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Enzyme function relies on the placement of chemistry defined by solvent and self-associative hydrogen bonding displayed by the protein backbone. Amyloids, long-range multi-peptide and -protein materials, can mimic enzyme functions while having a high proportion of stable self-associative backbone hydrogen bonds. Though catalytic amyloid structures have exhibited a degree of temperature and solvent stability, defining their full extremophilic properties and the molecular basis for such extreme activity has yet to be realized. Here we demonstrate that, like thermophilic enzymes, catalytic amyloid activity persists across high temperatures with an optimum activity at 81 °C where they are 30-fold more active than at room temperature. Unlike thermophilic enzymes, catalytic amyloids retain both activity and structure well above 100 °C as well as in the presence of co-solvents. Changes in backbone vibrational states are resolved

The solvent is an important, yet often forgotten part of a reaction mechanism. Many photochemical polymerizations are carried out using dimethyl sulfoxide (DMSO) as a way to promote the solubility of both the reactants and products, but its reactivity is rarely considered when initiation mechanisms are proposed. Herein, the oxidation of DMSO by an excited-state quinone is used to form initiating radicals resulting in the polymerization of methacrylate monomers, and the polymerization can be controlled with the addition of a chain transfer agent. This process leads to the formation of polymers with narrow molecular weight distribution, and the polymerization is able to be carried out in the presence of oxygen. A visible light absorbing substituted anthraquinone is synthesized, and nanosecond transient absorption spectroscopy is used to monitor the intermediates involved in the initiation mechanism. Photoproduct analysis indicates formation of methyl radicals as a result of DMSO oxidation. Furthermore, we show that the solvent outcompetes the chain transfer agent for interacting with the excited-state anthraquinone. These observations have a broad impact on photoinduced polymerizations performed in DMSO as many photocatalysts are strong oxidants in the excited state and are capable of reacting with the solvent. Therefore, the role of the solvent needs to be more carefully considered when proposing mechanisms for photoinduced polymerizations in DMSO.

Electrospinning serves as a versatile means of understanding the effects of strong cylindrical confinement on encapsulated liquid crystals (LCs) and is a promising technique for developing functional fabrics and surfaces. In this work, we use electrospinning to create core-sheath nanofibers composed of a polyvinylpyrrolidone (PVP) sheath doped with a photochromic, azobenzene-based surfactant, and a low-molecular weight nematic liquid crystal core. The incorporation of an azobenzene surfactant into the polymer sheath allows for photochemical control over the nematic to isotropic transition temperature of the LC core resulting in ultra violet (UV) irradiation-induced depression of the phase transition temperature. Owing to the photochromic nature of the surfactant, the photoinduced decrease in the transition temperature is reversed with visible light irradiation with no notable fatigue resistance. At high surfactant loading rates, the temperature of the photoinduced phase transition is reduced to below room temperature allowing for the birefringence of the nanofibers “on” and “off” with irradiation and requires no external heating. Based on these oberservations, we propose photoisomerization of the azobenzene-based surfactant at the PVP/LC interface leads to surface induced disorder of the LC core changing the orientation from planar axial to random with UV irradiation and reversing that change with visible irradiation. This is further substantiated by examinig the LC alignment within nanofibers by imaging the fibers with the addition of a quarter-wave retardation plate. This method adds to the growing set of tools available for the control of the phase behavior of encapsulated liquid crystals and expands the functionality of electrospun materials.

The encapsulation of liquid crystals (LCs) within semiflexible, nanoscale media has potential use for developing flexible photodisplays, electronic devices, and sensors. Here, coaxial electrospinni...

The rise in popularity of photochemically initiated reversible addition-fragmentation chain transfer (RAFT) polymerization (photoRAFT) along with the broad spectrum of proposed, and possible, initiation mechanisms result in the need for careful characterization of the photophysical properties of some common RAFT agents. Direct irradiation of the RAFT agent as a means to generate radicals, also known as the photoiniferter mechanism, is one commonly proposed mechanism. The current study shows that dithioesters and trithiocarbonates have the lowest singlet and triplet excited-state energy levels that are close to, or lower than, the C-S bond dissociation energies. Excitation of these agents into their S

Summary We introduce techniques for probing the dynamics of triplet states. We employ these tools, along with conventional techniques, to develop a detailed understanding of a complex chemical system: a negative-tone, radical photoresist for multiphoton absorption polymerization in which isopropylthioxanthone (ITX) is the photoinitiator. This work reveals that the same color of light used for the 2-photon excitation of ITX, leading to population of the triplet manifold through intersystem crossing, also depletes this triplet population via linear absorption followed by reverse intersystem crossing (RISC). Using spectroscopic tools and kinetic modeling, we identify the reactive triplet state and a non-reactive reservoir triplet state. We present compelling evidence that the deactivation channel involves RISC from an excited triplet state to a highly vibrationally excited level of the electronic ground state. The work described here offers the enticing possibility of understanding, and ultimately controlling, the photochemistry and photophysics of a broad range of triplet processes., Graphical abstract, Highlights • Development of triplet-state dynamics probes to complement existing techniques • A detailed, mechanistic understanding of the photophysics of isopropylthioxanthone • Demonstration of self-deactivation during multiphoton excitation • Higher apparent nonlinearities can be detrimental to resolution, Chemistry; Theoretical photophysics; Nonlinear optics

Confinement of liquid crystals (LCs) in polymeric fibers offers a promising strategy to control liquid crystal response to external stimuli. Here, the confinement of 4-cyano-4'-pentylbiphenyl (5CB), a nematic liquid crystal, within the core of coaxially electrospun fibers composed of poly(vinylpyrrolidone) (PVP) containing different surfactants is discussed. The effects of surfactant type, surfactant concentration, and core flow rate (confinement) on the LC behavior were demonstrated using polarized optical microscopy, scanning electron microscopy, differential scanning calorimetry, Raman, and dielectric spectroscopy. Introduction of surfactant dopants of varying hydrophilic and hydrophobic components into the sheath altered the interfacial interaction between the PVP sheath and the 5CB core of the fibers. Significant effects on the LC nematic to isotropic phase transition were attributed to changes in surface anchoring between the sheath and core. Confinement of nematic LCs in surfactant doped polymeric fibers demonstrates a facile method for tuning LC phase behavior.

Multicolor photolithography using visible light holds the promise of achieving wafer-scale patterning at pitches on the 10 nm scale. Although substantial progress has been made on multicolor techniques, a number of challenges remain to be met before the ultimate resolution of these methods can be reached. These challenges include the development of improved materials, creation of high-quality thin films, transitioning to exposure schemes that rely completely on linear absorption, scaling up to large-area patterning, and developing methods for effective pattern transfer. This paper discusses the state of the art in multicolor photolithography, presents some of the most recent advances in this field, and examines the prospects moving forward.

A photoreleasable protecting group activated by sequential absorption of two visible photons is designed, synthesized, and tested. Specifically, an anthraquinone-based chromophore is covalently attached to an N-alkylpicolinium ester. Photolysis of this linked system results in the clean release of a corresponding carboxylic acid. Through product analysis, laser flash photolysis, and steady-state UV–vis spectroscopy, it is demonstrated that carboxylate ion release is affected by sequential absorption of two photons. The initial photochemical step results in reduction of an anthraquinone chromophore to the corresponding hydroquinone. The latter either reacts with O2 to regenerate the starting material, or absorption of a second photon causes an electron transfer to the picolinium group triggering C–O bond scission and release of the carboxylate.

Product analysis along with fluorescence quenching and laser flash photolysis experiments demonstrate that it is possible to effect a net photochemical reduction of CO2 through photolysis of an excited state donor in the presence of 1,3-dimethylimidazolium-2-carboxylate.

Photolysis of anthraquinone or flavin photosensitizers in the presence of calcium EDTA complexes results in decomposition of the EDTA complex, releasing free Ca2+. In the case of the flavin sensitizers, it is shown that millimolar concentrations of Ca2+ can be released using visible light (>440 nm) and with quantum yields as high as 0.31. The utility of this system is further demonstrated by in situ photogelation of an alginate solution.

The clean and efficient photorelease of primary and secondary alcohols is reported from the deprotection of a new photoremovable protecting group, the 9-phenyltritylone (PTO) group. Deprotection is initiated by 350 nm excitation of the PTO chromophore in the presence of triethylamine or using 447 nm light in the presence of a visible light absorbing photocatalyst and triethylamine. Laser flash photolysis results are reported in support of a proposed deprotection mechanism for the release of alcohols on a ca. 20 μs time scale.