Frontier Molecules Group focuses on synthesis of frontier molecules possessing advanced functions and unique phenomena towards applications in security, sensing as well as bio- and medical usage. Our research contains methodologies of molecular design, synthesis, self-assembly, molecular recognition and hybridization with nanomaterials. We are aiming at development of world-top-level functional molecular materials with our original molecular design.

Development of Novel Functions and Phenomena Based on Our Original Frontier Molecules

The common and requisite core scientific technique in the Frontier Molecules Group is development of functional molecular materials by means of organic synthesis. We start from original molecular design, synthesis those uncommon molecules using molecular mutation and combinatorial methodologies, and try to obtain molecules that have novel, rarely exotic, functions as well as phenomena. Besides, methodologies of self-assembly, molecular recognition, and hybridization with other materials can be essential to architect unique molecular materials.

Potential applications from those uniquely developed molecular materials would be towards:

• security ink
• pressure-sensors and actuators for wearable/stretchable healthcare devices
• bio- and medical usage which need deep understanding the interactions between developing molecules and task-specific bio-moieties
• sensors and adsorbents (gases, alcohols, water content) for industry and safety

Solvent-free Luminous Molecular Liquids

・Angew. Chem. Int. Ed., 2012, 51, 3391-3395. [link]

Isolation of a π-core by covalently attached flexible hydrocarbon chains has been employed to synthesize blue-emitting oligo(p-phenylenevinylene) (OPV) liquids with tunable viscosity and optical properties. A solvent-free, stable, white-light emitting ink/paint, which can be applied onto various surfaces and even onto LEDs, was made by blending of liquid OPVs with emissive solid dopants.

Full-color Luminescence Tuning with Liquid Anthracenes

・Nature Communications, 2013, 4, 1969. [link]

Nonvolatile room-temperature luminescent molecular liquids are a new generation of organic soft materials. They possess high stability, versatile optical properties, solvent-free fluid behavior and can effectively accommodate dopant dye molecules. Here we introduce an approach to optimize anthracene-based liquid materials, focussing on enhanced stability, fluorescence quantum yield, color tunability and processability, with a view to flexible electronic applications. Enveloping the anthracene core in low-viscosity branched aliphatic chains results in stable, nonvolatile, emissive liquid materials. Up to 96% efficient energy-transfer-assisted tunable emission is achieved by doping a minute amount of acceptor dye in the solvent-free state. Furthermore, we use a thermoresponsive dopant to impart thermally controllable luminescence colors. The introduced strategy leading to diverse luminescence colors at a single blue-light excitation can be an innovative replacement for currently used luminescent materials, providing useful continuous emissive layers in developing foldable devices.

Supercooling Liquids

・Chem. Sci., 2018, 9, 6774-6778. [link]

Metastable states of soft matters are extensively used in designing stimuli-responsive materials. However, the non-steady properties may obstruct consistent performance. Here we report an approach to eradicate the indistinguishable metastable supercooled state of functional molecular liquids (FMLs), which remains as a liquid for weeks or months before crystallizing, via rational molecular design. The phases (solid, kinetically stable liquid, and supercooled liquid) of a model FML, branched alkyl chain-substituted 9,10-diphenylanthracene (DPA), are found to be governed by subtle alterations of the molecular structure (alkyl-DPA ratio and bulkiness of the DPA unit). We thus outline molecular design principles to avoid supercooled FML formation. Moreover, we demonstrate a practical technique to rapidly discriminate supercooled FMLs (within 5 h) by accelerating their crystallization in differential scanning calorimetry heating via pre-annealing or relatively slow scanning.

Viscoelastic Conjugated Polymer Fluids

・Angew. Chem. Int. Ed., 2019, 58, 9581-9585. [link]

The introduction of optoelectronic functions into viscoelastic polymers can yield highly sophisticated soft materials for biomedical devices and autonomous robotics. However, viscoelasticity and excellent optoelectronic properties are difficult to achieve because the presence of a large number of π-conjugated moieties drastically stiffens a polymer. Here, we report a variation of additive-free viscoelastic conjugated polymers (VE-CPs) at room temperature by using an intact π-conjugated backbone and bulky, yet flexible, alkyl side chains as “internal plasticizers.” Some of these polymers exhibit gel- and elastomer-like rheological behaviors without cross-linking or entanglement. Furthermore, binary blends of these VE-CPs exhibit a never-seen-before dynamic miscibility with self-restorable and mechanically induced fluorescence color changes.

(Collaboration with Prof. C. Pan @ Shenzhen University, China)

Self-assembly of “Hydrophobic Amphiphiles”, Alkylated Fullerene Molecules

Nature Chemistry, 2014, 6, 690-696. [link]

Supramolecular assembly can yield ordered structures by taking advantage of the cumulative effect of multiple non-covalent interactions between adjacent molecules. The thermodynamic origin of many self-assembled structures in water is the balance between the hydrophilic and hydrophobic segments of the molecule. Here, we show that this approach can be generalized to use solvophobic and solvophilic segments of fully hydrophobic alkylated fullerene molecules. Addition of n-alkanes results in their assembly—due to the antipathy of C₆₀ towards n-alkanes—into micelles and hexagonally packed gel-fibres containing insulated C₆₀ nanowires. The addition of pristine C₆₀ instead directs the assembly into lamellar mesophases by increasing the proportion of π-conjugated material in the mixture. The assembled structures contain a large fraction of optoelectronically active material and exhibit comparably high photoconductivities. This method is shown to be applicable to several alkyl–π-conjugated molecules, and can be used to construct organized functional materials with π-conjugated sections.

Self-Assembled and Nonassembled Alkylated-Fullerene Materials
・Acc. Chem. Res., 2019, 52, 1834-1843. [link]

[PI: Prof. Dr. Takashi Nakanishi]

Science of Metal Complex Sequences

See the following [link]

[PI: Dr. Kentaro Tashiro]

Supramolecular Polymer Wrapped Single-Walled Carbon Nanotube towards Portable Nerve Agent Sensor

・ACS Appl. Mater. Interface, 2017, 9, 38062-38067. [link]

・J. Am. Chem. Soc., 2016, 138, 8221-8227. [link]

Chemical sensors offer opportunities for improving personal security, safety, and health. To enable broad adoption of chemical sensors requires performance and cost advantages that are best realized from innovations in the design of the sensing (transduction) materials. Ideal materials are sensitive and selective to specific chemicals or chemical classes and provide a signal that is readily interfaced with portable electronic devices. Herein we report that wrapping single walled carbon nanotubes with metallo-supramolecular polymers creates sensory devices with a dosimetric (time- and concentration-integrated) increase in electrical conductivity that is triggered by electrophilic chemical substances such as diethylchlorophosphate, a nerve agent simulant. The mechanism of this process involves the disassembly of the supramolecular polymer, and we demonstrate its utility in a wireless inductively powered sensing system based on near-field communication technology. Specifically, the dosimeters can be powered and read wirelessly with conventional smartphones to create sensors with ultratrace detection limits.

[PI: Dr. Shinsuke Ishihara]