Azobenzene‐containing LC polymethacrylates highly photosensitive in broad spectral range

Two photosensitive chiral liquid crystalline azobenzene‐containing polymethacrylates having different length of flexible spacer connecting chromophores with backbone were synthesized and their phase behavior and photo‐optical properties were studied. Both polymers consist of lateral methyl substituents in ortho‐position of azobenzene chromophores providing high photosensitivity even in red spectral region as well as high thermal stability of photoinduced Z‐form of azobenzene chromophores. It is shown, that smectic phase (SmA*) formation in films of polymer with longer spacer predetermines its quite unusual spectral response to UV and subsequent visible light actions. The SmA* phase promotes spontaneous homeotropic alignment of azobenzene chromophores in polymer films. UV‐irradiation induces not only E‐Z isomerization but also results in disruption of homeotropic alignment, whereas subsequent visible light action enables to obtain films with the low degree of chromophores orientation. The photo‐orientation phenomena under the action of polarized light of different wavelength on polymer films were studied. The possibility of using red polarized light of moderate intensity for optical photorecording on polymer films is demonstrated. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2962–2970     

Photoreactive main‐chain liquid‐crystalline polyesters: Synthesis,characterization, and photochemistry

Three series of semiflexible and rigid main‐chain polyesters containing photoreactive mesogenic units derived from p‐phenylenediacrylic acid (PDA) and cinnamic acid have been synthesized by high‐temperature polycondensation. The thermal and mesomorphic properties of the polymers have been determined. The photochemical behavior of polymer P‐[1]‐T, which contains a PDA unit, has been studied both in solution and in films. In solution, [2+2] photocycloaddition, E/Z photoisomerization, and photo‐Fries rearrangement can take place. In contrast, the dominant process in spin‐coated films is the [2+2] photocycloaddition reaction, which causes crosslinking of the polymer. In films, the photochemistry and induction of anisotropy are strongly influenced by the aggregation of the PDA phenylester unit. A dichroism of about 0.2 has been induced in films by irradiation with linearly polarized UV light, and thus the capability of these films to induce optical anisotropy and align liquid crystals has been demonstrated. Liquid‐crystalline cells have been made with polarized irradiated films of P‐[1]‐T as aligning layers. A commercial liquid‐crystalline mixture has been used for this study, and a similar liquid‐crystalline order determined by polarized Fourier transform infrared to a commercial cell with rubbed polyimide as an aligning layer has been detected. Because of crosslinking of the irradiated P‐[1]‐T photoaligning layer, the photoinduced anisotropy is stable at high temperatures, and the liquid‐crystalline molecules are insoluble in the irradiated polymer. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4907–4921, 2005     

Effect of molecular weight of macro‐iniferter on electro‐optical properties of polymer dispersed liquid crystal films prepared by iniferter polymerization

Polymer dispersed liquid crystal (PDLC) films were prepared by a devised method, in which photo‐polymerization induced phase separation in a mixtures of a macro‐iniferter, methyl acrylater, and liquid crystal. The morphology of the obtained PDLC films was examined on a polarized optical microscopy, and the effect of molecular weight of MIs on the electro‐optical properties was deliberately investigated. Decreasing the molecular weight of MIs in the films led to formation of larger liquid crystal droplets and a lower V_th values. V_sat increased and the memory effect decreased because of the increased interface anchoring strength induced by the higher molecular weight of polymer matrices. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1530–1534, 2009     

Thermally enhanced photoinduced in‐plane reorientation in photo‐cross‐linkable polymer liquid crystalline films and its application to linear polarizer

Thermally enhanced photoinduced in‐plane molecular reorientation in new photo‐cross‐linkable polymer liquid crystalline (PPLC) films comprising 4‐[ω‐(4‐methoxycinnamoyloxy)alkyloxy]biphenyl side groups is explored using linearly polarized ultraviolet (LPUV) light exposure and subsequent annealing. The influence of the alkylene spacer length between the photo‐cross‐linkable group and the biphenyl mesogenic moiety is investigated. The straight‐line characteristics of the photoreactive mesogenic side group and the 4‐methoxycinnamoyl group play important roles in the high photoreactivity and the large thermally enhanced molecular reorientation, where the in‐plane order and the birefringence of the reoriented film are 0.61 and 0.18 are obtained. Finally, cooperative molecular reorientation of dichroic dyes doped in PPLC films is also achieved to fabricate a linear polarizer. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4712–4718, 2008     

Self‐sustained actuation from heat dissipation in liquid crystal polymer networks

Liquid crystal polymer networks (LCNs) lead the research geared toward macroscopic motion of materials. These actuators are molecularly programed to adapt their shape in response to external stimuli. Non‐photo‐responsive thin films of LCNs covered with heat absorbers (e.g., graphene or ink) are shown to continuously oscillate when exposed to light. The motion is governed by the heat dissipated at the film surface and the anisotropic thermal deformation of the network. The influence of the LC molecular alignment, the film thickness, and the LC matrix on the macroscopic motion is analyzed to probe the limits of the system. The insights gained from these experiments provide not only guidelines to create actuators by photo‐thermal or pure photo‐effects but also a simple method to generate mechanical oscillators for soft robotics and automated systems. © 2018 The Authors. Journal of Polymer Science Part A: Polymer Chemistry Published by Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1331–1336     

Photo and electrically switchable behavior of azobenzene containing pendant bent‐core liquid crystalline polymers

New class of photo and electrically switchable azobenzene containing pendant bent‐core liquid crystalline monomers ( AZBM 1, 2 , and 3 ) and their polymers ( AZBP 1, 2 , and 3 ) are reported. The synthesized precursors, monomers, and polymers were characterized by FT‐IR, ¹H, and ¹³C NMR spectroscopy. Thermal stability of polymers was examined by thermogravimetric analysis and revealed stable up to 260 °C. The mesophase transition of monomers and polymers are observed through polarized optical microscopy (POM) and further confirmed by differential scanning calorimetry (DSC). The electrically switching property of monomers and their polymers were studied by electro‐optical method. Among the three monomers AZBM 1, 2 , and 3 , AZBM 1 and 2 exhibit antiferroelectric (AF) switching and AZBM 3 exhibits ferroelectric (F) switching behavior. On the other hand, low molecular weight polymers ( AZMP 1, 2 , and 3 ) show weak AF and F switching behavior. The photo‐switching properties of bent‐core azo polymers are investigated using UV‐vis spectroscopy, trans to cis isomerization occurs around 25 s for AZBP‐1 and 30 s for AZBP‐2 and 3 in chloroform, whereas reverse processes take place around 80 and 90 s. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Synthesis and opto‐electrical properties of dendron‐containing poly(2,3‐diphenyl‐1,4‐phenylenevinylene) derivatives

A new series of poly(2,3‐diphenyl‐1,4‐phenylenevinylene) derivatives containing dendritic side groups were synthesized. Different generations of dendrons were integrated on the pendant phenyl ring to investigate their effect on optical and electrical properties of final polymers. Homopolymers can not be obtained via the Gilch polymerization because of sterically bulky dendrons. By controlling the feed ratio of different monomers during polymerization, dendron‐containing copolymers with high molecular weights were obtained. The UV–vis absorption and photoluminescent spectra of the thin films are pretty close; however, quantum efficiency is significantly enhanced with increasing the generation of dendrons. The electrochemical analysis reveals that hole‐injection is also improved by increasing dendritic generation. Double‐layer light‐emitting devices with the configuration of ITO/PEDOT:PSS/polymer/Ca/Al were fabricated. High generation dendrons bring benefit of improved device performance. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3440–3450, 2007     

Novel side‐chain liquid‐crystalline polyimide for film materials

A novel side‐chain liquid‐crystalline polyimide (SLCPI) was prepared via copolycondensation from 3,5‐diamino‐benzonic‐4′‐biphenyl ester, 4,4′‐diamino‐ biphenyl ether, and 3,3′,4,4′‐oxydiphthalic dianhydride. The energy‐minimized structure and liquid crystallinity of SLCPI were investigated by molecular modeling, differential scanning calorimetry (DSC), wide‐angle X‐ray scattering, and polarized optical microscopy, respectively. The results indicated that this polyimide (PI) with side‐chain mesogenic units exhibited a nematic NI phase. Because of the in situ self‐reinforcement of side‐chain mesogenic units, the improved tensile strength and modulus of PI films reached 270% and 300%, respectively. The coefficient of thermal expansion of films decreased by 40%. DSC and thermogravimetric analyses indicated that the phase‐transition temperature of SLCPI was above 240 °C, and the 5% weight‐loss temperature was above 520 °C. Moreover, copolycondensation of two diamines with dianhydride and incorporation of pendent mesogenic units diminished the regularity and symmetry of main chains; as a result, SLCPI exhibits good film processability. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 554–559, 2003     

Synthesis and structure‐activity relationship of several aromatic ketone‐based two‐photon initiators

Several novel aromatic ketone‐based two‐photon initiators containing triple bonds and dialkylamino groups were synthesized and the structure‐activity relationships were evaluated. Branched alkyl chains were used at the terminal donor groups to improve the solubility in the multifunctional monomers. Because of the long conjugation length and good coplanarity, the evaluated initiators showed large two‐photon cross section values, while their fluorescence lifetimes and quantum yields strongly depend on the solvent polarity. All novel initiators exhibited high activity in terms of two‐photon‐induced microfabrication. This is especially true for fluorenone‐based derivatives, which displayed much broader processing windows than well‐known highly active initiators from the literature and commercially available initiators. While the new photoinitiators gave high reactivity in two‐photon‐induced photopolymerization at concentration as low as 0.1% wt, these compounds are surprisingly stable under one photon condition and nearly no photo initiation activity was found in classical photo DSC experiment. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Conformation and luminescence characteristics of nanopoly[2‐metoxy‐5‐(2′‐ethyl‐hexyloxy)‐p‐phenylene vinylene] in two‐dimensional arrays

With anodic alumina with an ordered nanopore array used as a template, poly[2‐metoxy‐5‐(2′‐ethyl‐hexyloxy)‐p‐phenylene vinylene] (MEH–PPV) was embedded into the nanopores, and then two‐dimensional arrays of light‐emitting nanopolymers were prepared. By the measurement and analysis of photoluminescence and photoluminescence excitation spectra of the samples, it was demonstrated that the optical properties of the nano‐MEH–PPV arrays were obviously different from those of MEH–PPV films. The conformations of the MEH–PPV chains in the nanopores, films, and solutions and their effects on the optical properties were examined. It was determined experimentally that the conformations of the MEH–PPV chains in the solutions were maintained in the nano‐MEH–PPV arrays. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3037–3041, 2006     

Synthesis and characterization of highly conjugated side‐group‐substituted benzo[1,2‐b:4,5‐b′]dithiophene‐based copolymer for use in organic solar cells

A new donor–acceptor (D–A) conjugated copolymer based on benzo[1,2‐b:4,5‐b′]dithiophene (BDT) and thieno[3,4‐c]pyrrole‐4,6‐dione (TPD) was synthesized via a Stille cross‐coupling reaction. A highly conjugated thiophene‐based side group, tris(thienylenevinylene) (TTV), was incorporated into each BDT unit to generate the two‐dimensional D–A copolymer (PBDT‐TTV). An alkoxy‐substituted BDT‐based TPD copolymer (PBDT‐OR) was synthesized using the same polymerization method for comparison. PBDT‐TTV thin films produced two distinct absorption peaks. The shorter wavelength absorption (458 nm) was attributed to the BDT units containing the TTV group, and the longer wavelength band (567–616 nm) was attributed to intramolecular charge transfer between the BDT donor and the TPD acceptor. The highest occupied molecular orbital energy levels of PBDT‐OR and PBDT‐TTV were calculated to be −5.53 and −5.61 eV, respectively. PBDT‐TTV thin films harvested a broad solar spectrum covering the range 300–700 nm. A comparison with the PBDT‐OR films revealed stronger interchain π–π interactions in the PBDT‐TTV films and, thus, a higher hole mobility. A polymer solar cell device prepared using PBDT‐TTV as the active layer was found to exhibit a higher power conversion efficiency than a device prepared using PBDT‐OR under AM 1.5 G (100 mW/cm²) conditions. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 653–660     

Bioinspired core‐crosslinked micelles from thymine‐functionalized amphiphilic block copolymers: Hydrogen bonding and photo‐crosslinking study

Bioinspired core‐bound polymeric micelles, based on hydrogen bonding and photo‐crosslinking, of thymine have been prepared from poly(vinylbenzylthymine)‐b‐poly(vinylbenzyltriethylammonium chloride). The amphiphilic block copolymer was synthesized by 2,2‐tetramethylpiperidin‐1‐oxyl‐mediated living radical polymerization in water/ethylene glycol solution. Micelle characterization and critical micelle concentration measurements demonstrated that the hydrogen bonding of the attached thymine units stabilizes the micelles. Further, core‐crosslinked polymeric micelles were formed by ultraviolet (UV) radiation showing that the stability of the micelle could be controlled by the UV crosslinking of the attached thymines. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Highly redox‐stable and electrochromic aramids with morpholinyl‐substituted triphenylamine units

A novel morpholinyl‐substituted, triphenylamine‐based diamine monomer, namely 4,4′‐diamino‐4″‐(4‐morpholinyl)triphenylamine, was synthesized and polymerized with various aromatic dicarboxylic acids via the phosphorylation polyamidation reaction leading to a series of electroactive aromatic polyamides (aramids). All aramids were readily soluble in polar organic solvents and could be solution cast into tough and flexible films with high thermal stability. Cyclic voltammograms of the aramid films on the indium‐tin oxide‐coated glass substrate exhibited a pair of reversible oxidation waves with very low onset potentials of 0.36 − 0.41 V (vs. Ag/AgCl) in acetonitrile solution. The polymer films showed reversible electrochemical oxidation accompanied by strong color changes with high coloration efficiency, high contrast ratio, and rapid switching time. The optical transmittance change (Δ%T) at 650 nm between the neutral state and the fully oxidized state is up to 90%. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1289–1298     

Cinnamate‐functionalized poly(ester‐carbonate): Synthesis and its UV irradiation‐induced photo‐crosslinking

A functionalized cyclic carbonate monomer containing a cinnamate moiety, 5‐methyl‐5‐cinnamoyloxymethyl‐1,3‐dioxan‐2‐one (MC), was prepared for the first time with 1,1,1‐tri(hydroxymethyl) ethane as a starting material. Subsequent polymerization of the new cyclic carbonate and its copolymerization with L ‐lactide (LA) were successfully performed with diethyl zinc (ZnEt₂) as initiator/catalyst. NMR was used for microstructure identification of the obtained monomer and copolymers. Differential scanning calorimetry (DSC) was used to characterize the functionalized poly(ester‐carbonate). The results indicated that the copolymers displayed a single glass transition temperature (T_g) and the T_g decreased with increasing carbonate content and followed the Fox equation, indicative of a random microstructure of the copolymer. The photo‐crosslinking of the cinnamate‐carrying copolymer was also demonstrated. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 161–169, 2009     

Synthesis of thermal‐stable and photo‐crosslinkable polyfluorenes for the applications of polymer light‐emitting diodes

Three polyfluorene derivatives which have oxetane‐containing phenyl group at C‐9 position were synthesized via the palladium‐catalyzed Suzuki‐coupling reaction. The synthesized polymers PFB, PFG, and PFR emit blue, green, and red light, respectively. A double‐layer device with the configuration of ITO/PEDOT/polymer/Ca/Al using PFB as the active layer showed a threshold voltage of 5 V, a maximum brightness of 2030 cd/m², and a maximum current efficiency of 0.35 cd/A. Using PFG as the active layer, the device exhibited a threshold voltage of 6 V, a maximum brightness of 6447 cd/m², and a maximum current efficiency of 1.27 cd/A. Using PFR as the active layer, the device showed a threshold voltage of 4 V, a maximum brightness of 2135 cd/m², and a maximum current efficiency of 0.16 cd/A. Better electroluminescent performance was also found based on different design of device structures. Due to photo‐crosslinking property of oxetane groups, the UV‐exposed thin films are insoluble in common organic solvents. A device comprised of blue, green, and red‐emissive pixels was successfully fabricated by spin‐coating and photo‐lithographic processes. In addition, a white light‐emitting device with CIE coordinate of (0.34, 0.33) was achieved by blending PFR into a host material PFB as the active layer. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 516–524, 2010     

Micelles and reverse micelles with a photo and thermo double‐responsive block copolymer

A novel photo and thermo double‐responsive block copolymer was developed to fabricate micelles and reverse micelles in aqueous solution. The block copolymer was synthesized by ATRP block copolymerization of a spiropyran‐ containing methacrylate (SPMA) with di(ethylene glycol) methyl ether methacrylate (DEGMMA). By facile control of the photo irradiation and solution temperature, PSPMA‐core and PDEGMMA‐core micelles can be obtained, respectively. The thermo‐ and photo‐responsive micelles were used as smart polymeric nanocarriers for controlled encapsulation, triggered release, and re‐encapsulation of model drug coumarin 102. The double‐responsive self‐assembly and disassembly were tracked by dynamic light scattering, transmission electron microscopy, and fluorescence spectroscopy. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2855–2861, 2010     

Synthesis of through‐space conjugated polymers containing [2.2]paracyclophane and thieno[3,4‐b]pyrazine in the main chain

We synthesized through‐space conjugated polymers with [2.2]paracyclophane and thieno[3,4‐b]pyrazine units in the main chain by the Sonogashira–Hagihara coupling reaction. The obtained polymers were soluble in common organic solvents, and homogeneous thin films were readily obtained from the polymer solutions by spin‐coating techniques. The polymers exhibited the extension of the conjugation length via the through‐space interaction. The polymers showed orangish‐red emission with peak maxima of around 610 nm in diluted solutions and their thin films, which were derived from the thieno[3,4‐b]pyrazine moieties. The optical and electrochemical behaviors of the polymers containing pseudo‐para‐ and pseudo‐ortho‐linked [2.2]paracyclophane were identical. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009     

Photoresponsive water‐dispersible polyaniline nanoparticles through template synthesis with copolymer micelle containing coumarin groups

A novel kind of photosensitive water‐dispersible polyaniline (PANI) nanoparticles was designed and prepared by template synthesis using a photo‐responsive vinyl‐coumarin (VM)/2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid (AMPS) copolymer micelle containing coumarin moieties. The resulting PANI nanoparticles exhibited reversible photo‐crosslinking and photo‐decrosslinking behavior similar to coumarin moiety upon irradiation with different UV light as verified by UV–vis absorption. In addition, photoinduced size change of the PANI nanoparticles after 365 nm UV light irradiation was successfully monitored by dynamic light scattering and transmission electron microscopy measurements, further confirming the photosensitivity of the obtained PANI nanoparticles by the incorporation of VM/AMPS copolymer. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Side‐chain supramolecular polymers with induced supramolecular chirality through H‐bonding interactions

Side‐chain supramolecular polymers that show columnar mesomorphism have been prepared through H‐bonding interactions between a polyvinylpyridine polymer as H‐acceptor and different H‐donors derived from benzoic acid. These compounds have been designed according to a promesogenic structure, that is, either disk‐like or banana‐like, to promote stacking and therefore the formation of columnar arrangements. IR studies confirmed the formation of H‐bonds and demonstrated that the H‐bond intensity decreases upon increasing temperature. The mesophase organizations were studied by polarized optical microscopy, differential scanning calorimetry, and X‐ray diffraction. Associations containing poly‐3‐methyl‐4‐vinylpyridine showed supramolecular optical activity, as evidenced by circular dichroism studies on thin films. It is proposed that these supramolecular polymers adopt a helical structure that can be biased toward a given handedness by virtue of the configuration of the stereogenic centers in the peripheral tails of the acids. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5528–5541, 2008     

Reactive intermediates in the initiation step of the photo‐oxidation of MDMO‐PPV

Because oxygen cannot be fully eliminated from organic solar cells, the occurrence of oxidative photo‐degradation of the device in operating conditions has to be considered. Polyphenylene‐vinylene‐based photovoltaic devices have a short lifetime that currently limits their applications. In this article, we focus on various transient species that are potentially involved in the initiation step of the photo‐oxidation of poly[2‐methoxy‐5‐(3′,7′‐dimethyloctyloxy)‐1,4‐phenylenevinylene] (MDMO‐PPV). The role of the transient species was investigated by a combination of quenching and sensitization experiments. Complementary information was obtained by transient absorption spectroscopy. Results evidenced the fact that ¹O₂ was not the principal reactive intermediate involved in the photo‐oxidation of MDMO‐PPV. This result was in contradiction with previous reports. It was shown that the MDMO‐PPV^?+ radical cation was generated after excitation. The presence of oxygen and the photo‐aging favored the formation of the radical cation, suggesting that oxygen and photoproducts act as electron acceptors. The charged radicals formed are likely to evolve and give radicals that initiate the oxidation of the polymer by abstraction of the labile hydrogen in α position of the ether function and by addition on the double bonds. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6044–6052, 2009