Herein, we report the simple and direct cationic ring opening polymerization (CROP) of a nitroxide bearing 2-oxazoline monomer to yield redox-active poly[1-oxyl-2,2,6,6-tetramethylpiperidin-4-(2-oxazoline)] (PTOx) with no requirement for protecting group chemistries. The spin and redox activity of the polymer are quantitatively retained as confirmed by cyclic voltammetry and electron paramagnetic resonance spectroscopy, while yielding a comparable oxidation potential to that of PTMA in preliminary electrochemical characterization.
View Article and Find Full Text PDFNitroxide groups covalently grafted to carbon fibers are used as anchoring sites for TEMPO-terminated polymers (poly-n-butylacrylate and polystyrene) in a "graft to" surface modification strategy. All surface-modified fibers are evaluated for their physical properties, showing that several treatments have enhanced the tensile strength and Young's modulus compared to the control fibers. Up to an 18% increase in tensile strength and 12% in Young's modulus are observed.
View Article and Find Full Text PDFThermally activated delayed fluorescent (TADF) emitters have become the leading emissive materials for highly efficient organic light-emitting diodes (OLEDs). The deposition of these materials in scalable and cost-effective ways is paramount when looking toward the future of OLED applications. Herein, a simple OLED with fully solution-processed organic layers is introduced, where the TADF emissive layer is ink-jet printed.
View Article and Find Full Text PDFA photoresist-based on a light-stabilized dynamic material driven by an out-of-equilibrium photo-Diels-Alder reaction of triazolinediones with naphthalenes-whose ability to intrinsically degrade postprinting can be tuned by a simple adjustment of laser intensity during 3D laser lithography is introduced. The resist's ability to form stable networks under green light irradiation that degrade in the dark is transformed into a tunable degradable 3D printing material platform. In-depth characterization of the printed microstructures via atomic force microscopy before and during degradation reveals the high dependency of the final structures' properties on the writing parameters.
View Article and Find Full Text PDFCoordination cages with well-defined cavities show great promise in the field of catalysis on account of their unique combination of molecular confinement effects and transition-metal redox chemistry. Here, three coordination cages are reduced from their native 16 oxidation state to the 2 state in the gas phase without observable structural degradation. Using this method, the reaction rate constants for each reduction step were determined, with no noticeable differences arising following either the incorporation of a C -fullerene guest or alteration of the cage chemical structure.
View Article and Find Full Text PDFThe radical reactions of dimethylsulfoxide (DMSO) and tetrahydrothiophene-1-oxide (THTO) with reactive oxygen species (ROS) in the presence of a nitroxide radical scavenger have been evaluated both synthetically and in analytical practice. Fenton-mediated generation of oxygen-centred radicals produced several unusual products that reflect the fragmentation and ring-opening radical mechanisms of DMSO and THTO respectively. Addition of pollution-derived ROS to DMSO/THTO nitroxide solutions produced LC-MS detectable amounts of the same products isolated from the larger-scaled Fenton reactions.
View Article and Find Full Text PDFWe introduce a photochemical bond forming system, where two colours of light are required to trigger covalent bond formation. Specifically, we exploit a visible light cis/trans isomerization of chlorinated azobenzene, which can only undergo reaction with a photochemically generated ketene in its cis state. Detailed photophysical mapping of the reaction efficiencies at a wide range of monochromatic wavelengths revealed the optimum irradiation conditions.
View Article and Find Full Text PDFHerein, we demonstrate that the photochemical cleavage of linear polymers containing a midchain photocleavable moiety strongly depends on the chain length. Based on an -nitrobenzyl (NB) difunctional reversible addition-fragmentation chain-transfer agent, well-defined poly(methyl acrylate)s ( = 1.59-67.
View Article and Find Full Text PDFWe exploit two reactive chromophores to establish sequence-independent photochemical activation, employing -methyl benzaldehyde (MBA) and ,-(dimethylamino)pyrene aryl tetrazole (APAT) with -(2-hydroxy)ethyl maleimide (HEM), without any additives. Critically, the order of the irradiation sequence is irrelevant, as the shorter wavelength does not activate the higher wavelength activated species. Therefore, full sequence-independent λ-orthogonality is achieved through differences in both the reaction quantum yields ( and ) and wavelength-dependent reactivity profiles of the employed chromophores.
View Article and Find Full Text PDFHerein, we introduce the wavelength-orthogonal crosslinking of hydrogel networks using two red-shifted chromophores, i.e. acrylpyerene (AP, λ =410-490 nm) and styrylpyrido[2,3-b]pyrazine (SPP, λ =400-550 nm), able to undergo [2+2] photocycloaddition in the visible-light regime.
View Article and Find Full Text PDFPredicting wavelength-dependent photochemical reactivity is challenging. Herein, we revive the well-established tool of measuring action spectra and adapt the technique to map wavelength-resolved covalent bond formation and cleavage in what we term "photochemical action plots". Underpinned by tunable lasers, which allow excitation of molecules with near-perfect wavelength precision, the photoinduced reactivity of several reaction classes have been mapped in detail.
View Article and Find Full Text PDFElectrospray ionization-mass spectrometry (ESI-MS) of low-charging synthetic polymers typically produces mass spectra exhibiting a bias toward the low-mass region of the polymer mass distribution. To examine the origin(s) of this ionization bias, narrow dispersity polystyrene polymers ( < 1.10) were prepared with ionizable carboxylic acid end-groups at one or both chain termini.
View Article and Find Full Text PDFThe nitrile imine-mediated tetrazole-ene cycloaddition is a widely used class of photoligation. Optimizing the reaction outcome requires detailed knowledge of the tetrazole photoactivation profile, which can only partially be ascertained from absorption spectroscopy, or otherwise involves laborious reaction monitoring in solution. Photodissociation action spectroscopy (PDAS) combines the advantages of optical spectroscopy and mass spectrometry in that only absorption events resulting in a mass change are recorded, thus revealing the desired wavelength dependence of product formation.
View Article and Find Full Text PDFWe introduce a red-shifted tetrazole that is able to undergo efficient nitrile imine-mediated tetrazole-ene cycloaddition (NITEC) under blue and green light irradiation. We provide a detailed wavelength-dependent reactivity map, and employ a number of LEDs for high-conversion small molecule and polymer end-group modification.
View Article and Find Full Text PDFPredicting the conversion and selectivity of a photochemical experiment is a conceptually different challenge compared to thermally induced reactivity. Photochemical transformations do not currently have the same level of generalized analytical treatment due to the nature of light interaction with a photoreactive substrate. Herein, we bridge this critical gap by introducing a framework for the quantitative prediction of the time-dependent progress of photoreactions via common LEDs.
View Article and Find Full Text PDFWaste production associated with the use of non-degradable materials in packaging is a growing cause of environmental concern, with the polyurethane (PU) class being notorious for their lack of degradability. Herein, we incorporate photosensitive ortho-Nitrobenzyl units into PUs to achieve controllable photodegradability. We performed their photolysis in solution and thin films which can inform the design of degradable adhesives.
View Article and Find Full Text PDFHerein, we pioneer a wavelength-gated synthesis route to phenalene diimides. Consecutive Diels-Alder reactions of methylisophthalaldehydes and maleimides afford hexahydro-phenalene-1,6-diol diimides via 5-formyl-hexahydro-benzo[f]isoindoles as the intermediate. Both photoreactions are efficient (82-99 % yield) and exhibit excellent diastereoselectivity (62-98 % d.
View Article and Find Full Text PDFWe report a photochemical reaction system which requires activation by two colors of light. Specifically, a dual wavelength gated system is established by fusing the visible light mediated deprotection of a dithioacetal with the UV light activated Diels-Alder reaction of an o-methylbenzaldehyde with N-ethylmaleimide. Critically, both light sources are required to achieve the Diels-Alder adduct, irradiation with visible or UV light alone does not lead to the target product.
View Article and Find Full Text PDFHigh-performance polymers such as polymethacrylimides have outstanding properties, for example, a unique strength-to-weight ratio and a high thermal stability, usually coupled to a high glass transition temperature. However, the requirement of high processing temperatures caused by these high glass-transition temperatures is often not desired for melt extrusion processes. Herein, a novel and straightforward imidization process of poly(methacrylic anhydrides) is presented with different ratios of ammonia and N-isopropylamine that is induced by thermal treatment.
View Article and Find Full Text PDFWe report a photochemical flow setup that exploits λ-orthogonal reactions using two different colours of light (λ =350 nm and λ =410 nm) in sequential on-line irradiation steps. Critically, both photochemically reactive units (a visible-light reactive chalcone and a UV-activated photo-caged diene) are present in the reaction mixture. We demonstrate the power of two colour photoflow by the wavelength-selective end group modification of photo-caged polymer end groups and the subsequent polymer ring closure driven by a [2+2] cycloaddition.
View Article and Find Full Text PDFWe introduce a highly efficient photoligation system, affording a pro-fluorescent Diels-Alder product that, on demand, converts into an intensively fluorescent naphthalene via E1 elimination in the presence of catalytic amounts of acid. The Diels-Alder reaction of the photocaged diene (-quinodimethane ether or thioether) with electron-deficient alkynes is induced by UV or visible light. In contrast to previously reported ligation techniques directly leading to fluorescent products, the fluorescence is turned on after the photoligation.
View Article and Find Full Text PDFAn alternative synthetic route towards the widely employed electroactive poly(TEMPO methacrylate) (PTMA) via a thermally robust methoxyamine-protecting group is demonstrated herein. Protection of the radical moiety of hydroxy-TEMPO with a methyl functionality and subsequent esterification with methacrylic anhydride allows the high-yielding formation of the novel monomer methyl-TEMPO methacrylate (MTMA). The polymerization of MTMA to poly(MTMA) (PMTMA) is investigated via free radical polymerization and reversible addition-fragmentation chain-transfer polymerization (RAFT), a reversible-deactivation radical polymerization technique.
View Article and Find Full Text PDFThere remain several key challenges to existing therapeutic systems for cancer therapy, such as quantitatively determining the true, tissue-specific drug release profile , as well as reducing side-effects for an increased standard of care. Hence, it is crucial to engineer new materials that allow for a better understanding of the pharmacokinetic/pharmacodynamic behaviours of therapeutics. We have expanded on recent "click-to-release" bioorthogonal pro-drug activation of antibody-drug conjugates (ADCs) to develop a modular and controlled theranostic system for quantitatively assessing site-specific drug activation and deposition from a nanocarrier molecule, by employing defined chemistries.
View Article and Find Full Text PDFDonor-acceptor Stenhouse adducts (DASA) are popular photoswitches capable of toggling between two isomers depending on the light and temperature of the system. The cyclized polar form is accessed by visible-light irradiation, whereas the linear nonpolar form is recovered in the dark. Upon the formation of the cyclized form, the DASA contains a double bond featuring a β-carbon prone to nucleophilic attack.
View Article and Find Full Text PDFWe introduce the hybrid copolymerization of two disparate monomer classes (vinyl monomers and ring-strained cyclic olefins) via living photopolymerization. The living character of the polymerization technique (metal-free photo-ROMP) is demonstrated by consecutive chain-extensions. Further, we propose a mechanism for the copolymerization and analyze the copolymer structure in detail by high-resolution mass spectrometry.
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