Photochromic Behavior Research Articles

Gated Photochromism of Dithienylethene-Embedded Expanded Calixphyrins.

Dithienylethene (DTE)-embedded expanded porphyrins were synthesized and confirmed to be photochemically inactive due to the lowest excited state of the expanded porphyrins. On the other hand, DTE-embedded expanded calixphyrins exhibited reversible photochromism upon UV-irradiation to form colored closed forms, which reverted to colorless open forms upon red-light irradiation. The closed forms were oxidized with DDQ or the air to lock the recorded information by converting to photochemically inactive expanded porphyrins. This was unlocked by reduction with NaBH4 to restore expanded calixphyrins with photochromism activity. These gated photochromic behaviors were demonstrated in PMMA (polymethyl methacrylate) film.

Investigation of photochromic behavior of biodegradable MoO3/Sg-St nanocomposites

Now a days, the synthesis of α-MoO3 based photochromic materials are a subject of many investigations as they can modulate solar light transmittance automatically, according to wavelength, in response to UV irradiation and hence can adjust the indoor atmosphere to reduce the consumption of energy. In the present work, an attempt has been made to investigate the relation between coloring/bleaching rates of self-supporting, highly flexible α-MoO3/Sg-St (Sago-Starch) nanocomposites (NCs) fabricated via solution casting technique. The prepared samples were characterized using FESEM, XRD, FTIR, and UV–Vis–NIR spectroscopy. Nano-sheet morphology of the synthesized sample was ascertained using FESEM while XRD reveals the orthorhombic structure of MoO3 with an average crystallite size of 135 nm. The average thickness of nanosheets comes out to be 111.57 nm (using FESEM). FTIR spectroscopy depicts the strong interaction between α-MoO3 and Sg-St polymer confirming the successful incorporation of α-MoO3 in the Sg-St matrix. The value of Eg for virgin Sg-St comes out to be 4.56 ± 0.12 eV and decreases to 2.54 ± 0.07 eV for 10 wt% α-MoO3/Sg-St NC while the refractive index (n) increases from 1.53 for virgin Sg-St to 2.11 for 10 wt% α-MoO3/Sg-St NC at 450 nm wavelength. The value of tensile strength for virgin Sg-St is found to be 9.54 which increases to 17.07 after incorporation of 1 wt% of α-MoO3 suggesting the strong interfacial interaction of nanofiller with polymer matrix. The prepared NCs exhibited a fast response to UV exposure (<30 s) with high coloration efficiency; which makes them a highly acceptable material for photochromic smart windows. The maximum coloration efficiency ∼0.6071 and RDR (%) value of 75.29 corresponds to 1 wt% α-MoO3/Sg-St NC.

Dual Photo-/Electrochromic Pyromellitic Diimide-Based Coordination Polymer.

By the combination of N,N'-bis(carboxymethyl)-pyromellitic diimide (H2CMPMD, 1) and zinc ions, a novel PMD-based coordination polymer (CP), [Zn(CMPMD)(DMF)1.5]·0.5DMF (2) (DMF = N,N'-dimethylformamide), has been prepared and characterized. 1 and 2 exhibit completely different photochromic properties, which are mainly reflected in the photoresponsive rate (5 s for 1 vs 1 s for 2) and coloration contrast (from colorless to light green for 1 vs green for 2). This phenomenon should be attributed to the introduction of zinc ions and the consequent formation of the distinct interfacial contacts of electron donors (EDs) and electron acceptors (EAs) (dn-π = 3.404 and 3.448 Å for 1 vs dn-π = 3.343, 3.359, 3.398, and 3.495 Å for 2), suggesting a subtle modulating effect of metal ions on interfacial contacts, photoinduced intermolecular electron transfer (PIET) and photochromic behaviors. Interestingly, the photochromic performance of 2 can be enhanced after the removal of coordinated DMF, which might be ascribed to the decrease of the distance of EDs/EAs caused by lattice shrinkage, which further improves the efficiency of PIET. Meanwhile, 2 displays rapid electrochromic behavior with an obvious reversible color change from colorless to green, which can be used in an electrochromic device. This work develops a new type of EA for the construction of stimuli-responsive functional materials with excellent dual photo-/electrochromic properties.

Reversal in solvatochromism, photochromism and thermochromism in a new bis-azo dye based on naphthalen-1-amine

A novel bis-azo dye, 4,4′-((1E,1′E)-(oxybis(4,1-phenylene))bis(diazene-2,1-diyl))bis(naphthalen-1-amine) (abbreviated as 4odna) was synthesized and characterized by IR and 1H, 13C and 2D COSY-NMR spectroscopies, and mass spectrometry. Optical properties were evaluated using UV–vis absorption spectroscopy. The observed solvatochromism was ascribed to the presence of different azo or/and hydrazone forms in solution. The azo forms show both positive and negative solvatochromism, with the reversal occurring for solvents with ET(30) ∼45 kcal mol−1, while the hydrazone tautomer shows negative solvatochromism. Application of the multiparametric Catalán and Kamlet-Taft linear solvation energy models allowed to evaluate the dependence of the solvatochromism exhibited by 4odna on the hydrogen bond donating (HBD) and accepting (HBA) abilities of the solvent, as well as on their dipolarity (SdP) and polarizability (SP). Upon UV (λ = 311 nm) irradiation at room temperature, the compound was found to exhibit similar photochromic behavior in the polar-protic solvents methanol and ethanol, which is distinct from that observed in the polar-aprotic solvents dichloromethane, chloroform and chlorobenzene, with the hydrazone tautomer being photoconverted into the azo tautomer in the first group of solvents and vice-versa in the second group. In acetone, UV irradiation extensively transforms the compound into species with no absorption in the visible range, leading to fast discoloration of the solution. Temperature dependence of the color of the solutions of 4odna in ethanol and chlorobenzene was also evaluated, and reversible thermochromic behavior was observed in the first solvent. In chlorobenzene, no thermochromism was observed, but a change of color of the solution was promptly induced by the UV–vis broadband source beam of the spectrometer when the absorbance spectrum of the solution was being recorded at T = 115 °C, which demonstrates that the azo forms of 4odna undergo easy phototransformation into the hydrazone forms in this solvent at high temperature.

Photochromism of two 1D coordination polymers constructed by two ligands of 1-carboxyethyl-4,4′-bipyridinium and N,N′-bis(carboxyethyl)-4,4′-bipyridinium

In this paper, two one-dimensional (1D) coordination polymers were designed and prepared by 1-carboxyethyl-4,4′-bipyridinium (CEbpy) and N,N′-bis(carboxyethyl)-4,4′-bipyridinium (BCEbpy) ligands, i.e. {[Cu0.5(CEbpy)]·(1,2,4-H2BTC)·H2O}n (1) and {[Mn0.5(CEbpy)(H2O)]·[Mn(1,2,4-BTC)(H2O)5]·0.5(BCEbpy)·DMF·4H2O}n (2), indicating superior photochromic behavior and photoresponse properties. The crystal structures and electronic transport behaviors of two compounds were studied. Single crystal X-ray analyses reveal that compounds 1 and 2 crystallize in the triclinic space group P-1. Compound 1 exhibits intramolecular electron transport, whereas compound 2 exhibits both intramolecular and intermolecular electron transport, with a photo-response sequence that is 1 less than 2. The non-covalent interactions were investigated by the DFT method, demonstrating pi−pi interactions greatly promote the photoresponsive electron transfer for compounds 1 and 2.

Two new multi-functional coordination polymers exhibiting photochromic behavior and amine-selective sensing capability

Two new multi-functional coordination polymers exhibiting photochromic behavior and amine-selective sensing capability

KNN-based optical temperature sensing ceramics integrating negative thermal quenching and photochromic self-recovery behavior

Rare-earth ion (RE3+) doped materials with upconversion luminescence and photochromic (PC) effect have received widespread attention, but thermal quenching (TQ) at high temperature and energy-demanding PC recovery processes limit their practical applications. Herein, lanthanide ion doped (K0.5Nb0.5)NbO3 (KNN) based translucent ceramics were prepared, in which Tm3+/Yb3+ co-doped one displays optical versatility for potential applications in temperature sensors and anti-counterfeiting. By utilizing the large energy mismatch between Tm3+ and Yb3+, negative thermal quenching (NTQ) feature was achieved with the maximum relative sensitivity of 2.54 %K−1 at 213 K. Furthermore, by constructing appropriate intermediate traps, the ceramic exhibits a rapid PC self-recovery process within 30 min without external stimulation. The bifunctional specialty can expand the applications of KNN-based ceramics in optical area.

Effect of inclusion in sulfobutylether-β-cyclodextrin on the rate of merocyanine-spirobenzopyran reversible photochromic transformations

To gain insight into the effect of host-guest binding on the negative photochromic behavior, the reversible interconversion between a merocyanine dye and its spirobenzopyran (SP) isomer was studied in the cavity of sulfobutylether-β-cyclodextrin having on average 6.4 degrees of substitution (SBE6.4βCD). Depending on the acidity of the solution, trans-merocyanine (trans-MC) or its protonated form (trans-MCH+) were the thermodynamically most stable species both in water and in the interior of SBE6.4βCD. The association constant of 1:1 encapsulation significantly diminished in the series of SP > trans-MCH+ > trans-MC. Inclusion complex formation accelerated the visible-light-induced conversion to SP and efficiently slowed down the thermal back reaction in acidic and slightly basic medium alike. A good linear correlation was found between the logarithm of the frequency factors and the activation energies for the SP transformation to the colored most stable isomer within various types of macrocycles.

Structure and photochromic properties of two cadmium coordination polymers derived from viologen ligands

AbstractTwo novel 1D Cd‐based coordination polymers (CPs) {[Cd(MQ)(HBTC)(H2O)2] ⋅ (H2BTC) ⋅ 4H2O}n (1) and {[Cd(AQ)(HBTC)(H2O)Br] ⋅ 2H2O}n (2) have been prepared in the reaction of Cd2+ with different viologen ligands such as 1‐methyl‐4,4′‐bipyridinium bromide (MQBr) or 1‐amyl‐4,4′‐bipyridinium bromide (AQBr) in the presence of 1,3,5‐benzenetricarboxylic acid (H3BTC). The Cd2+ ions are bridged by HBTC2− anions to take shape a 1D configuration for two CPs. Additionally, 1 and 2 both show photochromism due to the photoinduced electron transfer (ET) from electron‐rich O atoms to electron‐deficient viologen moieties. Compared with 2, compound 1 has a rapid photoresponsive rate. The different photochromic behaviors have been discussed adequately.

Two crystalline Zn(II)-viologen compounds with photochromism, photomodulated luminescence and water-induced reversible crystal-to-amorphous transformation

In this work, two Zn(II)-viologen compounds, {[Zn(cpbpy)(L)](H2O)5}n (1) and [Zn(H2O)6](cpbpy)2(L)2(H2O)2 (2) (cpbpy = N-(3-carboxypyridin-5-yl)− 4,4′-bipyridinium, H2L = 1,4-benzenedicarboxylic acid) have been constructed via different synthetic routes. Structural analysis exhibits compound 1 features a two-dimension layered structure consisting of one-dimension [Zn(L)]n chains and bridging cpbpy ligands while compound 2 exists as a discrete monomeric structure. In a very short period of time, both compounds display electron-transfer photochromic behaviors. However, the photoproduct of compound 2 is more stable than compound 1 in air, which is attributed to better coplanarity of pyridyl rings of 4,4′-bipyridine moieties in compound 2. Also, both compounds show photomodulated luminescence properties. Strikingly, compound 2 also exhibits interesting water-induced reversible crystal-to-amorphous transformation accompanying with reversible luminescence switch behavior. To our knowledge, this is the first example of a crystalline viologen-based compound that displays water-induced reversible crystal-to-amorphous transformation.

Optical Control of Invertebrate nAChR and Behaviors with Dithienylethene-Imidacloprid.

Photopharmacology involving azobenzene or dithienylethene has changed established methods of studying receptor functions, allowing for increasing the spatiotemporal resolution. There are no photopharmacological tools available for the invertebrate nicotinic acetylcholine receptor (nAChR). Here, we report a photochromic ligand, dithienylethene-imidacloprid (DitIMI), using a dithienylethene photoswitch embedded in the nAChR agonist imidacloprid. It was found that DitIMI displayed good photochromism and fluorescence switching behaviors upon irradiation with UV/vis light in aqueous solution. We demonstrated that open-DitIMI has low spontaneous in vitro and in vivo activity but can be photoisomerized to a highly active closed-form. Surprisingly, the photoswitchable DitIMI showed a large difference in insecticidal activity between the open and closed forms, in which the insecticidal activity against Aphis craccivora of the ring-closed isomers for DitIMI was 355 times that of the corresponding ring-open isomers. This photoisomerization can further be translated to photomodulation of neuron membrane potential and behavioral responses of living mosquito larvae and American cockroaches. The photomanipulation of nACh neurotransmission opens new avenues to understanding inhibitory circuits in intact animals.

Kinetic Studies of WO3-Based Photochromism in Polyvinyl Alcohol Film.

Tungsten oxide (WO3) has been extensively studied for various photochromic applications. Blue coloration of WO3 is explained in terms of the intervalence charge transfer (IVCT) transition of electrons between W6+ and W5+. However, various absorption spectra with different shapes have been reported. Herein, a transparent film was prepared by drying aqueous solutions containing polyvinyl alcohol, WO3 nanoparticles and ethylene glycol (EG). For comparison, the photochromic behavior of an aqueous WO3 colloidal solution containing EG was also investigated. Under UV irradiation, a single intense peak was always observed at ca. 777 nm in the colloidal solution, but the absorption spectra of the film changed from a peak at 770 nm to two distinct peaks at 654 and 1003 nm. All absorption spectra observed with the film and the colloidal solution were deconvoluted into five peaks at 540, 640, 775, 984, and 1265 nm. Kinetic studies using the colloidal solution indicated that the coloration rates (r0) estimated at the deconvoluted peaks of 640, 775, and 984 nm followed the same rate law. On the other hand, in the case of the film, r0 evaluated at 640 or 984 nm was independent of the water amounts but increased proportionally to the EG amounts and the light intensity, although r0 at 775 nm significantly increased with the increasing amounts of water and EG. Raman and electron spin resonance spectroscopic observations of the film revealed that the photogenerated electrons migrated toward the terminal W═O moiety to accumulate and then a small anisotropic electron spin resonance signal appeared. Our study demonstrates that the absorption at 775 nm is due to IVCT between W6+ and W5+, which is stabilized with water in the bulk and the absorption peaks at 640 and 984 nm are attributable to IVCT on the WO3 surface.

Co-doping effect of Ce ions on Eu ion-doped Sr2SnO4 in terms of emission color tunability and intensity modulation

We investigated the co-doping effect of Ce3+ and Eu3+ ions on the visible emission of the single-layered perovskite Sr2SnO4. The Ce3+ single-doped Sr2SnO4 showed a sizable feature at approximately 260 nm in the photoluminescence excitation spectra and a broad peak at approximately 400 nm in the photoluminescence spectra. These peaks were attributed to the 4f–5d transitions of Ce3+. In the Ce3+ and Eu3+ co-doped samples, as the concentration of Ce3+ increased, the emission intensity of Eu3+ increased drastically with near-ultraviolet excitation due to the energy transfer from Ce3+ to Eu3+. Because of the changes in the relative emission intensities of the two ions, the colors emitted by phosphor were tuned from blue/orange to red. We also discussed the effect of Ce3+ doping on the photochromic behavior of Eu3+-doped Sr2SnO4, together with luminescence modulation.

Two novel photochromic compounds based on a thiazolothiazole extended viologen derivative

In the last few years, more and more attention has been paid to the application of chromic materials, and photo-active viologen groups have been broadly assembled into functional materials with photochromism. However, the limited research conducted to date indicates that the extended viologen photochromic compounds are rarely reported. Herein, a rigid thiazolothiazole extended viologen moiety H2TTVPCl2 (2,5-bis (pyridinium-4-yl) thiazolo [5,4-d] thiazole propionate dichloride) is selected to construct two novel photochromic compounds, namely {[Zn(TTVP)0.5(BTEC)0.5(H2O)2]·2H2O}n (1) and [(H2TTVP)(H4BTEC)0.5]·(H2O)·2Cl (2). 1 has a two-dimensional (2D) layered structure, while 2 has a zero-dimensional (0D) structure. As expected, 1 and 2 display photochromic behavior of electron transfer. Furthermore, the photo-controlled luminescence and potential application as inkless and erasable printing media are also investigated.

A novel photochromic complex based on a viologen ligand with rapid inkless and erasable printing, anti-counterfeiting and amine-selective responses

In this work, we have synthesized a novel complex {[Zn2(Bpybc)0.5(L)·H2O]·DMA·H2O}n (1) (H2BpybcCl2 = 1,1’-bis(4-carboxybenzyl)-4,4’-bipyridinium dichloride, H4L = 1,2,4,5-benzenetetracarboxylic acid) by solvothermal method. 1 has a 3D network stacking structure. 1 exhibits rapid and reversible photochromic behavior, showing the color change visible to the naked eye after being irradiated. 1 has been characterized by infrared spectroscopy, powder X-ray diffraction analysis, UV-vis absorption spectroscopy and electron paramagnetic resonance spectroscopy. The relationship between the structure of 1 and photochromic behavior has been discussed. 1 can be used as an anti-counterfeiting material and amine-selective response material at a fast speed. 1 can also be deposited on filter paper and used as an inkless and erasable printing medium. In addition, 1 has photomodulated fluorescence properties.

Oxygen vacancies in the Spotlight: On the engineering of intrinsic defects in highly defective TiO2 photocatalysts

Nanostructured oxide semiconductors are widely used in energy conversion, catalysis, sensing and environmental applications, due to their high stability, commercial availability, efficiency and low cost. Despite its crucial importance for the design of more efficient materials, the interplay between intrinsic and extrinsic defects is yet to be clarified. For example, oxygen vacancies (VO’s) can be either beneficial or detrimental to the desired performances, depending on a variety of factors. Here, we synthesize TiO2-x samples by the addition of three different N chemical sources (NH3, triethylamine, urea). X-ray absorption spectroscopy, confocal microscopy, UV–vis absorbance and fluorescence, are employed to explore the occurrence and location of VO’s both in real and energy spaces. High–grade bulk DFT simulations complement the experimental picture. Synergy between theory and experiment, on the one hand, estimates the relative VO’s content in the different samples from local structural information. On the other hand, a sharp optical transition at ≈2.7 eV serves an unequivocal spectral signature of bulk VO’s, allowing a semi-quantitative analysis by confocal microscopy. Surface oxygen vacancies do not display fluorescence features under UV pumping, possibly due to the reaction of surface defects with atmospheric O2. Thus, the comparison between local structure and confocal microscopy can discriminate surface-localized and bulk VO’s. Concurrently, UV-induced photochromism and visible light photodegradation shed light on the most effective reactive defects. Eventually, surface-localized oxygen vacancies are predominant where actual N substitutional doping occurs, leading to materials exhibiting visible-light activity and characteristic photochromic behaviour. Implications on strategies for concomitant VO engineering and extrinsic doping are discussed.

A Cu2+ triggered reversible photochromic system: the structure photochromic response relationship study and potential applications.

Fifteen rhodamine B hydrazide hydrazone (RhBHH) derivatives (compounds a-o) with various substituent groups at different position and their photochromic property triggered by Cu2+ were studied to illustrate the structure photochromic response relationship (SPRR). Three of them (compounds f-h) with a para-position hydroxyl group and two meta-position halogen substituents display Cu2+-triggered photochromic which is significantly different from the previous reports. It was found that halogen atoms, which were generally considered to have no remarkable regulation effect, exhibited great influences on the photochromic behaviour of RhBHH derivatives. Detail photochromic properties of the developed photochromic system were revealed by using compound g as the model substrate, and only Cu2+ displayed high selective trigger effect. Good reversible photochromic phenomenon was observed after stimulated with visible light irradiation and dark (or heat) bleaching consecutively. Furthermore, this photochromic system could be used in the preparation of photochromic glass, special security ink, molecular logic gate and two-dimensional code for security information storage.

Electric field-driven modulation in structural and luminescent properties of Eu3+-doped (1 − x)(Na0.5Bi0.5)TiO3 − xBaTiO3 relaxor ferroelectrics

We investigated the structural, electrical, and luminescent properties of Eu3+-doped (1 − x)(Na0.5Bi0.5)TiO3 − xBaTiO3 (NBT-BT:Eu) relaxor ferroelectrics for x = 0.00–0.08. The introduction of Eu3+ generated good emission properties in the samples without weakening their piezoelectric properties. Rietveld refinement structural analysis revealed that the structural phase of NBT-BT:Eu was a mixture of rhombohedral and monoclinic phases with a significant x-dependence. We observed that NBT-BT:Eu underwent a structural phase transformation upon the application of an electric field. Interestingly, the structural changes caused by poling led to a reduction in the emission of Eu3+. The poling-driven emission quenching behavior resulted from the increase in the local structural symmetry around Eu3+ in the poled samples. We also identified light-induced modulation in the emission of our samples, probably attributed to the photochromic behavior. The multifunctionality of NBT-BT:Eu paves the way for the development of a new type of optoelectronic material.

Dual Response to Light and Heat of a Metal–Organic Rotaxane Network Featuring Flexible Viologen‐Derived Structs

AbstractMetal–organic rotaxane compounds (MORCs) with supramolecular (pseudo)rotaxane motifs as main structures have inherent dynamic character, but their potential as responsive molecular machines is largely hampered by poor responsiveness to external stimuli. In this study, using a multi‐functionalized pseudorotaxane linker that combines two kinds of functionalities, a novel MORC, U‐bpybc‐CB8 (U refers to uranyl, bpybc refers to 1, 1’‐bis(4‐carboxybenzyl)‐4, 4’‐bipyridinium, and CB8 is cucurbit[8]uril), with multi‐responsive capability that can respond to both light and thermal stimuli, is reported. The characterization, combining spectra measurements and single‐crystal X‐ray diffraction, shows that, due to the involvement of viologen‐functionalized flexible organic dicarboxylate guest molecule in the CB8‐ involved pseudorotaxane ligand, the resultant uranyl‐based MORC exhibits photochromic behavior after UV or visible light irradiation. More interestingly, it is revealed that the exceptional thermal response of U‐bpybc‐CB8 as temperature increases from 170 to 270 K, i.e., volume expansion followed by contraction after the inflection temperature of ≈230 K, can be stemmed from the lattice flexibility of this metal–organic supramolecular network. The dual responsiveness of MORCs reported here demonstrates the potential of such supramolecular assemblies as smart molecular components like sensors and switches that respond to light irradiation or temperature changes.

Photochromic properties of five complexes derived from 1, 3, 5-benzenetricarboxylic acid and 1-(2-carboxyethyl)-4,4′-bipyridinium bromide

Non-photochromic and photochromic complexes [Ni1.5(CBbpy)(H2O)7]·(BTC)·5·.5H2O (1), {[Co(CBbpy)2(H2O)2]·(HBTC)·8H2O}n (2), {[MnNa(CBbpy)(BTC)(H2O)3]·H2O}n (3), {[Zn3(CBbpy)2(BTC)2(H2O)]·H2O}n (4), {[Cd(CBbpy)(HBTC)(H2O)]·H2O}n (5) based on the bipyridinium-based ligand 1-(2-carboxyethyl)-4,4′-bipyridinium bromide (HCBbpyBr) and 1,3,5-benzenetricarboxylic acid (H3BTC) have been successfully obtained by tuning different metal ions. Although five complexes contain the same bipyridinium ligand, only 3–5 possess reversible photochromic behavior. Unfortunately, 1 and 2 exhibit non-photochromic action when exposed to UV light for approximately 2 h. EPR spectra verify that photochromic course of 3–5 is derived from the formation of CBbpy radicals by photo-induced electron transfer after irradiation. The effect of diverse metal ions on the structure and photochromic action of the five complexes has been discussed.