03 Fakultät Chemie
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/4
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Item Open Access Autonomous adaption of intelligent humidity‐programmed hydrogel patches for tunable stiffness and drug release(2023) Pflumm, Stephan; Wiedemann, Yvonne; Fauser, Dominik; Safaraliyev, Javidan; Lunter, Dominique; Steeb, Holger; Ludwigs, SabineIntelligent humidity‐programmed hydrogel patches with high stretchability and tunable water‐uptake and ‐release are prepared by copolymerization and crosslinking of N‐isopropylacrylamide and oligo(ethylene glycol) comonomers. These intelligent elastomeric patches strongly respond to different humidities and temperatures in terms of mechanical properties which makes them applicable for soft robotics and smart skin applications where autonomous adaption to environmental conditions is a key requirement. It is shown that beyond using the hydrogel in the conventional state in aqueous media, new patches can be controlled by relative humidity. This humidity programming of the patches allows to tune drug release kinetics, opening potential application fields such as skin wound therapy and personalized medication. In situ dynamic‐mechanical measurements show a huge dependence on temperature and humidity. The glass transition temperature Tg shifts from around 60 °C at dry conditions to below 0 °C for 75% r.h. and higher. The storage modulus is tunable over more than four orders of magnitude from 0.6 up to 400 MPa. Time‐temperature superposition in master curves allows to extract relaxation times over 14 orders of magnitude. With strains at break of over 200% the patches are compliant with human skin and therefore patient‐friendly in terms of adapting to movements.Item Open Access Charge‐compensated n‐doped π‐conjugated polymers : toward both thermodynamic stability of n‐doped states in water and high electron conductivity(2022) Borrmann, Fabian; Tsuda, Takuya; Guskova, Olga; Kiriy, Nataliya; Hoffmann, Cedric; Neusser, David; Ludwigs, Sabine; Lappan, Uwe; Simon, Frank; Geisler, Martin; Debnath, Bipasha; Krupskaya, Yulia; Al‐Hussein, Mahmoud; Kiriy, AntonThe understanding and applications of electron‐conducting π‐conjugated polymers with naphtalene diimide (NDI) blocks show remarkable progress in recent years. Such polymers demonstrate a facilitated n‐doping due to the strong electron deficiency of the main polymer chain and the presence of the positively charged side groups stabilizing a negative charge of the n‐doped backbone. Here, the n‐type conducting NDI polymer with enhanced stability of its n‐doped states for prospective “in‐water” applications is developed. A combined experimental-theoretical approach is used to identify critical features and parameters that control the doping and electron transport process. The facilitated polymer reduction ability and the thermodynamic stability in water are confirmed by electrochemical measurements and doping studies. This material also demonstrates a high conductivity of 10-2 S cm-1 under ambient conditions and 10-1 S cm-1 in vacuum. The modeling explains the stabilizing effects for various dopants. The simulations show a significant doping‐induced “collapse” of the positively charged side chains on the core bearing a partial negative charge. This explains a decrease in the lamellar spacing observed in experiments. This study fundamentally enables a novel pathway for achieving both thermodynamic stability of the n‐doped states in water and the high electron conductivity of polymers.Item Open Access Asymmetric Rh diene catalysis under confinement : isoxazole ring‐contraction in mesoporous solids(2024) Marshall, Max; Dilruba, Zarfishan; Beurer, Ann‐Katrin; Bieck, Kira; Emmerling, Sebastian; Markus, Felix; Vogler, Charlotte; Ziegler, Felix; Fuhrer, Marina; Liu, Sherri S. Y.; Kousik, Shravan R.; Frey, Wolfgang; Traa, Yvonne; Bruckner, Johanna R.; Plietker, Bernd; Buchmeiser, Michael R.; Ludwigs, Sabine; Naumann, Stefan; Atanasova, Petia; Lotsch, Bettina V.; Zens, Anna; Laschat, SabineCovalent immobilization of chiral dienes in mesoporous solids for asymmetric heterogeneous catalysis is highly attractive. In order to study confinement effects in bimolecular vs monomolecular reactions, a series of pseudo‐C2‐symmetrical tetrahydropentalenes was synthesized and immobilized via click reaction on different mesoporous solids (silica, carbon, covalent organic frameworks) and compared with homogeneous conditions. Two types of Rh‐catalyzed reactions were studied: (a) bimolecular nucleophilic 1,2‐additions of phenylboroxine to N‐tosylimine and (b) monomolecular isomerization of isoxazole to 2H‐azirne. Polar support materials performed better than non‐polar ones. Under confinement, bimolecular reactions showed decreased yields, whereas yields in monomolecular reactions were only little affected. Regarding enantioselectivity the opposite trend was observed, i. e. effective enantiocontrol for bimolecular reactions but only little control for monomolecular reactions was found.Item Open Access Hybrid spintronic materials from conducting polymers with molecular quantum bits(2020) Kern, Michal; Tesi, Lorenzo; Neusser, David; Rußegger, Nadine; Winkler, Mario; Allgaier, Alexander; Gross, Yannic M.; Bechler, Stefan; Funk, Hannes S.; Chang, Li‐Te; Schulze, Jörg; Ludwigs, Sabine; Slageren, Joris vanHybrid materials consisting of organic semiconductors and molecular quantum bits promise to provide a novel platform for quantum spintronic applications. However, investigations of such materials, elucidating both the electrical and quantum dynamical properties of the same material have never been reported. Here the preparation of hybrid materials consisting of conducting polymers and molecular quantum bits is reported. Organic field‐effect transistor measurements demonstrate that the favorable electrical properties are preserved in the presence of the qubits. Chemical doping introduces charge carriers into the material, and variable‐temperature charge transport measurements reveal the existence of mobile charge carriers at temperatures as low as 15 K. Importantly, quantum coherence of the qubit is shown to be preserved up to temperatures of at least 30 K, that is, in the presence of mobile charge carriers. These results pave the way for employing such hybrid materials in novel molecular quantum spintronic architectures.Item Open Access In situ electrochemical investigations of inherently chiral 2,2′‐biindole architectures with oligothiophene terminals(2021) Malacrida, Claudia; Scapinello, Luca; Cirilli, Roberto; Grecchi, Sara; Penoni, Andrea; Benincori, Tiziana; Ludwigs, SabineThe synthesis and characterization of three new inherently chiral N,N′‐dipropyl‐3,3′‐diheteroaryl‐2,2′‐biindole monomers, nicknamed Ind2T4, Ind2T6 and Ind2Ph2T4, which differ in the number of thiophenes as terminals, are reported. In addition to a full monomer characterization, stable electroactive oligomeric films were obtained by electro‐oxidation upon cycling to potentials which activate the thiophene terminals. Cyclic voltammetry, UV‐Vis‐NIR spectroelectrochemistry and in situ conductance measurements show that oligomeric films of Ind2T6 present the best stability and electrochromic switching performance. Enantioselective tests with a chiral ferrocene amine clearly show the potential as chiral selectors for analytical and sensing purposes.Item Open Access Modular approach to creating functionalized surface arrays of molecular qubits(2023) Tesi, Lorenzo; Stemmler, Friedrich; Winkler, Mario; Liu, Sherri S. Y.; Das, Saunak; Sun, Xiuming; Zharnikov, Michael; Ludwigs, Sabine; Slageren, Joris vanThe quest for developing quantum technologies is driven by the promise of exponentially faster computations, ultrahigh performance sensing, and achieving thorough understanding of many‐particle quantum systems. Molecular spins are excellent qubit candidates because they feature long coherence times, are widely tunable through chemical synthesis, and can be interfaced with other quantum platforms such as superconducting qubits. A present challenge for molecular spin qubits is their integration in quantum devices, which requires arranging them in thin films or monolayers on surfaces. However, clear proof of the survival of quantum properties of molecular qubits on surfaces has not been reported so far. Furthermore, little is known about the change in spin dynamics of molecular qubits going from the bulk to monolayers. Here, a versatile bottom‐up method is reported to arrange molecular qubits as functional groups of self‐assembled monolayers (SAMs) on surfaces, combining molecular self‐organization and click chemistry. Coherence times of up to 13 µs demonstrate that qubit properties are maintained or even enhanced in the monolayer.Item Open Access A critical outlook for the pursuit of lower contact resistance in organic transistors(2021) Borchert, James W.; Weitz, R. Thomas; Ludwigs, Sabine; Klauk, HagenTo take full advantage of recent and anticipated improvements in the performance of organic semiconductors employed in organic transistors, the high contact resistance arising at the interfaces between the organic semiconductor and the source and drain contacts must be reduced significantly. To date, only a small portion of the accumulated research on organic thin‐film transistors (TFTs) has reported channel‐width‐normalized contact resistances below 100 Ωcm, well above what is regularly demonstrated in transistors based on inorganic semiconductors. A closer look at these cases and the relevant literature strongly suggests that the most significant factor leading to the lowest contact resistances in organic TFTs so far has been the control of the thin‐film morphology of the organic semiconductor. By contrast, approaches aimed at increasing the charge‐carrier density and/or reducing the intrinsic Schottky barrier height have so far played a relatively minor role in achieving the lowest contact resistances. Herein, the possible explanations for these observations are explored, including the prevalence of Fermi‐level pinning and the difficulties in forming optimized interfaces with organic semiconductors. An overview of the research on these topics is provided, and potential device‐engineering solutions are discussed based on recent advancements in the theoretical and experimental work on both organic and inorganic semiconductors.Item Open Access On the critical competition between singlet exciton decay and free charge generation in non-fullerene based organic solar cells with low energetic offsets(2024) Pranav, Manasi; Shukla, Atul; Moser, David; Rumeney, Julia; Liu, Wenlan; Wang, Rong; Sun, Bowen; Smeets, Sander; Tokmoldin, Nurlan; Cao, Yonglin; He, Guorui; Beitz, Thorben; Jaiser, Frank; Hultzsch, Thomas; Shoaee, Safa; Maes, Wouter; Lüer, Larry; Brabec, Christoph; Vandewal, Koen; Andrienko, Denis; Ludwigs, Sabine; Neher, DieterReducing voltage losses while maintaining high photocurrents is the holy grail of current research on non-fullerene acceptor (NFA) based organic solar cell. Recent focus lies in understanding the various fundamental mechanisms in organic blends with minimal energy offsets - particularly the relationship between ionization energy offset (ΔIE) and free charge generation. Here, we quantitatively probe this relationship in multiple NFA-based blends by mixing Y-series NFAs with PM6 of different molecular weights, covering a broad power conversion efficiency (PCE) range: from 15% down to 1%. Spectroelectrochemistry reveals that a ΔIE of more than 0.3 eV is necessary for efficient photocurrent generation. Bias-dependent time-delayed collection experiments reveal a very pronounced field-dependence of free charge generation for small ΔIE blends, which is mirrored by a strong and simultaneous field-dependence of the quantified photoluminescence from the NFA local singlet exciton (LE). We find that the decay of singlet excitons is the primary competition to free charge generation in low-offset NFA-based organic solar cells, with neither noticeable losses from charge-transfer (CT) decay nor evidence for LE–CT hybridization. In agreement with this conclusion, transient absorption spectroscopy consistently reveals that a smaller ΔIE slows the NFA exciton dissociation into free charges, albeit restorable by an electric field. Our experimental data align with Marcus theory calculations, supported by density functional theory simulations, for zero-field free charge generation and exciton decay efficiencies. We conclude that efficient photocurrent generation generally requires that the CT state is located below the LE, but that this restriction is lifted in systems with a small reorganization energy for charge transfer.