SYNTHESIS AND PHOTOCHROMISM OF ACRYLIC ESTER COPOLYMERS BEARING PENDANT VIOLOGEN GROUPS

A series of acrylic ester copolymers with viologen group as pendant were synthesizedthrough the reaction of MMA-EBA （Ethenyl bromoacetate） copolymer with 4-（4’-pyridyl）-N-alkyl （or arylalkyl） pyridiniums. These viologen copolymers can exchange their anionwith NH4PF6 in methanol to improve their solubility in organic solvents such as DMFand acetone. Compared with the corresponding low molecular viologens, these viologencopolymers have relatively lower color development rate under UV light and fade fasterin air due to less affinity to photo-reductant and deficiency of association between theircation radicals. Their photofatigue resistant ability is also slightly better than that of lowmolecular vinlogens.

Photochromism in CaS:Sm

The photochromism in CaS:Sm (from white to pink) was observed for the first time byexposing it to ultraviolet light. The experiments results show that the absorption intensity of Sm2+in the range of 500～600um was strongly increased after irradiation. This reveals that there is thevalence changing of Sm. If the sample was excited by visible light again, the pink color turned towhite, indicating that CaS:Sm has potential application in the field of storage material.

PHOTOCHROMISM AND LUMINESCENCE OF DOPANT CHROMOPHORES THROUGH TWO-PHOTON IONIZATION IN POLYMER FILMS

Two-photon ionization and recombination processes of an aromatic chromophore doped in polymer films were studied and the features of these processes were discussed in relation to photofunctional polymers. An aromatic molecule having low ionization potential, e.g., N,N,N',N'-tetramethyl-p-phenylene diamine doped in poly(methyl methacrylate)(PMMA) film was easily photoionized by intense laser light excitation, giving a colored radical cation (photochromism) and a trapped electron in PMMA matrix. As a reversed process, the radical cation recombined with the trapped electron, showing discoloration and emitting luminescence, either isothermal luminescence (ITL), or thermoluminescence (TL). In this report,ITL and TL through the charge recombination process were studied and the luminescence was suggested as a mean of the read-out of photorecording.

Photochromism of Hexatungstic Acid in DMF

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Crystal Structure and Crystalline State Multiphotochromism Properties of a Fused Diarylethene Dimer

The crystal structure of fused photochromic diarylethene dimer, 1,4-bis-[4-(4-{2-(5-phenyl)-2-methyl-thiophen-3-yl]-3,3,4,4,5,5-hexafluoro-cyclopent-1-enyl}-5-methyl-thiophen-2-yl) buta-1,3-diyne(1 oo, C46 H23 F12 S4) was determined by single-crystal X-ray diffraction analysis. This crystal belongs to the triclinic system, space group P1 with a = 7.546(3), b = 8.869(3), c = 16.196(5), α = 98.000(4)°, β = 100.803(4)°, γ = 98.449(4)°, Z = 2, V = 1037.6(6) ?~3, Dc = 1.496 mg/m^3, μ = 0.317, F(000) = 474, the final R = 0.0428 and wR = 0.1199 for 4115 observed reflections(I > 2σ(I)). Further study demonstrated this compound underwent reversible photochromism with color-switching between colorlessness and green in crystalline state. Upon 365 nm irradiation, the diarylethene shows one step photochromism to form isomer 1 oc. When irradiated with 312 nm, the stepwise photocyclization reactions occurred in diarylethene dimer through the line of 1 oo to 1 oc to 1 cc.

Structure, Photochromism and Liquid Crystal Properties of 1-Alkyl-2-(Arylazo)Imidazoles (Raai-C_nH_2n+1, n (Even) = 10 - 22)

Photochromism is the reversible structural change of the molecules upon light irradiation having different spectral pattern before and after irradiation. Liquid crystal (LC) is a long-range orientational order of the molecules in between solid and isotropic liquid phases which share the properties of the crystal and liquid phases. 1-Alkyl-2-(ary-lazo)imidazoles, (Raai-CnH2n+1, R = H, Me and n = 10, 12, 14, 16, 18, 20, 22) exhibits photochromism and two of them (Haai-C18H37 and Haai-C22H45) show Liquid crystal (LC) properties. One of these compounds, Meaai-C16H33 is structurally characterized by single crystal X-ray diffraction study. The compounds upon irradiation with UV light show E-to-Z isomerisation. Quantum yields (φE→Z) of E-to-Z isomerisation vary with the molar mass of the compounds. The reverse transformation, Z-to-E, is recorded in thermal condition. The activation energy (Ea) of isomerisation is determined by the controlled temperature reaction. Liquid crystal property of the molecules is examined by polarizing optical microscopy (POM) and DSC. The carbon chain length n = 18 shows nematic (N)-isotropic (I) phase transition and an unknown Smectic (Sm) phase is observed with n = 22 on heating cycle.

Rare earth inorganic-organic hybrid compounds based on Keggin-type polyoxometalate {SiW_(12)} with fast-responsive photochromism and switchable luminescence properties

Four rare earth inorganic-organic hybrid compounds based on Keggin-type polyoxometalate {SiW_(12)}with general formula [{RE(DMF)_(4)(H_(2)O)_4RE(DMF)_(6)}_(2){SiW_(12)O_(40)}_(3)](RE = La(1),Pr(2),Sm(3),Eu(4),DMF=N,N-dimethylformamide) were synthesized by the conventional solution method.Structure analyses indicate that four compounds are isostructural and are all built from three [SiW_(12)O_(40)]^(4-) polyoxoanions and DMF ligands linked by RE^(3+).Compounds 1-4 are extremely sensitive to UV light and present excellent photochromic properties,in which the coloring and fading time of samples are both no more than 2 min,and the reversible coloring-fading process can be repeated for at least 10 cycles with little fatigue,suggesting that compounds 1-4 can be a series of fast-responsive and durable photochromic materials.Moreover,the solid-state photoluminescence spectra of compounds 3(Sm) and 4(Eu)display strong characteristic emissions of rare earth ions based on f-f transitions.Meanwhile,compound4(Eu) has a longer fluorescence lifetime up to 566.74 μs.Notably,co mpounds 3(Sm) and 4(Eu) exhibit the switchable luminescence behavior induced by photochromism,which allows them to be used as potential molecular switches.

The guest CH_(3)CN molecule triggers solid-state photochromism in a Cu_(2)I_(2)-based MOF for advanced time-dependent encryption and inkless erasable printing

It remains a big challenge to develop solid-state stimuli-responsive materials for time-dependent information encryption and inkless erasable printing with long retention times.Herein,a 2D Cu_(2)I_(2)-based MOF with photoresponsive spiropyran(SP)groups orderly installed on its skeleton is developed.The structural isomerization from SP to colored merocyanine(MC)form can be triggered by removing the CH_(3)CN guests.Besides,the degree of structural isomerization and the retention time can be adjusted by controlling the amount of CH_(3)CN guests,exhibiting dynamic photochromic behavior with multicolor states and tunable retention time.Based on these advantages,time-dependent information encryption is successfully achieved.Furthermore,the long retention time(>72 h)of the MC form under daylight conditions in the CH_(3)CN-removed Cu_(2)I_(2)-based MOF and good repeatability make it promising in various applications,such as temporary calendars,price-cards,billboards,and reusable identity cards.This work provides a novel design strategy to fabricate multi-functional MOF-based smart materials for challenging applications of time-dependent information encryption and inkless erasable printing.

DL-Serine covalently modified multinuclear lanthanide-implanted arsenotungstates with fast photochromism

A series of DL-serine covalently modified multinuclear lanthanide implanted arsenotungstates K_(2)[{Ln(H_(2)O)_(7)}_(2){As_(4)W_(44)O_(137)(OH)_(18)(H_(2)O)_(2)(DL-Ser)_(2)}{Ln_(2)(H_(2)O)_(5)(DL-Ser)}_(2)]·65H_(2)O(DL-Ser=DL-serine,Ln=La(1),Ce(2),Pr(3))are obtained.Crystal structure analysis shows that these compounds are isomorphic and contain the basic[{As_(4)W_(44)O_(137)(OH)_(18)(H_(2)O)_(2)(DL-Ser)_(2)}{Ln_(2)(H_(2)O)_(5)(DL-Ser)}_(2)]^(8–)polyoxoanion constituted by two{As_(2)W_(19)O_(59)(OH)_(8)(H_(2)O)}^(6–)subunits,a[W_(6)O_(2)_(3)(OH)_(2)(DL-Ser)_(2)]_(14)–fragment,and two embedded[Ln_(2)(H_(2)O)_(5)(DL-Ser)]^(5+)groups,which further build into one dimensional linear chainlike structure via two peripheral Ln^(3+)ions.Most remarkably,these compounds exhibit rapid photochromic behaviors,which changed color quickly from white(1),yellow(2),green(3)to blue(1),brown(2)and glaucous(3)in ten minutes under UV irradiation,and that the colors gradually recovered in the dark for approximately 22 h.

Inclusion of methylviologen dication in a cadmium tetracyanoplatinate host clathrate showing photochromism and photoluminescence modulation

A cadmium tetracyanoplatinate host clathrate,(MV)[Cd_(2){Pt(CN)_(4)}_(3)]·2(H_(2)O)(1),including a methylviologen dication (MV^(2+)) was synthesized,and the crystal structures,photochromic and photoluminescence properties were investigated.In 1,the alternatively parallel stacking between the MV^(2+)dications as electron acceptors in the channels and the electron donors[Pt1(CN)_(4)]^(2-) units in the host frameworks give a unique donor-acceptor (DA) system.Under UV irradiation,the electron transfer between MV^(2+) and[Pt(CN)_(4)]^(2-) ions generates MV^(·+)radicals with a photochromic behavior from pale-yellow to blue.This process occurs through single-crystal-to-single-crystal (SCSC) transformation and obvious structure variation of viologen cations is successfully observed.Moreover,the spectral overlap between the emission bands of 1 and the absorption around 623 nm for the MV^(·+) radicals leads to a modulation of the photoluminescence.

Ultrasensitive photochromism and impedance dual response to weak visible light by solvated Pb(Ⅱ) modified polyoxomolybdate

Polyoxometalates (POMs) are important inorganic photochromic materials to be potentially applied in photo-induced switch,energy storage,and even the detection of light.However,due to the limited sensitivity of POMs,it is difficult to realize the photochromic response to weak visible light.In this paper,by the coordination of solvated Pb(Ⅱ),a new structure-defined chain-like polyoxomolybdate complex of[(Pb(DMF)_(4))^(3)(P_(2)Mo_(18)O_(62))_(2)]n(Pb_(3)Mo_(18) ,DMF=dimethylformamide) has been demonstrated by a facile solvent-diffusion approach.By virtue of interactions between Pb(DMF)_(4) and polyoxoanions,Pb_(3)Mo_(18) shows an ultrasensitive photochromic response to weak visible lights and forms the reduced’heteropoly blue’species through ligand-to-metal charge transfer (LMCT) process.A new mechanism is firstly proposed here that the 6s orbital lone electron pair on Pb(II) can effectively stabilize the generated hole of oxygen atoms as a result of O→Mo charge transfer.Through the proposed mechanism,the LMCT barrier is drastically lowered and allows the coloration to be occurred even upon weak visible light.Also,because the conductivity of Pb_(3)Mo_(18) enhances with the increase of reduction extent,its electrochemical impedance signals are proportionally response to irradiation intensity.Especially,for the first time,the polyoxomolybdate composite can be used to detect weak visible light,in which the optical signal can be converted into electrical signal output.Moreover,Pb_(3)Mo_(18) can be drip-coated on the surface of the screen printed chip electrode,which is facile to the detection of light by portable devices compatible with computers,mobile phones and other electronic equipment.This work not only highlights a new approach to the molecular design of photochromic POMs by the coordination of metal ions with the effect of inert electron pair,but also lays a foundation to extend the application of POMs as light signal sensors.

A Versatile Tetraphenylethene Derivative Bearing Excitation Wavelength Dependent Emission,Multistate Mechanochromism,Reversible Photochromism,and Circularly Polarized Luminescence and Its Applications in Multimodal Anticounterfeiting

Multimodal anticounterfeiting has become increasingly challenging in modern society to guarantee information security and the safety of property.In this study,a versatile cholesterol-containing tetraphenylethene derivative is shown to have multiple optical properties,including stimuli-responsive fluorescence,reversible photochromism,excitation wavelength dependent luminescence,and circularly polarized luminescence.After the application of diverse processing methods(writing,screen painting,drawing,and pyrography),we found that this molecule can serve as an anticounterfeiting toolbox to provide rich anticounterfeiting effects through the synergistical use of multiple optical properties.This work offers important insight for designing novel small organic molecules for advanced multimodal anticounterfeiting technology.

Chemometric analysis of femtosecond transient absorption spectroscopy data:Study of the photochromism of anils

Chemometric methods are applied for the purpose of extracting relevant information from transient absorption spectroscopy data probing the photochromism of molecules from the family of salicylidene aniline. The process consists of an ultrafast excited state intramolecular proton transfer occurring from an enol form which is then followed by a cis-trans isomerization to finally reach a trans-keto photo-product. This work focuses on the potential of combining multivariate curve resolution for modeling pure profiles and two dimensional correlation spectroscopy data analysis for providing information on the dynamics of spectral features. The results obtained for one derivative of salicylidene aniline provide information regarding the number of species created after the proton transfer and characterization of their absorption spectra and their kinetics in the picosecond time scale. The spectral resolution of two cis-keto* forms is proposed for the first time. It is also found that both cis-keto* species are involved in the formation of the trans-keto photo-product. The main precursor of the trans-keto photo-product is the cis-keto* form which has the shortest characteristic time.

Preparation and photochromism of Keggin-type molybdphosphoric acid/silica mesoporous composite thin films

Using tetraethoxysilane and 3-aminopropyltriethoxysilane as the silica sources, amino-functionalized organic/inorganic hybrid mesoporous silica thin films with 2-dimensional hexagonal structure have been synthesized by evaporation induced self-assembly process in the presence of cetyltrimethyl ammonium bromide templates under acid conditions. The Keggin-type molybdphosphoric acid (PMo) is incorporated into the mesoporous silica thin films with amino-groups by wetness impregnation, and the PMo/silica mesoporous composite thin films are obtained. The results of X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), and Fourier transform infrared (FTIR) spectra indicate the PMo molecules maintain Keggin structure and are homogeneously distributed inside mesopores. The composite thin films possess excellent reversible photochromic properties, and change from colorless to blue under ultraviolet irradiation. The photochromic mechanism of the composite thin films is studied by ultraviolet-visible (UV-vis), electron spin resonance (ESR) and X-ray photoelectron spectroscopy (XPS) spectra. It is shown that intervalence charge transfer (IVCT) and ligand-to-metal charge transfer (LMCT) are the main reasons of photochromism. PMo anions interact strongly with amino-groups of the mesoporous suface via hydrogen bond and electrostatic force. After ultraviolet irradiation, the charge transfer occurs by reduction of heteropolyanions accompanying the formation of heteropolyblues with multivalence Mo(VI, V), and the bleaching process of composite thin films is closely related to the presence of oxygen.

Structure and photochromism of spiropyran assemblies

Nanocluster assemblies of spiropyran compounds have been prepared by means of LB technique, and the relations between the subphase, pH value, condition of preparation and the structure of the fabricated LB film are systematically investigated. The stability, photochromic fatigue properties of the spiropyran LB film, which are of primary importance in optic signal storage applications, are also studied in detail. A kind of supermolecular film with homogeneously distributed J aggregates of similar granular size has been obtained with the optical resolution in the order of micrometer. Finally, a nondestructive readout method for such an LB film to be used as the optic signal storage film is proposed.

The effect of substituents and polymer media on photochromism kinetics of indolinospironaphthoxazine

The effect of substituents in indoline moiety and polymer media on photochromism and thermal decay processes of spirooxazine (ASP) was investigated. The thermal decoloration rate was decreased with increasing steric hindrance of substituents in l-position of indoline moiety. The stability of the colored forms was improved when the hydrogen in the 5-position of indoline moiety was replaced with electron-donating groups and was decreased when substituted by electron-withdrawing groups. In addition, the stability of the colored forms was related to properties of polymer media. The thermal decay rate decreased with an increase in the polarity and rigidity of polymer media. The themal decay kinetics of the colored forms obeyed biexponential decay law.

Acid/alkali gated photochromism of two diarylperfluorocyclopentenes

Two novel diarylfuorocyclopentenes, which underwent gated photochromism, were synthesized. It was found that the photochromic property of these diarylethenes could be switched by alternative addition of acids/alkalis, which could provide a new design strategy toward chemical threshold photoreaction.

Multiple anti-counterfeiting strategy by integrating up-conversion,down-shifting luminescence, phosphorescence and photochromism into Na YTiO4: Bi/Er phosphors

With the rapid development of science and technology,the high-security-level anti-counterfeiting technique is essential for ensuring property or information security.In this work,we prepared micron NaYTiO_(4):Bi/Er(NYT:Bi/Er) phosphors with integrating up-conversion(UC) photoluminescence,downshifting(DS) emission,phosphorescence and photochromism(PC) performances for advanced multiple anti-counterfeiting application.Owing to the abundant energy levels of Er^(3+)ions,the UC and DS luminescence behaviors are anticipated.Specifically,the yellow-green emission of Er^(3+)ions can be observed upon 980 nm excitation,and the bright green emission is demonstrated under 281 or 254 nm excitation due to the energy transitions of Er^(3+)ions and the energy transfer process from Bi^(3+)to Er^(3+)ions.Besides,the introduction of Bi^(3+)ions generates defect levels in the matrix and thus leads to phosphorescence.Furthermore,the repeatable PC performance could be triggered by the 365 nm irradiation and vanished with 450 nm illumination or thermal stimulation.To verify the practical usability of NYT:Bi/Er phosphors on anti-counterfeiting applications,some experiments are designed and successfully executed.It is believed that the NYT:Bi/Er phosphors can be a promising candidate for high-security-level multiple anti-counterfeiting.

Photo Switchable Two-step Photochromism in a Series of Ln-Phosphonate(Ln=Dy,Gd,Tb,Y)Dinuclear Complexes

Exploring the discrete complexes with multi-step coloration is still a challenge in the field of electron transfer photochromic materials. Herein, we synthesized a series of dinuclear Ln-diphosphonate compounds[Ln=Dy(1);Gd(2);Tb(3);Y(4)] with a remarkably and reversibly photoactive coloration phenomenon. These compounds showed two-step coloration behavior, which were the first discrete architectures in the reported electron transfer photochromic complexes. This two-step coloration phenomenon was originated from the large distortion of H3-TPT acceptors, which in turn reduced the π-conjugation of electron acceptors and slowed the decay process of electron transfer. The photogenerated stable doublet radicals originated from electron transfer from diphosphonate donor to polypyridine acceptor in these complexes were detected by UV-Vis and electron spin resonance(ESR) spectra. Furthermore, the photogenerated radicals were estimated by direct current magnetic susceptibilities and variable temperature ESR spectra, suggesting the doublet radicals in the dinuclear structure for all the compounds. This work revealed a series of discrete phosphonate-based systems with a multi-step coloration process, providing a new pathway for designing multicolor photochromic materials with potential photoswitching or other applications.

Instant Photochromism Caused by Radical Formation in Photocatalytic Decarboxylation of Dihydrothiazole Derivative

Main observation and conclusion A pair of new enantiomeric compounds,(R)/(S)-1,3,5-benzene-triyl-2,2',2”-tris(4,5-dihydrothiazole-4-carboxylic acid)(H3LRRR and H3LSSS)are synthesized in one step synthetic route with high yield.Instant photochromism has been investigated to elaborate the photocatalytic decarboxylation of the dihydrothiazole derivative by electron paramagnetic resonance spectroscopy(EPR),photoluminescence(PL),FT-IR,high resolution mass spectra,X-ray photoelectron spectroscopy and UV-Vis spectroscopic techniques.The results indicate that the photochromic transformation is originated from the formation of the radical during the photocatalytic decarboxylation of the 4,5-dihydrothiazole-4-carboxylic acid units.