Electrodeposition of ZnO nanorods on opaline replica as hierarchically structured systems Lorenz Steidl, Stefan Frank, Stefan A. L. Weber, Martin Panthöfer, Alexander Birkel, Dominik Koll, Rüdiger Berger, Wolfgang Tremel, Rudolf Zentel, J. Mater. Chem., 2011, 21, 1079-1085.
DOI 10.1039/c0jm02759f
We present a new method to prepare hierarchical structures by using ZnO replica and ZnO-coated PMMA opals as electrodes in an electrodeposition process of ZnO nanorods. Depending on the approach the nanorods can be either grown exclusively on top of the replica or inside the replica structures. Therefore two types of systems are accessible: 3D photonic crystals with a hierarchically structured surface consisting of nanorods and macroporous ZnO structures with an increased surface area.
Organic Nanosheets with Charged Surface: Two dimensional self-assembly of a non-symmetric bis-acylurea with pyridyl end group Jong-Uk Kim, Rudolf Zentel, Soft Matter, 2011, 7, 2019-2024.
DOI: 10.1039/C0SM00853B
We present a novel non-symmetric bis-acylurea that self-assembles into two dimensional nanosheet superstructures. The bis-acylurea (PyrC8Bn) has a pyridyl and a benzyl end group divided by a spacer group [–NHCONHCO–(CH2)8–CONHCONH–, C8] with two hydrogen bonding sites. Upon cooling a hot solution in ethanol, the molecule self-assembles into multilayered nanosheet structures due to the intermolecular biaxial hydrogen bonding. The surface charge of the nanosheets could be switched between positive and neutral by adjusting the pH. The charged character of the nanosheets was utilized in immobilizing negatively charged gold nanoparticles. An attempt to regulate the self-assembly allowed us to find a unique hierarchical structure of PyrC8Bn, where ultrathin (<10 nm) 2D lamellae growing within microspheres were observed. This superstructure with large surface area could serve as a template for inorganic catalytic materials.
A Heteroleptic Bis(tridentate)ruthenium(II) Polypyridine Complex with Improved Photophysical Properties and Integrated Functionalizability
Aaron Breivogel, Christoph Förster, Katja Heinze, Inorg. Chem. 2010, 49, 7052-7056.
DOI: 10.1021/ic1007236
The synthesis and photophysical properties of a ruthenium(II) complex bearing an electron-accepting 2,2′;6′,2′′-terpyridine ligand and an electron-donating N,N′-dimethyl-N,N′-dipyridin-2-ylpyridine-2,6-diamine (ddpd) ligand are presented. The heteroleptic complex is easily prepared isomerically pure and features intense low-energy metal-to-ligand charge-transfer (MLCT) absorption bands and intense room temperature MLCT emission with a long MLCT lifetime. The favorable photophysical properties are due to the strong ligand field imposed by the ddpd ligand.
Redox-responsive Organometallic Foldamers from Ferrocene Amino Acid: Solid-Phase Synthesis, Secondary Structure and Mixed-Valence Properties Daniel Siebler, Christoph Förster, Katja Heinze, Dalton Trans., 2011, 40, 3558-3575.
DOI: 10.1039/C0DT01528H
Oligoferrocenes Fmoc-Fcan-OMe (n = 3–5) are assembled in a stepwise precise manner from Fmoc-protected ferrocene amino acid Fmoc-Fca-OH (H-Fca-OH = 1-amino-1′-ferrocene carboxylic acid; Fmoc = 9-fluorenylmethyloxycarbonyl) via amide bonds on solid supports by sequential Fmoc deprotection, acid activation and coupling steps. The resulting well-defined oligomers form ordered zigzag structures in THF solution with characteristic hydrogen bonding patterns. Electrochemical experiments reveal sequential oxidations of the individual ferrocene units in these peptides giving mixed-valent cations. Optical intervalence electron transfer is detected by intervalence transitions in the near-IR.
Oligonuclear Ferrocene Amides: Mixed-valent Peptides and Potential Redox-switchable Foldamers Daniel Siebler, Michael Linseis, Teuta Gasi, Luca M. Carrella, Rainer F. Winter, Christoph Förster, Katja Heinze, Chem. Eur. J., 2011, 17, 4540-4551.
DOI: 10.1002/chem.201002101
Trinuclear ferrocene tris-amides were synthesized from an Fmoc- or Boc-protected ferrocene amino acid, and hydrogen-bonded zigzag conformations were determined by NMR spectroscopy, molecular modelling, and X-ray diffraction. In these ordered secondary structures orientation of the individual amide dipole moments approximately in the same direction results in a macrodipole moment similar to that of α-helices composed of α-amino acids. Unlike ordinary α-amino acids, the building blocks in these ferrocene amides with defined secondary structure can be sequentially oxidized to mono-, di-, and trications. Singly and doubly charged mixed-valent cations were probed experimentally by Vis/NIR, paramagnetic H NMR and Mössbauer spectroscopy and investigated theoretically by DFT calculations. According to the appearance of intervalence charge transfer (IVCT) bands in solution, the ferrocene/ferrocenium amides are described as Robin–Day class II mixed-valent systems. Mössbauer spectroscopy indicates trapped valences in the solid state. The secondary structure of trinuclear ferrocene tris-amides remains intact (coiled form) upon oxidation to mono- and dications according to DFT calculations, while oxidation to the trication should break the intramolecular hydrogen bonding and unfold the ferrocene peptide (uncoiled form).
(11J1) Enhanced Photovoltaic Performance of ZnO Nanoparticle/Poly(phenylene vinylene) Hybrid Photovoltaic Cells by Semiconducting Surfactant I. Park, Y. Lim, S. Noh, D. Lee, M. Meister, J. J. Amsden, F. Laquai, C. Lee, D. Y. Yoon, Org. Electr. 2011, 12, 424-428.
DOI:10.1016/j.orgel.2010.12.002
Hybrid films of ZnO nanoparticles and poly[2-methoxy-5-(3′,7′-dimethyloctyloxyl)-1,4-phenylene vinylene] (MDMO-PPV) were investigated as a model hybrid bulk heterojunction (HBHJ) photovoltaic cell which combines the simple processability and excellent electrical characteristics of inorganic nanoparticle acceptors and conjugated polymer donors. Improved photovoltaic performance was observed when the ZnO nanoparticles were stabilized with a new semiconducting surfactant, 2-(2-ethylhexyl)-1,3-dioxo-2,3-dihydro-1H-benzo[de]isoquinoline-6,7-dicarboxylic acid (BQ). We found that using the BQ surfactant increased the power conversion efficiency (1.23%) while a typical insulating surfactant, oleic acid (OA), decreased the efficiency (0.65%) despite the improvement of the ZnO dispersion, as compared to the HBHJ films prepared without a surfactant (0.75%). The underlying mechanism was delineated by hybrid-morphology study, photoluminescence spectroscopy, and photo-induced absorption spectroscopy.
Polythiophene:Perylene Diimide Solar Cells – The Impact of Alkyl-Substitution on the Photovoltaic Performance V. Kamm, G. Battagliarin, I.A. Howard, W. Pisula, A. Mavrinskiy, C. Li, K. Müllen, F. Laquai, Adv. Energy Mater. 2011, 1, 297-302.
DOI: 10.1002/aenm.201000006
The photovoltaic parameters, i.e., the short-circuit current, open-circuit voltage and device fill factor, of bulk heterojunction solar cells that use perylene diimide (PDI) derivatives as electron acceptors are often far below the theoretically expected values for reasons still not entirely understood. This article demonstrates that the photovoltaic characteristics of blend films of regioregular poly(3-hexylthiophene) (rr-P3HT) and PDI molecules are improved upon using a core-alkylated PDI derivative instead of the often used N-alkylated PDI molecules. A doubling of the power conversion efficiency of P3HT:PDI solar cells by using the core-alkylated PDI derivative is observed leading to an unprecedented power conversion efficiency of 0.5% for a P3HT:PDI solar cell under AM1.5 solar illumination. Furthermore, the optical properties of the novel PDI derivative are compared to two standard exclusively N-alkylated PDI derivatives by steady-state and time-resolved photoluminescence spectroscopy in solution and solid state. The experiments reveal that aggregation in the solid state determines the photophysics of all PDI derivatives. However, the emission energy and excited state lifetime of the aggregates are clearly influenced by the alkyl-substitution pattern through its effect on the packing of the PDI molecules. X-ray diffraction experiments before and after thermal annealing of PDI:polystyrene and PDI:P3HT blends reveal subtle differences in the packing characteristics of the different PDI derivatives and, problematically, that P3HT ordering is suppressed by all of the PDI derivatives.
Simple Chiral Urea Gelators, (R)- and (S)-2-heptylurea: Their Gelling Ability Enhanced by Chirality Jong-Uk Kim*, Dieter Schollmeyer, Martin Brehmer, Rudolf Zentel*, Journal of Colloid and Interface Science, 2011, 357, 428-433.
DOI: 10.1016/j.jcis.2011.02.006
Pure enantiomeric (R)- and (S)-2-heptylurea gelatinize nonpolar solvents and water by forming a 3D network of 1D fibrous supramolecular structures, while the racemate precipitates in lamellar crystals.
Two dimensional self-assembly of bis-acylureas having various functional end groups Jong-Uk Kim*, Riju Davis, Rudolf Zentel
Journal of Colloid and Interface Science, 2011, 359, 428-435.
DOI: 10.1016/j.jcis.2011.04.022
Bis-acylureas with various end functional groups self-organize upon cooling from hot solutions forming superstructures. Unless the functionalities are bulky, rigid, or reactive at crystallization conditions, the bis-acylureas self-assemble with lamellar molecular packing. The resulting nanosheet structures have flat surfaces that are molecularly flat over hundreds of nanometers.