TY - JOUR A1 - Li, Hongguang A1 - Babu, Sukumaran Santhosh A1 - Turner, Sarah T. A1 - Neher, Dieter A1 - Hollamby, Martin J. A1 - Seki, Tomohiro A1 - Yagai, Shiki A1 - Deguchi, Yonekazu A1 - Möhwald, Helmuth A1 - Nakanishi, Takashi T1 - Alkylated-C-60 based soft materials regulation of self-assembly and optoelectronic properties by chain branching JF - Journal of materials chemistry : C, Materials for optical and electronic devices N2 - Derivatization of fullerene (C-60) with branched aliphatic chains softens C-60-based materials and enables the formation of thermotropic liquid crystals and room temperature nonvolatile liquids. This work demonstrates that by carefully tuning parameters such as type, number and substituent position of the branched chains, liquid crystalline C-60 materials with mesophase temperatures suited for photovoltaic cell fabrication and room temperature nonvolatile liquid fullerenes with tunable viscosity can be obtained. In particular, compound 1, with branched chains, exhibits a smectic liquid crystalline phase extending from 84 degrees C to room temperature. Analysis of bulk heterojunction (BHJ) organic solar cells with a ca. 100 nm active layer of compound 1 and poly(3-hexylthiophene) (P3HT) as an electron acceptor and an electron donor, respectively, reveals an improved performance (power conversion efficiency, PCE: 1.6 + 0.1%) in comparison with another compound, 10 (PCE: 0.5 + 0.1%). The latter, in contrast to 1, carries linear aliphatic chains and thus forms a highly ordered solid lamellar phase at room temperature. The solar cell performance of 1 blended with P3HT approaches that of PCBM/P3HT for the same active layer thickness. This indicates that C-60 derivatives bearing branched tails are a promising class of electron acceptors in soft (flexible) photovoltaic devices. Y1 - 2013 U6 - https://doi.org/10.1039/c3tc00066d SN - 2050-7526 VL - 1 IS - 10 SP - 1943 EP - 1951 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Inal, Sahika A1 - Koelsch, Jonas D. A1 - Chiappisi, Leonardo A1 - Janietz, Dietmar A1 - Gradzielski, Michael A1 - Laschewsky, André A1 - Neher, Dieter T1 - Structure-related differences in the temperature-regulated fluorescence response of LCST type polymers JF - Journal of materials chemistry : C, Materials for optical and electronic devices N2 - We demonstrate new fluorophore-labelled materials based on acrylamide and on oligo(ethylene glycol) (OEG) bearing thermoresponsive polymers for sensing purposes and investigate their thermally induced solubility transitions. It is found that the emission properties of the polarity-sensitive (solvatochromic) naphthalimide derivative attached to three different thermoresponsive polymers are highly specific to the exact chemical structure of the macromolecule. While the dye emits very weakly below the LCST when incorporated into poly(N-isopropylacrylamide) (pNIPAm) or into a polyacrylate backbone bearing only short OEG side chains, it is strongly emissive in polymethacrylates with longer OEG side chains. Heating of the aqueous solutions above their cloud point provokes an abrupt increase of the fluorescence intensity of the labelled pNIPAm, whereas the emission properties of the dye are rather unaffected as OEG-based polyacrylates and methacrylates undergo phase transition. Correlated with laser light scattering studies, these findings are ascribed to the different degrees of pre-aggregation of the chains at low temperatures and to the extent of dehydration that the phase transition evokes. It is concluded that although the temperature-triggered changes in the macroscopic absorption characteristics, related to large-scale alterations of the polymer chain conformation and aggregation, are well detectable and similar for these LCST-type polymers, the micro-environment provided to the dye within each polymer network differs substantially. Considering sensing applications, this finding is of great importance since the temperature-regulated fluorescence response of the polymer depends more on the macromolecular architecture than the type of reporter fluorophore. Y1 - 2013 U6 - https://doi.org/10.1039/c3tc31304b SN - 2050-7526 VL - 1 IS - 40 SP - 6603 EP - 6612 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Inal, Sahika A1 - Kölsch, Jonas D. A1 - Sellrie, Frank A1 - Schenk, Jörg A. A1 - Wischerhoff, Erik A1 - Laschewsky, André A1 - Neher, Dieter T1 - A water soluble fluorescent polymer as a dual colour sensor for temperature and a specific protein JF - Journal of materials chemistry : B, Materials for biology and medicine N2 - We present two thermoresponsive water soluble copolymers prepared via free radical statistical copolymerization of N-isopropylacrylamide (NIPAm) and of oligo(ethylene glycol) methacrylates (OEGMAs), respectively, with a solvatochromic 7-(diethylamino)-3-carboxy-coumarin (DEAC)-functionalized monomer. In aqueous solutions, the NIPAm-based copolymer exhibits characteristic changes in its fluorescence profile in response to a change in solution temperature as well as to the presence of a specific protein, namely an anti-DEAC antibody. This polymer emits only weakly at low temperatures, but exhibits a marked fluorescence enhancement accompanied by a change in its emission colour when heated above its cloud point. Such drastic changes in the fluorescence and absorbance spectra are observed also upon injection of the anti-DEAC antibody, attributed to the specific binding of the antibody to DEAC moieties. Importantly, protein binding occurs exclusively when the polymer is in the well hydrated state below the cloud point, enabling a temperature control on the molecular recognition event. On the other hand, heating of the polymer-antibody complexes releases a fraction of the bound antibody. In the presence of the DEAC-functionalized monomer in this mixture, the released antibody competitively binds to the monomer and the antibody-free chains of the polymer undergo a more effective collapse and inter-aggregation. In contrast, the emission properties of the OEGMA-based analogous copolymer are rather insensitive to the thermally induced phase transition or to antibody binding. These opposite behaviours underline the need for a carefully tailored molecular design of responsive polymers aimed at specific applications, such as biosensing. Y1 - 2013 U6 - https://doi.org/10.1039/c3tb21245a SN - 2050-750X SN - 2050-7518 VL - 1 IS - 46 SP - 6373 EP - 6381 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Schubert, Marcel A1 - Preis, Eduard A1 - Blakesley, James C. A1 - Pingel, Patrick A1 - Scherf, Ullrich A1 - Neher, Dieter T1 - Mobility relaxation and electron trapping in a donor/acceptor copolymer JF - Physical review : B, Condensed matter and materials physics N2 - To address the nature of charge transport and the origin of severe (intrinsic) trapping in electron-transporting polymers, transient and steady-state charge transport measurements have been conducted on the prototype donor/acceptor copolymer poly[2,7-(9,9-dialkyl-fluorene)-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PFTBTT). A charge-generation layer technique is used to selectively address transport of the desired charge carrier type, to perform time-of-flight measurements on samples with < 200 nm thickness, and to combine the time-of-flight and the photocharge extraction by linearly increasing voltage (photo-CELIV) techniques to investigate charge carrier dynamics over a wide time range. Significant trapping of free electrons is observed in the bulk of dioctyl-substituted PFTBTT (alt-PF8TBTT), introducing a strong relaxation of the charge carrier mobility with time. We used Monte-Carlo simulation to simulate the measured transient data and found that all measurements can be modeled with a single parameter set, with the charge transport behavior determined by multiple trapping and detrapping of electrons in an exponential trap distribution. The influence of the concomitant mobility relaxation on the transient photocurrent characteristics in photo-CELIV experiments is discussed and shown to explain subtle features that were seen in former publications but were not yet assigned to electron trapping. Comparable studies on PFTBTT copolymers with chemical modifications of the side chains and backbone suggest that the observed electron trapping is not caused by a distinct chemical species but rather is related to interchain interactions. Y1 - 2013 U6 - https://doi.org/10.1103/PhysRevB.87.024203 SN - 1098-0121 VL - 87 IS - 2 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Salert, Beatrice Ch. D. A1 - Krueger, Hartmut A1 - Bagnich, Sergey A. A1 - Unger, Thomas A1 - Jaiser, Frank A1 - Al-Sa'di, Mahmoud A1 - Neher, Dieter A1 - Hayer, Anna A1 - Eberle, Thomas T1 - New polymer matrix system for phosphorescent organic light-emitting diodes and the role of the small molecular co-host JF - Journal of polymer science : A, Polymer chemistry N2 - A new matrix system for phosphorescent organic light-emitting diodes (OLEDs) based on an electron transporting component attached to an inert polymer backbone, an electronically neutral co-host, and a phosphorescent dye that serves as both emitter and hole conductor are presented. The inert co-host is used either as small molecules or covalently connected to the same chain as the electron-transporting host. The use of a small molecular inert co-host in the active layer is shown to be highly advantageous in comparison to a purely polymeric matrix bearing the same functionalities. Analysis of the dye phosphorescence decay in pure polymer, small molecular co-host film, and their blend lets to conclude that dye molecules distribute mostly in the small molecular co-host phase, where the co-host prevents agglomeration and self-quenching of the phosphorescence as well as energy transfer to the electron transporting units. In addition, the co-host accumulates at the anode interface where it acts as electron blocking layer and improves hole injection. This favorable phase separation between polymeric and small molecular components results in devices with efficiencies of about 47 cd/A at a luminance of 1000 cd/m(2). Investigation of OLED degradation demonstrates the presence of two time regimes: one fast component that leads to a strong decrease at short times followed by a slower decrease at longer times. Unlike the long time degradation, the efficiency loss that occurs at short times is reversible and can be recovered by annealing of the device at 180 degrees C. We also show that the long-time degradation must be related to a change of the optical and electrical bulk properties. KW - charge transport KW - conducting polymer KW - degradation KW - host-guest systems KW - light-emitting diodes KW - random copolymer KW - synthesis KW - UV-vis spectroscopy Y1 - 2013 U6 - https://doi.org/10.1002/pola.26409 SN - 0887-624X VL - 51 IS - 3 SP - 601 EP - 613 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Hoffmann, Sebastian T. A1 - Jaiser, Frank A1 - Hayer, Anna A1 - Baessler, Heinz A1 - Unger, Thomas A1 - Athanasopoulos, Stavros A1 - Neher, Dieter A1 - Koehler, Anna T1 - How Do Disorder, Reorganization, and Localization Influence the Hole Mobility in Conjugated Copolymers? JF - JOURNAL OF THE AMERICAN CHEMICAL SOCIETY N2 - In order to unravel the intricate interplay between disorder effects, molecular reorganization, and charge carrier localization, a comprehensive study was conducted on hole transport in a series of conjugated alternating phenanthrene indenofluorene copolymers. Each polymer in the series contained one further comonomer comprising monoamines, diamines, or amine-free structures, whose influence on the electronic, optical, and charge transport properties was studied. The series covered a wide range of highest occupied molecular orbital (HOMO) energies as determined by cyclovoltammetry. The mobility, inferred from time-of-flight (ToF) experiments as a function of temperature and electric field, was found to depend exponentially on the HOMO energy. Since possible origins for this effect include energetic disorder, polaronic effects, and wave function localization, the relevant parameters were determined using a range of methods. Disorder and molecular reorganization were established first by an analysis of absorption and emission measurements and second by an analysis of the ToF measurements. In addition, density functional theory calculations were carried out to determine how localized or delocalized holes on a polymer chain are and to compare calculated reorganization energies with those that have been inferred from optical spectra. In summary, we conclude that molecular reorganization has little effect on the hole mobility in this system while both disorder effects and hole localization in systems with low-lying HOMOs are predominant. In particular, as the energetic disorder is comparable for the copolymers, the absolute value of the hole mobility at room temperature is determined by the hole localization associated with the triarylamine moieties. Y1 - 2013 U6 - https://doi.org/10.1021/ja308820j SN - 0002-7863 VL - 135 IS - 5 SP - 1772 EP - 1782 PB - AMER CHEMICAL SOC CY - WASHINGTON ER - TY - JOUR A1 - Inal, Sahika A1 - Koelsch, Jonas D. A1 - Chiappisi, Leonardo A1 - Kraft, Mario A1 - Gutacker, Andrea A1 - Janietz, Dietmar A1 - Scherf, Ullrich A1 - Gradzielski, Michael A1 - Laschewsky, André A1 - Neher, Dieter T1 - Temperature-Regulated Fluorescence Characteristics of Supramolecular Assemblies Formed By a Smart Polymer and a Conjugated Polyelectrolyte JF - MACROMOLECULAR CHEMISTRY AND PHYSICS N2 - Aqueous mixtures of a coumarin-labeled non-ionic thermoresponsive copolymer and a cationic polythiophene exhibit marked changes in their fluorescence properties upon heating. At room temperature, emission from the label is significantly quenched due to energy transfer to the conjugated polyelectrolyte. Heating the mixture reduces the energy-transfer efficiency markedly, resulting in a clearly visible change of the emission color. Although the two macromolecules associate strongly at room temperature, the number of interacting sites is largely reduced upon the phase transition. Crucially, the intermolecular association does not suppress the responsiveness of the smart polymer, meaning that this concept should be applicable to chemo- or bioresponsive polymers with optical read-out, for example, as a sensor device. KW - aqueous solutions KW - conjugated polyelectrolytes KW - fluorescence (or Forster) KW - resonance energy transfer KW - phase transitions KW - thermoresponsive polymers Y1 - 2013 U6 - https://doi.org/10.1002/macp.201200493 SN - 1022-1352 VL - 214 IS - 4 SP - 435 EP - 445 PB - WILEY-V C H VERLAG GMBH CY - WEINHEIM ER - TY - JOUR A1 - Lu, Guanghao A1 - Blakesley, James C. A1 - Himmelberger, Scott A1 - Pingel, Patrick A1 - Frisch, Johannes A1 - Lieberwirth, Ingo A1 - Salzmann, Ingo A1 - Oehzelt, Martin A1 - Di Pietro, Riccardo A1 - Salleo, Alberto A1 - Koch, Norbert A1 - Neher, Dieter T1 - Moderate doping leads to high performance of semiconductor/insulator polymer blend transistors JF - Nature Communications N2 - Polymer transistors are being intensively developed for next-generation flexible electronics. Blends comprising a small amount of semiconducting polymer mixed into an insulating polymer matrix have simultaneously shown superior performance and environmental stability in organic field-effect transistors compared with the neat semiconductor. Here we show that such blends actually perform very poorly in the undoped state, and that mobility and on/off ratio are improved dramatically upon moderate doping. Structural investigations show that these blend layers feature nanometre-scale semiconductor domains and a vertical composition gradient. This particular morphology enables a quasi three-dimensional spatial distribution of semiconductor pathways within the insulating matrix, in which charge accumulation and depletion via a gate bias is substantially different from neat semiconductor, and where high on-current and low off-current are simultaneously realized in the stable doped state. Adding only 5 wt% of a semiconducting polymer to a polystyrene matrix, we realized an environmentally stable inverter with gain up to 60. Y1 - 2013 U6 - https://doi.org/10.1038/ncomms2587 SN - 2041-1723 VL - 4 IS - 1-2 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Pingel, P. A1 - Neher, Dieter T1 - Comprehensive picture of p-type doping of P3HT with the molecular acceptor F(4)TCNQ JF - Physical review : B, Condensed matter and materials physics N2 - By means of optical spectroscopy, Kelvin probe, and conductivity measurements, we study the p-type doping of the donor polymer poly(3-hexylthiophene), P3HT, with the molecular acceptor tetrafluorotetracyanoquin-odimethane, F(4)TCNQ, covering a broad range of molar doping ratios from the ppm to the percent regime. Thorough quantitative analysis of the specific near-infrared absorption bands of ionized F(4)TCNQ reveals that almost every F(4)TCNQ dopant undergoes integer charge transfer with a P3HT site. However, only about 5% of these charge carrier pairs are found to dissociate and contribute a free hole for electrical conduction. The nonlinear behavior of the conductivity on doping ratio is rationalized by a numerical mobility model that accounts for the broadening of the energetic distribution of transport sites by the Coulomb potentials of ionized F(4)TCNQ dopants. DOI: 10.1103/PhysRevB.87.115209 Y1 - 2013 U6 - https://doi.org/10.1103/PhysRevB.87.115209 SN - 1098-0121 VL - 87 IS - 11 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Shalom, Menny A1 - Inal, Sahika A1 - Fettkenhauer, Christian A1 - Neher, Dieter A1 - Antonietti, Markus T1 - Improving Carbon Nitride Photocatalysis by Supramolecular Preorganization of Monomers JF - Journal of the American Chemical Society N2 - Here we report a new and simple synthetic pathway to form ordered, hollow carbon nitride structures, using a cyanuric acid melamine (CM) complex in ethanol as a starting product. A detailed analysis of the optical and photocatalytic properties shows that optimum hollow carbon nitride structures are formed after 8 h of condensation. For this condensation time, we find a significantly reduced fluorescence intensity and lifetime, indicating the formation of new, nonradiative deactivation pathways, probably involving charge-transfer processes. Enhanced charge transfer is seen as well from a drastic increase of the photocatalytic activity in the degradation of rhodamine B dye, which is shown to proceed via photoinduced hole transfer. Moreover, we show that various CM morphologies can be obtained using different solvents, which leads to diverse ordered carbon nitride architectures. In all cases, the CM-C3N4 structures exhibited superior photocatalytic activity compared to the bulk material. The utilization of CM hydrogen-bonded complexes opens new opportunities for the significant improvement of carbon nitride synthesis, structure, and optical properties toward an efficient photoactive material for catalysis. Y1 - 2013 U6 - https://doi.org/10.1021/ja402521s SN - 0002-7863 VL - 135 IS - 19 SP - 7118 EP - 7121 PB - American Chemical Society CY - Washington ER -