Photochromic Monomer Research Articles

Excitation-wavelength-dependent fluorescent organohydrogel for dynamic information anti-counterfeiting

Anti-counterfeiting labels with various fluorescent colors are of great importance in information encryption-decryption, but are still limited to static information display. Therefore, it is urgent to develop new materials and encryption-decryption logic for improving the security level of secret information. In this study, an organohydrogel made up of poly(N,N-dimethylacrylamide) (pDMA) hydrogel network and polyoctadecyl methacrylate (pSMA) organogel network that copolymerized with two fluorophores, 6-acrylamidopicolinic acid moieties (6APA, fluorescent ligand) and spiropyran units (SPMA, photochromic monomer), was prepared by a two-step interpenetrating method. As UV light of 365 nm and 254 nm can both cleave Cspiro-O bonds of SPMA, and the green fluorescence of 6APA-Tb3+ can only be excited by 254 nm light, the organohydrogel displays yellow and red under the irradiation of 254 nm and 365 nm, respectively. In addition to wavelength selectivity, these two fluorophores are thermal-responsive, leading to the fluorescence variation of the organohydrogel during heating process. As a result, secret information loaded on the organohydrogel can be decrypted by the irradiation of UV light, and the authenticity of the information can be further identified by thermal stimulation. Our fluorescent organohydrogel can act as an effective anti-counterfeiting label to improve the information security and protect the information from being cracked.

Synthesis and properties of photochromic polymer contain spiro-oxazine induced by ultraviolet light

ABSTRACT The special photochromic mechanism of spiro-oxazine (SO) refers to low thermostability and weak fatigue resistance. High light transmittance and biocompatibility are the two advantages of polymethyl methacrylate (PMMA), but it does not perform well in terms of tensile strength. Here, a new type of SO (1-(4'methacryloyloxybutyl)- 3,3-dimethyl-9'-hydroxy- 3H-spiro-naphthyl oxazine) was synthesized and introduced as a photochromic monomer into methyl methacrylate (MMA) system, which is an environment-friendly method. Compared with other photochromic polymers that have been reported, the advantages of this material mainly perform in the following areas: (1) The active group was introduced into the N-alkyl chain of SO and copolymerized with PMMA, and the fading rate of the photochromic polymer was dropped by 76.3% compared to SO. (2) Physical and chemical methods were used to improve the flexibility of PMMA-SO. The tensile strength of polymers has been reduced to 3.92 MPa. It also has a high elongation of 269.84% at a break. (3) PMMA-SO still has a significant fatigue resistance after 25 cycles of UV and visible light irradiation. In the future, it has potential applications in the fields of smart glass, data storage, biomimetic materials, and so on.

Heterogeneous Fluorescent Organohydrogel Enables Dynamic Anti‐Counterfeiting

AbstractFluorescent patterns showing the unique color change in response to external stimuli are of considerable interest for their applications in anti‐counterfeiting. However, there is still a lack of intelligent fluorescent patterns with high‐security levels, presenting a dynamic display of encrypted information. In this study, a fluorescent organohydrogel is fabricated through a two‐step interpenetrating technique, leading to the co‐existence of naphthalimide moieties (DEAN, green‐yellow fluorescent monomer) contained Poly(N,N‐dimethylacrylamide) (PDMA) hydrogel network and Polyoctadecyl methacrylate (PSMA) organogel network bearing spiropyran moieties (SPMA, photochromic monomer). Due to the unique heterogeneous networks, the fluorescence color goes through a continuous change from green to yellow to red via the fluorescence resonance energy transfer (FRET) process with the extension of irradiation time. In addition, when H+ is introduced into the system, SP units exhibit transformation into the protonated merocyanine (MCH+) rather than merocyanine (MC) under UV light, which inhibits the FRET process. By selectively being treated with H+, the fluorescent organohydrogel can act as an effective platform for encrypting secret information, making them more difficult to forge.

Screen-printed photochromic textiles with high fastness prepared by self-adhesive polymer latex particles

Photochromic textiles have received increasing attention due to their wearable properties and reversible discoloration. However, improving the poor fastness of photochromic textiles is always a problem. In this paper, the self-adhesive polymer (PSBM-SP) latex particles based on spiropyran were prepared and then applied to obtain photochromic textiles with high fastness. The PSBM-SP latex particles were prepared via semi-continuous emulsion polymerization of styrene (St), n-butyl acrylate (BA), vinyltrimethoxysilane (VTMS), and a self-synthesized polymerizable photochromic monomer (SPMA). The chemical structure of SPMA was confirmed by 1H NMR and FT-IR. Results of UV–vis spectra indicated that the discoloration and fading process of PSBM-SP latex particles can be completed within 120 s and 150 s under ultraviolet and visible irradiation, respectively. The PSBM-SP latex particles retained good photochromic properties after the alternating ultraviolet and visible light for irradiation 30 times. Then, the PSBM-SP latex particles were used to prepare the screen-printed photochromic textiles by the chemical crosslinking and film formation, which showed softer hand feel and better fastness than the conventional printing with a large number of binders. Importantly, the prepared photochromic textiles had a fast UV-response performance and maintained impressive reusability after experiencing 30 washing cycles, proving their great potential in wearable and flexible textile-based photochromic materials.

Synthesis and characterization of multi stimuli-responsive block copolymer-silica hybrid nanocomposite with core-shell structure via RAFT polymerization

A novel multi stimuli-responsive silica nanocomposite with a core-shell structure is synthesized using reversible addition-fragmentation chain transfer (RAFT) polymerization. The SiO2 nanoparticles are chemically modified via 3-(trimethoxylsilyl) propyl methacrylate (MPS) which they are used in the core of nanocomposite. The macro-RAFT agent is prepared by RAFT polymerization of N-isopropylacrylamide (NIPAM), spirooxazine acryloyl monomer (SOM), and 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid (DDMAT as a RAFT agent). Finally, the smart nanocomposite is prepared by reaction between the macro-RAFT agent and 2-(Dimethylamino) ethyl methacrylate (DMAEMA) as a monomer. SOM as a photochromic monomer, DMAEMA and NIPAM as temperature and pH sensitive were used in the synthesized nanocomposite. The finally smart nanocomposite was characterized by using FT-IR, 1H NMR, UV–Vis, GPC, DLS, and TEM techniques. The responsiveness of synthesized smart nanocomposite in different conditions (UV–Vis light, pH, temperature and the combination of pH and temperature) was investigated. The results show that the fabricated smart nanocomposite are good candidate nanomaterials for sensors application.

Photochromic Monomer and Coordination Polymer Based Hybrid Tetra-arylethenes

New multifunctional tetra-arylethene and its one-dimensional coordination polymer were constructed. Their structures were confirmed and the behavior of photochromism and fluorescence were investiga...

Switchable two-photon imaging of RGD-functionalized polynorbornenes with enhanced cellular uptake in living cells

Two-photon imaging polynorbornenes were fabricated directly from photochromic spiropyran, RGD peptides and hydrophilic PEG monomers via modular ROMP.

Photoresponsive phase separation of a poly(NIPAAm-co-SPO-co-fluorophore) random copolymer in W/O droplet.

The photoresponsive phase separation of a poly(N-isopropylacrylamide-co-spironaphthoxazine methacryloyl-co-allyl-2-(2,6-bis((E)-4-(diphenylamino)styryl)-4H-pyran-4-ylidene)-2-cyanoacetate) random copolymer, i.e., poly(NIPAAm-co-SPO-co-fluorophore), in water-in-oil (W/O) droplets is described. The photoresponsive aqueous droplets were generated in the coflow regime of a simple tubular microfluidic device. The phase separation of the copolymer in the W/O droplets was induced by UV light at 365 nm and was affected significantly by the presence of 2,2-diethoxyacetophenone (DEAP) and sorbitan monooleate (Span 80). When the droplets were subjected to UV irradiation for more than 2 min, the phase-separated copolymer was transferred completely from the aqueous droplet to the continuous phase of hexadecane. The phase separation arises from the photoisomerization shifting the spiro to the merocyanine form of the SPO pendant group in the copolymer, which in turn reduces the hydrophilicity of the copolymer via attractive hydrogen-bonding interactions between the merocyanine group and hydrophobic additives, i.e., Span 80, DEAP, and some stable fragments derived from the photocleavage of DEAP under UV irradiation. These interactions cause the copolymer to associate with the additives and then accelerate the phase separation of the copolymer and subsequent phase transfer of copolymer aggregates. The separate effects of DEAP and Span 80 were also investigated by UV spectrophotometric analysis of the rate coefficient of the reverse transformation (merocyanine to spiro) of the photochromic monomer. We propose a mechanism of phase separation of the copolymer in the W/O droplet based on the NMR and GC-MASS analyses of DEAP.

Diarylethene-based photochromic polyurethanes for multistate optical memories

Photochromic polyurethanes (PPUs) are synthesised by reaction between a diarylethene end-capped with hydroxyl groups and an aliphatic diisocyanate. In situpolymerisation provides amorphous films with remarkable optical properties. The possibility to vary the amount and the chemical structure of the photochromic monomer without affecting the reactivity of the polymerization allows one to tune in a wide range the optical properties of these films. In addition, different diarylethenes can be mixed together to give copolymers which may find application as photochromic layers for multistate optical memories. A setup for a non-destructive readout based on Raman signal is proposed.

Multiresponsive Spiropyran-Based Copolymers Synthesized by Atom Transfer Radical Polymerization

Multiresponsive spiropyran-based random copolymers were synthesized by atom transfer radical polymerization. The polymers were prepared by the copolymerization of 2-(dimethylamino)ethyl methacrylate (DMAEMA) with the photochromic monomer 1′,3′,3′-trimethyl-6-methacryloyloxyspiro(2H-1-benzopyran-2,2′-indoline) (SP). The solvatochromic, pH, temperature, and light responsive behavior of the PDMAEMA-co-PSP polymers in solution was monitored by UV/vis spectroscopy. The copolymers exhibited “reverse photochromism” and stabilized the planar zwitterionic form of the chromophore, leading to “negative solvatochromism” upon increasing the polarity of the solvent, in contrast to a poly(methyl methacrylate)-co-PSP analogue which stabilized a nonpolar photoisomer and exhibited negligible sensitivity to the polarity of the surrounding medium, before irradiation. Moreover, the PDMAEMA-co-PSP copolymers exhibited a reversible pH-responsive character in aqueous media; the addition of a strong acid induced the SP-to-merocya...

Fast Photochromic Polymers Carrying [2.2]Paracyclophane-Bridged Imidazole Dimer

The synthesis and photochromic behavior of the fast photochromic polymers carrying [2.2]paracyclophane-bridged imidazole dimer are demonstrated. A significant feature of this synthetic strategy is that we can modify the photochromic properties such as coloration/decoloration rate, coloring, and photosensitivity via the stepwise synthetic approach of the imidazole dimer system. Notably, the photochromic behavior of the polymers is not affected by the environment around the photochromes and copolymerization with other monomers in both solution and film, which cannot be realized in any other conventional photochromic systems. The comparable photochromic behavior of the homopolymers and copolymers in solution and film indicates that the photochromic unit is independent from the local environment, which allows effective molecular design of the photochromic monomer unit to accomplish desired photochromic properties of the polymer.

Dual responsive poly(N‐isopropylacrylamide) hydrogels having spironaphthoxazines as pendant groups

AbstractStimuli responsive hydrogels (PNIPAAm‐MSp) with a thermoresponsive backbone and photochromic pendant groups were synthesized via free radical polymerization using N‐isopropylacrylamide, modified spironaphthoxazines with a polymerizable double bond (MSp) as photochromic monomer, the crosslinker N,N′‐methylenebis(acrylamide) and the initiator 2,2′‐azobis(isobutyronitrile) in dimethylsulfoxide. The polymers are dual responsive, in that poly(N‐isopropylacrylamide) (PNIPAAm) responds to temperature changes whereas the pendant spironaphthoxazines respond to light. Irradiation enhanced the water absorption of the polymers while increases in temperature decreased it. The irradiated PNIPAAm‐MSp showed best water absorption at 0 °C (Q = 3.25) while water desorbed at higher temperatures (35 °C; Q = 0.30); where Q is the amount of water absorbed by a gram of dry polymer. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3318–3325, 2009

Synthesis of Poly(glycidyl Methacrylate-r-photochromic Monomer) by ATRP

The preparation of the random photochromic copolymer poly(glycidyl methacrylate-r-1′-(2-methacryloxyethyl)-6-nitro-3′,3′-dimethylspiro-[2H-1]-benzopyran-2,2′-indoline) by ATRP is reported, which can be used for the preparation of smart materials. Narrow homopolymers obtained from glycidyl methacrylate (GMA) are prepared when HMTETA-copper bromide and ethyl 2-methyl-2-bromo-propionate are used as the catalytic system with methyl-ethyl-ketone at 50°C. By using a molar ratio of 1:1 ligand:initiator, good correlations between experimental and theoretical molecular weights and narrow molecular weight distribution are obtained. These experimental conditions are also employed for the copolymerization of GMA with a photochromic monomer, where again good control of the polymerization reaction is obtained. The copolymer is fully characterized by spectroscopic techniques. The reactivity ratios are calculated according to the extended Kelen-Tüdos method, while the composition of the copolymer is calculated by NMR. Determination of r GMA and r PHM gives a value of 0.985 for GMA and 0.596 for the photochromic monomer.

Synthesis and characterization of novel liquid‐crystalline copolymers containing thermally stable photochromic groups

AbstractTo overcome the defects of the thermal instability of azobenzene, a series of novel photochromic, chiral, liquid‐crystalline monomers and polymers were synthesized from (+)‐camphor. The copolymerization of the photochromic monomers with comonomers was carried out. The synthesized monomers and polymers were identified with nuclear magnetic resonance, Fourier transform infrared, and elemental analysis. The composition of the copolymers was estimated with elemental analysis. The specific rotation of the chiral compounds and polymers was evaluated. The thermal stability and phases of the polymers during heating and cooling cycles were studied with differential scanning calorimetry and thermogravimetric analysis. The phases of the polymers were identified with polarized optical microscopy textures and X‐ray diffraction analysis. The distance between the layers of smectic liquid crystals was estimated from the diffraction angles. Photoisomerization of the configurational E/Z structures was investigated with an ultraviolet–visible spectrophotometer with 300‐nm ultraviolet irradiation. The thermal stability of the Z‐structural segment in the polymers was confirmed through the heating of the polymer at 70 °C for over 10 h. The photoisomerization and thermal stability of the CC bond in the polymeric materials were demonstrated through a series of novel chiral polymers synthesized in this investigation. Both the polarity of the center part and the molecular length at the ends of the molecules were found to be necessary factors for the formation of liquid‐crystalline molecules. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2026–2037, 2007

Synthesis of Photochromic Monomers Derived from 1′‐(2‐Methacryloxyethyl)‐3,3‐Dimethyl‐2‐[2H]‐Spirobenzopyran Indoline

The syntheses of five photochromic monomers derived from N‐ (2‐methacryloxyethyl)‐3′, 3′‐dimethylspiro‐[2H‐1] benzopyrane‐2, 2′‐indoline are reported. The preparation of these compounds involves the heterogeneous reaction between the N‐(hydroxyethyl)‐2,3,3‐trimethylindolenonium bromide and methacryloyl chloride in a polar solvent. The esterificated salt is easily purified by crystallization in chloroform‐hexane. Further condensation with the proper 2‐hydroxybenzaldehyde produces the photochromic monomer in high yield. This method can also be applied in the preparation of other spiropyrane derivatives.

Synthesis, spectroscopic characterization and alignment of novel azobenzene‐containing monomers

A series of novel bifunctionalized photochromic monomers were synthesized, focusing on those with polymerizable acrylic/methacrylic groups attached to both ends of an azobenzene core via flexible spacers. The phase behaviour of the monomers was investigated using DSC, polarizing optical microscopy and X‐ray diffraction. The change in UV‐vis absorbance of the monomers under illumination with non‐polarized/polarized UV light was studied for both solutions and thin films; also studied was its relaxation in the dark. On illumination with LPUV light, in‐plane reorientation of the molecules normal to the polarization of the exciting UV light, and aggregation of the molecules in the films, were found.

Ultra‐High‐Density Photochromic Main‐Chain 1,2‐Dithienylcyclopentene Polymers Prepared Using Ring‐Opening Metathesis Polymerization

Ring‐opening metathesis polymerization is used to construct the well‐known photoresponsive 1,2‐dithienylethene backbone for the generation of ultra‐high‐density photochromic main‐chain polymers (see Figure). The photochromic monomer unit can be easily functionalized to create polymers with diverse structural and electronic properties. Both lipophilic and hydrophilic versions of the polymer have been prepared.

Novel photosensitive polyurethanes based on photochromic dithienylethene monomers: synthesis, characterization and photophysical properties of a new film-building material for photonic applications

Abstract The synthesis of a novel photochromic dithienylethene-based polyurethane and its characterization by optical spectroscopy and scanning tunneling microscopy are presented. This linear polyurethane builds up perfect free-standing films suited for photonic applications. Moreover it may be extruded to long mechanically stable fibers. The photochromic reactions of the polyurethane, as being the electrocyclic ring-closure and ring-opening reactions of the dithienylethene unit in the polymer backbone, occur in a completely reversible and highly efficient fashion.

Synthesis and properties of photochromic cholesteric liquid crystalline polysiloxane containing chiral mesogens and azobenzene photochromic groups

AbstractA series of novel thermotropic side‐chain liquid crystalline polymers(P0–P12) were synthesized by grafting copolymerization of mesogenic monomer cholesteryl undecylenate (M1) and photochromic monomer 4‐allyoxy‐4′‐nitroazobenzene (M2) on polymethylhydrosiloxane. The chemical structures of polymers were characterized by infrared (IR) and ultraviolet (UV) spectroscopy. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to measure the thermal properties of those polymers, and the mesogenic properties were characterized by polarized optical micrograph, DSC, wide‐angle X‐ray diffraction and small‐angle X‐ray scattering. The glass transition temperatures (Tgs) of the polymers increased from P0 to P4 and decreased from P5 to P12. The clearing point temperatures (Tis) of the polymers P1–P12 were lower than that of P0, but increased from P1 to P4 and decreased from P5 to P12. They showed thermotropic liquid crystalline properties in a broad mesogenic region at temperatures >100°C. The polymers P0–P8 exhibited a cholesteric mesophase with oily streaks and lined texture, and polymers P9–P12 showed a chiral smectic mesogenic phase with a layered texture. All of the polymers were thermally stable to ∼ 320°C. The UV‐induced trans–cis photoisomerization was investigated for the azo monomer and polymers P8 and P12. The solution of the azo monomer and liquid crystalline polymers P8 and P12 can undergo photoisomerization, and the environments of the azo group were responsible for the aforementioned photochemical process. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2155–2162, 2002

Light-Controllable Chiral Photochromic Multifunctional Liquid Crystal Polymers

ABSTRACTA new family of light-controllable chiral photochromic multifunctional liquid crystalline (LC) side-chain acrylic polymers consisting of nematogenic, chiral and photochromic monomer units was obtained. The new principle of photoregulation of the helical supramolecular structure and optical properties of the binary and ternary chiral photochromic LC polymers based on the change of helical twisting power of the chiral photochromic monomer units was developed. The features of photooptical behaviour of LC polymers possessing the dual photochromism and the peculiarities of optical data recording based on the photochemical spectral gap burning were presented and discussed. The synthesized polymers are shown to be promising candidates for colour data recording and storage.