Kenro Totani

Photoresponsive Hydrogel Microstructure Fabricated by Two-Photon Initiated Polymerization

A photoresponsive polymeric hydrogel cantilever that deflects under illumination has been fabricated by using two-photon three-dimensional lithography. The hydrogel was prepared from a comonomer solution containing acryloylacetone, acrylamide, and N,N′-methylene bisacrylamide. The photoresponse of the cantilever was activated by photoexcitation of acetylacetone groups at 244 nm. Deflection of the cantilever by ∼ 45° was effected upon UV irradiation for 20 min.

Large reverse saturable absorption under weak continuous incoherent light

In materials showing reverse saturable absorption (RSA), the optical absorbance increases as the power of the light incident on them increases. To date, RSA has only been observed when very intense light sources, such as short-pulse lasers, are used. Here, we show that hydroxyl steroidal matrices embedding properly designed aromatic molecules as acceptors and transition-metal complexes as donors exhibit high RSA on exposure to weak incoherent light at room temperature and in air. Accumulation by photosensitization of long-lived room-temperature triplet excitons in acceptors with a large triplet-triplet absorption coefficient allows a nonlinear increase in absorbance also under low-power irradiation conditions. As a consequence, continuous exposure to weak light significantly decreases the transmittance of thin films fabricated with these compounds. These optical limiting properties may be used to protect eyes and light sensors from exposure to intense radiation generated by incoherent sources and for other light-absorption applications that have not been realized with conventional RSA materials.

Highly sensitive two-photon chromophores applied to three-dimensional lithographic microfabrication: design, synthesis and characterization towards two-photon absorption cross section

A series of D–π–A–π–D type chromophores were synthesized by the dehydration reaction of 4-R2N-benzaldehye (R = Ph, Bun, Et, Me) and diaminomaleonitrile (corresponding to the chromophores 1, 2, 3 and 4, respectively), in which a polar imino double bond (–CN–) replaced the double bond (–CHCH–) in the π-conjugated centers. Femtosecond laser induced fluorescence intensity was used to evaluate two-photon absorption (TPA) cross sections, δ, using a USB-2000 CCD. Results show a change of terminal groups from Ph2N– to Me2N– influenced the δ value significantly through a change of the quantum yield, φ. However, the two-photon absorption peak position was only slightly affected. The chromophores 2 and 3 were found to afford polymers in the presence of the functional triacrylate monomer at low laser power at 755 and 820 nm. This demonstrated that the enhanced δ value was not a main factor in the improvement of chromophore two-photon photosensitivity. Such information can be useful in the design of more efficient two-photon chromophores for imaging and power-limiting applications.

Highly efficient two-photon initiated polymerization in solvent by using a novel two-photon chromophore and co-initiators

Highly efficient two-photon initiated polymerization in solvent was carried out in a three-component system, which consisted of a novel D-π-A-π-D type chromophore (1 or 2, respectively), the co-initiator, 2, 6-diisopropyl-N,N-dimethylaniline (DDA) and diphenyliodoinum salt, Ph2I+PF6−(PIP). We measured the quasi two-photon polymerization rates (Rp) based on scanning speed and the width of the written protruding line. Polymerization rates of the chromophore 1 and 2 were found to be 113 µm3 s−1 and 157 µm3 s−1 in the case of the laser power 4.5 mW at 820 nm (pulse width: 85 fs, repetition rate 82 MHz ) respectively. In order to estimate the mechanism of the photochemical reaction, the change of UV absorption of the three-component system, T–T transient absorption and the cyclic voltammetry (CV) of the novel chromophores were measured. Correlated with the CV, we interpreted that highly efficient electron transfer between DDA and the chromophore contributed to the long-lived radical cations of the chromophore. As a result, the generation of both DDA radicals and phenyl radicals was ascribed to high sensitivity in TPIP.

Scattering-Type Polarizers Consisting of Fiber/Matrix and Methods to Enhance Polarization Property

A nonabsorbed-type polarizer consisting of aligned birefringent fiber/isotropic polymer composites was fabricated. By selecting a matrix polymer with the appropriate refractive index that was matched with the ordinary refractive index or extraordinary refractive index of the fiber, two different types of film were obtained. Both of these different types of film showed the polarization property due to the scattering and transmission depending on the polarization direction. Furthermore, taking advantage of these different optical characteristics between the two types of film, we fabricated an efficient polarizer by combining two films vertically, which was expected to achieve a high contrast ratio between two components of polarization light.

P‐166: Novel Reflective Type Polarizer Using Birefringent Fibers

We fabricate a novel reflective type polarizer using optical anisotropy. The polarizer is produced from highly aligned fiber/resin composites in which the refractive index of fibers is matched with isotropic refractive index of a matrix resin. The single-piece transmittance and the polarizing efficiency are found to be 39.8%, and 94.9%, respectively.