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Aromatic belts, ultrashort carbon nanotubes, and related structures, are emerging molecular entities in the fields of organic electronics and supramolecular chemistry owing to their structural rigidity, fully fused π-conjugation, and well-defined cavity. Synthesis of aromatic belts with embedded thiophene structures, which manifest significant optoelectronic and conductive properties, has not yet been achieved. Herein, we report the synthesis of thiophene-fused aromatic belts (thiophene belts) via one-step sulfur cross-linking reaction of partially fluorinated cycloparaphenylenes. Their structural features, including unidirectional columnar stacking with high dipole moment in crystals, two-dimensional layer assembly on metal surfaces, and photophysical properties, such as long-lifetime phosphorescence, are uncovered. These distinctive features of the thiophene belts should inspire a range of applications such as optoelectronic devices and polar materials. Synthesis of aromatic belts with embedded thiophene structures, which manifest significant optoelectronic and conductive properties, has not yet been achieved. Herein, the authors report the synthesis of thiophene-fused aromatic belts via one-step sulfur cross-linking reaction of partially fluorinated cycloparaphenylenes. [ABSTRACT FROM AUTHOR]

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Azoarene isomerization lies at the heart of numerous applications, from catalysis or energy storage to photopharmacology. While efficient switching between their E and Z isomers predominantly relies on UV light, a recent study by Klajn and co‐workers introduced visible light sensitization of E azoarenes and their subsequent isomerization as a tool coined disequilibration by sensitization under confinement (DESC) to obtain high yields of the Z isomer. This host–guest approach is, however, still constrained to minimally substituted azoarenes with limited applicability in advanced molecular systems. Herein, we expand DESC for the assembly of surfactants at the air–water interface. Leveraging our expertise with photoswitchable amphiphiles, we induce substantial alterations of the water surface tension through reversible arylazopyrazole isomerization. After studying the binding of charged surfactants to the host, we find that the surface activity differences upon visible light switching for both isomers are comparable to those obtained by UV light excitation. The method is demonstrated on a large concentration range and can be activated using green or red light, depending on the sensitizer chosen. The straightforward implementation of photoswitch sensitization in a complex molecular network showcases how DESC enables the improvement of existing systems and the development of novel applications driven by visible light. [ABSTRACT FROM AUTHOR]

This study investigates unexpected competitive host–guest interactions of β‐cyclodextrin (β‐CD), which can occur with polymers in aqueous solution, using the examples of the two polymers poly(oligo(ethylene glycol) methyl ether methacrylate) and poly(glycerol mono methacrylate). Systematic structural modifications of the polymer provide insight into the host–guest interaction with β‐CD and the competition between side chains and end groups such as hydrophobic end groups remaining from reversible addition fragmentation chain transfer polymerization or intentionally implemented molecular recognition units such as arylazopyrazole photoswitches. [ABSTRACT FROM AUTHOR]

Copyright of Angewandte Chemie is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Inspired by nature, self‐regulation can be introduced in synthetic hydrogels by incorporating chemo‐mechanical signals or coupled chemical reactions to maintain or adapt the material's physico‐chemical properties when exposed to external triggers. In this work, we present redox and light dual stimuli responsive hydrogels capable of rapidly adapting the polymer crosslinking network while maintaining hydrogel stability. Upon irradiation with UV light, polymer hydrogels containing redox responsive disulfide crosslinks and light responsive ortho‐nitrobenzyl moieties show a release of payload accompanied by adaptation of the hydrogel network towards higher stiffness due to in situ crosslinking by S‐nitrosylation. Whereas the hydrogel design allows the network to either become softer in presence of reducing agent glutathione or stiffer upon UV irradiation, simultaneous application of both stimuli induces network self‐regulation resulting in a pulsatile form of payload release from the hydrogel. Finally, adaptive stiffness was used to make tunable hydrogels as substrates for different cell lines. [ABSTRACT FROM AUTHOR]

Arylazopyrazoles (AAPs) are an important class of molecular photoswitches with high photostationary states (PSS) and long thermal lifetimes. The ultrafast photoisomerization of four water-soluble arylazopyrazoles, all of them featuring an ortho-dimethylated pyrazole ring, is studied by narrowband femtosecond transient absorption spectroscopy and ab initio molecular dynamics simulations. Upon S1 (nπ*) photoexcitation of the planar E-isomers (E-AAPs), excited-state bi-exponential decays with time constants τ1 in the 220–440 fs range and τ2 in the 1.4–1.8 ps range are observed, comparable to those reported for azobenzene (AB). This is indicative of the same photoisomerization mechanism as has been reported for ABs. In contrast to the planar E-AAPs, a twisted E-AAP with two methyl groups in ortho-position of the phenyl ring displays faster initial photoswitching with τ1 = 170 ± 10 fs and τ2 = 1.6 ± 0.1 ps. Our static DFT calculations and ab initio molecular dynamics simulations of E-AAPs on the S0 and S1 potential energy surfaces suggest that twisted E-isomer azo photoswitches exhibit faster initial photoisomerization dynamics out of the Franck–Condon region due to a weaker π-coordination of the central CNNC unit to the aromatic ligands. [ABSTRACT FROM AUTHOR]

The design of responsive liquid crystals enables a diversity of technological applications. Especially photochromic liquid crystals gained a lot of interest in recent years due to the excellent spatiotemporal control of their phase transitions. In this work we present calamitic light responsive mesogens based on a library of arylazopyrazole photoswitches. These compounds show liquid‐crystalline behavior as shown by differential scanning calorimetry, grazing incidence X‐ray diffraction and polarized optical microscopy. UV‐vis spectroscopy and NMR analysis confirmed the excellent photophysical properties in solution and thin film. Additionally, polarized optical microscopy studies of the pristine compounds show reversible phase transition upon irradiation with light. Moreover, as a dopant in the commercially available liquid crystal 4‐cyano‐4′‐pentylbiphenyl (5CB), the temperature range was reduced to ambient temperatures while preserving the photophysical properties. Remarkably, this co‐assembled system shows reversible liquid‐crystalline to isotropic phase transition upon irradiation with light of different wavelengths. The spatiotemporal control of the phase transition of the liquid crystals offers opportunities in the development of optical devices. [ABSTRACT FROM AUTHOR]

Optical neural networks (ONNs) hold great potential for faster and more energy‐efficient information processing in coherent photonic circuits. To realize ONNs, linear combinations and nonlinear activation functions have to be implemented in an optical fashion. Optical nonlinearities are, however, still difficult to achieve, and existing designs are usually too inflexible to offer different activation functions as used in artificial neural networks. Herein, the nonlinear properties of the large and highly adaptive class of photoswitchable chemical compounds is made accessible as activation functions in ONNs by employing photo‐induced isomerization in azobenzenes to steer activation behavior through nonlinear modulation of an information‐carrying optical signal. The strength of the nonlinearity can be controlled by the chemical concentration while a physically motivated model describes the experimental data for systematically varied photoswitching parameters, resulting in a tunable yet interpretable activation function. Employing such an activation function in a neural network then allows to gauge its strength and perform established classification tasks. The work combines recent advances with photoswitchable chemical compounds and optical neural networks to enable control over the design of nonlinear activation functions, thus opening exciting perspectives for explaining the emergence of intelligent behavior in neural networks. [ABSTRACT FROM AUTHOR]

Copyright of Angewandte Chemie is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)