Wireless Electrochemical Gel Actuators.

Soft actuators generate motion in response to external stimuli and are indispensable for soft robots, particularly future miniature robots with complex structure and motion. Similarly to conventional hard robots, electricity is suitable for the stimulation. However, previous electrochemical soft actuators require a tethered connection to a power supply, limiting their size, structure, and motion. Here, wireless electrochemical soft actuators composed of hydrogels and driven by bipolar electrochemistry are reported. Viologen, which dimerizes by one-electron reduction and dissociates by one-electron oxidation, is incorporated in the side chains of the gel networks and works as a reversible cross-link. Wireless and reversible electrochemical actuation of the hydrogels, i.e., muscle-like shrinking and swelling, is demonstrated at microscopic and even macroscopic scales.

Thermally Stable Photomechanical Molecular Hinge: Sterically Hindered Stiff-Stilbene Photoswitch Mechanically Isomerizes.

Molecular photoswitches are extensively used as molecular machines because of the small structures, simple motions, and advantages of light including high spatiotemporal resolution. Applications of photoswitches depend on the mechanical responses, in other words, whether they can generate motions against mechanical forces as actuators or can be activated and controlled by mechanical forces as mechanophores. Sterically hindered stiff stilbene (HSS) is a promising photoswitch offering large hinge-like motions in the E/Z isomerization, high thermal stability of the Z isomer, which is relatively unstable compared to the E isomer, with a half-life of ca. 1000 years at room temperature, and near-quantitative two-way photoisomerization. However, its mechanical response is entirely unexplored. Here, we elucidate the mechanochemical reactivity of HSS by incorporating one Z or E isomer into the center of polymer chains, ultrasonicating the polymer solutions, and stretching the polymer films to apply elongational forces to the embedded HSS. The present study demonstrated that HSS mechanically isomerizes only in the Z to E direction and reversibly isomerizes in combination with UV light, i.e., works as a photomechanical hinge. The photomechanically inducible but thermally irreversible hinge-like motions render HSS unique and promise unconventional applications differently from existing photoswitches, mechanophores, and hinges.

Impact of Nitroxyl Radicals on Photovoltaic Conversion Properties of Dye-Sensitized Solar Cells.

Nitroxyl radicals, characterized by unique redox properties, have been investigated for their potential influence on the photovoltaic conversion properties of dye-sensitized solar cells (DSSCs). In this study, we investigated the influence of nitroxyl radicals as donor sites in DSSCs. We observed that the redox activity of nitroxyl radicals significantly enhanced the photovoltaic conversion efficiency of DSSCs; this finding can offer new insights into the application of these radicals in solar energy conversion. Furthermore, we found that increasing the proportion of nitroxyl radicals improved the DSSC performance. Through a combination of experimental and analytical approaches, we elucidated the mechanism underlying this enhancement and highlighted the potential for more efficient DSSCs using nitroxyl radicals as key components. These findings provide new avenues for developing advanced DSSCs with improved performances and sustainability.

Thermoelectric Properties of Conductive Freestanding Films Prepared from PEDOT:PSS Aqueous Dispersion and Ionic Liquids.

In this study, freestanding poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films modified with an ionic liquid (IL) were synthesized assuming modulization. These films were easily peeled off the glass substrate in water, producing hydrophobic and flexible freestanding films that exhibited extremely high mechanical strengths. The thermoelectric properties of the IL-doped PEDOT:PSS films depended on the amount of IL incorporated. To analyze the mechanism of this dependence in detail, the compositions, higher-order structures, and electronic states of the polymer films were studied by X-ray photoelectron spectroscopy, X-ray diffraction analysis, and electronic absorption spectroscopy. In addition, the carrier density in the polymer film was quantified using electrochemical techniques, and its correlation with the thermoelectric conversion properties was analyzed.

Sterically Hindered Stiff-Stilbene Photoswitch Offers Large Motions, 90% Two-Way Photoisomerization, and High Thermal Stability.

Molecular photoswitches have been widely used as molecular machines in various fields due to the small structures and simple motions generated in reversible isomerization. However, common photoswitches, as represented by azobenzene (AB), cannot combine both large motions and high thermal stability, which are critically important for some practical applications in addition to high photoisomerization yields. Here, we focus on a promising photoswitch, stiff stilbene (SS), and its derivative, sterically hindered SS (HSS). The detailed investigation of their performance with a comparison to AB demonstrated that HSS is an outstanding photoswitch offering larger motions than AB and SS, ca. 90% photoisomerization in both E-to-Z and Z-to-E directions, and significantly high thermal stability with a half-life of ca. 1000 years at room temperature. The superior performance of HSS promises its use in various applications, even where previous photoswitches have troubles and are unavailable.

Self-doped conducting polymers in biomedical engineering: Synthesis, characterization, current applications and perspectives.

Recent studies willingly agree that conducting polymers (CPs) are attractive materials for biomedical engineering purposes, mainly because of their unique physicochemical characteristics combining electrical conductivity and high biocompatibility. Nevertheless, the applicability of CPs is restricted by their limited stability under physiological conditions, associated with a decrease in electrical conductivity upon dedoping. Accordingly, modifying chemical structure of CPs to exhibit a self-doping effect seems to be an appealing approach aimed to enhance their functionality. The aim of this review is to provide a current state-of-the-art in the research concerning self-doped CPs, particularly those with potential biomedical applications. After presenting a library of available structure modifications, we describe their physicochemical characteristics, focusing on achievable conductivities, electrochemical, optical and mechanical behaviour, as well as biological properties. To highlight high applicability of self-doped CPs in biomedical engineering, we elaborate on biomedical areas benefiting most from using this type of conducting materials.

Seebeck coefficients of regioregular poly(3-hexylthiophene) correlated with doping levels.

Thermoelectric properties of regioregular poly(3-hexylthiophene) (P3HT) were investigated in correlation with doping level measured by a potential-step chronocoulometry (PSC) method. It was found that the log-log plot of Seebeck coefficients against doping levels showed a good linearity, whose slope value was around -1.

Electrical Characteristics of Pentacene Films on Cross-Linked Polymeric Insulators of Varying Thicknesses.

Pentacene films vacuum-sublimed on a cross-linked polymeric insulator (CPVP-C6) prepared using poly(4-vinylphenol) (PVP) and 1,6-bis(trichlorosilyl)hexane (C6) were studied with a special concern on possible influences of the CPVP-C6 thickness on the electrical characteristics of the pentacene films. It was found that the conductivities of the pentacene films on a thin CPVP-C6 film (10 nm) were approximately 2 orders of magnitude higher than those on a glass substrate and increased slightly with the increase in the thickness of the underlying CPVP-C6 film. In addition, the X-ray diffraction measurements showed that the stacking structure of pentacene molecules was remarkably enhanced by increasing the thickness of the CPVP-C6 film, suggesting that the increase in conductivity is due, at least in part, to the improvement in carrier mobilities caused by the growth of large pentacene grains. An attempt to directly evaluate carrier mobilities using pentacene/CPVP-C6 field-effect transistors was made, and a seeming increase in the carrier mobilities observed with the increase in the CPVP-C6 thickness was ascribed to a hygroscopic nature of the CPVP-C6 film, which was evidenced by the capacitance and quartz crystal microbalance measurements. Possible reasons are discussed to explain the enhanced conductivities of the pentacene films on the increased thicknesses of CPVP-C6.

Dye-sensitized solar cells based on D-π-A fluorescent dyes with two pyridyl groups as an electron-withdrawing-injecting anchoring group.

D-π-A fluorescent dye with two pyridyl groups as an electron-withdrawing-injecting anchoring group possessing a high coordinate bonding ability to Lewis acid sites on the TiO2 surface, which can lead to high dye loading on the TiO2 film and efficient electron injection, has been developed as a new type of D-π-A dye sensitizer for dye-sensitized solar cells.

Intermolecular distances of carboxylated TEMPO derivatives on TiO2 evaluated by spin-probe ESR.

Nearest-neighbor intermolecular distances of molecules adsorbed on the surface of nanocrystalline TiO(2) particles were evaluated by the electron spin resonance (ESR) technique with molecules having a nitroxide radical and a carboxyl group as a spin probe to clarify their aggregation behaviors on TiO(2) and the influence of coadsorbates.

Effective and selective bisphenol A synthesis on a layered silicate with spatially arranged sulfonic acid.

The silylated derivatives of a layered alkali silicate, magadiite, modified with propylsulfonic or arylsulfonic acid were synthesized and used as catalysts for an acid-catalyzed condensation of phenol with acetone. The propylsulfonated magadiites with a different amount of the attached silyl group were synthesized by the silylation of the dodecylammonium-exchanged magadiite with the tuned amount of 3-(mercaptopropyl)trimethoxysilane and the subsequent oxidation of the attached thiol to sulfonic acid. The arylsulfonated magadiite was synthesized by the silylation of the dodecylammonium-exchanged magadiite with 2-(4-chlorosulfonylphenyl)ethyltrimethoxysilane and the subsequent hydrolysis of the attached sulfonyl chloride to sulfonic acid. The X-ray diffraction (XRD) patterns and elemental mappings of the products, and the photoluminescent spectra of the Eu(3+)-exchanged products suggested that propylsulfonic or arylsulfonic acid was homogeneously distributed in the interlayer space. When all the sulfonated materials were used as an acid catalyst for condensation between phenol and acetone, p,p' bisphenol A selectively formed over the o,p' isomer, and higher yield and selectivity were attained on the catalysts with larger amount of the attached sulfonic acid. When the interlayer space of the propylsulfonated magadiite was expanded by the co-attachment of octadecylsilyl group, lower selectivity was obtained. The arylsulfonated magadiite showed considerably higher p,p' bisphenol A yield than the propylsulfonated magadiites.

Development of a simple method for fabrication of transparent conductive films with high mechanical strength.

We have developed a simple method of fabricating transparent conductive films with a high mechanical strength on glass and indium tin oxide substrates. It does not require a large excess of organic solvents and polymerization catalysts and can yield smooth films by spin-coating of a mixture of a commercially available aqueous dispersion of poly(3,4-ethylenedioxythiophene)-poly(4-styrene sulfonate) and a neat liquid of tetraethyl orthosilicate. Preparation conditions such as feed ratio, kinds of additives, and annealing temperature and time were optimized to give highly conductive, transparent and mechanically strong films.

Dye-sensitized solar cells based on donor-π-acceptor fluorescent dyes with a pyridine ring as an electron-withdrawing-injecting anchoring group.

A new-type of donor-acceptor π-conjugated (D-π-A) fluorescent dyes NI3-NI8 with a pyridine ring as electron-withdrawing-injecting anchoring group have been developed and their photovoltaic performances in dye-sensitized solar cells (DSSCs) are investigated. The short-circuit photocurrent densities and solar energy-to-electricity conversion yields of DSSCs based on NI3-NI8 are greater than those for the conventional D-π-A dye sensitizers NI1 and NI2 with a carboxyl group as the electron-withdrawing anchoring group. The IR spectra of NI3-NI8 adsorbed on TiO(2) indicate the formation of coordinate bonds between the pyridine ring of dyes NI3-NI8 and the Lewis acid sites (exposed Ti(n+) cations) of the TiO(2) surface. This work demonstrates that the pyridine rings of D-π-A dye sensitizers that form a coordinate bond with the Lewis acid site of a TiO(2) surface are promising candidates as not only electron-withdrawing anchoring group but also electron-injecting group, rather than the carboxyl groups of the conventional D-π-A dye sensitizers that form an ester linkage with the Brønsted acid sites of the TiO(2) surface.

Fluorescence PET (photo-induced electron transfer) sensors for water based on anthracene-boronic acid ester.

Anthracene-boronic acid ester as a new class of fluorescence PET sensors for detection of a trace amount of water in organic solvents has been designed and developed.

Detection of water in organic solvents by photo-induced electron transfer method.

A new class of fluorescence sensor for detection of water in organic solvents based on photo-induced electron transfer (PET) of anthracene coupled with an amino acid has been designed and developed.

Synthesis and fluorescence and electrochemical properties of D-pi-A structural isomers of benzofuro[2,3-c]oxazolo[4,5-a]carbazole-type and benzofuro[2,3-c]oxazolo[5,4-a]carbazole-type fluorescent dyes.

Heteropolycyclic donor--acceptor (D--A) structural isomers of benzofuro[2,3-c]oxazolo[4,5-a]carbazole-type (2a-f) and benzofuro[2,3-c]oxazolo[5,4-a]carbazole-type fluorescent dyes (3a-f), which differ in the position of oxygen and nitrogen atoms of the oxazole ring, have been synthesized, and their photophysical and electrochemical properties have been investigated. The fluorescent dyes 2a-f exhibit much stronger intramolecular charge transfer (ICT) absorption and fluorescence bands than 3a-f. Both of the D-pi-A structural isomers showed bathochromic shifts of the fluorescence band and a decrease in the fluorescence quantum yields with increasing solvent polarity (i.e., positive fluorescence solvatochromism), and the bathochromic shifts for 3a-f were larger than those for 2a-f. The fluorescent dyes 2a-c and 3a-c, which have cyano and carboxyl groups, and carboxylic acid ester as electron-withdrawing substituents, exhibited significant fluorescence solvatochromic properties, compared to 2e, 2f, 3e and 3f without an electron-withdrawing substituent. The fluorescence solvatochromism of the fluorescent dyes were analyzed with the Lippert-Mataga correlation. Moreover, to elucidate the differences of photophysical properties among the fluorescent dyes, we have performed time-resolved fluorescence spectroscopic measurements, and a change of the electronic or molecular structures between the ground and excited states was evaluated by a comparison of the experimental radiative rate constant (k(r)) with the Strickler-Berg rate constant (kSB(r)). The electrochemical properties of 2a-f and 3a-f were determined by cyclic voltammetry, which demonstrated that these fluorescent dyes have similar HOMO energy levels, but different LUMO energy levels. Semi-empirical molecular orbital calculations (AM1 and INDO/S) have been carried out to elucidate the effects of the substituents and chromophore skeleton on photophysical properties of the two D-pi-A structural isomers. These studies indicated that the ICT characteristics in the excited state are different among the fluorescent dyes, which is a principal reason for the differences of the fluorescence solvatochromism and the substituent dependent fluorescence properties among the two D-pi-A structural isomers.

Trapping of atomic hydrogens in cage-shaped silsesquioxanes by electric discharge.

A simple and safe technique which is based on glow discharge is demonstrated for stable encapsulation of H atoms in cage-shaped silsesquioxanes at room temperature, leading to the encapsulation yield of ca. 10(-4) H atoms per molecule for 10-minute discharging, much faster than the conventional gamma-ray irradiation technique.

Photovoltaic performance of dye-sensitized solar cells based on donor-acceptor pi-conjugated benzofuro[2,3-c]oxazolo[4,5-a]carbazole-type fluorescent dyes with a carboxyl group at different positions of the chromophore skeleton.

Donor-acceptor pi-conjugated benzofuro[2,3-c]oxazolo[4,5-a]carbazole-type fluorescent dyes 3a, 3b, 8a, and 8b with a carboxyl group at different positions of the chromophore skeleton have been designed and synthesized. The absorption and fluorescence spectra and cyclic voltammograms of the fluorescent dyes agree very well, showing that the position of the carboxyl group has a negligible influence on the photophysical and electrochemical properties of these dyes. When these dyes are used in dye-sensitized solar cells, however, their photovolatic performances are considerably different. The short-circuit photocurrents and energy conversion efficiencies under a simulated solar light increase in the order: 3a (2.12 mA cm(-2), 1.00%) approximately 3b (2.10 mA cm(-2), 1.06%) > 8b (1.50 mA cm(-2), 0.67%) > 8a (0.84 mA cm(-2), 0.34%). Based on semi-empirical molecular orbital calculations (AM1 and INDO/S) together with spectral analyses and their photovolatic performance, the relationships between the observed photovolatic properties and the chemical structures of the benzofuro[2,3-c]oxazolo[4,5-a]carbazole-type fluorescent dyes are discussed. It is found that strong interaction between a TiO(2) surface and the electron accepting moiety of the dye leads to a high photovoltaic performance.

Evaluation of absolute configuration of naphthylphenyl-substituted oligosilanes by CD exciton chirality method.

Absolute configurations of methylnaphthylphenyl-substituted oligosilanes, MeNpPhSi*SiMeR(1)R(2) [2 (R(1), R(2)=Me), 3 (R(1)=Me, R(2)=Ph), 4 (R(1), R(2)=Ph), and 5 (R(1)=Me, R(2)=SiMe(3))] were predicted by circular dichroism (CD) exciton chirality method. The sigma-pi conjugation effect of oligosilylene units (sigma-linkage) with pi-electron systems caused an intense red-shift of (1)L(a,Ph) transition band of the oligosilanes as shown in UV/VIS and made it possible to observe clear CD exciton chirality between the two aromatic chromophores on chiral silicon atom.