Takashi Hiraga

Plugging a Molecular Wire into Photosystem I: Reconstitution of the Photoelectric Conversion System on a Gold Electrode

Plug and play: Photoinduced electron transfer occurs from photoexcited P700 in photosystem I (PSI) to a gold surface (see picture). A novel molecular connector system is used, in which an artificial molecular wire, which is assembled on the gold surface, was plugged into PSI by reconstitution. Analysis of the photoelectron transfer kinetics proved both the output of electrons from PSI and the effectiveness of the molecular wire.

Photosensor based on an FET utilizing a biocomponent of photosystem I for use in imaging devices.

We have investigated a photosensor that consists of a field emission transistor (FET) utilizing the biocomponent of the photosystem I (PSI) protein complex for use in an imaging device. The PSI was immobilized on a gold electrode via the self-assembling monolayer (SAM) of 3-mercapto-1-propanesulfonic acid sodium salt to obtain a PSI-modified gold electrode. As for the PSI-modified gold electrode, the basic photoresponses originating from the excitation of PSI, including the photocurrent (106 nA) and the photoresponse of the open-circuit voltage (photo-Voc: 28.6 mV), were characterized. Then, the PSI-modified gold electrode was linked to the gate of the FET using a lead line, and the device was successfully driven by the photoelectric signals from the PSI like a voltage follower circuit. Further, we successfully demonstrated that the PSI-based FET acts as a photosensor in imaging devices.

Doping of functional materials into poly (p-phenylene vinylene) by the vapor transportation method

Poly(p-phenylene vinylene) (PPV) is a promising material, but shows poor processability, such as doping, due to its insolubility and infusibility. Therefore, the development of a standard and easy method of dye doping into PPV is important for device fabrication using PPV. We developed a simple method for the dispersal of dyes into PPV without deformation. Using this method, it was possible to change the color of PPV from yellow to green by doping with the blue dye 1,4-(N,N’-diethylamino)anthraquinone (SV59). The amount of SV59 doped into PPV was ∼2.7wt%. The fluorescence color of PPV could be changed from green to red by 2 min dispersal of 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran.

Nanometer scale marker for fluorescent microscopy

To establish a calibration method of optical performance in fluorescence microscopy, we fabricated a fluorescent nanometer-scale marker by combining a dry dye method for polymer film and fine lithography. The marker has a 50 nm line-and-space fluorescent pattern, finer than the optical diffraction limit. A spin-coated poly(methyl methacrylate) thin film on a silicon wafer was densely doped with Rhodamine 6G using a simple vacuum process, named the vapor-transportation method, and then the pattern was formed on the film using electron-beam lithography. The figure accuracy of the fabricated marker was calibrated by electron microscopes. Using this marker, one can quantitatively evaluate the optical properties; i.e., the contrast-transfer function, the point-spread function, magnification, and so on. To show practical use of the marker, we demonstrated the evaluation of a fluorescent microscope system.

Measurement of contrast transfer function in super-resolution microscopy using two-color fluorescence dip spectroscopy

The contrast transfer function (CTF) of super-resolution microscopy was quantitatively investigated using a fluorescent scale. The scale has minute fluorescent line patterns, finer than 100 nm, and is suitable for measuring CTF in super-resolution microscopy. The measured CTF shows that super-resolution microscopy can indeed improve the optical properties of fluorescent images and enable us to observe a structure with the spatial resolution overcoming the diffraction limit. From the CTF, it has been found that super-resolution microcopy can resolve a 100 nm line-and-space pattern and provides a contrast of 10%. The CTF corresponds to a PSF with a full-width at half-maximum (FWHM) of 130 nm. An evaluation using a 100 nmφ fluorescent bead consistently supports the results given by the CTF for super-resolution microscopy.

A novel formation method of thin polymer film with densely dispersed organic dye by using vacuum technique

Abstract A novel method of thin film formation of organic materials using a vacuum technique is proposed. An organic dye with a high sublimation pressure is loaded in a crucible along with a thin polymer film. After pumping down, the crucible is sealed, then placed in a constant temperature oven. The vapor of dye dissolves into the polymer film, thus forming a thin dye-containing layer.

Preparation of smooth polymer thin film using spray method under vacuum

Polymers such as poly(methyl methacrylate) (PMMA) doped with N-[9-(2-carboxyphenyl)-6-(diethylamino)-3H-xanthen-3-ylidene]-N-ethylethanaminium chloride (Rhodamine B) can be prepared as thin films using a spray method under vacuum. Smooth films without dust and solvent residues can be obtained by annealing the films above the glass transition temperature (Tg) after they have been prepared using a conventional spray method under vacuum.

Coaxial Configuration of the Gating and Signal Light for a Switching Device of a Dye-Dissolved Polymer Film.

New optical switching devices aimed at the post-liquid-crystal market are currently expected to emerge. We have developed an all-optical system in which the signal light was controlled by the gating light using a thin-film device composed of organic nanoparticles dispersed in a polymer film. Coaxial gating and signal laser beams are focused together onto the thin-film device; this configuration is essential in the present work. The signal light of 694 nm wavelength was switched from a higher transmittance state to a lower transmittance state by irradiating 633-nm-wavelength gating light where the signal light was deflected by a thermal lens temporarily formed by the gating light. The all-optical switching device using the thermal lens method in a nanoparticle-dye-dispersed thin film is the first attempt at using a solid-state system instead of a liquid system currently under investigation, and sub-microsecond operation has been attempted with the organic device.

Fabrication of Fluorescence Micropatterns to Photoresists by Selective Doping of Fluorescent Dye Using Vapor Transportation Method

We report a novel patterning process that adds fluorescence to a positive-type photoresist by doping vapor of the fluorescent dye, 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)4H-pyran (DCM), using a simple vacuum process called vapor transportation method. DCM-doped photoresist films were examined by UV-vis absorption spectroscopy, fluorescent spectroscopy, and optical microscopy. When DCM vapor was used to dope unexposed films at temperatures above 140°C, absorption and fluorescence peaks due to DCM were detected. In contrast, when DCM vapor was used to dope exposed films, no absorption and only weak fluorescence peaks were detected. These results indicated the selective doping of DCM vapor into unexposed photoresist films. When DCM vapor reached the surfaces of micropatterned photoresist films with both unexposed and exposed areas, DCM was doped selectively into the unexposed areas of the films, resulting in the production of micropatterns with DCM molecules in the patterned films.

Whitening of Polymer Light-Emitting Diodes by Dispersing Vapor of an Orange Fluorescent Dye into a Blue-Emitting Polymer Film

Whitening of polymer light-emitting diodes (PLEDs) based on the blue-emitting poly(9,9-dioctylfluorene) (PDOF) films was possible by dispersing vapor of an orange fluorescent dye 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM) into the film by means of the solution-free vapor transportation method (VTM). Devices prepared with this method showed good color stability with bias voltage increase, while those formed with conventional spin-coating, where dyes and polymers were mixed in a solution (solution-mixed), showed color change from yellow to white-yellow. The maximum luminance of the PLED formed by the VTM was higher than that formed by conventional spin-coating process.