive optical readout behaviors of Sr3SnMO7: Eu3+ (M = Sn, Si, Ge, Ti, Zr, and Hf) driven by photochromism and tuned by partial cation substitution

Here, we report a series of Eu3+-doped Sr3SnMO7 (M = Sn, Si, Ge, Ti, Zr, or Hf) phosphors, which exhibited both photochromism and luminescence switching. Under alternating UV (254 nm) light irradiation and visible light/thermal stimulus, the obtained samples showed a reversible color change from the initial white color to brown. Based on photochromism and red luminescence, the red emission could be effectively modulated. Most interestingly, the Eu3+ red emission could be reversibly modulated by alternating UV and visible light/thermal treatment with excellent reproducibility, which can be used as non-destructive optical information write-in and read-out. In the case of the Sr3SnMO7 host, the band gap could be clearly changed from 3.64 to 4.41 eV through partial cation substitution, resulting in an evident effect on the photochromism and photoluminescence modulation performance. This provides a new method for tuning the photochromism and photoluminescence modulation properties. These results suggest that Sr3SnMO7:Eu3+ phosphors with photochromism and luminescence switching properties constitute a class of promising candidates for the development of optical data storage devices. On the basis of their luminescence modulation behavior, a model with non-radiative energy transfer from the luminescent centers to the color center was developed.

(K,Na)NbO3ferroelectrics: a new class of solid-state photochromic materials with reversible luminescence switching behavior

A kind of new photosensitive material, Sm doped K0.5Na0.5NbO3(KNN) ceramics, exhibits excellent photochromism and reversible luminescence switching properties.

Self-assembly and mechanochromic luminescence switching of trifluoromethyl substituted 1,3,4-oxadiazole derivatives

Stimuli responsive luminescence switching, liquid crystalline and gelation properties of 1,3,4-oxadiazole derivatives were investigated.

Multistimuli-Responsive Luminescence Switching of Pyrazine Derivative Based Donor-Acceptor-Donor Luminophores.

Three symmetrical donor-acceptor-donor (D-A-D) luminophores (C1, C2, and C3) with pyrazine derivatives as electron-withdrawing groups have been developed for multistimuli-responsive luminescence switching. For comparison, reference compounds R1 and R2 without the pyrazine moiety have also been synthesized. Intramolecular charge transfer (ICT) interactions can be found for all D-A-D luminophores owing to the electron-withdrawing properties of the two imine nitrogen atoms in the pyrazine ring and the electron-donating properties of the other two amine nitrogen atoms in the two triphenylamine units. Moreover, luminophores C1, C2, and C3 exhibit "on-off-on" luminescence switching properties in mixtures of water/tetrahydrofuran with increasing water content, which is different from the "on-off" switching for typical aggregation-caused quenching (ACQ) materials and "off-on" switching for traditional aggregation-induced emission (AIE) materials. Additionally, upon grinding the pristine samples, luminophores C1, C2, and C3 display bathochromically shifted photoluminescence maxima that can be recovered by either solvent fuming or thermal annealing treatments. The piezofluorochromic (PFC) properties are more pronounced than those for reference compounds R1 and R2, which indicates that D-A molecules have the ability to amplify the PFC effect by tuning the ICT interactions upon tiny structural changes under pressure. Furthermore, the target luminophores demonstrate acid-responsive photoluminescence spectra that can be recovered in either basic or ambient environments. These results suggest that D-A complexes are potential candidates for multistimuli-responsive luminescence switching because their ICT profiles can be facilely tuned with tiny external stimuli.

PH and DNA luminescence switching, DNA photocleavage and cytotoxic properties of two thiophene-containing ruthenium(II) complexes

Two new Ru(II) complexes, [Ru(Htip)3]Cl2 (1) and [Ru(Htip)2(dppz)]Cl2 (2), were synthesised and were characterised. The ground- and excited-state acid–base properties of 1 and 2 were studied and demonstrated that 1 acted as a pH-induced “on–off–on” luminescence switch. The binding behaviours of 1 and 2 to calf thymus DNA were studied with absorption and emission spectroscopy, DNA viscosities and density functional theory calculations. 2 was found to act as a DNA molecular light switch and as an efficient photocleaver of pUC 18 DNA. The cytotoxicities of the complexes were evaluated with the MTT method and it was found that 1 displayed apparent anticancer activity against MCF-7 cell, whereas 2 exhibited more potent and wider-spectrum antitumor activities against all cancer cell lines tested.

Off–on–off pH luminescence switching and DNA binding properties of a free terpyridine-appended ruthenium complex

A ruthenium(II) complex [Ru(bpy)2(HL1)](ClO4)2·3H2O {bpy=2,2′-bipyridine and HL1=2-(2,6-di(pyridin-2-yl)pyridin-4-yl)-1H-imidazo[4,5-f][1,10]phenanthroline}, denoted as RuHL1, was synthesized and characterized by elemental analysis, proton nuclear magnetic resonance spectroscopy, and mass spectrometry. The pH effects on the UV–visible (UV–vis) absorption and emission spectra and the luminescence lifetimes of RuHL1 have been studied, and their ground- and excited-state acid ionization constants were derived. The complex was found to exhibit pH-induced “off–on–off” luminescence switching properties via protonation/deprotonation of the grafted imidazole and terpyridyl groups. A pH-induced emission on–off intensity ratio of 166 was observed as pH was increased from 2.00 to 5.44, which is one of the largest values observed among imidazole-containing Ru(II) complex-based acidic-pH-induced pH luminescence switches. RuHL1 also strongly binds to calf thymus DNA in mixed binding modes involving classic intercalation and partial intercalation, as determined by UV–vis absorption and emission spectrophotometric DNA titration, ethidium bromide displacement, DNA denaturation and DNA viscosity measurements.

Microstructural Aspects of the CePO4:Tb3+ Phosphor for Luminescence Sensing

Ceramic powders and thin films of cerium phosphate doped with trivalent terbium ions (CePO4:Tb3+) were synthesized from liquid phases, and their microstructures were modulated to investigate the relationship between the structure and the luminescence switching property responsive to redox reactions. Aqueous KMnO4 and L(+)‐ascorbic acid solutions were used to evaluate the redox response of CePO4:Tb3+, appearing as luminescence quenching and recovering, respectively. The particle shape and size of the powder samples depended on heat‐treatment conditions, which had also a large influence on the switching property. As‐prepared nanorod particles were more sensitive to the redox reactions than heat‐treated larger spherical particles, indicating that the switching was governed by the surface state of the particles. The thickness of the thin‐film samples was also an important factor to determine the response to the redox reactions. In any case, our results demonstrate that it is important to control the microstructure of the CePO4:Tb3+ materials for their use in luminescence switching devices for the redox monitoring.

PH luminescence switch, DNA binding and photocleavage, and cytotoxicity of a dinuclear ruthenium complex

The ground- and excited-state acid-base properties of [Ru2(bpy)4(H2bipt)]Cl4 1 {bpy = 2,2'-bipyridine, H2bipt = 2,5-bis[1,10]phenanthrolin[4,5-f]-imidazol-2-yl)thiophene} are investigated by emission and UV-visible absorption spectrophotometric pH titrations. The DNA binding properties of 1 are studied by means of DNA viscosity and optical spectroscopic techniques of UV-visible absorption and emission spectral titrations, steady-state emission quenching with ferrocyanide, ethidium bromide competitive binding, and DNA thermal denaturation as well as density functional theoretical calculations. The DNA photocleavage and singlet oxygen generation properties as well as in vitro anticancer activities against five cancer cell lines are studied as well. The results demonstrated that pH-induced luminescence switching, DNA binding, and anticancer properties of 1 are much improved with respect to those of the mononuclear analog [Ru(bpy)2(Htip)]Cl2 {Htip = 2-(thiophen-2-yl)-1H-imidazo[4,5-f][1,10]phenanthroline}.