Seiichi Furumi

Hierarchical Assembly of a Phthalhydrazide-Functionalized Helicene†

Exploration of a general principle to control the morphology and electronic states of assemblies based on p-conjugated molecules in order to create various functional materials with optimized p-electronic properties has been an important research target in supramolecular chemistry. Among pconjugated molecules, helicenes, which consist of orthoannulated aromatic rings that have a helical chirality, have attracted much attention because of their inherent chirality, which has recently led to promising applications in asymmetric catalysis, enantioselective molecular recognition, and chirooptical or electrooptical functional materials. For example, nonracemic helicene molecules form supramolecular architectures in organogels, the liquid-crystalline phase, and crystals to form aggregates that exhibit second-order nonlinear optical (NLO) and chirooptical properties. In these assemblies, helicenes accumulate around 1D structures. In order to construct such a system, we chose a disk-shaped trimer formation of phthalhydrazide units, in which the resulting trimeric disk is known to assemble into 1D structures. 6] Rational introduction of a helicene moiety into the phthalhydrazide unit would lead to a new supramolecular assembly of helicenes, which would exhibit intriguing chirooptical properties. Herein we report a new helicene 1 that bears a phthalhydrazide unit as a multiple-hydrogenbonding site (Scheme 1). We found that the trimeric disk

Electrical control of the structure and lasing in chiral photonic band-gap liquid crystals

This letter describes the electrical control of structure and lasing in the photonic bandgaps of cholesteric liquid crystals (CLCs). Photoexcitation of dye-doped CLC cells with a linearly polarized laser gives rise to laser emission at the edge(s) of the chiral photonic band gap. Applying voltages to the optically pumped CLC cells enables reversible switching of the laser action as a result of the structural changes in the chiral photonic band gap.

Enantioselective Synthesis and Enhanced Circularly Polarized Luminescence of S-Shaped Double Azahelicenes

The enantioselective synthesis of azahelicenes and S-shaped double azahelicenes has been achieved via the Au-catalyzed sequential intramolecular hydroarylation of alkynes. The use of excess AgOTf toward a Au(I) complex is crucial for this transformation. Interestingly, the circularly polarized luminescence activity of the S-shaped double azahelicenes was significantly higher than that of the azahelicenes.

Thermally Assisted Photonic Inversion of Supramolecular Handedness

Spiraling into control: A photoresponsive supramolecular assembly demonstrates that light, along with heating (Δ) and cooling (), can cause chiral communication between molecules. This effect leads to bias in the helicity of the complex, causing a reversible switching of macroscopic handedness, as shown by a reversal of sign of the circularly polarized luminescence (CPL) that is emitted.

Phototunable photonic bandgap in a chiral liquid crystal laser device

This letter describes the phototunable photonic bandgap of cholesteric liquid crystal (CLC) doped with a fluorescent dye to generate the distributed feedback effect. Photoirradiation of the dye-doped CLC cell under UV light at 254 nm resulted in continuous changes in the chiral photonic bandgap from 550 to 720 nm due to photolysis reaction of the cholesteryl iodide embedded in the CLC host. We showed that the laser oscillation wavelength could be controlled in a wide wavelength range from 610 to 700 nm by photoassisted adjustment of CLC photonic bandgaps.

Glass‐Forming Cholesteric Liquid Crystal Oligomers for New Tunable Solid‐State Laser

[*] Dr. S. Furumi National Institute for Materials Science (NIMS) 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047 (Japan) E-mail: furumi.seiichi@nims.go.jp Prof. Dr. N. Tamaoki National Institute of Advanced Industrial Science and Technology (AIST) Tsukuba Central 5, 1-1-1 Higashi, Tsukuba 305-8565 (Japan) E-mail: tamaoki@es.hokudai.ac.jp [+] Present address: Research Institute for Electronic Science (RIES), Hokkaido University, N20, W10, Kita-ku, Sapporo 001-0020 (Japan)

Aligned 1-D nanorods of a π-gelator exhibit molecular orientation and excitation energy transport different from entangled fiber networks.

Linear π-gelators self-assemble into entangled fibers in which the molecules are arranged perpendicular to the fiber long axis. However, orientation of gelator molecules in a direction parallel to the long axes of the one-dimensional (1-D) structures remains challenging. Herein we demonstrate that, at the air-water interface, an oligo(p-phenylenevinylene)-derived π-gelator forms aligned nanorods of 340 ± 120 nm length and 34 ± 5 nm width, in which the gelator molecules are reoriented parallel to the long axis of the rods. The orientation change of the molecules results in distinct excited-state properties upon local photoexcitation, as evidenced by near-field scanning optical microscopy. A detailed understanding of the mechanism by which excitation energy migrates through these 1-D molecular assemblies might help in the design of supramolecular structures with improved charge-transport properties.

Widely Tunable Lasing in a Colloidal Crystal Gel Film Permanently Stabilized by an Ionic Liquid

Widely tunable laser action by low threshold optical excitation can be realized by a colloidal crystal gel (CC-G) film permanently stabilized by a non-volatile ionic liquid. The CC-G film consists of a non-close-packed structure of microparticles immobilized in a polymer gel. Optical excitation with green light gives rise to a single and very narrow laser emission with red color. The single laser emission peak can be tuned in a wide wavelength range by applying mechanical stress.

Recent progress in chiral photonic band-gap liquid crystals for laser applications

This article describes a brief review of recent research advances in chiral liquid crystals (CLCs) for laser applications. The CLC molecules have an intrinsic capability to spontaneously organize supramolecular helical assemblages consisting of liquid crystalline layers through their helical twisting power. Such CLC supramolecular helical structures can be regarded as one-dimensional photonic crystals (PhCs). Owing to their supramolecular helical structures, the CLCs show negative birefringence along the helical axis. Selective reflection of circularly polarized light is the most unique and important optical property in order to generate internal distributed feedback effect for optically-excited laser emission. When a fluorescent dye is embedded in the CLC medium, optical excitation gives rise to stimulated laser emission peak(s) at the band edge(s) and/or within the CLC selective reflection. Furthermore, the optically-excited laser emission peaks can be controlled by external stimuli through the self-organization of CLC molecules. This review introduces the research background of CLCs carried out on the PhC realm, and highlights intriguing precedents of various CLC materials for laser applications. It would be greatly advantageous to fabricate active CLC laser devices by controlling the supramolecular helical structures. Taking account of the peculiar features, we can envisage that a wide variety of supramolecular helical structures of CLC materials will play leading roles in next-generation optoelectronic molecular devices.

Synthesis and efficient circularly polarized light emission of an optically active hyperbranched poly(fluorenevinylene) derivative

An optically active, hyperbranched poly(fluorenevinylene) derivative was synthesized by polymerization of (-)-2,4,7-tris(bromomethyl)-9-neomenthyl-9-pentylfluorene. A spin-coated film sample of the polymer exhibited efficient circularly polarized light (CPL) emission in the visible range of 400-700 nm on photo excitation even without annealing processes leading to chain ordering.