Giseop Kwak

Fluorescent Actuator Based on Microporous Conjugated Polymer with Intramolecular Stack Structure

IO N Artifi cial smart materials that respond to external stimuli, such as heat, light, chemicals, and electric fi elds, have recently attracted considerable attention for applications to actuators and sensors. [ 1 ] An wide range of conjugated polymers have been developed as functional active materials not only for soft actuation but also for optical sensing. [ 1h , 2 ] To our best knowledge, however, there are no reports on conjugated polymers showing a simultaneous optical output signal and actuation behavior. The actuation of soft materials in response to chemical stimuli is based on a reversible expansion/contraction in volume. [ 3 ]

Synthesis, Characterization and Optical Properties of a Novel Si‐Containing σ‐π‐Conjugated Hyperbranched Polymer

The polymerization of bis(4-ethynylphenyl)methylsilane catalyzed by RhI(PPh 3 ) 3 afforded a regio- and stereoregular hyperbranched polymer, hb-poly[(methylsilylene)bis(1,4-phenylene-trans-vinylene)] (poly(1)), containing 95% trans-vinylene moieties. The weight loss of this polymer at 900°C in N 2 was 9%. Poly(1) displayed and absorption due to π-π* transition around 275 nm as a shoulder and a weak absorption around 330 nm due to π-to-σ charge transfer, which was hardly seen in the corresponding linear polymer.

Fabrication and characterization of collagen-immobilized porous PHBV/HA nanocomposite scaffolds for bone tissue engineering

The porous composite scaffolds (PHBV/HA) consisting of poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and hydroxyapatite (HA) were fabricated using a hot-press machine and salt-leaching. Collagen (type I) was then immobilized on the surface of the porous PHBV/HA composite scaffolds to improve tissue compatibility. The structure and morphology of the collagen-immobilized composite scaffolds (PHBV/HA/Col) were investigated using a scanning electron microscope (SEM), Fourier transform infrared (FTIR), and electron spectroscopy for chemical analysis (ESCA). The potential of the porous PHBV/HA/Col composite scaffolds for use as a bone scaffold was assessed by an experiment with osteoblast cells (MC3T3-E1) in terms of cell adhesion, proliferation, and differentiation. The results showed that the PHBV/HA/Col composite scaffolds possess better cell adhesion and significantly higher proliferation and differentiation than the PHBV/HA composite scaffolds and the PHBV scaffolds. These results suggest that the PHBV/HA/Col composite scaffolds have a high potential for use in the field of bone regeneration and tissue engineering.

Optically Active Conjugated Polymer from Solvent Chirality Transfer Polymerization in Monoterpenes

Disubstituted acetylene monomers [1,2-diphenylacetylenes (DPAs: DPA-pC1, DPA-mC1, DPA-pC8); 1-phenyl-2-hexylacetylene (PHA-pC1)] are tested for asymmetric polymerization in chiral monoterpenes used as solvents and compared with the corresponding monosubstituted acetylene monomer [1-phenylacetylene (PA-pC1)]. DPA-pC1 containing a trimethylsilyl group in the para-position of the phenyl ring produces an optically active polymer with a large Cotton effect, despite the absence of a stereogenic center. The polymer sample obtained by polymerization in 87% ee (-)-α-pinene shows the strongest CD signal (gCD value at 385 nm: ∼3.2 × 10⁻³). The Cotton bands of the polymers obtained in (-)- and (+)-α-pinenes show the opposite sign in the CD signals. Theoretical calculations show that only the cis-cisoid model adopts a helical conformation. A time-correlated single photon counting experiment shows that the emission of the chiral polymer originates from a virtually single excited species with a 98% component fraction. This polymer solution does not show any significant decrease in gCD value over a wide temperature range of 20 to 80 °C. No noticeable decrease in the gCD value is detected when the polymer solution is kept at relatively low temperatures for a prolonged period (35 d). In contrast, the other polymers show no CD signal.

Photoisomerization and emission properties of trans- and cis-poly(dimethylsilylenephenylenevinylene)s

The photoirradiation of trans- and cis-poly(dimethylsilylenephenylenevinylene)s gave cis-rich mixtures at equilibrium states. The degree of the photoisomerization could be exactly evaluated by comparing the UV spectra of the photoirradiated solutions with those of the trans and cis polymers. The geometric configuration of the trans and cis polymers was thermally stable and hardly changed even though they were heated. The trans and cis polymers exhibited different emission properties; e.g., trans polymer; λ max = 400 nm, quantum yield 3.4 × 10 -3 ; cis polymer: λ max = 380 nm, quantum yield = 1.5 × 10 -1 .

Properties, Functions, Chemical Transformation, Nano-, and Hybrid Materials of Poly(diphenylacetylene)s toward Sensor and Actuator Applications

ABSTRACT This review examines poly(diphenylacetylene)s (PDPAs) as a special class of conjugated polymers. Various properties of PDPAs, including liquid crystallinity, fluorescence (FL) emission, and chirality are described in detail. The FL origin of PDPAs is intramolecular excimer emission that comes from the intramolecular stack structure of side phenyl rings. PDPAs show remarkable FL responses to external stimuli such as solvents, heat, surface tension, and pressure. PDPAs are easily transformed to desired forms via polymer reactions, chiral solvent annealing, and coupling with long alkyl chains. Very useful nanomaterials and hybrid materials can be prepared by chain quenching and in situ hybridization methods. PDPAs and their nano- and hybrid materials show highly advanced functions toward sensors and actuators.

Switching in molecular shapes: main chain length driven rod-circle transition of isolated helical polysilanes

Unique conformations such as rod, semicircle, and circle structures of isolated semi-flexible helical polysilanes were observed by atomic force microscopy (AFM); the chain topology was significantly related to the chain length (molecular weight) on the surfaces.

Fluorescence turn-on response of a conjugated polyelectrolyte with intramolecular stack structure to biomacromolecules

An anionic conjugated polyelectrolyte based on polydiphenylacetylene showed a significant fluorescence turn-on response to positively-charged proteins through a conformational relaxation of its intramolecular stack structure.

Fluorescent Molecular Rotor-in-Paraffin Waxes for Thermometry and Biometric Identification

Novel thermoresponsive sensor systems consisting of a molecular rotor (MR) and paraffin wax (PW) were developed for various thermometric and biometric identification applications. Polydiphenylacetylenes (PDPAs) coupled with long alkyl chains were used as MRs, and PWs of hydrocarbons having 16-20 carbons were utilized as phase-change materials. The PDPAs were successfully dissolved in the molten PWs and did not act as an impurity that prevents phase transition of the PWs. These PDPA-in-PW hybrids had almost the same enthalpies and phase-transition temperatures as the corresponding pure PWs. The hybrids exhibited highly reversible fluorescence (FL) changes at the critical temperatures during phase transition of the PWs. These hybrids were impregnated into common filter paper in the molten state by absorption or were encapsulated into urea resin to enhance their mechanical integrity and cyclic stability during repeated use. The wax papers could be utilized in highly advanced applications including FL image writing/erasing, an array-type thermo-indicator, and fingerprint/palmprint identification. The present findings should facilitate the development of novel fluorescent sensor systems for biometric identification and are potentially applicable for biological and biomedical thermometry.

Remarkable Change in Fluorescence Emission of Poly(diphenylacetylene) Film via in situ Desilylation Reaction: Correlation with Variations in Microporous Structure, Chain Conformation, and Lamellar Layer Distance

Fluorescence (FL) emission properties, microporous structures, energy-minimized chain conformations, and lamellar layer structures of the silicon-containing poly(diphenylacetylene) derivative of p-PTMSDPA before and after desilylation were investigated. The nitrogen-adsorption isotherms of p-PTMSDPA film before and after desilylation were typical of type I, indicating microporous structures. The BET surface area and pore volume of the p-PTMSDPA film were significantly reduced after the desilylation reaction, simultaneously, its FL emission intensity remarkably decreased. The theoretical calculation on both model compounds of p-PTMSDPA and its desilylated polymer, PDPA, showed a remarkable difference in chain conformation: The side phenyl rings of p-PTMSDPA are discontinuously arranged in a zig-zag pattern, while the PDPA is continuously coiled in a helical manner. The lamellar layer distance (LLD) in the p-PTMSDPA film significantly decreased after the desilylation reaction.