A Photowelding Strategy for Conductivity Restoration in Flexible Circuits

Magnetically locked Janus particle clusters with orientation-dependent motion in AC electric fields

Active particles, or micromotors, locally dissipate energy to drive locomotion at small length scales. The type of trajectory is generally fixed and dictated by the geometry and composition of the particle, which can be challenging to tune using conventional fabrication procedures. Here, we report a simple, bottom-up method to magnetically assemble gold-coated polystyrene Janus particles into "locked" clusters that display diverse trajectories when stimulated by AC electric fields. The orientation of particles within each cluster gives rise to distinct modes of locomotion, including translational, rotational, trochoidal, helical, and orbital. We model this system using a simplified rigid beads model and demonstrate qualitative agreement between the predicted and experimentally observed cluster trajectories. Overall, this system provides a facile means to scalably create micromotors with a range of well-defined motions from discrete building blocks.

A Photopatternable Conjugated Polymer with Thermal-Annealing-Promoted Interchain Stacking for Highly Stable Anti-Counterfeiting Materials

Photoresponsive polymers can be conveniently used to fabricate anti-counterfeiting materials through photopatterning. However, an unsolved problem is that ambient light and heat can damage anti-counterfeiting patterns on photoresponsive polymers. Herein, photo- and thermostable anti-counterfeiting materials are developed by photopatterning and thermal annealing of a photoresponsive conjugated polymer (MC-Azo). MC-Azo contains alternating azobenzene and fluorene units in the polymer backbone. To prepare an anti-counterfeiting material, an MC-Azo film is irradiated with polarized blue light through a photomask, and then thermally annealed under the pressure of a photonic stamp. This strategy generates a highly secure anti-counterfeiting material with dual patterns, which is stable to sunlight and heat over 200 °C. A key for the stability is that thermal annealing promotes interchain stacking, which converts photoresponsive MC-Azo to a photostable material. Another key for the stability is that the conjugated structure endows MC-Azo with desirable thermal properties. This study shows that the design of photopatternable conjugated polymers with thermal-annealing-promoted interchain stacking provides a new strategy for the development of highly stable and secure anti-counterfeiting materials.

Visible Light-Driven Micromotor with Incident-Angle-Controlled Motion and Dynamic Collective Behavior

Light-driven micromotor has become one of the research focuses in the past decade, and its motion behavior is usually controlled by light intensity, polarization, and light wavelength. Herein, the light incident angle is utilized to control the motion behavior of silica/Au/pentacene (SiO₂/Au/PEN) spherical Janus micromotor. Under tilted irradiation, a single micromotor shows positive phototactic moving behavior without the addition of external chemical fuels, which relies on the photocatalytic reactions and the self-electrophoresis mechanism. Interestingly, when the incident light is tuned to the vertical angle, the SiO₂/Au/PEN micromotor stops moving. Similarly, a number of SiO₂/Au/PEN micromotors exhibit the same "on-off" motion change, which is dependent on the light incident angle. More interestingly, the "on-off" motion of the SiO₂/Au/PEN microparticles under vertical light irradiation results in the formation of the agglomeration with position and size precisely controlled by light. In addition, the resulting aggregation exhibits light-controlled dynamic migration behavior. The incident angle control thus opens up new opportunities for the motion control of the micromotors for diverse applications.

Evolution of High-Valent Nickela-Electrocatalyzed C-H Activation: From Cross(-Electrophile)-Couplings to Electrooxidative C-H Transformations

C-H activation has emerged as one of the most efficient tools for the formation of carbon-carbon and carbon-heteroatom bonds, avoiding the use of prefunctionalized materials. In spite of tremendous progress in the field, stoichiometric quantities of toxic and/or costly chemical redox reagents, such as silver(I) or copper(II) salts, are largely required for oxidative C-H activations. Recently, electrosynthesis has experienced a remarkable renaissance that enables the use of storable, safe and waste-free electric current as a redox equivalent. While major recent momentum was gained in electrocatalyzed C-H activations by 4d and 5d metals, user-friendly and inexpensive nickela-electrocatalysis has until recently proven elusive for oxidative C-H activations. Herein, the early developments of nickela-electrocatalyzed reductive cross-electrophile couplings as well as net-redox-neutral cross-couplings are first introduced. The focus of this Minireview is, however, the recent emergence of nickel-catalyzed electrooxidative C-H activations until April 2020.