Photoresponsive Properties Research Articles

Photomodulated Electro-optical Response in Self-Supporting Liquid Crystalline Physical Gels.

Photoresponsive liquid crystal (LC) physical gels have attracted more and more attention because of the nature of strong response via light stimulus. Although many efforts on the breaking and recovering of physical gels through photoisomerization have been focused, fast electro-optical response and high mechanical properties even upon light irradiations are difficult to achieve at the same time. In this work, two kinds of azobenzene-containing gelators (AG1 and AG2) with different terminal groups were designed and synthesized. Both gelators could induce the nematic LC P0616A self-assemble into anisotropic phase-separated LC physical gels at low contents. Their phase-transition behavior, thermal stability, microstructure, and mechanical strength were systematically studied. Compared with AG2 in P0616A, the P0616A/AG1 gels showed better mechanical property. When the gelator content was above 3 wt %, the P0616A/AG1 gels possessed good self-supporting ability with a storage modulus more than 104 Pa. Thus, the photoresponsive electro-optical properties and structures of P0616A/AG1 gels were focused in detail. It was surprising that the electro-optical response speed of the P0616A/AG1 gels could be promoted upon UV irradiation. In particular, the decay time (τoff) was only about half when compared with the initial state, whereas the gels still exhibited good self-supporting ability; also the network of the LC physical gels had no change at macro- and microstructural levels. These exciting results would open a door for the application of this material in electro-optical devices.

Enhanced Thermal Ageing Stability of Mechanophore in Polyurethane Network by Introducing Polyhedral Oligomeric Silsesquioxanes (POSS)

AbstractSpiropyran (SP) shows excellent ability in light‐ or force‐triggered color and fluorescence generation. However, it has the fatal weakness of poor antithermal bleaching properties in polymers, especially when exposed to severe environments, which will shorten the life of mechanical responsive materials. Here, a strategy is reported to protect SP through incorporation of multifunctional polyhedral oligomeric silsesquioxanes (POSS) as cross‐linkers into a polyurethane network. The introduction of POSS not only improves the mechanical strength of the elastomer, but also enhances the thermal stability of the mechanophore, showing much more sensitive force‐responsive and photoresponsive properties, especially after thermal annealing. POSS contributes to the construction of a 3D network and hinders the mobility of the hard domains of molecular chains, thus enhancing the thermal stability of the mechanophore in the network. The strategy can not only extend the life of the stimuli‐responsive materials, but also promote the application temperature of the mechanically responsive polymers.

Enhanced Photoresponsive Properties of Perovskite Films on Metal Oxide LaAlO3 Substrates

We report enhanced photoresponsive properties of planar-type perovskite films fabricated by spin-coating method on metal oxide LaAlO3 substrates. The reliable Ilight/Idark ratio (>104), responsivity (70 mA/W), detectivity (1.5 × 1010 Jones), and photoresponsive time (0.26 ms) of films on LaAlO3 substrates are achieved. These results are caused by the abundant La vacancies at the surface of LaAlO3 substrates after the plasma treatment, which would form the build-in electric field at the interface and meanwhile induce the sub-band gap photoluminescence. Thus, the photon-generated carrier separation and density are increased. Our results pave a way for promoting photoresponsive properties by the interface effect and create an opportunity for future high-performance photodetectors based on perovskites.

Magnetism Control by Doping in LaAlO3/SrTiO3 Heterointerfaces.

Magnetic two-dimensional electron gases at the oxide interfaces are always one of the key issues in spintronics, giving rise to intriguing magnetotransport properties. However, reports about magnetic two-dimensional electron gases remain elusive. Here, we obtain the magnetic order of LaAlO3/SrTiO3 systems by introducing magnetic dopants at the La site. The transport properties with a characteristic of metallic behavior at the interfaces are investigated. More significantly, magnetic-doped samples exhibit obvious magnetic hysteresis loops and the mobility is enhanced. Meanwhile, the photoresponsive experiments are realized by irradiating all samples with a 360 nm light. Compared to magnetism, the effects of dopants on photoresponsive and relaxation properties are negligible because the behavior originates from SrTiO3 substrates. This work paves a way for revealing and better controlling the magnetic properties of oxide heterointerfaces.

Effects of source/drain electrode contact length on the photoresponsive properties of organic field-effect transistors

With the continual increase of the carrier mobility of organic semiconductors, there is a great need for optimizing the contact between source/drain electrode and organics in order to further improve the performance of organic field-effect transistors. The effects of Au source/drain electrode contact length on the photosensitivity in pentacene-based organic field-effect transistors were systematically investigated. The results show that at a given gate voltage and drain voltage, the drain current increases with the contact length at first and then tends to saturate at a contact length of 0.7 mm. It is observed that the effective mobility under illumination, both in the linear region and the saturation region, as well as the photoresponsivity and the external quantum efficiency, increase with contact length. All of these can be attributed to the reduction of contact resistance with the increase of contact length. Moreover, analytical expressions were derived and successfully describe the measured dependence of the drain current on the contact length.

Self-cleaning membranes for water purification by co-deposition of photo-mobile 4,4′-azodianiline and bio-adhesive polydopamine

Stimuli-responsive membranes have been widely explored to mitigate fouling on the membrane surface to achieve the stable performance of water purification. Herein, a facile one-step coating of photo-mobile materials on membrane surface was developed to impart self-cleaning property upon exposure alternatively to ultraviolet (UV) and visible light. Specifically, photo-mobile 4,4′-azodianiline (AZO) and a bio-adhesive polydopamine (PDA) were co-deposited on the surface of ultrafiltration (UF) membranes. The effect of the coating layer on the surface hydrophilicity and pure water permeance was systematically evaluated. The photoresponsive properties of AZO in solutions and thin films with PDA was characterized using UV–Vis absorption spectroscopy. When exposed with UV light, AZO undergoes photoisomerization from trans-AZO to cis-AZO, decreasing the volume, while the exposure to visible light enables the transition from the cis- to trans- configuration, increasing the volume. The resulted self-cleaning behavior of the modified membranes through the reversible volume change is demonstrated in treating 1 g/L bovine serum albumin (BSA) solution. After exposure to the alternative UV/vis light, the AZO-coated UF membranes showed an increased water permeance by ~160%.

Formation of Anisotropic Liquid Crystalline Nanoparticles via Polymerization-Induced Hierarchical Self-Assembly.

Polymeric nanoparticles (NPs) containing liquid crystalline (LC) mesogens with tunable anisotropic morphologies have applications in various fields, but their preparation typically suffers from tedious and low-throughput approaches. Here we present an efficient route to the preparation of anisotropic morphologies of azobenzene-containing block copolymers (BCPs) at high solids content via a polymerization-induced hierarchical self-assembly in ethanol. Various anisotropic NPs, including cuboids, short belts, lamellae, and ellipsoidal vesicles, have been obtained in a remarkably broad range of BCP compositions. The NPs exhibit a smectic phase with ordered stripes when observed under TEM. This internal LC ordering plays a significant role on the formation of these intriguing anisotropic morphologies. Morphological transitions from anisotropic to isotropic spheres can be obtained upon UV illumination due to the photoresponsive properties of the azobenzene mesogens. This work significantly expands the scope of accessible morphologies in PISA and suggests that the under explored LC BCPs may have an impactful role in the PISA field.

Theranostic nanoplatform based on polypyrrole nanoparticles for photoacoustic imaging and photothermal therapy

Development of effective theranostic nanoplatforms against malignant tumor is still a challenge. With desirable near-infrared (NIR) light-responsive properties, polypyrrole nanoparticles (PPy NPs) are one of the promising theranostic candidates for cancer photoacoustic imaging and photothermal therapy. Here, PPy NPs with distinct sizes were prepared using a facile aqueous dispersion polymerization method. The formed PPy NPs are uniform in size with narrow size distribution. Characterization data show that PPy NPs with a diameter around 50 nm (P50) display stronger absorption in the NIR range compared to 40 and 60 nm PPy NPs, which further influences their photo-responsive properties. Due to their higher NIR absorption, P50 NPs have better photoacoustic imaging property and photothermal conversion ability than the other two kinds of PPy NPs. The photothermal stability of P50 NPs was proved to be excellent. The CCK-8 assays show that PPy NPs have obvious acute cytotoxicity within 6 h and desirable cytocompatibility for longer incubation time (12 and 24 h). After 6-h incubation, P50 NPs could be internalized by HeLa cells. Their photothermal tumor ablation effect was demonstrated under 808-nm laser irradiation. These findings may provide in-depth understanding of the PPy-based multifunctional nanomaterials for the development of theranostic systems against cancer.

Uniaxial alignment of ZnO nanowires via light-induced directional migration of azopolymeric microspheres

The photo-responsive properties of azopolymers have attracted significant attention due to their vast potential for use in a broad range of applications. Upon exposure to light, azopolymers undergo reversible trans-cis isomerization, which results in mass transport in the polymer matrix. Harnessing this photofluidization process, we explored the feasibility of utilizing azopolymers as a director to align one-dimensional (1D) nanomaterials. Azopolymer nanocomposite microparticles containing ZnO nanowires (NWs) were microfluidically synthesized and illuminated with a linearly polarized laser with varying exposure times. Upon gradual anisotropic reconfiguration of the azopolymers, uniaxial alignment of the internally stored NWs with an axial ratio greater than ten was successfully attained along the direction of polarized light. This result demonstrates the prospect of using the photo-induced mass migration of azopolymers for non-invasive manipulation of nanomaterials for various optical or electronic device applications.

Preparation of redox- and photo-responsive ferrocene- and azobenzene-based polymer films and their properties

A series of redox- and photo-responsive copolymers, poly(2-(methacryloyloxy)ethyl ferrocenecarboxylate-co-4-methacryloylamino-4′-nitroazobenzene) (P(FcEMA-co-MAAzo)s) were synthesized using free radical polymerization. The synthesized copolymers were characterized by 1H NMR, FT-IR, gel permeation chromatography (GPC) and thermogravimetric analysis (TGA). Cyclic voltammetry (CV) and Ultraviolet–visible (UV–vis) absorption studies showed redox- and photo-responsive properties of the synthesized copolymers in the solution. P(FcEMA-co-MAAzo)s films were prepared by spin-coating or drop-coating method and these films were found to be redox- and photo-responsive. The color of the prepared films could be adjusted by the redox stimulus, while UV–vis absorption properties of the prepared films could be adjusted by changing wavelength of light. It was found that these synthesized films show potential application for high density information storage.

Liquid crystal gelators with photo-responsive and AIE properties

trans-Cn-Chol present smectic A phase and photo-responsive SmA–isotropic phase transition, and their organogels exhibit aggregation-induced emission and photo-responsive gel–sol transition.

Steric hindrance effect on the thermo- and photo-responsive properties of pyrene-based polymers

We synthesized a novel series of pyrene-based thermo- and photo-dual responsive polymers named poly(pyren-1-yl-o(m,p)-vinylbenzoate) (P(Py-o(m,p)-VB)). And the influence of the steric hindrance effect on LCST-type phase behaviors and photocleavage properties has been studied.

Phenylazopyridine as Switch in Photochemical Reactions. A Detailed Computational Description of the Mechanism of Its Photoisomerization.

Azo compounds are organic photochromic systems that have the possibility of switching between cis and trans isomers under irradiation. The different photochemical properties of these isomers make azo compounds into good light-triggered switches, and their significantly different geometries make them very interesting as components in molecular engines or mechanical switches. For instance, azo ligands are used in coordination complexes to trigger photoresponsive properties. The light-induced trans-to-cis isomerization of phenylazopyridine (PAPy) plays a fundamental role in the room-temperature switchable spin crossover of Ni-porphyrin derivatives. In this work, we present a computational study developed at the SA-CASSCF/CASPT2 level (State Averaged Complete Active Space Self Consistent Field/CAS second order Perturbation Theory) to elucidate the mechanism, up to now unknown, of the cis–trans photoisomerization of 3-PAPy. We have analyzed the possible reaction pathways along its lowest excited states, generated by excitation of one or two electrons from the lone pairs of the N atoms of the azo group (nazoπ*2 and nazo2π*2 states), from a π delocalized molecular orbital (ππ* state), or from the lone pair of the N atom of the pyridine moiety (npyπ* state). Our results show that the mechanism proceeds mainly along the rotation coordinate in both the nazoπ* and ππ* excited states, although the nazo2π*2 state can also be populated temporarily, while the npyπ* does not intervene in the reaction. For rotationally constrained systems, accessible paths to reach the cis minimum along planar geometries have also been located, again on the nazoπ* and ππ* potential energy surfaces, while the nazo2π*2 and npyπ* states are not involved in the reaction. The relative energies of the different paths differ from those found for azobenzene in a previous work, so our results predict some differences between the reactivities of both compounds.

Atomic-level molybdenum oxide nanorings with full-spectrum absorption and photoresponsive properties

Superthin nanostructures, particularly with atomic-level thicknesses, typically display unique optical properties because of their exceptional light–matter interactions. Here, we report a facile strategy for the synthesis of sulfur-doped molybdenum oxide nanorings with an atomic-level size (thickness of 0.5 nm) and a tunable ring-in-ring architecture. These atomic-level nanorings displayed strong photo-absorption in both the visible and infrared-light ranges and acted as a photothermal agent. Under irradiation with an 808 nm laser with an intensity of 1 W/cm2, a composite of the nanorings embedded in polydimethylsiloxane showed an ultrafast photothermal effect, delivering a local temperature of up to 400 °C within 20 s, which to the best of our knowledge is the highest temperature by light irradiation reported to date. Meanwhile, the resulting nanorings were also employed as a photoinitiator to remotely induce a visible-light shape memory response, self-healing, reshaping performance and reversible actuation of dynamic three-dimensional structures. This study demonstrates an advancement towards controlling atomic-level-sized nanostructures and achieving greatly enhanced optical performances for optoelectronics.

The mechanoresponsive self-assembly of spiropyran doped films with dual sensitivity

Spiropyran as photo- and mechano- response material has attracted great attention for wide applications. However, there are few reports on the mechanoresponsive self-assembly of spiropyran with tunable morphologies. In this work, spiropyran doped PDMS films with mechanic and photo dual response are fabricated by novel biomimetic methods. Interestingly, the morphologies of these films can be transformed from smooth surface to small hole structures due to the self-assembly of spiropyran. Only mechanical forces can induce the morphological changes of the films accordingly the conversion of ring-closed spiropyran and ring-opened merocyanine. In addition, these films exhibit good photoresponsive properties: reversible changes of UV-Vis absorption, colour and wettability.

Synthesis, self-assembly, metal binding properties of triazole azobenzene based polycatenar dyes through click chemistry

Two series of novel polycatenar dyes consisting of a triazole azobenzene core were synthesized efficiently by copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. These compounds can self-assemble into SmC and Colhex/p6mm liquid-crystalline phases, and form multistimuli responsive organogels. Bicontinuous cubic phase (CubV) could be induced in the binary system of a bicatenar compound with SmC phase and a hexacatenar compound with Colhex/p6mm phase. Photophysical investigation indicates that these compounds have reversible photoresponsive properties in solution, liquid-crystalline and gel states. They can also act as chemosensors of Fe3+ and sodium dithionite with high selectivity.

Photo responsive silver nanoparticles incorporated liquid crystalline elastomer nanocomposites based on surface plasmon resonance

We reported a nano-Ag/liquid crystalline elastomer(LCE) nanocomposite by incorporating silver nanoparticles into a monodomain polysiloxane-based LCE matrix via a novel experimental protocol. The photo-thermo-mechanical actuation of the LCE matrix was realized via the surface plasmon resonance of silver nanoparticles while converting light into heat. The photoresponsive properties of nano-Ag/LCE nanocomposites were investigated with varying illumination intensities and silver nanoparticle doping concentrations(0.04% to 0.2%, mass fraction). The nano-Ag/LCE nanocomposites show sensitive deformation under irradiation due to their excellent photo-thermal conversion efficiency, and this photostimulated muscle-like actuation is fully reversible via the on-off behavior of light. Incorporating silver nanoparticles into the LCE matrix also improves the mechanical properties and enhances the load-actuation capability of the material.

Epoxy‐Based Azopolymers with Enhanced Photoresponsive Properties Obtained by Cationic Homopolymerization

AbstractAzopolymers are highly versatile materials due to their unique photoresponsive properties. In this contribution, a novel azo‐modified epoxy network is synthesized by cationic homopolymerization with boron trifluoride monoethylamine (BF3.MEA) complex as initiator. The effect of the addition of a fixed content of amino‐functionalized azo chromophore, Disperse Orange 3, into the polymer matrix is studied in detail. First of all, the thermal curing cycle is optimized by means of differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR) measurements. Then, the resulting bulk azo‐modified epoxy networks are characterized by means of thermogravimetric analysis (TGA), FTIR, DSC, UV–vis spectroscopy, and rheological measurements. Finally, the optical response of thin films of these materials is determined. The results evidence that azo‐modified epoxy networks obtained by cationic polymerization with optimized curing cycle display high Tg values, high maximum photoinduced birefringence, fast writing speed, and exceptionally high remnant anisotropy. Therefore, this material is a promising candidate to be used for optical storage applications.

Preparation and properties of magnetic–photoresponsive oil‐absorption resins

ABSTRACTA novel magnetic–photoresponsive oil‐absorption resin (MPOAR) was synthesized via the suspension polymerization technique. Scanning electron microscopy surface morphology analysis indicated that the surface of MPOAR exhibited pore structures with different sizes. The effects of various factors in the preparation of MPOAR on the oil absorbency were studied. We found that the amount of the crosslinking agent 4′4‐bis‐(methacryloylamino)azobenzen (Azo‐CL‐M), porogenic agent (ethyl acetate), initiator (azobisisobutyronitrile), and modified Fe3O4 had great effects on the oil absorbencies of the prepared polymer resins. The saturated absorption capacities of MPOAR for various organic solvents were determined, and we found that MPOAR could absorb 19.7 times its dry weight in CH2Cl2, 18.4 times its dry weight in CCl4, and 16.7 times its dry weight in CHCl3, respectively. In addition, the oil‐absorbent beads could absorb the oils floating on water well. In particular, the saturated absorbed MPOAR could be easily collected from water by an external magnetic field. More importantly, the photoresponsive properties of the MPOAR materials could be used to accelerate the release of the absorbed oil under UV irradiation. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45756.

The visible light responsive properties of organogel based on anthracene-substituted acylhydrazone derivative

Aggregation-induced emission-active 4-(3,4,5-bis(octyloxy)phenyl-9-anthracene acylhydrazone (AHP-T8) has been designed and synthesized, and the photo-responsive properties of organogel and xerogel irradiated by visible light were investigated systematically. AHP-T8 can form thermo-reversible gels in some of the tested solvents. The enhanced fluorescence emission has been observed after gelation although the dilute solution of AHP-T8 was almost non-fluorescent. When the organogel was exposed under visible light, the gel-sol phase transition occurred, and the corresponding morphology, fluorescence intensity, intermolecular hydrogen bonding and the structure all changed. In addition, the xerogel is more sensitive to visible light than that of organogel. The photoresponsive behaviour of AHP-T8 upon irradiation by visible light was demonstrated to be due to the E-Z isomerizations of CN group, rather than the photodimerization of anthracene groups