|
内容記述 |
1. Introduction<br /> Construction of well ordered surface structures with functional molecular<br />building blocks have attracted much attentions because of their potential applications<br />for novel functional materials. In recent years, surface modification using<br />self-assembly of organic molecules has been significantly advanced by scanning<br />tunneling microscopy (STM) in ultra-high-vacuum (UHV)<sup>1,2</sup> or under ambient<br />conditions.<sup>3,4,5,6,7,8</sup>Especially, in situ</i> STM at the solid-liquid interfaces<sup>3</sup> is a powerful<br />and useful technique to characterize local surface structure, electronic state and<br />surface dynamics of materials composed by organic molecules with submolecular<br />resolution. Numbers of self-assembled structures on surfaces have been observed using <i>in situ</i> STM at the solid-liquid interface. <sup>3,4,5, 6,7,8</sup> However, few report focused on<br />influence of intermolecular and/or moleculai-surface interactions of the component<br />molecules systematically for the stable structures formed at the solid-liquid interface. <br />I have investigated systematically the effects of the molecular structure on<br />self-organized structure of porphyrin and naphthalenediimide, and their surface<br />dynamics to explore new surface modification method based on self-assembled<br />structures<br /><br />2. Investigation of Vanadyl and Cobalt(II) Octaethylporphyrin Self-Assembled<br />Monolayer Arrays on Highly Oriented Pyrolytic Graphite (HOPG) by STM<br /> Porphyrin and related compounds not only play an important role in<br />photosynthesis, biochemistry and catalysis in nature, but are also important<br />candidates for building blocks of future molecular devices.<sup>9</sup> These compounds also have attracted significant attentions in the fields of life science, material science and<br />physics because of their unique electronic structures, spectroscopic properties based<br />on the large conjugated π-electron system and existence of metal coordination sites. <br />Fundamental characterization of porphyrin metallate self-assembled structures by<br />STM will contribute significantly to future applications of molecular devices. <br />Two-dimensional crystals of ［2,3,7,8,12,13,17,18-octaethyl 21<i>H</i>,23<i>H</i>-porphine］<br />vanadium（IV)oxide and cobalt(II) (VOOEP and CoOEP, respectively) at the interface of<br />1-tetradecene and HOPG surface were studied by STM. The lattice parameters were<br />determined for VOOEP (<i>a</i> = 1.61±0.1 nm, <i>b</i>= 1.46±0.05 nm, <i>Γ</i>=61±3<small>○</small>) and CoOEP<br />(<i>a</i> = 1.48±0.08 nm, <i>b</i>= 1.42±0.07nm, <i>Γ</i>=62.0±4<small>○</small>), which were calibrated using the<br />HOPG lattice as the reference. High-resolution STM showed different type of the<br />images for these two porphyrin molecules. The STM image of VOOEP was a square<br />shape with four fold bright spots probably corresponding to the π-system of the<br />porphyrin ring, and that of CoOEP showed a bright spot at the center metal site. <br />3. Effect of Alkyl Chain Length to the Two-Dimensional Structure and STS Studies of<br />N, N'-bis(alkyl)naphthalenediimide on HOPG<br /> Long alkyl chains are widely utilized as "anchor" groups for immobilizing<br />organic molecules on graphite surface under ambient conditions in STM measurements. <br />However, few report focused on effects of the alkyl chain length to self-assembled<br />structures on HOPG systematically. STM investigations of self assembled structures<br />of N,N'-bis(alkyl)naphthalenediimide (NDI) with a series alkyl chains ranging from<br />propyl to octadecyl were carried out at l-tetradecene/HOPG interface. NDI derivatives<br />were prepared by the usual condensation reactions. Each NDI derivatives is<br />abbreviated as CX-NDI (X is the corresponding carbon number of alkyl chains). The<br />self'-assembled structure of them on HOPG showed strong dependence on the alkyl<br />chain length. I classified them into six types; (1) linear arrays with row lattice<br />structure was observed in C3-NDI and C4-NDI, (2) chiral windmill structure in C4 and<br />C5-NDI, (3) honeycomb structure in C6〜C9-NDI, (4) chiral honeycomb structure in C10<br />and C12-NDI, (5) pseudo honeycomb structure containing super lattice in C11-NDI, (6) <br />typical alkyl lamellar structure in C13〜C18-NDI. In the self-assembled structure of C4, <br />C5, C10, C11 and C12-NDI, meta-stable state structures were also observed. Molecular<br />dynamics (MD) simulation for C3, C4, C9 and C18 are well coincident with the STM<br />observations. Results of STM, MD simulation and X-ray single crystallography of<br />C4-NDI clearly suggest that CH/O hydrogen bonding interaction is the critical driving<br />force for the self-assembling. <br /><br />4. Surface Dynamics and Nano-Size-Manipulation on Self-Assembled N,N'-bis(alkyl)<br />naphthalenediimide on Graphite<br /> During the STM observation of the self-assembled structure of NDI, thermally<br />meta-stable states were found. I investigated dependence of the self-assembled<br />structure of C11-NDI on temperature. A distort honeycomb structure was observed as a<br />meta-stable state of C11-NDI, which converted to the thermally stable structure<br />containing super lattice upon heating. The dynamic transition of' the former<br />structure to the latter was also observed. <br /><br />5. Conclusion<br /> I have investigated self-assembled structures of porphyrin and NDI derivatives in<br />order to explore new self-assembled method and phenomena of surface dynamics. <br /> Self-assembled structures of two metallo octaethylporphyrins, VOOEP and CoOEP, <br />were structurally characterized using STM. High-resolution STM images reflecting<br />difference of the central metal were obtained. <br /> Self assembled structures of NDI with a series of alkyl chain length ranging from<br />propyl to octadecyl (excluding heptadecyl) were characterized using STM at<br />1-tetradecene / HOPG interface. Structural transition induced by the difference of<br />alkyl chain length was observed on self-assembled 2D structures of NDI derivatives. <br />Competition of inter-molecular CH/O type hydrogen bonding interaction and intermolecular alkyl-alkyl interaction lead to complex self-assembled structures on<br />HOPG. Thermal effects to the self-assembled structures were also investigated. <br />Direct observation of a local structural transition was succeeded on C11-NDI<br />self-assembled structure. <br /> These surface studies described above will open a new method for self-assembled and solution-processed nano-fabrication. |
要旨・審査要旨 (308.7 kB)
