Synthesis,Electronic, and Morphological Properties of Tetrahedral Oligothiophenes with n‐Hexyl Terminal Groups

A series of tetrahedral oligothiophenes bearing n‐hexyl groups at the α‐positions of the terminal thiophene rings, (n‐C₆H₁₃(C₄H₂S)_n)₄C (Hex‐TnTM; n=1–4), has been synthesized by Kosugi–Migita–Stille coupling as a key reaction. Thanks to the improved solubility afforded by the terminal n‐hexyl groups, the largest homologue (n=4) was successfully obtained. Whereas the smaller derivatives (n=1, 2) were obtained as liquid substances, the larger derivatives (n=3, 4) were obtained as solids. Hex‐T3 TM partially adopts syn conformations between the adjacent thiophene rings in the crystal, probably owing to the packing force. Hex‐T3 TM not only appeared in the crystalline state but also the amorphous state, which was stable to up to 80 °C. Regardless of the terminal groups, the derivatives of n=2 exhibited a broad fluorescence with large Stokes shifts compared to the corresponding linear analogues, thereby suggesting the presence of intramolecular interactions between the bithiophene moieties. Interactions between terthiophene branches was also suggested in the radical cations of Hex‐T3 TM by cyclic voltammetry measurements.     

On amide exchange reaction of polymide precursor

The reaction of poly(amic acid) (PAA) derived from pyromellitic dianhydride (PMDA) and oxydianiline (ODA) with 1-aminopyrene (APy) in solution as a model of amide exchange reaction between PAAs was studied in the temperature range of 0–60°C using viscometry and light-scattering (LS) measurements. The decrease in the weight-average molecular weight (M?_w) of PAA in N,N-dimethylacetamide (DMAc) solution with time and the acceleration of M?_w drop due to the increase in storage temperature or the addition of APy into PAA solution were observed. Apparent activation energies (E_a) for scission of PAA chains were similar: about 13 kcal/mol in PAA/DMAc and PAA/APy/DMAc, respectively. When stored at 60°C for a week, the number of scissions per polymer chain in PAA/DMAc is about 2, but is about 5 in PAA/DMAc with a large amount of APy. The result indicates that the M?_w drop accelerated by the addition of APy is attributed to amide exchange reaction between PAA Chains and monofunctional APy. It was concluded from the dependence of M?_w drop on Apy concentration that the exchange reaction between different PAA molecules during storage of PAA/PAA solution may scarcely occur under the conditions (storage time and temperature) used for preparation of PAA/PAA blends.     

Photophysical processes in aromatic polyimides. Studies with model compounds

Emission mechanism in an aromatic polyimide, PI(BPDA/PDA), derived from biphenyltetracarboxylic dianhydride and p-phenylene diamine were studied with ultraviolet visible absorption and fluorescence spectra of a series of the model compounds. The excitation spectrum of the intermolecular charge-transfer (CT) fluorescence peaking around 550 nm of PI(BPDA/PDA) thin film was completely consistent with the absorption spectrum, indicating that the intermolecular CT fluorescence emission of PI(BPDA/PDA) film is not caused by direct excitation of the CT absorption band, but by light absorption due to structural units in the polymer backbone. The UV-vis. absorption spectra of the model compounds corresponding to the structural units in PI(BPDA/PDA) showed that the longest wavelength absorption band is due to the biphenylbisimide moiety. The band was assigned as π, π* transition with the polarization spectrum of the model compound. The fluorescence spectra of the model compounds changed sensitively depending on the conformation around N-phenyl bond. The lifetime measurement for the model compounds suggested that intramolecular CT process occurs very rapidly. © 1993 John Wiley & Sons, Inc.     

Volume study on the exclusion of lithium naphthylsulfonate from lithium decylsulfonate micelles

Densities of aqueous solutions of lithium 1-naphthylsulfonate (1-LiNSO)–lithium decylsulfonate (LiDeSO) and 2-LiNSO–LiDeSO mixtures were measured as a function of total molality and composition of the mixtures. The partial derivative of the solution with respect to the total molality was calculated for the monomer and micellar regions. It was found that the values of the partial derivative are larger for the 2-LiNSO–LiDeSO system than for the 1-LiNSO–LiDeSO system. This fact is attributable to the larger value of the partial molar volume of monomer of 2-LiNSO than that of 1-LiNSO. For the two systems, the micellar molar volume of the mixtures varied linearly with the composition from the partial molar volumes of 1- and 2-LiNSO in their single systems to the micellar molar volume in the single LiDeSO system. Miscibility of the solutes in the mixed micelles was examined by drawing the critical micelle concentration (CMC) vs composition diagrams. The diagrams for the 1- and 2-isomers coincided with each other and showed that molecules of 1- and 2-LiNSO are excluded from the micelles. The contribution of the micelle-unforming component to the volume of micelle formation is positive and large because of the exclusion from the micelles. On the other hand, the contribution of the micelle-forming component to the volume of micelle formation is unchanged. The dependence of the monomer molalities of LiNSO and LiDeSO on the total molality, evaluated by means of the CMC vs composition diagrams, substantiated the validity of the approximations used in the derivation of the equations in this study.     

CONDITIONS OF ORGANOSOL FORMATION FROM METAL SOAPS IN HIGHER ALCOHOLS AND THE SHAPE OF THE DISPERSED PARTICLES

Seven bivalent metal soaps and six trivalent metal soaps were prepared from the various kinds of fatty acids. Upon heating metal soap suspensions in organic solvents, organosols of metal oxides were formed and they showed the special characteristics in color. The scanning electron microscopic examination of the organosol particles showed the spherical, cubic, or irregular shape of 0.3~3.0 μm size. The shape and size of the particles were affected by the type of netal, the concentration of soaps, heating temperature, and the presence of a reducing agent. No relationship between the particles size of organosol and the carbon number of metal soaps was observed in this study. The stable organosol of monodispersed particles were successfully formed upon heating from Co, Mn and Fe metal soaps in 1-decanol containing a reducing agent.     

Speckle Reduction of Kinoform Reconstruction Utilizing the 2π Ambiguity of Image Phase Differences

An iterative speckle reduction method is proposed to reduce the speckle noise in the reconstruction of kinoforms. Because a kinoform only has phase modulation, the phase freedom of the reconstructed image is usually utilized for spectrum smoothing. We consider the speckle noise as isolated zeros among the discrete reconstructed points. An isolated zero leads to a 2 circle of the image phase differences. Our proposed iterative speckle reduction method changes the image phase to avoid the 2 circles in the reconstructed points. Computer simulations are shown to demonstrate the effect of our method.     

Chain polymerization of diacetylene compound multilayer films on the topmost surface initiated by a scanning tunneling microscope tip

Chain polymerizations of diacetylene compound multilayer films on graphite substrates were examined with a scanning tunneling microscope (STM) at the liquid/solid interface of the phenyloctane solution. The first layer grew very quickly into many small domains. This was followed by the slow formation of the piled up layers into much larger domains. Chain polymerization on the topmost surface layer could be initiated by applying a pulsed voltage between the STM tip and the substrate, usually producing a long polymer of submicrometer length. In contrast, polymerizations on the underlying layer were never observed. This can be explained by a conformation model in which the polymer backbone is lifted up.     

Miscibility and interaction between 1-alkanol and short-chain phosphocholine in the adsorbed film and micelles

The miscibility and interaction of 1-hexanol (C6OH) and 1-heptanol (C7OH) with 1,2-dihexanoyl-sn-glycero-3-phosphocholine (DHPC) in the adsorbed films and micelles were investigated by measuring the surface tension of aqueous C6OH-DHPC and aqueous C7OH-DHPC solutions. The surface density, the mean molecular area, the composition of the adsorbed film, and the excess Gibbs energy of adsorption g(H,E), were estimated. Further, the critical micelle concentration of the mixtures was determined from the surface tension versus molality curves; the micellar composition was calculated. The miscibility of the 1-alkanols and DHPC molecules in the adsorbed film and micelles was examined using the phase diagram of adsorption (PDA) and that of micellization (PDM). The PDA and the composition dependence of g(H,E) indicated the non-ideal mixing of the 1-alkanols and DHPC molecules due to the attractive interaction between the molecules in the adsorbed film, while the PDM indicated that the 1-alkanol molecules were not incorporated in the micelles within DHPC rich region. The dependence of the mean molecular area of the mixtures on the surface composition suggested that the packing property of the adsorbed film depends on the chain length of 1-alkanol: C6OH expands the DHPC adsorbed film more than C7OH.