Towards Sustainable Materials: A Review of Acylhydrazone Chemistry for Reversible Polymers.

Transitioning towards a circular economy, extensive research has focused on dynamic covalent bonds (DCBs) to pave the way for more sustainable materials. These bonds enable debonding and rebonding on demand, as well as facilitating end-of-life recycling. Acylhydrazone/hydrazone chemistry offers a material with high stability under neutral and basic conditions making it a promising candidate for materials research, though the material is susceptible to acid degradation. However, this degradation under acidic conditions can be exploited, making it widely applicable in self-healing and biomedical fields, with potential for reprocessing and recycling. This review highlights studies exploring the reversibility of acylhydrazone/hydrazone bonds in various polymers, altering their properties, and utilizing them in applications such as self-healing, reprocessing, and recycling. The review also focuses on how the mechanical properties are affected by the presence of dynamic linkages, and methods to improve the mechanical performance.

Linear Coordination Polymer Synthesis from Bis-Catechol Functionalized RAFT Polymers.

Catechol-Fe(III) complexes contain some of the strongest known metal-chelate coordination bonds. Despite this, they have until now not been utilized in (polymeric linker) linear coordination polymer (LCP) synthesis. With the view of generating catechol end-functional polymers, a new, symmetrical bis-catechol functionalized trithiocarbonate reversible addition fragmentation chain transfer (RAFT) agent is synthesized (CatDMAT). Acrylamide (AM) and dimethylacrylamide (DMA) polymerizations are conducted with CatDMAT using direct photoactivation RAFT polymerization to yield bis-catechol end-functionalized homo- and block-copolymers of molecular weight 10-15 kDa. Catechol-Fe(III) LCPs are successfully formed from the telechelic catechol polymers by bis-complexation to Fe(III). The tetrahedral bis-complex is detected by UV-vis spectroscopy (λmax  = 570 nm), while increases in relative viscosity and Mn,GPC over their respective uncomplexed polymers confirm the occurrence of supramolecular polymerization. The catechol-LCPs are shown to undergo oxidation and crosslinking in aqueous solution after 24 h.

Astrochemistry and Astrobiology: Materials Sciencein Wonderland?

Astrochemistry and astrobiology, the fascinating disciplines that strive to unravel the origin of life, have opened unprecedented and unpredicted vistas into exotic compounds as well as extreme or complex reaction conditions of potential relevance for a broad variety of applications. Representative, and so far little explored sources of inspiration include complex organic systems, such as polycyclic aromatic hydrocarbons (PAHs) and their derivatives; hydrogen cyanide (HCN) and formamide (HCONH2) oligomers and polymers, like aminomalononitrile (AMN)-derived species; and exotic processes, such as solid-state photoreactions on mineral surfaces, phosphorylation by minerals, cold ice irradiation and proton bombardment, and thermal transformations in fumaroles. In addition, meteorites and minerals like forsterite, which dominate dust chemistry in the interstellar medium, may open new avenues for the discovery of innovative catalytic processes and unconventional methodologies. The aim of this review was to offer concise and inspiring, rather than comprehensive, examples of astrochemistry-related materials and systems that may be of relevance in areas such as surface functionalization, nanostructures, and hybrid material design, and for innovative technological solutions. The potential of computational methods to predict new properties from spectroscopic data and to assess plausible reaction pathways on both kinetic and thermodynamic grounds has also been highlighted.

Facile One-step Micropatterning Using Photodegradable Methacrylated Gelatin Hydrogels for Improved Cardiomyocyte Organization and Alignment.

Hydrogels are often employed as temporary platforms for cell proliferation and tissue organization in vitro. Researchers have incorporated photodegradable moieties into synthetic polymeric hydrogels as a means of achieving spatiotemporal control over material properties. In this study protein-based photodegradable hydrogels composed of methacrylated gelatin (GelMA) and a crosslinker containing o-nitrobenzyl ester groups have been developed. The hydrogels are able to degrade rapidly and specifically in response to UV light and can be photopatterned to a variety of shapes and dimensions in a one-step process. Micropatterned photodegradable hydrogels are shown to improve cell distribution, alignment and beating regularity of cultured neonatal rat cardiomyocytes. Overall this work introduces a new class of photodegradable hydrogel based on natural and biofunctional polymers as cell culture substrates for improving cellular organization and function.

Photodegradable Gelatin-Based Hydrogels Prepared by Bioorthogonal Click Chemistry for Cell Encapsulation and Release.

In this study, we present a method for the fabrication of in situ forming gelatin and poly(ethylene glycol)-based hydrogels utilizing bioorthogonal, strain-promoted alkyne-azide cycloaddition as the cross-linking reaction. By incorporating nitrobenzyl moieties within the network structure, these hydrogels can be designed to be degradable upon irradiation with low intensity UV light, allowing precise photopatterning. Fibroblast cells encapsulated within these hydrogels were viable at 14 days and could be readily harvested using a light trigger. Potential applications of this new class of injectable hydrogel include its use as a 3D culturing platform that allows the capture and release of cells, as well as light-triggered cell delivery in regenerative medicine.

Introducing manganese complexes as redox mediators for dye-sensitized solar cells.

The abundance and low toxicity of manganese have led us to explore the application of manganese complexes as redox mediators for dye sensitized solar cells (DSCs), a promising solar energy conversion technology which mimics some of the key processes in photosynthesis during its operation. In this paper, we report the development of a DSC electrolyte based on the tris(acetylacetonato)manganese(iii)/(iv), [Mn(acac)3](0/1+), redox couple. PEDOT-coated FTO glass was used as a counter electrode instead of the conventionally used platinum. The influence of a number of device parameters on the DSC performance was studied, including the concentration of the reduced and oxidized mediator species, the concentration of specific additives (4-tert-butylpyridine, lithium tetrafluoroborate, and chenodeoxycholic acid) and the thickness of the TiO2 working electrode. These studies were carried out with a new donor-π-acceptor sensitizer K4. Maximum energy conversion efficiencies of 3.8% at simulated one Sun irradiation (AM 1.5 G; 1000 W m(-2)) with an open circuit voltage (VOC) of 765 mV, a short-circuit current (JSC) of 7.8 mA cm(-2) and a fill factor (FF) of 0.72 were obtained. Application of the commercially available MK2 and N719 sensitizers resulted in an energy conversion efficiency of 4.4% with a VOC of 733 mV and a JSC of 8.6 mA cm(-2) for MK2 and a VOC of 771 mV and a JSC of 7.9 mA cm(-2) for N719. Both dyes exhibit higher incident photon to current conversion efficiencies (IPCEs) than K4.

Photoinitiated alkyne-azide click and radical cross-linking reactions for the patterning of PEG hydrogels.

The photolithographical patterning of hydrogels based solely on the surface immobilization and cross-linking of alkyne-functionalized poly(ethylene glycol) (PEG-tetraalkyne) is described. Photogenerated radicals as well as UV absorption by a copper chelating ligand result in the photochemical redox reduction of Cu(II) to Cu(I). This catalyzes the alkyne-azide click reaction to graft the hydrogels onto an azide-functionalized plasma polymer (N(3)PP) film. The photogenerated radicals were also able to abstract hydrogen atoms from PEG-tetraalkyne to form poly(α-alkoxy) radicals. These radicals can initiate cross-linking by addition to the alkynes and intermolecular recombination to form the PEG hydrogels. Spatially controlling the two photoinitiated reactions by UV exposure through a photomask leads to surface patterned hydrogels, with thicknesses that were tunable from tens to several hundreds of nanometers. The patterned PEG hydrogels (ca. 60 µm wide lines) were capable of resisting the attachment of L929 mouse fibroblast cells, resulting in surfaces with spatially controlled cell attachment. The patterned hydrogel surface also demonstrated spatially resolved chemical functionality, as postsynthetic modification of the hydrogels was successfully carried out with azide-functionalized fluorescent dyes via subsequent alkyne-azide click reactions.

High-photosensitive resin for super-resolution direct-laser-writing based on photoinhibited polymerization.

An ethoxylated bis-phenol-A dimethacrylate based photoresin BPE-100 of relatively high photosensitivity and modulus is used for the creation of sub-50 nm features. This is achieved by using the direct laser writing technique based on the single-photon photoinhibited polymerization. The super-resolution feature is realized by overlapping two laser beams of different wavelengths to enable the wavelength-controlled activation of photoinitiating and photoinhibiting processes in the polymerization. The increased photosensitivity of the photoresin promotes a fast curing speed and enhances the photopolymerization efficiency. Using the photoresin BPE-100, we achieve 40 nm dots for the first time in the super-resolution fabrication technique based on the photoinhibited polymerization, and a minimum linewidth of 130 nm. The influence of the power of the inhibiting laser and the exposure time on the feature size is studied and the results agree well with the prediction obtained from a simulation based on a non-steady-state kinetic model.

Enhanced Photovoltaic Efficiency via Control of Self-Assembly in Cyanopyridone-Based Oligothiophene Donors.

The optoelectronic properties of functional π-conjugated organic materials are affected by their ability to self-assemble within thin films of devices. There are limited reports that demonstrate the positive impact of self-assembly on the photovoltaic performance of organic solar cells. Here, we demonstrate that hydrogen-bonded supramolecular arrays of a cyanopyridone-based oligothiophene donor, CP6, show notable improvement in photovoltaic performance upon self-assembly into a nanofibrous network. The honeycomb-like blend network exhibited higher hole mobility, leading to efficient charge generation and transport. The photovoltaic performance of CP6 was superior to that of two structural analogues, CP5 and CP1, and was attributed to the enhanced capability of CP6 to self-assemble into a film morphology favorable for BHJ devices. The BHJ devices comprising CP6 and the conventional fullerene acceptor (PC71BM) exhibited an efficiency of 7.26%, which is greater than that of CP5 (5.19%) and CP1 (3.11%) and is among the best-performing, cyanopyridone-based oligothiophene donors described to date.

CO2 triggering and controlling orthogonally multiresponsive photochromic systems.

We report a new generic method of reversibly controlling the photochromism of spiropyrans. It was found that the photochromic effect of spiropyrans can be reversibly switched on and off by addition and removal of carbon dioxide (CO(2)) to spiropyran in alcohol solutions containing an amidine (i.e., DBU) that acts as a CO(2) sensitizer. Spiropyrans are not photochromic in the presence of DBU but photochromic when CO(2) is subsequently added to the solution. The CO(2) is readily removed by inert gas bubbling, thus allowing facile activation and deactivation of the photochromic effect. Carbon dioxide, without the presence of the sensitizing amidine, had no effect on photochromism of the spiropyrans. Other photochromic dyes classes such as spirooxazines and chromenes are not affected by this CO(2)/DBU stimulus. As a result, orthogonal activation of mixtures of spirooxazines and spiropyrans was achieved to provide four color states (clear, yellow, green, and blue) by varying the combinations of the stimuli of UV, visible light, CO(2), and CO(2) depleted. This finding now permits the many applications using spiropyrans to be CO(2) responsive.

Targeting of cancer cells using click-functionalized polymer capsules.

Targeted delivery of drugs to specific cells allows a high therapeutic dose to be delivered to the target site with minimal harmful side effects. Combining targeting molecules with nanoengineered drug carriers, such as polymer capsules, micelles and polymersomes, has significant potential to improve the therapeutic delivery and index of a range of drugs. We present a general approach for functionalization of low-fouling, nanoengineered polymer capsules with antibodies using click chemistry. We demonstrate that antibody (Ab)-functionalized capsules specifically bind to colorectal cancer cells even when the target cells constitute less than 0.1% of the total cell population. This precise targeting offers promise for drug delivery applications.

Surface "click" chemistry on brominated plasma polymer thin films.

A brominated plasma polymer (BrPP) thin film was fabricated on a variety of substrate surfaces (silicon wafers, glass, gold, and polymers) via the radio frequency glow discharge of 1-bromopropane. This BrPP thin film was highly adherent and stable and was found to be a useful platform for secondary reactions, leading to surfaces with specific chemical functionalities. Following nucleophilic exchange, an azide-functionalized PP thin film was prepared that was reactive toward two different alkynes via the copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction, a paradigm of "click" chemistry. "Click" microcontact printing (microCP) of a fluorescent alkyne was also successfully carried out, demonstrating the versatility and functionality of this new class of reactive thin film plasma polymer coatings.

Photochromic spirooxazines functionalized with oligomers: investigation of core-oligomer interactions and photomerocyanine isomer interconversion using NMR spectroscopy and DFT.

Photochromic spirooxazines functionalized with poly(ethylene glycol) (PEG) and poly(dimethylsiloxane) (PDMS) oligomers were monitored using NMR spectroscopy at temperatures between 193 and 233 K before and after in situ exposure to UV irradiation. NOESY and ROESY experiments reveal the TTC (trans-s-trans-cis) isomer to be the dominant merocyanine isomer formed on photolysis, with some CTC (cis-s-trans-cis) isomer also present. Significant ROE cross peaks were observed between the "bulk" of the oligomeric units and protons across the entire photochromic core of the molecule, the intensity of these cross peaks suggesting that the interaction of the oligomer side chain and core of the molecule is significantly enhanced by the permanent attachment, especially with the PDMS side chain. The 2D NMR spectra indicate that there is exchange between the TTC and CTC isomers even at 193 K. This isomerization of the parent spirooxazine compounds, lacking the oligomeric side chains, was found to be acid-catalyzed, and DFT calculations support the strong possibility that it is the protonated merocyanine form that undergoes the facile isomerization process. Interconversion of the different merocyanine isomers is suggested to be fast on the NMR time scale under many experimental conditions, precluding the observation of different isomers using NMR spectroscopy at room temperature.

Free radical polymers with tunable and selective bio- and chemical degradability.

A versatile synthetic strategy has been developed which enables the facile incorporation of cleavable functional groups, i.e., esters, thioesters, and disulfides, into the carbon-carbon backbone of vinyl-based polymers. Through the synthesis of novel cyclic monomers, RAFT-mediated radical ring-opening copolymerizations with traditional vinyl monomers such as methyl methacrylate, N,N-dimethylaminoethyl methacrylate, and 2-hydroxyethyl methacrylate lead to the introduction of controlled degradability into these widely used vinyl copolymer systems. An additional benefit of this strategy is the inherent versatility available through the incorporation of cyclic monomers containing diverse functional groups such as esters, thioesters, disulfides, and silyl ether units that allow degradation under basic/acidic, reductive, or enzymatic conditions. By integrating multiple, orthogonal cyclic monomers into linear copolymer backbones, well-defined systems with programmable degradation profiles are obtained which allows for tunable, selective, and stepwise degradation of the vinyl polymer backbones.

Quantum-rod dispersed photopolymers for multi-dimensional photonic applications.

Nanocrystal quantum rods (QRs) have been identified as an important potential key to future photonic devices because of their unique two-photon (2P) excitation, large 2P absorption cross section and polarization sensitivity. 2P excitation in a conventional solid photosensitive medium has driven all-optical devices towards three-dimensional (3D) platform architectures such as 3D photonic crystals, optical circuits and optical memory. The development of a QR-sensitized medium should allow for a polarization-dependent change in refractive index. Such a localized polarization control inside the focus can confine the light not only in 3D but also in additional polarization domain. Here we report on the first 2P absorption excitation of QR-dispersed photopolymers and its application to the fabrication of polarization switched waveguides, multi-dimensional optical patterning and optical memory. This fabrication was achieved by a 2P excited energy transfer process between QRs and azo dyes which facilitated 3D localized polarization sensitivity resulting in the control of light in four dimensions.

Ultra-high molecular weight linear coordination polymers with terpyridine ligands.

Ultra-high molecular weight (UHMW, M n > 1000 kDa) polymeric drift control adjuvants (DCAs) for agricultural spraying are prone to mechanical degradation and rapidly lose performance. To overcome this, we have designed linear coordination polymers (LCPs) composed of 400 kDa telechelic bis-terpyridine end-functionalised polyacrylamide units, which 'self-heal' upon shearing through reformation of coordination bonds. After addition of Fe(ii) to dilute aqueous solutions of the terpyridine telechelics, UHMW LCPs were obtained as demonstrated by UV-vis spectroscopy, MALS GPC and intrinsic viscosity measurements. Importantly, these UHMW LCPs were shown to function as effective DCAs, reducing the formation of fine 'driftable' droplets during spray testing at concentrations as low as 100 ppm. Following mechanically-induced coordination bond-scission, the UHMW LCPs were found to recover up to 90% of their performance compared to un-sheared samples, at a rate dependent on the transition metal ion used to form the complex.

Electrochemically protected copper(I)-catalyzed azide-alkyne cycloaddition.

The copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction has found broad application in myriad fields. For the most demanding applications that require high yields at low substrate concentrations, highly active but air-sensitive copper complexes must be used. We describe here the use of an electrochemical potential to maintain catalysts in the active Cu(I) oxidation state in the presence of air. This simple procedure efficiently achieves excellent yields of CuAAC products from both small-molecule and protein substrates without the use of potentially damaging chemical reducing agents. A new water-soluble carboxylated version of the popular tris(benzyltriazolylmethyl)amine (TBTA) ligand is also described. Cyclic voltammetry revealed reversible or quasi-reversible electrochemical redox behavior of copper complexes of the TBTA derivative (2; E(1/2)=60 mV vs. Ag/AgCl), sulfonated bathophenanthroline (3; E(1/2)=-60 mV), and sulfonated tris(benzimidazoylmethyl)amine (4; E(1/2) approximately -70 mV), and showed catalytic turnover to be rapid relative to the voltammetry time scale. Under the influence of a -200 mV potential that was established by using a reticulated vitreous carbon working electrode, CuSO4 and 3 formed a superior catalyst. Electrochemically protected bioconjugations in air were performed by using bacteriophage Qbeta that was derivatized with azide moieties at surface lysine residues. Complete derivatization of more than 600 reactive sites per particle was demonstrated within 12 h of electrolysis with substoichiometric quantities of Cu3.

An efficient non-fullerene acceptor based on central and peripheral naphthalene diimides.

Through the coupling of central and terminal naphthalene diimide functionalities, a unique non-fullerene electron acceptor, coded as N10, was designed, synthesized, characterized and applied in solution-processable bulk-heterojunction devices. The target N10 displayed good solubility, excellent thermal stability and energy levels complementing those of the conventional donor polymer poly(3-hexyl thiophene) (P3HT). An excellent power conversion efficiency of 7.65% was obtained in simple BHJ devices (P3HT : N10 1 : 1.2), which is the highest observed so far for NDI core-based non-fullerene acceptors.

Adhesive Prebiotic Chemistry Inspired Coatings for Bone Contacting Applications.

New and improved bone-contacting medical devices are required to provide excellent bioactivity at the biointerface. Here, we have used coatings based on prebiotic chemistry inspired polymerization of aminomalonitrile (AMN) in combination with comonomers 3,4-di- and 3,4,5-trihydroxybenzaldehyde (DHBA and THBA). The comonomers were incorporated into the AMN coatings to enhance polymerization kinetics, adhesive properties, metal binding efficacy, and human mesenchymal stem cell (hMSC) response. Incorporation of DHBA and THBA as separate comonomers enhanced the polymerization kinetics compared to that of AMN polymerization alone, with 30 mol % THBA (30T) resulting in a 6-fold increase in thickness over 24 h. Furthermore, the adhesion of AMN coatings to silicon was enhanced when copolymerized with the HBA monomers, where the interfacial adhesion of the 30T coating was increased 20-fold. The ability of the coatings to incorporate zinc ions was investigated, and X-ray photoelectron spectroscopy (XPS) analysis demonstrated that incorporating 30T increased the binding efficiency 4-fold compared to that of AMN alone. The attachment, proliferation, and morphology of human mesenchymal stem cells (hMSC) on these coatings was investigated and reported. Finally, the utility of the coatings as osteogenic support matrices via the induced osteogenic differentiation of hMSCs is reported. The AMN and 30T coatings resulted in the greatest efficiency of osteogenic differentiation, as measured by intracellular ALP activity and mineralization. Incorporation of zinc had a stimulatory effect on hMSC proliferation with 30T coatings, while enhanced mineralization was observed with the zinc functionalized AMN and 30T coatings. This study highlights the potential of prebiotic chemistry inspired coatings in biomedical applications.

Non-fullerene acceptors based on central naphthalene diimide flanked by rhodanine or 1,3-indanedione.

Through the combination of central naphthalene diimide and terminal rhodanine or 1,3-indanedione functionalities, two new non-fullerene electron acceptors, coded as N3 and N4, were designed, synthesized and characterized. Both of the materials exhibited good solubility, thermal stability, and displayed energy levels matching those of the conventional and routinely used donor polymer poly(3-hexyl thiophene) (P3HT). A high power conversion efficiency of 4.76% was obtained in simple, solution-processable bulk-heterojunction devices (P3HT : N3 1 : 1.2) which is the best result for central NDI-based small molecular non-fullerene acceptors.