New materials are advancing the field of soft robotics. Composite films of magnetic iron microparticles dispersed in a shape memory polymer matrix are demonstrated for reconfigurable, remotely ...actuated soft robots. The composite films simultaneously respond to magnetic fields and light. Temporary shapes obtained through combined magnetic actuation and photothermal heating can be locked by switching off the light and magnetic field. Subsequent illumination in the absence of the magnetic field drives recovery of the permanent shape. In cantilevers and flowers, multiple cycles of locking and unlocking are demonstrated. Scrolls show that the permanent shape of the film can be programmed, and they can be frozen in intermediate configurations. Bistable snappers can be magnetically and optically actuated, as well as biased, by controlling the permanent shape. Grabbers can pick up and release objects repeatedly. Simulations of combined photothermal heating and magnetic actuation are useful for guiding the design of new devices.
The study of excited-state energy diffusion has had an important impact in the development and optimization of organic electronics. For instance, optimizing excited-state energy migration in the ...photoactive layer in an organic solar cell device has been shown to yield efficient solar energy conversion. Despite the crucial role that energy migration plays in molecular electronic device physics, there is still a great deal to be explored to establish how molecular orientation impacts energy diffusion mechanisms. In this work, we have synthesized a new library of solution-processable, Zn (alkoxycarbonyl)phenylporphyrins containing butyl (ZnTCB
PP), hexyl (ZnTCH
PP), 2-ethylhexyl (ZnTCEH
PP), and octyl (ZnTCO
PP) alkoxycarbonyl groups. We establish that, by varying the length of the peripheral alkyl chains on the metalloporphyrin macrocycle, preferential orientation and molecular self-assembly is observed in solution-processed thin films. The resultant arrangement of molecules consequently affects the electronic and photophysical characteristics of the metalloporphyrin thin films. The various molecular arrangements in the porphyrin thin films and their resultant impact were determined using UV-Vis absorption spectroscopy, steady-state and time-resolved fluorescence emission lifetimes, and X-ray diffraction in thin films. The films were doped with C
quencher molecules and the change in fluorescence was measured to derive a relative quenching efficiency. Using emission decay, relative quenching efficiency, and dopant volume fraction as input, insights on exciton diffusion coefficient and exciton diffusion lengths were obtained from a Monte Carlo simulation. The octyl derivative (ZnTCO
PP) showed the strongest relative fluorescence quenching and, therefore, the highest exciton diffusion coefficient (5.29 × 10
cm
s
) and longest exciton diffusion length (~81 nm). The octyl derivative also showed the strongest out-of-plane stacking among the metalloporphyrins studied. This work demonstrates how molecular self-assembly can be used to modulate and direct exciton diffusion in solution-processable metalloporphyrin thin films engineered for optoelectronic and photonic applications.
Stimuli‐responsive 3radialene radical anions dimerize reversibly in a controlled manner. An unprecedented tristate switching mechanism can be achieved by changing the solvent environment, ...temperature, or salinity of the solution. This allows the radical to be toggled between the free radical, a π‐dimer, and a σ‐dimer, which exhibit dramatically different optical, magnetic, and redox properties. The addition of salt to the radialene catholyte solution in an aqueous redox flow battery (RFB) converts the σ‐dimer to the π‐dimer and increases the electrochemical reversibility and stability of the charged species, which are advantageous for galvanostatic charge–discharge studies at neutral pH. More information can be found in the Research Article by Arthur H. Winter, C. Bejger, and co‐workers (DOI: 10.1002/chem.202302829). Illustration by Frank A. Martinez.
The design of metal–organic frameworks (MOFs) that incorporate more than one metal cluster constituent is a challenging task. Conventional one‐pot reaction protocols require judicious selection of ...ligand and metal ion precursors, yet remain unpredictable. Stable, preformed nanoclusters, with ligand shells that can undergo additional coordination‐driven reactions, provide a platform for assembling multi‐cluster solids with precision. Herein, a discrete Co6S8(PTA)6 (PTA=1,3,5‐triaza‐7‐phosphaadamantane) superatomic‐metalloligand is assembled into a three‐dimensional (3D) coordination polymer comprising Cu4I4 secondary building units (SBUs). The resulting heterobimetallic framework (1) contains two distinct cluster constituents and bifunctional PTA linkers. Solid‐state diffuse reflectance studies reveal that 1 is an optical semiconductor with a band‐gap of 1.59 eV. Framework‐modified electrodes exhibit reversible redox behavior in the solid state arising from the Co6S8 superatoms, which remain intact during framework synthesis.
Superatom MOF: A heterobimetallic MOF containing two‐distinct cluster units was prepared using a hierarchical approach. The framework contains Co6S8 and Cu4I4 entities and exhibits reversible redox activity in the solid state.
Here, we show for the first time that main-chain organometallic polymers (MCOPs) can be prepared from Janus N-heterocyclic carbene (NHC) linkers and polynuclear cluster nodes. The crosslinked ...framework Co4S4-MCOP is synthesized via ligand displacement reactions and undergoes reversible electron transfer in the solid state. Discrete molecular cluster species can be excised from the framework by digesting the solid in solutions of excess monocarbene. Finally, we demonstrate a synthetic route to monodisperse framework particles via coordination modulation.
The hexacyano3radialene radical anion (1) is an attractive catholyte material for use in redox flow battery (RFB) applications. The substitution of cyano groups with ester moieties enhances ...solubility while maintaining redox reversibility and favorable redox potentials. Here we show that these ester‐functionalized, hexasubstituted 3radialene radical anions dimerize reversibly in water. The dimerization mode is dependent on the substitution pattern and can be switched in solution. Stimuli‐responsive behavior is achieved by exploiting an unprecedented tristate switching mechanism, wherein the radical can be toggled between the free radical, a π‐dimer, and a σ‐dimer‐each with dramatically different optical, magnetic, and redox properties‐by changing the solvent environment, temperature, or salinity. The symmetric, triester‐tricyano3radialene (3) forms a solvent‐responsive, σ‐dimer in water that converts to the radical anion with the addition of organic solvents or to a π‐dimer in brine solutions. Diester‐tetracyano3radialene (2) exists primarily as a π‐dimer in aqueous solutions and a radical anion in organic solvents. The dimerization behavior of both 2 and 3 is temperature dependent in methanol solutions. Dimerization equilibrium has a direct impact on catholyte stability during galvanostatic charge–discharge cycling in static H‐cells. Specifically, conditions that favor the free radical anion or π‐dimer exhibit significantly enhanced cycling profiles.
Ester‐substituted 3radialene radical anions dimerize in solutions of water. The dimerization mode is structure specific and can be controlled by using heat, solvent, and salt. These results provide guidance for increasing the capacity of aqueous redox flow batteries containing radialene catholytes. A buildup of σ‐dimer prevents stable charge–discharge cycling. The formation of π‐dimers through the addition of salt increases the stability of the charged species.
Here, we show for the first time that main-chain organometallic polymers (MCOPs) can be prepared from Janus N-heterocyclic carbene (NHC) linkers and polynuclear cluster nodes. The crosslinked ...framework Co
S
-MCOP is synthesized
ligand displacement reactions and undergoes reversible electron transfer in the solid state. Discrete molecular cluster species can be excised from the framework by digesting the solid in solutions of excess monocarbene. Finally, we demonstrate a synthetic route to monodisperse framework particles
coordination modulation.
A scarlet fever outbreak occurred in Hong Kong in 2011. The majority of cases resulted in the isolation of Streptococcus pyogenes emm12 with multiple antibiotic resistances. Phylogenetic analysis of ...22 emm12 scarlet fever outbreak isolates, 7 temporally and geographically matched emm12 non-scarlet fever isolates, and 18 emm12 strains isolated during 2005-2010 indicated the outbreak was multiclonal. Genome sequencing of 2 nonclonal scarlet fever isolates (HKU16 and HKU30), coupled with diagnostic polymerase chain reaction assays, identified 2 mobile genetic elements distributed across the major lineages: a 64.9-kb integrative and conjugative element encoding tetracycline and macrolide resistance and a 46.4-kb prophage encoding superantigens SSA and SpeC and the DNase Spd1. Phenotypic comparison of HKU16 and HKU30 with the S. pyogenes M1T1 strain 5448 revealed that HKU16 displays increased adherence to HEp-2 human epithelial cells, whereas HKU16, HKU30, and 5448 exhibit equivalent resistance to neutrophils and virulence in a humanized plasminogen murine model. However, in contrast to M1T1, the virulence of HKU16 and HKU30 was not associated with covRS mutation. The multiclonal nature of the emm12 scarlet fever isolates suggests that factors such as mobile genetic elements, environmental factors, and host immune status may have contributed to the 2011 scarlet fever outbreak.
Invited for the cover of this issue is Christopher Bejger and co‐workers at UNC Charlotte, Columbia University, and Donghua University. The image depicts a pair of star clusters in the constellation ...Perseus as the structure of two metal clusters in the reported framework. Read the full text of the article at 10.1002/chem.20201215.
“We found that we can prepare atomically precise coordination polymers containing two different metal‐cluster units. The way in which this material was synthesized is also noteworthy. Most heterobimetallic frameworks are made via one‐pot protocols. Our team used a stepwise approach with a discrete Co6S8 “superatom” building block serving as the monomer.” Read more about the story behind the cover in the Cover Profile and about the research itself on page 12523 ff. (DOI: 10.1002/chem.202001215).
PDF
