Ling-Xiang Guo

A room-temperature two-stage thiol–ene photoaddition approach towards monodomain liquid crystalline elastomers

Monodomain liquid crystalline elastomers (LCEs) with anisotropic, loosely crosslinked polymeric matrices have attracted intense scientific attention due to their widespread applications in stimuli-responsive soft actuators. However, traditional synthetic pathways towards monodomain LCEs require complicated procedures, elevated reaction temperatures, and a prolonged preparation time ranging from several hours to even several days. In this manuscript, we report a fast room-temperature one-pot, two-stage thiol–ene photoaddition method to synthesize monodomain polysiloxane-based LCE films. The first stage is a partial thiol–ene photo-crosslinking of poly(3-mercaptopropylmethylsiloxanes) and vinyl-terminated mesogens and crosslinkers in solution, the second stage is a complete thiol–ene photo-crosslinking of the uniaxially-stretched pre-crosslinked LCE film. Starting from mesogenic monomers, the whole preparation process can be finished in less than 30 minutes, and all the preparation experiments are performed at room temperature, in open air. We believe that this facile one-pot, two-stage thiol–ene photoaddition method can open a new route for the fast and robust production of monodomain LCE shape memory materials.

Photo-responsive polysiloxane-based azobenzene liquid crystalline polymers prepared by thiol-ene click chemistry

ABSTRACT In this work, a novel polysiloxane-based azobenzene-containing liquid crystalline polymer (LCP) PMMS-A44V6 has been designed and synthesized via a facile thiol-ene click chemistry method by grafting a side-on azobenzene mesogenic group A44V6 onto poly-[3-mercaptopropylmethylsiloxane] (PMMS) backbone. 1H NMR, 13C NMR, GPC, TGA, DSC, POM and WAXS were used to investigate the mesogenic properties and photo-responsive behaviour of PMMS-A44V6. Taking advantage of the azobenzene’s trans–cis isomerization effect, PMMS-A44V6 can perform an isotropization process under UV irradiation in its nematic phase. Initially, the isotropization process starts in a linearly decreasing manner with a rate of ca −6.5 × 105 intensity/s, and eventually finishes in an exponential decrease regime to form cis-azobenzene moieties. The reversible UV-response behaviour of PMMS-A44V6 can be performed in a relatively low temperature range of 30 ~ 75°C, which might help this azobenzene-containing LCP material to find potential application in control devices. GRAPHICAL ABSTRACT

Indeno[1,2-b]fluorene-based novel donor–acceptor conjugated copolymers: Electron acceptor engineering and polymer backbone planarization

A series of conjugated copolymers based on indeno[1,2-b]fluorene as donor unit with different acceptor units have been synthesized to explore the influences of molecular backbone planarization and acceptor electronegativity on charge transport and photovoltaic properties. Polymer incorporating 2,3-diphenylquinoxaline acceptor moiety shows poor light-harvesting capacity and inferior photovoltaic efficiency of 0.5% due to twisted geometry. By introducing the stronger acceptor thiadiazolo[3,4-c]pyridine in polymer, intramolecular charge transfer is enhanced, giving rise to improved absorption property and photovoltaic efficiency of 1.39%. However, the polymer backbone is still twisted. When thiophene-flanked diketopyrrolopyrrole (DPP) is incorporated as electron acceptor, the polymer exhibits a more planar molecular geometry, yielding a broader and red-shifted absorption spectrum as well as a significantly improved hole mobility of 1.46E-2 cm2 V−1 s−1. However, the photovoltaic device efficiency is only enhanced to be 1.69%. The low-lying lowest unoccupied molecular orbital of −3.95 eV as a result of the strong electron deficiency of the DPP unit may lead to the inefficient charge dissociation and increase the charge recombination, which may give rise to the limit photovoltaic performance.

Hydrogen-bonding induced melamine-core supramolecular discotic liquid crystals

Recognition of melamine is not only of importance for the food industry but also an interesting scientific research topic. The objective of this work is to screen suitable hydrogen-bonding complementary compounds for the construction of melamine-core supramolecular discotic liquid crystal (LC) materials which might provide a LC perspective for detection and separation of melamine in the future. We design and synthesize five categories of long-alkyl-tailed compounds bearing different hydrogen-bonding complementary functional groups, including benzoic acid, cyanuric acid, homophthalimide, succinimide and thymine derivatives. The experimental results demonstrate that the imidodicarbonyl unit is the best hydrogen-bonding complementary functional group of melamine. Furthermore, the heterocyclic ring size markedly influences the hydrogen-bonding strength of the melamine-imidodicarbonyl unit complex. Most importantly, liquid crystallinity can be generated from these hydrogen-bonding supramolecular complexes. In particular, a variety of columnar mesomorphic orders (such as hexagonal columnar, rectangular columnar, and square columnar phases) can be effectively achieved by functionalization of thymine or succinimide units and modulation of the molar ratios of melamine and these hydrogen-bonding complementary compounds.

Functionalization of side chain terminals with fused aromatic rings in carbazole–diketopyrrolopyrrole based conjugated polymers for improved charge transport properties

In recent years, side chain engineering has been proven to play a critical role in the development of high performance conjugated polymers for organic electronics. Here, we report a new strategy to improve charge transport property through side chain functionalization. A series of carbazole–diketopyrrolopyrrole based conjugated polymers P1, P2 and P3 with different side chains have been designed and synthesized. For P2 and P3, a pyrene and carbazole unit were incorporated into the terminal of the alkyl side chain, respectively. Thermal properties, crystallinities, UV-vis absorptions, electrochemical properties as well as charge transport properties of the polymers were investigated in detail. Interestingly, results showed that incorporation of the fused aromatic ring into the side chain terminal not only changed the absorption and electrochemical properties, but also affected the charge transport properties. The pyrene and carbazole group in the side chain terminal significantly promoted aggregation of the polymer chains, which would provide short-range order for improved charge carrier mobility. Compared to the hole mobility (0.019 cm2 V−1 s−1) for polymer P1 with the whole alkyl chains, increased hole mobilities of 0.081 cm2 V−1 s−1 and 0.052 cm2 V−1 s−1 were achieved for polymer P2 and polymer P3, respectively. It is worthy to note that our strategy gives rise to no increment of the crystallinity of the polymer, being beneficial for the practical application of soft electronics since high crystallinity of the material usually leads to poor thin film uniformity and weak mechanical resilience. In this respect, we offer a promising tool to aid rational polymer design for enhanced charge transport property.

An entropy-driven ring-opening metathesis polymerization approach towards main-chain liquid crystalline polymers

The known synthetic methods of preparing main-chain liquid crystalline polymers (MCLCPs) are rather limited to several polycondensation reactions. However, the nature of step-growth polycondensation endows the corresponding MCLCPs with relatively low molecular weights and broad molecular weight distributions. In this manuscript, an entropy-driven ring-opening metathesis polymerization (ED-ROMP) approach is for the first time applied in producing a MCLCP by polymerizing a macrocyclic olefin monomer containing one cyclohexanecarboxylic acid phenyl ester group as a mesogenic core and one icos-10-enedicarbonyl group as a flexible aliphatic chain. For comparison, Yamaguchi macrolactonization and ring-closing metathesis (RCM) methods are used to synthesize the macrocyclic olefin monomer, and it turns out that although the macrolactonization method can prepare a pure macrocyclic monomer, the RCM strategy is advantageous in providing a much higher overall reaction yield. Furthermore, compared with a traditional acyclic diene metathesis (ADMET) polymerization of mesogenic α,ω-diene, the ED-ROMP approach starting with the same monomer-to-catalyst ratio, releases no heat or volatiles during the reaction, and can efficiently provide MCLCPs with much higher molecular weights over a shorter reaction time.

Thiol–ene photoimmobilization of chymotrypsin on polysiloxane gels for enzymatic peptide synthesis

Chemical incorporation of enzymes onto polymeric materials has recently attracted intense scientific attention. Cross-linked polysiloxane gels as a typical super-hydrophobic support, are a good candidate for supporting enzymes in low-water organic medium to efficiently catalyze peptide synthesis because the hydrophobic polysiloxane matrix can prevent water from attacking the acyl-enzyme intermediate, which is beneficial for the shift in equilibrium to peptide formation. In this work, we develop a facile strategy to photoimmobilize olefin-functionalized chymotrypsin onto cross-linked polysiloxane gels via UV-initiated thiol–ene click chemistry. The impacts of water addition amount, heat-treatment and recyclability of the immobilized chymotrypsin influencing the peptide synthesis efficiency are investigated. Compared with the native chymotrypsin, polysiloxane-immobilized chymotrypsin showed advantageous catalytic activity, higher thermal stability and superior recyclability.

A cut-and-paste strategy towards liquid crystal elastomers with complex shape morphing

Nowadays, with the rapid progress in soft robotics and aerospace technology, novel soft actuator materials with reversible and complex shape morphing capabilities, such as helical curling, buckling, accordion-like folding, self-oscillating, waving and other three-dimensional motion modes, are highly desirable. In this manuscript, we report a new cut-and-paste method to construct liquid crystal elastomer actuators with complex shape morphing by combining dynamic covalent chemistry with the traditional surface-treated liquid crystal cell preparation strategy. In brief, we synthesize monodomain liquid crystal elastomer films with exchangeable disulfide crosslinkers through in situ photopolymerization in anti-parallel surface-rubbed cells, cut the obtained uniaxial-aligned liquid crystal elastomer films into pieces and paste them together via dynamic disulfide exchange to form versatile shaped soft actuator materials.

Long-term-stable, solution-processable, electrochromic carbon nanotubes/polymer composite for smart supercapacitor with wide working potential window

Electrochromic supercapacitor (SC) as a multifunctional energy storage device has very important research significance and a broad space for development. The unavoidable challenge for an electrochromic SC is the simultaneous achievement of high energy density, flexibility, and outstanding stability through the use of economically feasible materials and simple manufacturing processes. Despite great efforts in the development of electrochromic SC electrode materials, serious challenges remain for many materials to achieve versatile processability due to their poor solubility. In addition, the voltage window is quite narrow and energy density is relatively low, which limit practical applications. Herein, a novel solution-processable composite material, MWCNT–PBDTC, has been synthesized through direct Williamson reaction between hydroxylated carbon nanotubes (MWCNT-OH) and the conjugated polymer PBDTC-Br with the side chain terminal functionalized with bromo moiety. The electrochromic and electrochemical properties of MWCNT–PBDTC films, obtained by spin-coating, were investigated in detail. Furthermore, an electrochromic symmetrical SC device using MWCNT–PBDTC films as the electrodes was fabricated with PMMA-based solid electrolyte, delivering a high energy density of 174.7 W h kg−1 and a quite wide working potential window of 4.8 V. The cycling stability of the SC was also tested, and the results indicated that the specific capacitance still could retain well over 96% of the initial value after 5000 consecutive charging/discharging cycles. Meanwhile, the SC device exhibited a distinct and reversible color transition from brown (discharged state) to gray (charged state), with a high optical contrast at a wavelength of 465 nm. In short, the novel electrochromic composite could be applied as one of the most promising electrode materials for smart SC devices.