Supramolecular Engineering of Oligothiophene Nanorods without Insulators: Hierarchical Association of Rosettes and Photovoltaic Properties

Supramolecular rosettes of oligothiophenes that do not bear long aliphatic tails have been designed as semiconducting nanomaterials for solution‐processable bulk heterojunction solar cells. The rosettes consist of six barbiturated thienyl[oligo(hexylthiophene)] units (Bar‐T‐hT_n; n=3,4,5) aggregated by multiple hydrogen bonds, which have been directly visualized by scanning tunneling microscopy (STM) at a solid–liquid interface. ¹H NMR spectroscopy in [D₈]toluene showed that Bar‐T‐hT_n exists as a mixture of monomers and small hydrogen‐bonded aggregates. Hierarchical organization of the hydrogen‐bonded aggregates took place through π–π stacking interactions upon casting their toluene solutions, resulting in the growth of highly ordered nanorods whose widths are consistent with the diameters of the rosettes. The nanorods could be generated in the presence of soluble fullerene derivatives via solution casting or the annealing of the resulting thin films. The solar cells fabricated based on these bulk heterojunction films showed power conversion efficiencies of 1–3 %, which are far higher than those of the non‐hydrogen‐bonded reference oligothiophene and the derivative that possesses long aliphatic tails.     

Mössbauer spectroscopic study on glaze of pottery

Iron-barium glaze was prepared from commercially available materials for ceramic arts and from chemical reagents, and investigated by means of Mössbauer spectroscopy and an electron probe micro analyzer (EPMA). Mössbauer spectra showed a doublet of paramagnetic high-spin Fe(II) and Fe(III) incorporated into aluminosilicate, and the magnetically-split hyperfine structures of hematite and magnetite, depending on the iron content and firing conditions. The EPMA indicated striped patterns on the secondary electron images, and the fluorescent X-ray analysis proved that the patterns are due to the heterogeneous distribution of elements in the glaze.     

On the Betti number of the image of a generic map

Let be a differentiable map of a closed m-dimensional manifold into an (m + k)-dimensional manifold with k > 0. We show, assuming that f is generic in a certain sense, that f is an embedding if and only if the (m - k + 1)-th Betti numbers with respect to the Čech homology of M and f(M) coincide, under a certain condition on the stable normal bundle of f. This generalizes the authors' previous result for immersions with normal crossings [BS1]. As a corollary, we obtain the converse of the Jordan-Brouwer theorem for codimension-1 generic maps, which is a generalization of the results of [BR, BMS1, BMS2, Sae1] for immersions with normal crossings. Received: January 3, 1996     

Preparation and properties of surface-active organocobalt complexes having long-chain alkyl groups

New types of surface-active organocobaltocenium(I) complexes, η-C_nH_2n+1X-C₅H₄(ηC₅H₅)₂Co⁺Y^? and(η-C_nH_2n+1X-C₅H₄)Co⁺Y^? (n = 6–16; X not present, NHCO or OCO; Y = Cl or PF₆) were prepared and their surface character studied. (1) The critical micelle concentrations of the cobaltocenium chlorides were much lower than those of corresponding trimethylammonium-type cationic surfactants. (2) The surface-active character of the cobaltocenium chlorides in aqueous solution (and the redox potentials of the hexafluorophosphates in acetonitrile) were affected by the substituents (X) in the cyclopentadienyl groups. (3) The surface activities of the cobaltocenium salts were lost on reduction with NaBH₄ to afford (alkyl-substituted cyclopentadiene) cyclopentadienylcobalt (0) complexes which were surface-inactive but could be re-oxidized to afford the surface-active cobaltoceium(I) salts. The cobalt complexes mentioned above may be the first examples of redoxresponsive surfactants.     

Regular homotopy classes of immersions of 3-manifolds into 5-space

 We give geometric formulae which enable us to detect (completely in some cases) the regular homotopy class of an immersion with trivial normal bundle of a closed oriented 3-manifold into 5-space. These are analogues of the geometric formulae for the Smale invariants due to Ekholm and the second author. As a corollary, we show that two embeddings into 5-space of a closed oriented 3-manifold with no 2-torsion in the second cohomology are regularly homotopic if and only if they have Seifert surfaces with the same signature. We also show that there exist two embeddings $F_0$ and of the 3-torus T ³ with the following properties: (1) is regularly homotopic to F ₈ for some immersion , and (2) the immersion h as above cannot be chosen from a regular homotopy class containing an embedding. Received: 29 March 2001     

Superstructure-dependent optical and electrical properties of an unusual face-to-face, pi-stacked, one-dimensional assembly of dehydrobenzo[12]annulene in the crystalline state

To develop a novel pi-conjugated molecule-based supramolecular assembly, we designed and synthesized trisdehydrotribenzo[12]annulene ([12]DBA) derivative 2 with three carboxyl groups at the periphery. Recrystallization of 2 from DMSO gave a crystal of the solvate 23 DMSO. Crystallographic analysis revealed, to our surprise, that a face-to-face pi-stacked one-dimensional (1D) assembly of 2 was achieved and that the DMSO molecule played a significant role as a "structure-dominant element" in the crystal. This is the first example of [12]DBA to stack completely orthogonal to the columnar axis. To reveal its superstructure-dependent optical and electrical properties, 2 and its parent molecule 1, which crystallizes in a herringbone fashion, were subjected to fluorescence spectroscopic analysis and charge-carrier mobility measurements in crystalline states. The 1D stacked structure of 2 provides a red-shifted, broadened, weakened fluorescence profile (lambda(max) = 545 nm, phi(F) = 0.01), compared to 1 (lambda(max) = 491 nm, phi(F) = 0.12), due to strong interactions between the p orbitals of the stacked molecules. The charge-carrier mobility of the single crystal of 23 DMSO, as well as 1, was determined by flash photolysis time-resolved microwave conductivity (FP-TRMC) measurements. The single crystal of 23 DMSO revealed significantly-anisotropic charge mobility (sigma(mu) = 1.5x10(-1) cm(2) V(-1) s(-1)) along the columnar axis (crystallographic c axis). This value is 12 times larger than that along the orthogonal axis (the a axis).     

Membrane-Vesicle-Mediated Interbacterial Communication Activates Silent Secondary Metabolite Production

Most bacterial biosynthetic gene clusters (BGCs) are “silent BGCs” that are expressed poorly or not at all under normal culture conditions. However, silent BGCs, even in part, may be conditionally expressed in response to external stimuli in the original bacterial habitats. The growing knowledge of bacterial membrane vesicles (MVs) suggests that they could be promising imitators of the exogenous stimulants, especially given their functions as signaling mediators in bacterial cell-to-cell communication. Therefore, we envisioned that MVs added to bacterial cultures could activate diverse silent BGCs. Herein, we employed Burkholderia multivorans MVs, which induced silent metabolites in a wide range of bacteria in Actinobacteria, Bacteroidetes and Proteobacteria phyla. A mechanistic analysis of MV-induced metabolite production in Xenorhabdus innexi suggested that the B. multivorans MVs activate silent metabolite production by inhibiting quorum sensing in X. innexi. In turn, the X. innexi MVs carrying some MV-induced peptides suppressed the growth of B. multivorans, highlighting the interspecies communication between B. multivorans and X. innexi through MV exchange.     

Synthesis of Furoxans (1,2,5‐oxadiazole 2‐oxides) from Styrenes and Nitrosonium Tetrafluoroborate in Non‐Acidic Media and Mechanistic Study

Diverse furoxans (1,2,5‐oxadiazole 2‐oxides) were synthesized from the corresponding styrenes using nitrosonium tetrafluoroborate as the nitrosation reagent in pyridine (basic media) or dichloromethane (neutral media). Acid‐sensitive functional groups were tolerated under these conditions. The probable reaction mechanism was elucidated. The experimental results support an ionic reaction pathway in contrast to the conventional acidic conditions with a radical mechanism.     

Organic Donor–Acceptor Assemblies form Coaxial p–n Heterojunctions with High Photoconductivity

The formation of coaxial p–n heterojunctions by mesoscale alignment of self‐sorted donor and acceptor molecules, important to achieve high photocurrent generation in organic semiconductor‐based assemblies, remains a challenging topic. Herein, we show that mixing a p‐type π gelator (TTV) with an n‐type semiconductor (PBI) results in the formation of self‐sorted fibers which are coaxially aligned to form interfacial p–n heterojunctions. UV/Vis absorption spectroscopy, powder X‐ray diffraction studies, atomic force microscopy, and Kelvin‐probe force microscopy revealed an initial self‐sorting at the molecular level and a subsequent mesoscale self‐assembly of the resulted supramolecular fibers leading to coaxially aligned p–n heterojunctions. A flash photolysis time‐resolved microwave conductivity (FP‐TRMC) study revealed a 12‐fold enhancement in the anisotropic photoconductivity of TTV/PBI coaxial fibers when compared to the individual assemblies of the donor/acceptor molecules.