The development of methods to detect damage in macromolecular materials is of paramount importance to understand their mechanical failure and the structure–property relationships of polymers. Mechanofluorophores are useful and sensitive molecular motifs for this purpose. However, to date, tailoring of their optical properties remains challenging and correlating emission intensity to force induced material damage and the respective events on the molecular level is complicated by intrinsic limitations of fluorescence and its detection techniques. Now, this is tackled by developing the first stress‐sensing motif that relies on photon upconversion. By combining the Diels–Alder adduct of a π‐extended anthracene with the porphyrin‐based triplet sensitizer PtOEP in polymers, triplet–triplet annihilation photon upconversion of green to blue light is mechanochemically activated in solution as well as in the solid state.

The potential of colloidal crystals for applications in optics and photonics has been recognized since the description of spontaneous self-assembly of monodisperse colloids into periodic opaline geometries. Provided with a laser gain medium, these direct assemblies generate optical feedback and have prospective use as lasers or frequency converters; however, problems associated with the colloidal crystal integrity and low loading fractions of the gain medium in the self-assembled resonator structure have prevented their realization to date. Here, we circumvent these problems by synthesizing monodisperse conjugated polymer colloids, which consist entirely of gain medium. We coassemble these colloids together with a sol-gel precursor to achieve encapsulated photonic crystals, which can be applied via inkjet printing. These conjugated polymer photonic crystals exhibit single line laser emission upon optical pumping. This technique circumvents time-consuming micro- and nanofabrication steps as well as error-prone backfilling and etching procedures, providing an effortless way to generate laser geometries.

Concentration polarization is a diffusion‐limited phenomenon for ion transport in electrodialysis based desalination processes. Once a so‐called limiting current is reached, the resistance of the system rises notably manifested as a plateau region in the current–voltage curves. For long it is hypothesized that altering the surface properties of the membrane can overcome the diffusional transport limitation by the induction of electroconvective vortices mixing the laminar boundary layer. To systematically investigate the influence of geometrical and chemical membrane surface topology on the evolution of electroconvection, circular patterns of polystyrene, poly(2‐vinylpyridine) (P2VP), and P2VP microgels are inkjet printed on cation‐exchange membranes. All types of patterns cause an insignificant increase in membrane resistance but they reduce the plateau lengths indicating the desired accelerated onset of electroconvection. In case of polystyrene (PS) patterns, the drop in plateau length results in a small reduction in transport resistance for overlimiting currents. However, membranes modified with linear P2VP and P2VP microgel patterns do exhibit a significantly decreased resistance in this region at a simultaneous increase of the limiting current density. Direct numerical simulations support the interpretation that the surface charge of the printed patterns influences the direction of the vortices being advantageous during ion transport toward the membrane.

Here, we present a hybrid organic/inorganic photonic composite, which generates laser emission from the organic material after pumping the inorganic component. The composite consists of a methylammonium lead-halide perovskite matrix CH 3 NH 3 Pb(Br x Cl (1−x) ) 3 and monodisperse poly(fluorene-co-divinylbenzene) particles, which have excellent optical feedback and gain. Micrometer-sized conjugated polymer particles (CPPs) are deposited together with the perovskite precursor from solution using a single-step vertical deposition method. The particles self-assemble into a photonic crystal and the perovskite forms an inorganic matrix in the interstitial space. Energy transfer to the polymer particles after optically pumping the metal-halide perovskite is studied in two systems with different halide ratios in the perovskite (Br to Cl: 1/9 and 4/6) to control the overlap of the perovskite emission energy with the absorption of the particles. From time-resolved photoluminescence experiments, we observe nonradiative energy transfer from the perovskite to the particle in both coassemblies; however, increased spectral overlap of perovskite emission and particle absorption enhances energy transfer efficiency by 37%. Because of the ordered assembly of the CPPs, we observe laser emission after energy transfer from the Cl-rich perovskite matrix at fluences of 13 mJ/cm 2 . Our report of a hybrid material system that combines the excellent optoelectronic properties of metal-halide perovskites with the outstanding optical properties of conjugated polymers represents a new approach and progress in the pursuit of electrically pumped polymer lasers.