Kenji Kanazawa

A hygroelectric generator capable of high current output has been developed by combining a deliquescent salt and reverse electrodialysis.

We have developed a novel microwave (MW) soldering system using a cylindrical single-mode TM₁₁₀ MW cavity that spatially separates the electric fields at the top and bottom of the cavity and the magnetic field at the center of the cavity. This MW reactor system automatically detects the suitable resonance frequency and provides the optimum MW irradiation conditions in the cylindrical cavity via a power feedback loop. Furthermore, we investigated the temperature properties of electrodes by MW heating with the simulation of a magnetic field in the TM₁₁₀ cavity toward the mounting of electronic components by MW heating. We also developed a short-time melting technology for solder paste on polyimide substrate using MW heating and succeeded in mounting a temperature sensor using the novel MW heating system without damaging the electronic components, electronic circuits, and the substrate.

A europium(III) [Eu(III)] complex and a viologen derivative were covalently immobilized on a porous titanium(IV) dioxide (TiO ₂ ) electrode by the interaction of carboxyl and phosphate groups with the surface, demonstrating electrochemically induced photoluminescence and coloration switching. The modulation of emission and coloration using the functional Eu(III)‐viologen modified TiO ₂ electrode was achieved by an electrochemical reaction between TiO ₂ and the viologen derivative. Luminescence control was induced via electron and energy transfer from the Eu(III) complex to TiO ₂ and the linked viologen derivative. The dual functional electrode showed a high on‐off emission contrast (81:1), short response time (off: 2.5 s at −0.8 V, on: 5 s at 0 V), and high stability (over 150 cycles) for both emission and coloration control.

An electroswitching device that enables modulation of both photoluminescence and coloration was obtained. The device consisted of luminescent lanthanide(III) complex Eu(hfa)₃(TPPO)₂ (photoluminescence material) and an diheptyl viologen HV²⁺ (electrochromic material). Coloration and emission control were achieved by only electrochemical reactions of HV²⁺. The coloration of the device was controlled by HV²⁺ electrochromism. Photoluminescence control was also achieved by the HV²⁺ electrochromism via intermolecular energy transfer from the excited states of Eu(III) ions to colored HV^+·. However, there were some problems that the response time of switching between emission and coloration was quite slow (approximately 15 minutes), and the representation stability of switching between emission and coloration was low. These problems would be caused by absence of counter electrode reaction material against HV²⁺ redox. In order to improve the response time of the cell and decrease the driving voltage for dual-mode representation, we introduced prussian blue (PB) modified electrode as an electrochromical counter redox material.

The electroresponsive switching of red photoluminescence based on the electrochemical coloration of cyan–magenta–green (CMG) viologen components was achieved by combining a luminescent Eu³⁺chelate and viologen derivatives, resulting in CMG coloration in a single cell.

The multi-color switching of electrofluorochromism was examined from the thin electrofluorochromic (EF) films of polyfluorene (PFO) and poly(propylenedioxythiophene–phenylene) (P(ProDOT-Ph)). The PFO and P(ProDOT-Ph) films showed vivid blue and yellow fluorescence, respectively, at neutral state but their emission was quenched upon application of oxidation potential leading to ion radical states. The fluorescence from the polymer films was reversibly switched to vivid color when the films were returned to their neutral states. The EF color switching ratio (r_c1/c2) between the fluorescent state (c1) and dark (c2) state for the yellow color EF device with P(ProDOT-Ph) film was about four times higher than that of the PFO. Because the two polymer films have different colors and working potentials, a multi-color switching device was fabricated by coating the P(ProDOT-Ph) and PFO films onto working and counter electrodes, respectively. The multi-color EF device showed fluorescence switching from blue (B) to white (W) to yellow (Y), and vice versa, depending on the applied potential. The r_c1/c2 for yellow (c1) and blue (c2) switching (Y/B) was larger (9.71) than those for Y/W and W/B. Moreover, the EF switching for Y/B in the multi-EF device was also very effective and showed the largest EF efficiency (E_EF = 3.82 × 10⁶) among the EF color switching.

Electrochemical modulation of red luminescence from a europium(III) complex has been demonstrated. In order to elucidate the mechanism of luminescence modulation, its cyclic voltammogram, absorption spectra, emission spectra, emission lifetime, and emission quantum yield were measured. From these measurements, the modulation of emission was found to be achieved through an electrochemical reaction of TiO₂, which is facilitated by electron transfer between the europium(III) complex and TiO₂. Subsequent immobilization of the europium(III) complex on a TiO₂ electrode resulted in an on–off emission contrast of 74 : 1, with the response time and repetition stability of the emission switching being considerably improved.

Multifunctional electroswitching of both emission and coloration was demonstrated by using fluoran derivatives in an electrolytic solution. Further, in order to investigate changes in the photophysical properties induced by electrical stimuli, we measured cyclic voltammogram, absorption spetra, emission spectra, and molecular orbital calculation. The mechanism for this electroswitching was attributed to the reversible electrochemically induced closing and opening of the lactone ring in the fluoran molecule. All neutral fluoran molecules were colorless and did not exhibit any fluorescence, while the oxidized (lactone ring-opened form) molecule was yellow and displayed a green fluorescence as a consequence of the extended, planar, conjugated system. Furthermore, this fluoran molecule achieved reversible electroswitchable emission and coloration with high on/off contrast.