Taichi Ikeda

Stacked-Layer Heterostructure Films of 2D Thiophene Nanosheets and Graphene for High-Rate All-Solid-State Pseudocapacitors with Enhanced Volumetric Capacitance

Stacked-layer heterostructure films of 2D thiophene nanosheets and electrochemically exfoliated graphene are constructed for ultrahigh-rate all-solid-state flexible pseudocapacitors and micro-supercapacitors with superior volumetric capacitance due to the synergetic effect of the ultrathin pseudocapacitive thiophene nanosheets and the capacitive electrochemically exfoliated graphene.

A bistable poly[2]catenane forms nanosuperstructures

Side-chain poly[2]catenanes at the click of a switch! A bistable side-chain poly[2]catenane has been synthesized and found to form hierarchical self-assembled hollow superstructures of nanoscale dimensions in solution. Molecular electromechanical switching (see picture) of the material is demonstrated, and the ground-state equilibrium thermodynamics and switching kinetics are examined as the initial steps towards processible molecular-based electronic devices and nanoelectromechanical systems.

From Thiophene [2]Rotaxane to Polythiophene Polyrotaxane

The polythiophene polyrotaxane was synthesized through electrochemical polymerization of the [2]rotaxane consisting of the electron-rich dumbbell-shaped sexithiophene and the electron-deficient cyclophane of cyclobis(paraquat-p-phenylene). The optical and electrochemical property of the polythiophene polyrotaxane film was characterized. The material reported herein is attractive not only as a component for constructing the macromolecular machine but also as a new type of insulated molecular wire having donor-acceptor interaction between the macrocycle and the conductive polymer.

Alkyl Chain Length Dependence of the Self-Organized Structure of Alkyl-Substituted Phthalocyanines

The alkyl chain length on alkyl-substituted phthalocyanines (C(n)OPc) dependence of their self-organized structures was examined in this study. STM results indicated that the symmetry of ordered structures decreased as the alkyl chain became longer, with the exception of C(6)OPc, which preferentially formed a quasi-3-fold symmetrical structure. This could be explained by the fact that the C(n)OPc molecules are most likely to form densely packed structures. With C(n)OPc, when n = 4 to 10, the self-organized structures were dependent on the competition between how densely the molecules were arranged and how loose the intermolecular interaction energy was, caused by the formation of the densely packed structure. However, with C(n)OPc, when n = 10-18, the molecules tended to form densely packed structures by reducing the symmetry, even though the C(n)OPc molecules were distorted. When C(12)OPc and cobalt phthalocyanine were coadsorbed, the mixed system exhibited a four-fold symmetrical structure, which is rarely observed in C(12)OPc.

Luminescence properties of metallo-supramolecular coordination polymers assembled from pyridine ring functionalized ditopic bis-terpyridines and Ru(II) ion

We present the study of photophysical properties of several Ru(II)-based metallo-supramolecular coordination polymers (MEPEs) constructed from various ditopic bis-terpyridines (bis-tpy) bearing electron-rich (OMe) or electron-deficient (Br) groups at the 6-position of the pyridyl periphery and having different spacers for connecting the two tpy moieties. The MEPEs are distinct from the frequently reported analogues derived from unsubstituted tpy. The photophysical properties such as emission spectroscopic properties and lifetime at both room temperature and 77 K are presented. The MEPEs are luminescent at room temperature with quantum yields (Φlum) < 10−6 and lifetimes on a timescale of nanoseconds (τ = ca. 6.6–22.4 ns), and display strong luminescence at 77 K with Φlum = ca. 0.21–2.5 × 10−2 and lifetimes on a timescale of microseconds (τ = ca. 2.4–7.9 μs). More importantly, we find that introduction of either an electron-rich or an electron-deficient functional group at the 6-position of the ligands results in a clearly decreased absorption intensity of the derived MEPEs. This result is in contrast to the reported data in the literature where an increased intensity was observed when substitution occurred at the 4′-position of tpys, regardless of the electron-rich or electron-deficient nature of the substituents. In accordance with the absorption behaviour, substitution at the 6-position also leads to a notably different effect on the luminescent properties of the complexes. Thus, our results provide an alternative strategy for the de novo design of new materials.

Molecular motion of surface-immobilized double-decker phthalocyanine complexes.

The molecular motion of surface-immobilized double-decker phthalocyanine complexes was examined using STM. (C(8)OPc)(2)Ce (1), (C(12)OPc)(2)Ce (2), and (C(8)OPc)Ce(Pc) (3) double-decker complexes, of which two ligands contained Pc nuclei, formed well-ordered self-organized structures on their own. Square-shaped top Pc ligands were clearly observed for complexes 1, 2, and 3 even though free space presented around the top ligands caused by mixing the complexes with template molecules. However, the details of the shapes of the top ligands of complexes 1, 2, and 3 were changed by the surrounding environment. The surrounding environment was considered to have influenced the mobility of the top ligands. Another complex, (C(8)OPc)Ce(TPP) (4), had difficulty forming a self-organized structure by itself. Complex 4 could have been immobilized by coadsorbing on the substrate with the C(8)OPc template, but the intramolecular structure of the top ligands of complex 4 was difficult to observe. The results strongly suggested that combinations of molecules composed of double-decker complexes as well as the free space presented around a top ligand are important factors that control the molecular motion of immobilized double-decker complexes on solid surfaces.

Electrochromic Properties of Polythiophene Polyrotaxane Film

The electrochromic properties of a polythiophene polyrotaxane film consisting of a polythiophene backbone wrapped by the tetra-cationic cyclophane, cyclobis(paraquat-p-phenylene), were characterized. A naked reference polythiophene film, i.e., polythiophene without tetra-cationic cyclophane, was also characterized. The surface morphology and thickness of the film (L) were observed by atomic force microscopy. The surface of the naked reference polythiophene film has micrometer-scale polythiophene aggregates, which causes the darker color of the film and smaller color contrast in the electrochromic process. The polythiophene polyrotaxane gives a more homogeneous and brighter colored film owing to the suppression of molecular interactions between the polythiophene chains by the tetra-cationic cyclophanes. Potential-step chronoamperometric measurement provided the area density of the oxidizable sites (Γ) and the apparent diffusion coefficient of the charge transport in the film. From linear relationship between L and Γ, the concentrations of the oxidizable sites in the polythiophene polyrotaxane and naked reference polythiophene films were calculated to be 1.3 and 2.4 mmol cm(-3), respectively. Interestingly, the polythiophene polyrotaxane film afforded a significantly larger apparent diffusion coefficient than the naked reference polythiophene film. This result suggests that the rate-determining step of the charge transport is not the electron hopping between the polythiophene chains but the transport of charge-compensating counterions from the solvent into the polythiophene. We believe that the counteranions of the tetra-cationic cyclophane provide a pathway allowing the charge-compensating counteranions to migrate from the solvent to polythiophene. The polythiophene polyrotaxane film showed faster color change than the naked reference polythiophene film in the electrochromic reaction. These results indicate that our polythiophene polyrotaxane is a better electrochromic material than the naked reference polythiophene.

Thiophene donor-acceptor [2]rotaxanes

A series of the thiophene donor-acceptor [2]rotaxanes have been synthesized based on the inclusion complexes of cyclobis(paraquat- p-phenylene) (CBPQT4+) with thiophene, bithiophene, and terthiophene. The maximum wavelength of the charge-transfer band strongly depends on the number of thiophene units, while the association constant does not. These donor-acceptor pairs will be fascinating constituents for optoelectronic and electromechanical materials.

Study on the solution properties of thermo-responsive polyrotaxanes with different numbers of cyclic molecules

Polyrotaxanes, in which different numbers of β-cyclodextrins (β-CDs) were threaded on the triblock copolymer of poly(ethylene glycol) (PEG) and poly(propylene glycol) (PPG) capped with fluorescein-4-isothiocyanate (FITC), were prepared, and their solution properties under alkaline conditions were characterized in terms of the localization of β-CDs on the triblock copolymer and intermolecular association. Below the critical association concentration (CAC), the location of the β-CDs on the triblock copolymer was analyzed by 1H NMR. It was confirmed that the majority of the β-CDs moved towards the PPG segment with increasing temperature, regardless of the number of threading β-CDs. Above CAC, intermolecular association of the polyrotaxanes was characterized by static light scattering measurements. The association number of the polyrotaxanes decreased with increasing the number of the threading β-CDs, and the temperature dependence on the association number was reduced with increasing the number of the threading β-CDs. It is considered that the threading of β-CDs on the triblock copolymer eliminates the intermolecular interaction. These findings suggest that the number of β-CDs in the polyrotaxanes is a key parameter for the solution properties of the thermo-responsive polyrotaxanes.

Electrochromic materials using mechanically interlocked molecules

Abstract Recent investigations on the design and synthesis of electrochromic materials based on switchable three-station [2]catenanes are summarized. The reasoning and preliminary experiments behind the design of electrochemically controllable red–green–blue (RGB), donor–acceptor [2]catenanes are presented. A basis for color generation is discussed in which the tetracationic cyclophane, cyclobis(paraquat-p-phenylene), serves as the π-electron deficient ring which circumrotates between three π-electron rich recognition sites within a macrocyclic polyether, generating the three different colors (RGB) based on the different charge transfer interactions between the tetracationic cyclophane and recognition sites based on 1,5-dioxynaphthalene (R), tetrathiafulvalene (G) and benzidine (B). Issues relating to the realization of an RGB [2]catenane are raised and discussed: they include (i) color tuning, (ii) thermodynamic considerations, (iii) electrochemistry on model compounds, (iv) molecular design, (v) the electrochemical behavior of three-station [2]catenanes and (vi) electrochromism in polymer gel matrices. Finally, the challenges that need to be met in the future if the ideal RGB catenane is to be prepared, are outlined.