Search

An azobenzene-containing siloxane-based adhesive polymer was synthesized with azobenzene moieties as hard segments and siloxane moieties as soft segments. Upon UV irradiation, the adhesive energies...

Dendrimers are well-defined, highly branched macromolecules that have been widely applied in the fields of catalysis, sensing, and biomedicine. Here, we present a novel multifunctional photochromic dendrimer fabricated through grafting azobenzene units onto dendrimers, which not only enables controlled switching of adhesives and effective repair of coating scratches but also realizes high-performance solar energy storage and on-demand heat release. The switchable adhesives and healable coatings of azobenzene-containing dendrimers are attributed to the reversible solid-to-liquid transitions because trans-isomers and cis-isomers have different glass transition temperatures. The adhesion strengths increase significantly with the increase in dendrimer generations, wherein the adhesion strength of fifth-generation photochromic dendrimers (G5-Azo) can reach up to 1.62 MPa, five times higher than that of pristine azobenzenes. The solar energy storage and heat release of dendrimer solar thermal fuels, the isomers of which possess different chemical energies, can be also enhanced remarkably with the amplification of azobenzene groups on dendrimers. The storage energy density of G5-Azo can reach 59 W h kg-1, which is much higher than that of pristine azobenzenes (36 W h kg-1). The G5-Azo fuels exhibit a 5.2 °C temperature difference between cis-isomers and trans-isomers. These findings provide a new perspective and tremendously attractive avenue for the fabrication of photoswitchable adhesives and coatings and solar thermal fuels with dendrimer structures.

Here, we report a novel polymeric nanoparticle prepared by the self-assembly of amphiphilic copolymers containing a fluorescent naphthalimide (NAPH) and a photochromic spiropyran (SP), which posses...

Multiple stimuli-responsive nanoparticles that could respond to visible-light, pH and host-guest interactions were fabricated by self-assembly of tetra-ortho-methoxy-substituted azobenzene (mAzo) functionalized poly(dimethylaminoethyl methacrylate) (PDMAEMA) (PDMAEMA-mAzo), which was synthesized by quaternization between the azobenzene derivative (mAzo-Br) and the dimethylaminoethyl units of PDMAEMA. The amphiphilic azobenzene-functionalized polymer (PDMAEMA-mAzo) would self-assemble into a micellar nanoparticle consisting of hydrophobic mAzo groups as a core and hydrophilic PDMAEMA segments as a shell. Under green light irradiation, the azobenzene could isomerize from the trans form to the cis, while the morphology of the nanoparticle changed little and the loaded Nile red would not be released. At acidic condition, the azobenzene mAzo and PDMAEMA could be protonated and the nanoparticle was swollen and the loaded Nile red would be released. When mixed with cyclodextrin (CD), the nanoparticles were dissociated due to the formation of the host-guest complex of CD and azobenzene. Upon green light irradiation, the trans azobenzene changed to the cis form and the host-guest interaction could be disrupted, where the cis-azobenzene-containing polymer would self-assemble into nanoparticles. The dissociation of the nanoparticles upon addition of CD would induce the release of loaded Nile red. The prepared multiple-responsive azobenzene functionalized polymer nanoparticles may offer significant opportunities for diverse applications in the fields of nanotechnology and biotechnology for controlled release as smart nanocarriers.

Lodging in cereal crops can result in yield loss and harvesting difficulties for growers. Application of plant growth regulator (PGR) has been an indispensable management practice to reduce lodging problems that are often exacerbated during high wind growing conditions and/or high nitrogen (N)/water environments, but the data is limited in the Columbia Basin of Oregon. The objective of this research was to evaluate the effect of two PGR products (chlormequat chloride-CC, trinexapac-ethyl-TE) at different rates and application timings on two soft white winter wheat varieties (ORCH-102 and SY Ovation). Crop growth (stem height and thickness), yield-related (spike density as ears m&minus, 2, seeds per spike, grain weight) and quality parameters (test weight, protein) were measured for two cropping seasons from October 2017 to July 2019 following the application of the two PGR products at tillering (GS21-26), stem elongation (GS30-32), and/or flag leaf (GS37-39) stages under a high-N fertilizer scenario. In both growing seasons, no lodging problems were recorded for any treatments. The plant height was reduced after PGR application, but the impact on stem thickness was limited. PGR application slightly affected wheat yield, yield components, testing weight, and protein level in both growing seasons. Our results suggested that the effect of PGR application is relatively limited if no lodging problem occurred.

Here, a novel triple-responsive graphene oxide hybrid supramolecular hydrogel based on the electrostatic self-assembly between graphene oxide and a quaternized polymer and the host-guest inclusion between α-cyclodextrins and poly(ethylene glycol) monomethyl ether (mPEG) was constructed. The quaternized polymer was synthesized by quaternization between pH-sensitive poly( N, N-dimethylaminoethyl methacrylate) and bromine end-capped poly(ethylene glycol) monomethyl ether. The supramolecular hydrogels prepared from the host-guest inclusion of poly(ethylene glycol) monomethyl ether and α-cyclodextrins would turn into a mobile sol phase when the temperature was increased above a certain temperature (Tgel-sol). Graphene oxide sheets not only acted as a core material to provide additional cross-linking but also absorbed NIR light and converted NIR light into heat to trigger the gel-sol transition. The constructed graphene oxide hybrid cyclodextrin-based supramolecular hydrogels could respond to NIR light, temperature, and pH, which could be beneficial for controlled release of cargoes and would hold great promise in the field of delivery systems.

Stimuli-responsive luminogens with aggregation-induced emission (AIE) properties have attracted more and more attention for their intense emission in the aggregated state and tunable physicochemical performances. Nevertheless, it still remains challenging to design multifunctional AIE luminogens (AIEgens) with multi-responsive moieties and tunable fluorescence and morphologies. Here, a novel multifunctional AIEgen (DAS-BA) is elaborately designed based on the synergistic effect of twisted intramolecular charge-transfer (TICT), restriction of intramolecular motions (RIM), and excited-state intramolecular proton transfer (ESIPT). DAS-BA not only possesses triple pH-responsivenesses and long-wavelength emission, but also shows corresponding transition in its fluorescence and self-assembled morphologies. Under strong alkaline conditions, owing to the deprotonation of phenolic hydroxyl group, the red emission of DAS-BA is quenched and the molecular assemblies change from micro-rods to nano-rods. However, under weak acidic conditions, the red fluorescence dramatically shifts to yellow-green and the assemblies strikingly transform from micro-rods to nano-spheres due to the protonation of diethylamino moieties. Further acidification can hydrolyze the Schiff base, resulting in fluorescence quenching and destruction of the nano-spheres. Based on the reversible protonation process of diethylamino moiety, DAS-BA exhibits CO2-activated reversible fluorescence switching. Furthermore, DAS-BA has been successfully applied in anti-counterfeit and dual encryption, photo-patterning and molecular logic gates.

Here we report a facile method to construct reversible visible-light-responsive switching from antibacterial to bioadhesion by host-guest self-assembly of β-cyclodextrin (β-CD) and azobenzene functionalized polycation/polyanion. The visible-light-responsible azobenzene functionalized polycation, poly{6-[(2,6-dimethoxyphenyl)azo-4-(2′,6′-dimethoxy)phenoxy]propyl dimethylaminoethyl methacrylate-random-poly(2-(N,N-dimethylaminoethyl) methacrylate) (Azo-PDMAEMA), was synthesized via quaternization reaction between 2,6,2′,6′-tetramethoxy-4-(3-bromopropoxy)azobenzene (AzoOMeBr) and poly(2-(N,N-dimethylaminoethyl) methacrylate) (PDMAEMA), and the polyanion, poly{6-[(2,6-dimethoxyphenyl)azo-4-(2′,6′-dimethoxy) phenoxy]hexyl acrylate-random-acrylic acid} (Azo-PAA), was synthesized via esterification reaction between 2,6,2′,6′-tetramethoxy-4-(6-hydroxyhexyloxy) azobenzene (AzoOMeOH) and poly(acryloyl chloride) (PAC) and subsequent hydrolysis reactions. The switch surface could be achieved via the alternate host-guest assembly of Azo-PDMAEMA and Azo-PAA onto a β-CD-terminated substratum (Sub-CD) through visible light irradiation. The positively charged Azo-PDMAEMA with quaternary ammonium groups exhibited antimicrobial properties and few bacteria were adhered on the surface, while the negatively charged Azo-PAA with carboxyl acid groups exhibited excellent bioadhesive properties and a large number of bacteria were adhered. Interestingly, the switch between antibacterial and bioadhesive could be realized upon visible light irradiation via alternate assembly of Azo-PDMAEMA and Azo-PAA. The proposed approach to manufacturing visible-light-responsive surface with reversible and alterable biofunctionality switching between antibacterial and bioadhesive is simple and efficient, which is promising for preparation of multifunctional polymeric surfaces to encounter multifarious demands for the biomedical and biotechnological applications. Statement of Significance Light has attracted great attention in building biointerfaces for its precise spatiotemporal control and convenient operation. However, UV light may damage to biological samples and living tissues, which will limit its applications. This study demonstrates a novel visible-light-responsive surface fabricated through reversible assembly of azobenzene functionalized polycations/polyanions on cyclodextrin (CD)-terminated substrate by host-guest interactions between the visible-light-responsive azobenzene mAzo and CD, which has not been examined previously. It is noted that the azobenzene functionalized polycations show strong antibacterial activities, while the polyanions show excellent bioadhesive properties, as can be switched through the alternate assembly upon visible-light irradiation. This facile and versatile approach to visible-light-responsive surfaces holds great potential for switching of bioadhesion.

A near-infrared (NIR) responsive DNA probe has been developed for DNA hybridization detection with characteristics of high efficient Forster resonance energy transfer (FRET) from small (∼10 nm) upconversion nanoparticles (UCNPs) to nucleic acid stain SYBR Green I (SG, a specific intercalator of double-stranded DNA). The positively charged UCNPs were prepared and facilely attached with single DNA strands by coordination interaction, which acted as probes to detect the DNA targets in the presence of SG. This probe possesses not only the superiority of the NIR-excitation nature of UCNPs which could minimize the autofluorescence background from biomolecules and the photodamage to biological specimens, but also the advantages of facile preparation and high FRET signals. The FRET efficiencies could increase significantly from 2.6% to 12.5% and then to 26% when the size of UCNPs reduced from 94 nm to 30 nm and to 10 nm, respectively. The 10 nm-UCNP-based DNA probe could reach a lower detection limit of complementary ssDNA2 at 3.2 nM and three-base mismatched ssDNA2-M3 at 7.6 nM. The high sensitivity and selectivity of the probe may endow the system with great potential in fluorescence-based biosensing under the irradiation of NIR light.

Here, a novel near-infrared (NIR)/ultraviolet (UV) light-, pH- and temperature-responsive amphiphilic polymer, poly(ethylene glycol)-block-poly(dimethylaminoethyl methacrylate)@2-diazo-1,2-naphthoquinone (PEG-PDMAEMA@DNQ), is synthesized via an atom transfer radical polymerization (ATRP) and quaternization reaction. In aqueous solution, this amphiphilic polymer could self-assemble into spherical assemblies with hydrophobic NIR/UV light and base responsive DNQ moieties as the core and hydrophilic PEG and pH/temperature-responsive PDMAEMA as the corona. The NIR/UV light- and pH-sensitive absorbances of the polymer were characterized by UV-vis spectroscopy. Under 365 nm UV or 808 nm NIR irradiation, the characteristic absorption intensity of DNQ gradually decreased, indicating that DNQ converted to 3-indenecarboxylic acid (3-IC) via the Wolff rearrangement. Under acidic conditions, the absorption spectra changed little, while the absorption peak at around 400 nm decreased and a new absorption peak at 350 nm appeared under basic conditions. The morphological changes of the assemblies, which could be dissociated after UV/NIR irradiation, swollen under acidic conditions, while turned into nanocapsules under basic conditions and shrunk above the lower critical solution temperature (LCST), were revealed by transmission electron microscopy (TEM) and dynamic light scattering (DLS). The loaded hydrophobic model molecules coumarin 102 could be released from the assemblies in response to NIR, UV light and pH. More importantly, the release efficiency could be enhanced dramatically under combined stimulation. The reported NIR/UV light- and pH-responsive polymer assemblies would have great potential as nanocarriers for controlled release.

A robust light-responsive coating based on Janus composite particles is achieved. First, strawberry-like silica Janus particles are synthesized by the sol-gel process at a patchy emulsion interface. One side of the silica Janus particles possesses nanoscale roughness, and the other side is flat. Then, spiropyran-containing polymer brushes are grafted onto the coarse hemispherical side of the as-synthesized Janus particles, and the other flat side is modified with imidazoline groups. The light-responsive polymer brush-terminated coarse hemispherical sides direct toward the air when the Janus composite particles self-organize into a layer on the surface of epoxy resin substrate. The imidazoline groups react with the epoxy groups in the epoxy resin to form a robust smart coating. The coating can be reversibly triggered between hydrophobic and hydrophilic by UV and visible-light irradiation, which is attributed to the isomerization of spiropyran moieties. When the hydrophobic ring-closed spiropyran form is prominent, HeLa cells can be effectively captured onto the coating. After UV light irradiation, the ring-closed spiropyran form changes to the hydrophilic ring-opened zwitterionic merocyanine form, and then the captured cells are released. This work shows promising potential for engineering advanced smart biointerfaces.

Here a novel quadruple-responsive nanocarrier based on reduced graphene oxide/mesoporous silica sandwich-like nanocomposites (rGO@MS) modified by pH- and temperature-responsive poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) with a linker of disulfide was constructed via surface-initiated atom transfer radical polymerization. The polymer chains would be used as gatekeepers to control the release of the loaded cargo molecules under pH, temperature, NIR light and redox stimuli. The cargo molecules (rhodamine B) were demonstrated to release from the polymer-modified nanocomposites triggered by the quadruple-stimuli. It is noted that the release of the loaded rhodamine B from the nanocarriers could be enhanced greatly under the synergistic effect of multiple stimuli. The prepared quadruple-responsive polymer-modified nanocomposites show a bright prospect in the field of smart nanocarriers for controlled release.

Chlorophyll (Chl) is one of the most important classes of light-absorbing pigments in photosynthesis, and the proportion of Chl in leaves is closely related to vegetation nutrient status. Remote sensing-based estimation of Chl content holds great potential for evaluating crop growth status in agricultural management, precision farming and ecosystem monitoring. Recent studies have shown that steady-state fluorescence contributed up to 2% on the apparent reflectance in the 750-nm spectral region of plant and also provided additional evidence for fluorescence in-filling of the atmospheric oxygen absorption band at a central wavelength of 760 nm (O2-A band). In this study, an in situ hyperspectral remote sensing approach zwas employed to estimate corn Chl content at the canopy level by using chlorophyll fluorescence (ChlF) signals in the O2-A absorption band. Two new spectral indices, REArea760 (sum of first derivative reflectance between 755 and 763 nm) and REA760 (maximum of first derivative reflectance between 755 and 763 nm), derived from the first derivative spectra in the O2-A band, were proposed for estimating the corn canopy Chl content (CCC). They were compared with the performance of published indices measured at ground level, including the MERIS Terrestrial Chlorophyll Index (MTCI), Optimized Soil-Adjusted Vegetation Index 2 (OSAVI2), Modified Chlorophyll Absorption Ratio Index 2 (MCARI2), SR710, REArea (sum of first derivative reflectance between 680 and 780 nm), REA (maximum value of first derivative reflectance between 680 and 780 nm), and mND705. The results indicated that corn Chl content at the canopy level was better predicted by the new indices (with R2 = 0.835) than the published indices (with R2 ranging from 0.676 to 0.826). The two new indices ranked in the top four according to their summed ranks by integrating the ranks of RMSE and R2 of CCC linear regression models. ChlF originates only from chlorophyll in the photosynthetic apparatus and therefore is less sensitive to soil, wood, and dead biomass interference. Moreover, due to the fluorescence in-filling of the O2-A band and the amplified effect on spectrum signals by derivative operation, the spectral derivative indices in the O2-A band have great potential for estimating the CCC.

Selenium (Se) concentrations in soils and plants are low in the Pacific Northwest, and consequently, in livestock consuming locally-grown forages. Applying sodium selenate with traditional nitrogen-phosphorus-potassium-sulfur (NPKS) fertilizers provides a cost-effective Se agronomic biofortification method for increasing forage Se concentrations and maintaining optimum health and productivity of livestock. This 2-year study was conducted across Oregon on four representative forage fields: orchardgrass (Dactylis glomerata L.) in Terrebonne (central Oregon), grass-clover mixture in Roseburg (southwestern Oregon), and both grass mixture and alfalfa (Medicago sativa L.) fields in Union (eastern Oregon). Using a split plot design with double-repeated measures (2017 and 2018 with first, second, third, and residual harvest cuts each year), we determined the effect of springtime Se foliar application rate (0, 45, or 90 g Se ha−1 from sodium selenate; whole plot) and NPKS fertilization (none, NPK/PK fertilization, or NPKS/PKS fertilization; subplot; NPKS amounts adapted to meet forage and soil requirements) on total Se concentration and beneficial Se species in forages. Forage Se concentrations increased linearly with foliar sodium selenate application, doubling with each additional 45 g Se ha−1 application (first cut median: 0.11, 2.06, and 4.15 mg kg−1 dry matter, respectively). Nearly all incorporated Se was contained in the first two cuts (87 % and 9 % in first and second cuts, respectively) and most applied selenate was metabolized to selenomethionine. NPK/PK fertilization decreased Se concentrations in second and latter cut forages from Se-amended fields, whereas sulfur fertilization decreased forage Se concentrations from non-Se amended fields. Among forages, alfalfa had greater Se concentrations under low soil Se conditions, whereas grass-dominated forages had higher Se concentrations after Se-amendment. In conclusion, springtime sodium selenate foliar application is an effective management strategy to increase forage total Se concentrations and highly bioavailable selenomethionine concentrations across Oregon, and should be implemented to meet local forage and livestock requirements.

Here a novel photo, pH, and redox triple-responsive nanogel of poly(acrylic acid-co-spiropyran methacrylate) crosslinked by disulfide-containing N,N-bis(acryloyl)cystamine was prepared. Upon UV light irradiation or at low pH, the hydrophobic spiropyran (SP) isomerized to the hydrophilic merocyanine (MC) and the nanogels swelled-up. Upon the addition of reductant agents, the nanogels were disrupted due to the oxidative scission of the disulfide crosslinkers. The anticancer drug doxorubicin (Dox) could be loaded into the nanogels based on electrostatic interactions with the acrylic acids on the NGs, which would be released upon the stimulation of light, pH and DTT. The in vitro cytotoxicity study indicates that the nanogels loaded with anticancer drugs could kill the cancer cells effectively and the effect would be enhanced when irradiated by UV light. Interestingly, the isomerized MC in nanogels could emit intensive green light even endocytosed into the nucleus of the cancer cells, which afforded great potential in fluorescence cell imaging.

Novel photodegradable polymer nanocapsules were prepared from hydrophilic monomers N-isopropylacrylamide (NIPAM) and methacrylic acid (MAA), and the hydrophobic cross-linker 5-(methacryloyloxy)-2-nitrobenzyl methacrylate (ONB) by the interfacial polymerization–emulsion templating approach, in which polymeric chains in the nanocapsule shell were cross-linked during the one-pot free radical polymerization by the photocleavable cross-linker ONB predissolved in dimethyldiethoxysilane (DMDES) emulsion templates. These prepared polymer nanocapsules possess a uniform morphology with a size around 550 nm. Upon UV light irradiation, the monodisperse polymer nanocapsules undergo light-induced degradation due to the photocleavage reaction of o-nitrobenzyl ester-based linkers in the nanocapsule shell. Furthermore, hydrophobic cargo molecules can be encapsulated into the polymer nanocapsules. Either burst release of the encapsulated hydrophobic cargo molecules by UV light irradiation, or slow release by pH, or synergistic release by these two stimuli can be realized. The prepared photodegradable polymer nanocapsules could be widely applied in the field of smart nanocarriers for controlled cargo delivery.

A novel visible light responsive polymeric multilayer was constructed by layer-by-layer (LbL) electrostatic self-assembly, from which the trapping/release of cargoes via azobenzene/cyclodextrin-based host–guest interactions could be realized upon light stimulation. Visible light responsive poly{6-[(2,6-dimethoxyphenyl)azo-4-(2′,6′ dimethoxy)phenoxy]propyl dimethylaminoethyl methacrylate-random-poly(2-(N,N-dimethylaminoethyl) methacrylate)} (Azo-PDMAEMA) was synthesized, which was used as a polycation to combine with polyacrylic acid (PAA) for the construction of multilayers through the LbL electrostatic self-assembly technique. The cargo molecules, cyclodextrins modified with rhodamine B, could be loaded into the multilayers via the interaction between the trans azobenzene and cyclodextrin. Green light would induce isomerization of azobenzene from the trans-configuration to the cis, which disassembled the host–guest complex and resulted in the release of cargoes from the multilayers. Upon blue light irradiation, the cis azobenzene could recover to the trans form, thus a stable inclusion complex would be formed and the cargoes could be reloaded into the multilayers again. It is noted that the visible-light-controlled trapping/release of cargoes from the multilayers could be reconstructed reliably and conveniently. The electrostatically self-assembled multilayers of the prepared azobenzene-functionalized polymers combined with cyclodextrin show great potential in reversible trapping and release of cargoes controlled by visible light.

Here a near-infrared light and pH responsive nanocomposite comprising spiropyran-functionalized amphiphilic polymers and upconversion nanoparticles (UCNPs) is reported, which is prepared through the self-assembly of the amphiphilic polymers and the encapsulation of the UCNPs in the core of the self-assemblies. Upon near-infrared light irradiation, the upconversion fluorescence can induce the hydrophobic spiropyran to be isomerized to the hydrophilic merocyanine and disrupt the spherical morphology of the nanocomposites. Meanwhile, at low pH, the hydrophobic spiropyran can be also protonated to become hydrophilic merocyanine, and the self-assemblies are swollen. Model molecules, hydrophobic Coumarin 102, are demonstrated to be released from the nanocomposites triggered by the near-infrared light and acidic pH. In addition, the cytotoxicity of the nanocomposites loaded with anticancer drugs Doxorubicin on cancer cells indicates that the loaded drugs can be released and kill the cells effectively and the eff...

A visible light and pH responsive anticancer drug delivery system based on polymer-coated mesoporous silica nanoparticles (MSNs) has been developed. Perylene-functionalized poly(dimethylaminoethyl methacrylates) sensitive to visible light and pH are electrostatically attached on the surface of MSNs to seal the nanopores. Stimulation of visible light and acid can unseal the nanopores to induce controlled drug release from the MSNs. More interestingly, the release can be enhanced under the combined stimulation of the dual-stimuli. The synergistic effect of visible light and acid stimulation on the efficient release of anticancer drugs from the nanohybrids endows the system with great potential for cancer therapy.

Here we report a photo, temperature and pH responsive copolymer which was conveniently synthesized by quaternization between the spiropyran derivative (SPN–Cl) and dimethylaminoethyl units of poly(dimethylaminoethyl methacrylate) (PDMAEMA). In aqueous solution, the synthesized copolymer P(DMAEMA-SP) could self-assemble into polymeric nanoparticles. The spiropyran-quaternized segments endow the system with UV and visible light responsiveness and un-quaternized segments of PDMAEMA endow the system with temperature and pH responsiveness. Multiple stimuli-triggered morphological changes of the polymeric nanoparticles were revealed by transmission electron microscopy (TEM) and dynamic light scattering (DLS). The controlled release of hydrophobic dyes from the polymeric nanoparticles under the stimulation of UV light, temperature and pH could be realized. When the stimuli such as pH and UV light were synergistically applied, the release efficiency of encapsulated molecules would be enhanced greatly. The multiple stimuli-responsive self-assembled polymeric nanoparticles show promising potential as new nanocarriers for precisely controlled release of encapsulated molecules.

A series of amphiphilic azobenzene-functionalized poly(dimethylaminoethyl methacrylates) have been synthesized by quaternization between [3-(4-(4-bromo-butyloxy)phenyl)-trifluoromethyl]-diazene and the dimethylaminoethyl units of poly(dimethylaminoethyl methacrylate) (PDMAEMA). The azobenzene-functionalized polymers could self-assemble into micellar nanoparticles in water. Upon UV light irradiation, the spherical nanoparticles could only swell a little. Although the loaded nile red could not be released from the nanoparticles under UV light irradiation, the fluorescence intensity of nile red changed reversibly when altering UV and visible light irradiation. At pH 3, the nanoparticles could be swelled greatly and the loaded nile red could be released completely. At pH 10, the nanoparticles could be shrunk and the loaded nile red could be released a little. At high temperature, the nanoparticles could be shrunk, where little nile red could be released from the nanoparticles, while the fluorescence intensity of nile red could change reversibly during the heating and cooling processes.

We report the synthesis of light-triggered Janus composite nanosheets and their Janus performance. Onto the amine-group terminated side of silica Janus nanosheets, a photo-responsive spiropyran-containing polymer (PSPMA) brush has been prepared by ATRP, while the other side terminated with hydrophobic octyl groups is preserved. Upon UV irradiation, the hydrophobic PSPMA side becomes hydrophilic since the hydrophobic spiropyran changes to the hydrophilic zwitterionic merocyanine form (or vice versa with visible light). Consequently, the PSPMA/silica composite nanosheets become Janus from hydrophobic or vice versa. The Janus composite nanosheets can serve as a responsive solid emulsifier, thus the stability of the emulsions can be remotely triggered with light. Unlike those pH- or temperature-responsive Janus materials, the light-triggering process requires no additional input of chemicals or thermal energy.

A novel visible light responsive random copolymer consisting of hydrophobic azobenzene-containing acrylate units and hydrophilic acrylic acid units has been prepared. The azobenzene molecule bearing methoxy groups at all four ortho positions is readily synthesized by one-step conversion of diazotization. The as-prepared polymer can self-assemble into nanoparticles in water due to its amphiphilic nature. The tetra-o-methoxy-substituted azobenzene-functionalized polymer can exhibit the trans-to-cis photoswitching under the irradiation with green light of 520 nm and the cis-to-trans photoswitching under the irradiation with blue light of 420 nm in both solution and aggregate state. The morphologies of the self-assembled nanoparticles are revealed by TEM and DLS. The controlled release of loaded molecules from the nanoparticles can be realized by adjusting pH value since the copolymer possesses pH responsive acrylic acid groups. The fluorescence of loaded Nile Red in the nanoparticles can be tuned upon the visible light irradiation. The reversible photoswitching of the azobenzene-functionalized polymer under visible light may endow the polymer with wide applications without using ultraviolet light at all. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 2768–2775

A novel hybrid hydrogel composed of sodium alginate (SA), bacterial cellulose (BC) and multi-walled carbon nanotubes (MWCNTs) was synthesized using CaCl2 as a crosslinking agent. The hydrogel (BC/SA/MWCNTs) was proposed as a pH and electric field dual-stimulus responsive drug delivery system. Various amounts of MWCNTs were doped into the BC/SA in order to obtain the highest electric sensitivity of the composite hydrogel. The releasing profile of the drug from the hybrid hydrogels demonstrated the dual pH-/electric-sensitive property of the composite hydrogel. The amount of drug released, which was found to be dependent on the applied electric current strength, was greater under the electrical stimulus compared with that under passive diffusion. The electric-enhanced releasing behaviour was selective to the pH value of the surrounding culture. In neutral conditions, release curves under an electric voltage showed obvious electric-sensitivity. In acidic or alkaline conditions, release curves with or without an applied electric voltage showed little difference. A pulsatile pattern of drug release was observed by switching “on and off” the electric stimulus. In neutral conditions, drug release from the hydrogel showed a significant pulsatile characteristic. The overall performance of the BC/SA/MWCNTs hybrid hydrogel demonstrated that MWCNTs as additives played a synergistic role in the control release performance of the drug delivery system.

A spiropyran-based amphiphilic random copolymer was synthesized and self-assembled into photo-, pH-, and thermo-responsive micellar nanoparticles. The triple-stimuli triggered morphological changes of the nanoparticles were revealed by TEM and DLS. Highly efficient controlled release of encapsulated molecules, coumarin 102, from the nanoparticles under stimulation of UV light, acid and the combined stimuli could be realized.

A label-free complex probe composed of a water-soluble fluorescent pyrene-functionalized polymer, ssDNA, and a nucleic acid stain (SG) is presented here, which can detect DNA sequence via FRET from pyrene excimer to SG. Complementary and one-base mismatched strands at nanomolar concentrations can be distinguished by the examination of the FRET fluorescence intensity of SG. This novel strategy for detecting DNA using the fluorescent pyrene-functionalized polymer not only affords a simple label-free method to detect nucleic acid sequence but also endows the detection with high sensitivity and selectivity, which may find wide applications for optical biosensing.

A series of photo, temperature, and pH-responsive polymers have been synthesized by the quaternization of poly(dimethylaminoethyl methacrylate) (PDMAEMA) with 1-(bromomethyl)pyrene. Nanoparticles self-assembled from the pyrene-functionalized polymers in aqueous solution are demonstrated by transmission electron microscopy (TEM) and dynamic light scattering (DLS), the morphology of which can be changed under external stimulation by UV light, temperature, and pH. With the increase of the functionalization degree, the lower critical solution temperature (LCST) and the photo response of the pyrene-functionalized polymer increases, while the critical aggregation concentration (CAC) and the pH response decreases. The controlled release of encapsulated molecules such as Nile Red (NR)and anticancer drug doxorubicin (DOX) can be achieved under the triple stimulation from the self-assembled nanoparticles.

In this paper, we reported that ZnO nanoparticles (NPs) film modified with C-60 pyrrolidine tris-acid ethyl ester (PyC60) was used as cathode buffer layer in inverted polymer solar cells. The resultant device with a blend of PTB7:PC71BM as photoactive materials exhibited an open-circuit voltage (V-OC) of 0.753 V, a short-circuit current (J(SC)) of 16.04 mA cm(-2), a fill factor (FF) of 72.5%, and an overall power conversion efficiency (PCE) of 8.76%. It was higher than the control devices based on sole ZnO NPs film or ZnO: PyC60 hybrid film as cathode buffer layer. It was found that the morphology improvement of ZnO/PyC60 film contributed to reducing series loss and interfacial charge recombination. In addition, it improved the interfacial contact with photoactive layer. The results increased electron injection and collection efficiency, and improved FF. (C) 2014 Elsevier B.V. All rights reserved.

A perylene-functionalized polycation was synthesized by quaternization of poly(4-vinylpyridine) with bromomethyl-perylene and methyl iodide, which exhibited a unique aggregation-induced emission (AIE) effect. The synthesized polycation and polyanion ssDNA could form a complex probe to detect DNA hybridization. Upon adding noncomplementary ssDNA, the fluorescence of the complex probe increased due to the AIE effect; upon adding complementary ssDNA, the fluorescence intensity changed little due to the combined effects of AIE and duplex-quenching resulting from the intercalation of perylene into the duplex.

Stimuli-responsive polymeric nanoparticles with a core of hydrophobic azobenzene-containing acrylate units and a shell of hydrophilic acrylic acid units were prepared from a novel photo- and pH-responsive amphiphilic random azobenzene copolymer. Upon UV light irradiation, the trans azobenzene changed to the cis form and thus the water contact angle and the absorption of water on the polymer film could be changed, while little effect was exerted on the morphology of the nanoparticles although the polarity of the core of nanoparticles increased. Adjusting pH of the nanoparticle solution could exert a strong effect on the morphology of the nanoparticles. The prime nanoparticles (pH 6) changed to nanoparticle aggregates at pH 3, and to swollen nanoparticles at pH 11. The controlled release of Nile Red from the nanoparticles under the stimuli was demonstrated.

We used cesium stearate (CsSt) to modify the interface of the electron-extracting contact in inverted organic solar cells. Surface microstructure, optical properties, and electrical characterization as well as exciton generation rate and dissociation probability were investigated to understand the impact of CsSt on the interface contact. The results indicated that by incorporation of CsSt, the surface morphology and energy level as well as conductivity of a zinc oxide (ZnO) film were improved. On the basis of the above properties, highly efficient inverted organic solar cells have been demonstrated by using a ZnO nanoparticle film and CsSt stacked bilayer structure as the cathode interfacial layer. The insertion of a CsSt layer between the ZnO film and active layer improved the electron extraction efficiency, and a high power conversion efficiency (PCE) of 8.69% was achieved. The PCE was improved by 20% as compared to the reference device using a ZnO-only electron extraction layer.

Recently, shape-memory materials (SMMs) have attracted considerable attention due to their superior properties and potential applications. Up to now, the UV–vis–NIR photochemical response for SMMs still remains a challenge. Here, UV–vis–NIR photo-activated composites are successfully prepared via incorporating an azobenzene compound 4-cyano-4′-pentyloxyazobenzene (5CAZ) and upconversion nanoparticles (UCNPs) into shape-memory polyurethane (SMPU) matrices. The mechanically-stretched composite films exhibit photomechanical bending deformations when exposed to UV/vis/NIR light and shape recovery on heating. Furthermore, the biomimetic finger bending can be successfully achieved via light irradiation on different regions of the film, which would pave a path towards biomimetic actuators and functional devices owing to the unique UV–vis–NIR photochemically responsive and shape-memory properties.

A photo- and pH-responsive electrospun polymer film composed of a carboxy-azobenzene polymer (PAZO) and polystyrene (PS) has been fabricated. The wettability can be switched in response to pH varia...

In this work, hybrid hydrogels composed of bacterial cellulose nanofibers (nf-BC) and sodium alginate (SA) were prepared as a dual-stimuli responsive release system. The pH and electric field stimulus-responsive swelling properties and the stimulus-responsive drug release behaviors of the nf-BC/SA hybrid hydrogels using Ibuprofen as a model drug, were investigated in vitro. As the pH changed from 1.5 to 11.8, the swelling ratio increased from less than 8 times compared with its dry weight at acidic conditions to more than 13 times when the pH value was 11.8. When the electric field changed from 0 to 0.5 V, the hybrid hydrogels also showed an increasing swelling ratio from 8 times to 14 times their dry weight. The release of Ibuprofen (IBU) could be controlled by the action of deprotonation or protonation of calcium alginate in the hydrogels under different pH conditions, faster in alkaline conditions and slower in acidic conditions. Furthermore, the drug release from the hybrid hydrogels could be enhanced with an applied electric stimulus. The drug release mechanism under pH and applied electric field could be interpreted by the superposition of both Fickian diffusion and case-II transport based on Peppas' semi-empirical equation. The nf-BC/SA hybrid hydrogels with dual pH- and electro-response were new promising candidates as controlled drug delivery systems.

With the aim of achieving surface-mediated enantioselective adsorption, the self-assembly of chiral oligo(p-phenylenevinylene) (OPV3T) with nucleosides is investigated at the liquid/solid interface by means of scanning tunneling microscopy and molecular modeling. OPV3T enantiomers form mirror related hexameric rosette patterns. The DNA nucleoside, thymidine, does not self-assemble into stable adlayers but coadsorbs with OPV3T on the surface, leading to a pattern transformation of OPV3T from rosettes to dimers, and a change in chiral expression as well. Diastereoselective recognition between OPV3T and thymidine enantiomers can be used to resolve thymidine enantiomers at an achiral surface with an OPV3T enantiomer as the resolving agent. The impact of molar ratio and concentration on the self-assembly and chiral resolution is systematically investigated. Because there is no interaction between OPV3T and thymidine in solution, the liquid/solid interface acts as the platform for the chiral resolution of thymidine enantiomers.

A simple water-soluble pyrene-functionalized cationic polyelectrolyte poly(4- vinylpyridine) quaternary ammonium (P4VP-Py-Bu) was designed and synthesized from poly(4-vinylpyridine) by two-step quaternization with 1-(bromomethyl)pyrene and 1-bromobutane. The polymer could be bound with a single-stranded DNA (ssDNA) by electrostatic interactions and hydrophobic interactions to form a fluorescent complex probe for the detection of DNA hybridization. When the complementary ssDNA was added into the complex probe solution to form DNA duplex, the fluorescence emission intensity decreased more greatly compared with that by the addition of non-complementary ssDNA. It is inferred that the pyrene moieties of P4VP-Py-Bu could be intercalated into DNA duplex base-pairs, thus the fluorescence quenching by nucleotide bases was strengthened. Both the circular dichroism spectra and the fluorescence quenching induced by iodide confirmed this supposed intercalation.

A novel pyrene-labeled polyelectrolyte (Py-PDMAEMA+) has been prepared by atom transfer radical polymerization (ATRP) for detection of DNA hybridization. The electrostatic and hydrophobic interactions between Py-PDMAEMA+ and ssDNA (hairpin or linear DNA) kept them forming a complex probe which could be used as a turn-off fluorescent sensor. The fluorescence intensity of the probe decreased upon adding the complementary strand, since the pyrene moiety could be intercalated into the duplex and thus the fluorescence quenching by nucleotide bases was strengthened. The proposed intercalation mode was confirmed by the circular dichroism spectra and the fluorescence quenching study with iodide. This pyrene-labeled polyelectrolyte combined with ssDNA may establish a novel fluorescence sensing system for DNA hybridization.

Cell adhesion behaviors of stimuli-responsive surfaces have attracted significant attention for their potential biomedical applications. Distinct from temperature and pH stimuli, photoswitching avoids the extra input of thermal energy or chemicals. Herein, we designed a novel reusable cyclodextrin (CD)-modified surface to realize photoswitched specific cell release utilizing host–guest interactions between CD and azobenzene. The azobenzene-grafted specific cell capture agent was assembled onto the CD-modified surface to form a smart surface controlling cell adhesion by light radiation. After UV light irradiation, the azobenzene switched from trans- to cis-isomers, and the cis-azobenzene was not recognized by CD due to the unmatched host–guest pairs; thus, the captured MCF-7 cells could be released. Light-triggered specific cancer cell release with high efficiency may afford a smart surface with significant potential applications for the isolation and analysis of circulating tumor cells.

A simple and low-cost method is reported here for synthesizing polymer dots (PDs) using branched polyethyleneimine and peryleneimide derivatives as precursors heated in dimethylacetamide. The as-prepared PDs can be well-dispersed in water and show excitation-dependent fluorescence, stable fluorescence over a wide range (pH = 5.0 - 9.0), and high photostability. It is demonstrated that the prepared PDs can be used as a novel fluorescent sensing platform for sensitive and selective detection of Fe (III) ions. The fluorescent PDs may be applied to promising applications in chemical sensors for metal ions, as well as biological imaging or biological labeling for their excellent fluorescence properties.

Stimuli-responsive surfaces that can regulate and control cell adhesion have attracted much attention for their great potential in diverse biomedical applications. Unlike for pH- and temperature-responsive surfaces, the process of photoswitching requires no additional input of chemicals or thermal energy. In this work, two different photoresponsive azobenzene films are synthesized by chemisorption and electrostatic layer-by-layer (LbL) assembly techniques. The LbL film exhibits a relatively loose packing of azobenzene chromophores compared with the chemisorbed film. The changes in trans/cis isomer ratio of the azobenzene moiety and the corresponding wettability of the LbL films are larger than those of the chemisorbed films under UV light irradiation. The tendency for cell adhesion on the LbL films decreases markedly after UV light irradiation, whereas adhesion on the chemisorbed films decreases only slightly, because the azobenzene chromophores stay densely packed. Interestingly, the tendency for cell adhesion can be considerably increased on rough substrates, the roughness being introduced by use of photolithography and inductively coupled plasma deep etching techniques. For the chemisorbed films on rough substrates, the amount of cells that adhere also changes slightly after UV light irradiation, whereas, the amount of cells that adhere to LbL films on rough substrates decreases significantly.

Single- or few-layered h-BN nanosheets (BNNSs) are analogous to graphene and possess unique properties. However, their technological applications were severely hindered by the low production efficiency of BNNSs. We reported here a study in which BNNSs were efficiently produced by exfoliating bulk h-BN powder in thionyl chloride without using any dispersion agents. The BNNSs yield was as high as 20%, and it could be doubled through the second round of exfoliation of the h-BN precipitate. Microscopic results revealed that the BNNSs generally consisted of 3–20 layers. Pd nanoparticles were successfully immobilized and uniformly distributed on BNNS surfaces through the deposition–precipitation method. The resultant Pd–BNNS catalyst exhibited high catalytic activity and recyclability for the hydrogenation of nitro aromatics, demonstrating that BNNSs served as a promising platform to fabricate heterogeneous catalysts.

Built-in detector: A quaternized copolymer containing pyrene is described, which can bind to single-stranded DNA by electrostatic interactions to form a novel complex probe for the detection of DNA hybridization through strengthened fluorescence quenching through its intercalation into double-stranded DNA (see figure).

The photocontrolled phase transitions and reflection behaviors of a smectic liquid crystal, 4-octyl-4'-cyanobiphenyl (8CB), tuned by a chiral azobenzene, are systematically investigated. For the smectic 8CB doped with the chiral azobenzene (1R)-(-)-4-n-hexyl-4'-menthylazobenzene (ABE), the initial smectic phase can be switched to cholesteric and then to isotropic upon UV irradiation due to the trans-to-cis photoisomerization of ABE; however, no reflection band is observed. For the smectic 8CB doped with ABE and the chiral agent (S)-(-)-1,1'-binaphthyl-2,2'-diol (BN), a reflection band located in the short-wavelength infrared region is observed, which disappears after further UV irradiation. For the smectic 8CB doped with ABE and a chiral agent with higher helical twisting power, (S)-2,2'-methylendioxy-1,1'-binaphthalene (DBN), a phototunable system with cholesteric pitch short enough to reflect visible light is demonstrated. With a given concentration of the chiral dopant DBN, a reversible reflection color transition is realized tuned by the isomerization of azobenzene. The reverse phase transition from isotropic to cholesteric and then to smectic can be recovered upon visible irradiation. The photocontrolled phase transitions in smectic liquid crystals and the corresponding changes in reflection band switched by photoisomerization of azobenzene may provide impetus for their practical application in optical memories, displays, and switches.

Photoresponsive polymeric films fabricated by a facile electrostatic self-assembly technique are utilized to switch protein adsorption by light irradiation. The introduction of SiO(2) nanoparticles on the substrate results in a large reversible change of both wettability and protein adsorption.

Through the looking glass: A reflection color transition is demonstrated in a smectic liquid crystal doped with a photochromic azobenzene and a chiral agent with high helical twisting power. The reflection color can be switched reversibly due to the isomerization of azobenzene upon UV/visible irradiation.

The photoresponsive behaviors of a smectic liquid crystal, 8CB, tuned by an azobenzene chromophore have been systematically investigated. For the smectic 8CB doped with the azobenzene chromophore, 4-n-hexyl-4′-(1-bromopropyloxy)azobenzene (AB), the smectic phase could be switched to nematic and then to isotropic phase induced by the trans-to-cisphotoisomerization of AB upon UV irradiation. For the smectic 8CB doped with AB and the chiral molecule, (S)-(−)-1, 1′-binaphthyl-2, 2′-diol (BD), the smectic phase could be switched to the cholesteric phase and then to the isotropic phase. The initial phase could be recovered when the cis isomer changed to the trans isomer upon visible irradiation. The switching of the position of reflection band of the liquid crystal mixtures could be also realized by photoisomerization. The photoresponsive behaviors are dependent on the composition ratios and the temperature performed in the study.

Background: Successful development of biofuels from biomass feedstocks depends on high yields and acceptable quality. We investigated the chemical composition of ten perennial grasses and mixtures across environments in North Dakota, USA. The contents of neutral detergent fiber (NDF), acid detergent fiber, acid detergent lignin (ADL), hemicellulose (HCE), cellulose (CE) and ash were determined. Results: Biomass chemical composition was affected by environment and species/mixtures, and their interaction. Biomass under drier conditions had higher NDF, ADL and HCE contents but lower CE contents. Tall and intermediate wheatgrass had higher NDF, acid detergent fiber and CE but lower ash contents than the other species and mixtures. Switchgrass and mixtures had higher HCE. Tall wheatgrass and Sunburst switchgrass had the lowest ADL content as compared with other species. Biomass with higher yield had higher cellulose content but lower ash content. Conclusion: Combined with higher yields, tall and intermediate w...

A new water-soluble fluorescent conjugated polyelectrolyte, poly[9,9-bis(3′-butyrate)fluoren-2,7-yl] sodium (BBS-PF), was studied as a fluorescent probe for protein sensing. The conjugated polyelectrolyte BBS-PF shows high fluorescence sensitivity to cytochrome c, lysozyme, and bovine serum albumin (BSA). The Stern–Volmer constant (Ksv) in cytochrome c was measured to be as high as 6.1 × 107 L/mol, approximately twice as that of the other two. Interestingly, it is found that BSA slightly enhances the fluorescence of BBS-PF rather than quenches the fluorescence at its micromolar concentrations. The excitation spectra confirm that the interaction of BBS-PF with the proteins could be different. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

This work describes a comprehensive study of hydrogels based on polyethylene glycol diacrylates (PEGDAs) with the molecular weight (MW) range of 400–2000. The blends of low- and high-molecular weight PEGDA macromers with different ratios were photopolymerized under visible light irradiation, using a blue light sensitive photoinitiator Irgacure819, at the total polymer concentration of 60 wt %. Swelling ratios, wetting property, elastic moduli, transparency, and the microstructure of the resulting hydrogels were investigated. Among them, equilibrium water contents, hydrophilicity, and mesh size of the hydrogels increased while the elastic moduli decreased when increased the PEGDA MW or the content of higher MW PEGDA in the blends. Most of the hydrogels possessed excellent transparency in visible region. The viability of L929 cells on the surface of hydrogel was also estimated. All the selected hydrogels exhibited a relatively high proliferation rate, which demonstrated this hydrogel system with photoinitiator Irgacure819 had good biocompatibility. These results show the properties of PEGDA hydrogel could be easily adjusted by varying PEGDA MW or the ratios of low- and high-MW macromers in the composites. It could be helpful for the design of proper PEGDA hydrogels in the applications as tissue engineering or drug delivery system. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

The synthesis and characterization of a shape-persistent triphenylene–butadiynylene macrocycle formed by intermolecular Glaser-coupling of two “half-rings” and also by intramolecular coupling of the appropriate open dimer, respectively, are described in detail. The investigation of the photophysics has revealed that—compared to its open dimer—the macrocycle is more conjugated in the ground state and less so in the excited state, a result of the diacetylene bending in the macrocycle due to its constrained topology. The macrocycle is decorated with flexible side groups that support its adsorption on highly oriented pyrolytic graphite (HOPG) where a concentration-dependence of the 2D-structure is observed by means of scanning tunnelling microscopy (STM). The flexible side groups also guarantee a high compound solubility even in nonpolar solvents (cyclohexane). However, solvophobic interactions lead to the formation of a tube-like superstructure, as revealed by dynamic light scattering, X-ray scattering and atomic force microscopy.