Longer and stronger; stiff but not brittle Hydrogels are highly water-swollen, cross-linked polymers. Although they can be highly deformed, they tend to be weak, and methods to strengthen or toughen them tend to reduce stretchability. Two papers now report strategies to create tough but deformable hydrogels (see the Perspective by Bosnjak and Silberstein). Wang et al . introduced a toughening mechanism by storing releasable extra chain length in the stiff part of a double-network hydrogel. A high applied force triggered the opening of cycling strands that were only activated at high chain extension. Kim et al . synthesized acrylamide gels in which dense entanglements could be achieved by using unusually low amounts of water, cross-linker, and initiator during the synthesis. This approach improves the mechanical strength in solid form while also improving the wear resistance once swollen as a hydrogel. —MSL

NIM-7 is demonstrated to be a multicomponent fluorescent probe that accumulates in both lipid droplets and lysosomes after entering cells, giving rise to yellow and red fluorescence emission, respectively. This allows the two organelles to be visualized concurrently.

Owing to their superior display quality and flexibility, organic light-emitting diodes (OLEDs) have been leading the innovation in flat panel displays and lighting applications. Unfortunately, the spin statistics make OLEDs using conventional organic fluorescent emitters very inefficient, with an upper limit to their internal quantum efficiency (IQE) of 25% due to the fact Although numerous thermally activated delayed fluorescence (TADF) organic light-emitting diodes (OLEDs) have been demonstrated, efficient blue or even sky-blue TADF-based nondoped solution-processed devices are still very rare. Herein, through-space charge transfer (TSCT) and through-bond charge transfer (TBCT) effects are skillfully incorporated, as well as the multi-(donor/ acceptor) characteristic, into one molecule. The former allows this material to show small singlet-triplet energy splitting (ΔE ST ) and a high transition dipole moment. The latter, on the one hand, further lights up multichannel reverse intersystem crossing (RISC) to increase triplet exciton utilization via degenerating molecular orbitals. On the other hand, the nature of the molecular twisted structure effectively suppresses intermolecular packing to obtain high photoluminescence quantum yield (PLQY) in neat flims. Consequently, using this design strategy, T-CNDF-T-tCz containing three donor and three acceptor units, successfully realizes a small ΔE ST (≈0.03 eV) and a high PLQY (≈0.76) at the same time; hence the nondoped solution-processed sky-blue TADF-OLED displays record-breaking efficiency among the solution processbased nondoped sky-blue OLEDs, with high brightness over 5200 cd m −2 and external quantum efficiency up to 21.0%.