Michael Sommer

The influence of reaction conditions of polyhydroxyalkylations on molar mass, end groups and chain topology is investigated using SEC and MALDI-ToF. Macrocycle formation and chain termination protocols are evaluated.

Magneto‐ionics is a promising technology for unconventional magnetic data storage and energy‐efficient computing. In magneto‐ionic devices, voltage‐triggered ionic processes are exploited to control magnetic properties of an electrode in an electrolyte. Liquid electrolytes typically generate magneto‐ionic effects at lower voltages compared to solid electrolytes, but complicate electronic integration, posing the risk of leakage. Here, we introduce polymer electrolytes for hydroxide‐ and hydrogen‐based magneto‐ionic devices, which enable magneto‐ionic effects at voltages of ∼2 V. For the hydroxide device, a polymer separator soaked in alkaline solution, a gel polymer electrolyte, and an anion exchange membrane are combined with Fe/FeO _x nanofilm electrodes. In all three cases, a large voltage‐induced decrease in magnetic coercivity up to 66% is achieved. In the hydrogen device, a proton exchange membrane is utilized to load Co/Pd multilayer electrodes with hydrogen, leading to a coercivity increase. Direct comparison to corresponding liquid magneto‐ionic devices reveals a drastically improved reversibility for the hydrogen polymer device, while the hydroxide polymer devices exhibit an increased energy efficiency by up to a factor of four. Polymer‐based electrolytes could fully replace liquid electrolytes in magneto‐ionics and enable the design of energy‐efficient devices for magnetic data storage and spintronics.

Kinked polyphenylenes, poly(meta, meta, para-phenylene) (PmmpP), with ethylene oxide (EO) side chains are used as solid polymer electrolytes (SPEs) for Li+ conduction. The meta-kinks in P(EO-mmpP) effectively suppress side-chain crystallization and enhance backbone flexibility, resulting in amorphous materials with outstanding ductility and tunable toughness. Varying the EO chain length from three to five units enables tuning of the glass transition temperature (Tg), mechanical properties, and ionic conductivity. Dynamic mechanical thermal analysis reveals two transitions for the side and main chains. While the temperature of side-chain relaxation is independent of side-chain length, the temperature of main-chain relaxation, which is closely related to Tg, decreases with increasing side-chain length. The SPEs exhibit excellent miscibility with LiTFSI upon simple kneading, forming transparent, flexible, and free-standing films. Ionic conductivities increase with increasing side-chain length following Arrhenius behavior. The activation energies (EA) decrease with increasing side-chain length. However, the EA of local Li+ dynamics from temperature-dependent 7Li NMR measurements increases with increasing EO side-chain length due to stronger complexation. As a result, the Tg is dominating local effects of local Li+ dynamics and thus governs bulk ionic conductivity. This effect is further enhanced by external plasticization, furnishing a conductivity of 0.483 mS/cm at 80 °C.

Synthetic complexity is a decisive aspect for absorber material availability in organic photovoltaics (OPVs). By using direct arylation polycondensation (DAP), a new route to the donor polymer PBDT-T2-TPD is presented. DAP allows to reduce the amount of toxic chemicals and simplifies the reaction scheme at the same time. Furthermore, this new route allows to vary the molar mass of PBDT-T2-TPD and thus enables the investigation of chain length-dependent OPV parameters in devices with the non-fullerene L8-BO as acceptor. An increasing molar mass results in an improvement of the open-circuit voltage, the fill factor and the power conversion efficiency, while the short-circuit current density saturates after an initial increase. These changes arise from reduced non-radiative voltage losses and enhanced mobility–lifetime products. The performance of the best performing DAP material is at least as

Covalent mechanophores use mechanical energy to facilitate thermal crossing of their activation barrier, resulting in color changes that are mostly governed by reaction kinetics. Here, we develop a B–N-functionalized donor-acceptor mechanochromophore based on a borylated thiophene benzotriazole motif that exhibits an extremely low barrier and fast switching kinetics. Thus, the thermal equilibrium between the B–N closed and open states is thermodynamically controlled, with reversion of the B–N open to the closed form in the absence of an external force taking place on the order of 10-10s. B–N coordination significantly perturbates the intrinsic charge-transfer character leading to strong mechanochromic changes. Force stabilizes the open form, shifts the equilibrium and increases the HOMO–LUMO gap. Increasing the steric demand at the boron center enables force control, rendering pN-scale forces detectable. Additionally, the B–N mechanophore displays photoswitching and enables selective solvent vapor sensing.

Among the various n-type dopants used in organic electronics, NDMBI-H is the most common. However, precise control of the doping levels is still elusive, with reported conductivities varying by orders of magnitude for similar systems. In this study, we investigate a frequently underestimated factor: the mixing time during co-solution processing. Our focus is on a prototypical system involving NDMBI-H-doped PCBM processed in chloroform. Remarkably, we observe a decline in conductivity with prolonged mixing times that does not occur when the single components are stored individually. We establish a correlation between this behavior and characteristic signatures in the 1H NMR spectra of pristine compounds and mixtures. We attribute the decline in conductivity to the reactive nature of chloroform and extend our findings to four more organic semiconductors with different backbones. We find that choosing a suitable solvent and controlling the mixing time allow us to increase the conductivity of doped PCBM to up to 2.64 S/cm through a straightforward bulk doping process, representing a substantial improvement compared to values obtained using additives or more complex procedures.

We employed photoluminescence (PL) from mechanochromophores covalently linked into the backbone of a glassy polymer as optical force sensors (“optical springs”) to resolve forces acting along polymer chains in spin-coated thin films. From the shift of the peak position of the PL spectrum, we deduced changes in the main force. Changes in the shape of the spectra were interpreted as alterations in populations of polymer chains experiencing lower and higher forces than the main force. Depending on the conditions of spin coating, expressed through a preparation parameter pev, we observed distinct changes in the corresponding PL spectra of the resulting polymer films, reflecting characteristic variations in the distribution of forces acting along polymer chains as a function of pev. Our results allowed to link the forces acting along individual polymer chains in spin-coated polymer films with macroscopically detected residual stresses, with the latter reflecting the combined and cooperative response of a large ensemble of polymer chains. Interestingly, residual stresses and the forces acting along individual polymer chains did not exhibit the same dependence on pev.

A new n-type conjugated polymer is prepared using aldol polycondensation. The backbone is designed to be linear, coplanar and to have a low LUMO energy level. A bisisatin monomer is made in four steps only under metal-free and ambient conditions. Key to the linear and coplanar structure is the bridging of two isatin motifs by a thiazolothiazole unit. Aldol copolymers with benzodifuranone afford polymers with low LUMO energy levels of ∼ −4.2 eV without using halogens. Defect formation during aldol polycondensation is studied quantitatively using monofunctional model compounds. Besides known defects such as homocouplings, fused analogs are observed along with other defects. Zinc stearate is identified as a superior catalyst, with defects being mostly absent in model reactions. This is in contrast to all other catalytic conditions used, including common literature protocols. Importantly, water must be continuously removed from the reaction to prevent the formation of defects. From these results, protocols are selected that lead to different defect densities in aldol copolymers. Spectroscopic methods confirm the defective nature of aldol polymers but offer limited structural insight into their nature and abundance. Electrospray deposition scanning tunneling microscopy enables direct identification and quantification of defect structures, revealing both similar trends and notable differences in their relative frequencies between small-molecule model systems and full polymers, rationalized by differences in reaction equilibria and chain mobility. Alongside introducing a new low LUMO n-type polymer synthesized via a metal-free route, this study opens pathways toward defect-free aldol polymers, which are otherwise intrinsically prone to defect formation.

Varying the hydrophilic/hydrophobic ratio in block copolymer binders for AEMWE allows to control ion exchange capacity, swelling and ionic conductivity, leading to superior single-cell performance with current densities of 3800 mA cm ⁻² at 2 V.