Masaya Mitsuishi

Characterization of an ultrathin polymer optode and its application to temperature sensors based on luminescent europium complexesElectronic supplementary information (ESI) available: surface plasmon curves and X-ray diffraction pattern of p(DDA-Eu(TTA)3Phen) LB films. See http://www.rsc.org/suppdata/jm/b3/b307309b/

This paper focuses on an ultrathin polymer optode containing europium complexes (p(DDA-Eu(TTA)3Phen)). Ultrathin films were prepared by the Langmuir–Blodgett (LB) technique; a mixed solution of poly(N-dodecylacrylamide) (pDDA) and tris(4,4,4-trifluoro-1-(2-thienyl)-1,3-butanediono)-1,10-phenanthroline europium(III) (Eu(TTA)3Phen) was spread onto a water subphase and the condensed monolayer was transferred onto a solid substrate. The spectroscopic properties and layer structure of p(DDA-Eu(TTA)3Phen) LB films were investigated by UV-Vis spectroscopy, fluorescence spectroscopy, time-resolved luminescence decay measurement, X-ray diffraction, and surface plasmon spectroscopy. It was found that europium complexes were uniformly distributed in the ultrathin films compared with a cast film. The p(DDA-Eu(TTA)3Phen) optodes showed efficient sensitivity to temperature in the range of 320 to 370 K. The findings demonstrate that the p(DDA-Eu(TTA)3Phen) optode is a good candidate for temperature sensitive sensors.

Nonlinear optical properties of novel fullerene-ferrocene hybrid molecules

A series of novel fullerene–ferrocene derivatives has been synthesized and their NLO properties investigated. Ferrocene acts as a donor and fullerene as a good acceptor, leading to large hyperpolarizabilities, especially in the case of the compound with the longest π-conjugation system, which exhibits the highest β value.

Nonlinear optical studies of fullerene–arylethyne hybrids

The fullerene–arylethyne hybrids 2 and 3 were synthesized in order to investigate their NLO activities. The β values for 2 and 3 were obtained by hyper Rayleigh scattering measurements. The arylethynyl fullerenes 3a–f exhibit β values in the range 20–361 × 10−30 esu. Interestingly, the β values for 3a,b are higher than those for 3c–f; a good correlation was obtained between the Hammett σp values of the para substituents of 3 and their β values. The 1H-NMR and E1/2 data indicate that the fullerene moieties of 3 attract electrons from the arylethynyl groups in the ground state. The β values for 2a–c are higher than those for 3a–f; the para-carborane–fullerene dyad 2c exhibits an exceptionally high β value (1189 × 10−30 esu). The electronic characteristics of the carbon and boron clusters are discussed.

Characterization of the molecular environment of polymer Langmuir-Blodgett films using a pyrene fluorescent probe

The molecular environment of polymer Langmuir−Blodgett (LB) films with different alkyl chain length, poly(N-dodecyl acrylamide) (pDDA) and poly(tert-pentyl acrylamide) (ptPA), which are copolymerized with a small amount of 1-pyrenylmethyl acrylate (PyMA) comonomer as a luminescent probe, was investigated by means of the surface pressure (π)−area (A) isotherms, UV−vis spectroscopy, and fluorescence spectroscopy. The pyrene ring orients perpendicular to the p(DDA/PyMA) layer in both the monolayer at the air/water interface and LB multilayers, while the pyrene moiety of p(tPA/PyMA) takes a parallel orientation to its layer plane. The pyrene residue is more exposed to its surroundings in p(tPA/PyMA) LB films and therefore sensitive to solvent polarity. The measurement of fluorescence anisotropy confirmed that the pyrene was densely packed in the LB films. These findings suggest that the molecular orientation of luminescent molecules can be controlled when the length of side chains is changed by only several a...

Photolithographic properties of ultrathin polymer Langmuir–Blodgett films containing anthracene moieties

This study investigated the unique photolithographic properties of poly(N-neopentyl methacrylamide-co-9-anthrylmethyl methacrylate) (p(nPMA-AMMA)) ultrathin films prepared by the Langmuir–Blodgett (LB) technique. The copolymer forms a stable monolayer on a water surface and LB films with any desired number of layers. The nPMA group in the LB film acts as a photodecomposition group under irradiation at 254 nm. On the other hand, photodimerization occurred between anthracene groups under irradiation at 365 nm. Consequently, positive-tone and negative-tone patterns were printed on a silicon wafer by choosing a suitable irradiation light wavelength. Etching resistance of p(nPMA-AMMA) LB films was also investigated in a nanometer regime permitting etching of gold or copper films.

Free-standing ultrathin films with universal thickness from nanometer to micrometer by polymer nanosheet assembly

Fabrication of smooth and flexible free-standing films with universal thickness and a highly ordered layer structure is described in this paper. N-Dodecylacrylamide polymer forms a well-defined monolayer on a water surface. The acrylamide polymer chains are strongly associated by hydrogen bonding of amide groups in the monolayer, thereby forming a two-dimensional network (polymer nanosheet). The monolayer is transferable onto a substrate using the Langmuir–Blodgett (LB) method with regular deposition, even for more than 700 layers. The deposited polymer multilayers on a substrate where a sacrificial film had been coated in advance were peeled off safely in solution, yielding a free-standing film with a uniform thickness depending on the number of multilayers. Results showed that the film has a highly oriented layer structure in which the alkyl side chain orients vertically and the polymer backbone lies between the hydrophobic layers. The film thickness from nanometer scale to micrometer scale is controllable by various deposited layers maintaining a constant thickness (3.3 nm) per bilayer. A minimum free-standing ultrathin film with bilayer thickness (3.3 nm) was obtained. It resembles a biomembrane. Two-dimensional hydrogen bonding network formation between polymer backbones and molecular interaction between alkyl side chains contribute to the free-standing film formation and to its smooth surface.

Quasi-solid-state optical logic devices based on redox polymer nanosheet assembly.

We report fabrication of a quasi-solid-state optical logic gate based on a polymer nanosheet photodiode. Two amphiphilic copolymers, p(DDA/Ru) and p(DDA/Fc), which respectively have a ruthenium dipyridyl complex and a ferrocene derivative as a redox molecule, are synthesized to produce redox polymer nanosheets. To construct polymer nanosheet photodiodes, two redox polymer nanosheets were assembled onto an indium-tinoxide (ITO) electrode in a tailor-made manner. The ITO electrode was connected with a counter electrode using an agarose gel electrolyte. The simple two-electrode system performs as a quasi-solid-state polymer nanosheet photodiode (QS-PNP). The photocurrent flow direction of QS-PNP can be controlled to be anodic or be cathodic by changing the deposition order of the redox polymer nanosheets. The anodic and cathodic QS-PNPs were applied to construct optical OR and XOR logic gates. The OR logic gate was fabricated by connecting the anodic and cathodic QS-PNP in a series; XOR logic was fabricated by connecting two anodic QS-PNPs in series. In optical logic gates, excitations of p(DDA/Ru) were used as input signals, and photocurrent was used as an output signal. These optical logic gates operate in a quasi-solid-state in a simple two-electrode configuration, which facilitates integration of the logic elements.

Bottom-up Design of Hybrid Polymer Nanoassemblies Elucidates Plasmon-Enhanced Second Harmonic Generation from Nonlinear Optical Dyes

Flexible design of hybrid polymer nanoassemblies consisting of nonlinear optical (NLO) polymer nanosheets and gold nanoparticle alignment was done to elucidate near-field effects of localized surface plasmon (LSP) coupling, which was generated from coupled gold nanoparticles, on enhanced second harmonic generation (SHG) from nonlinear optical (NLO) dyes in hybrid nanoassemblies. Structurally well-defined hybrid polymer nanoassemblies comprising NLO polymer nanosheets and aligned gold nanoparticles were fabricated using bottom-up approaches: Langmuir-Blodgett (LB) technique and nanoparticle adsorption. Two hybrid polymer nanoassembled structures were particularly examined: a single-layer NLO polymer nanosheet and gold nanoparticle monolayer (single-layer structure) exhibiting intralayer LSP coupling, and a single-layer NLO polymer nanosheet sandwiched between two-layer gold nanoparticle monolayers (sandwich structure). The latter enables interlayer LSP coupling between the two gold nanoparticle monolayers. Dependence of SHG intensity on the distance between the NLO layer and nanoparticle layer was examined according to the LB layer structure and gold nanoparticle size variation. The SH light intensity from the NLO polymer nanosheet decreased almost exponentially with increasing spacer distance between the NLO polymer nanosheet and gold nanoparticle monolayer in both single-layer and sandwich structures. The decay length depends strongly on the gold nanoparticle size, indicating effective spatial distance for enhanced SHG from NLO polymer nanosheets. Theoretical calculations were used to study the enhancement mechanism. Finite difference time domain (FDTD) calculations reproduced the exponential behavior of SH light intensity as a function of separation distance, which confirmed the importance of coupled gold nanoparticle formation and parallel geometry of near-field coupling of the coupled gold nanoparticles with NLO polymer nanosheets for efficient SHG enhancement. Dipole-type LSP coupling along the long axis of adjacent gold nanoparticles at the fundamental frequency dominates enhancement of SHG from NLO dyes oriented parallel to the long axis of LSP coupling, which occurs at the center of the Au NPs.

Ferroelectricity of poly(vinylidene fluoride) homopolymer Langmuir–Blodgett nanofilms

As-deposited poly(vinylidene fluoride) (PVDF) Langmuir–Blodgett (LB) nanofilms with a complete β phase show a remarkably high remanent polarization (Pr), about 6.6 μC cm−2 at 81 nm. Extrinsic switching characteristics of the nanofilms are demonstrated. Results also show that highly oriented PVDF homopolymer LB nanofilms down to 12 nm with no post-treatment retain robust room-temperature ferroelectric polarization switching that is greater than 105 operation cycles, with longer standing fatigue endurance than those of PVDF copolymer nanofilms.

Photodegradable polymer LB films for nano-lithographic imaging techniques

Abstract A new type of polymer Langmuir–Blodgett (LB) films composed of N-dodecylacrylamide (DDA), which is known to form a stable monolayer, and a photodegradable monomer, tert-butyl-4-vinylphenyl carbonate (tBVPC), were prepared with the aim of developing a novel thin-film positive-tone resist. The copolymer [p(DDA-tBVPC)] could form a stable, condensed monolayer, even at high compositions of tBVPC (53 mol.%), and the monolayer could be successfully transferred onto solid supports, such as quartz, glass, and silicon slides, giving Y-type uniform LB films. The polymer LB films could be efficiently decomposed by deep UV irradiation, and after development with alkaline solution, a clear positive tone pattern with a line width of 0.75 μm, which is the highest resolution of the photomask employed, was visible. Moreover, it was found that these copolymer LB films with nm thickness show high resistance performance to an etching process. These fascinating features of the copolymer LB films show them to be potential candidates as key materials in nano-lithography.