Ken'ichi Koseki

The photo- and thermal cis-trans isomerization of [23](4,4′)azobenzenophane

Four isomers, EEE, EEZ, EZZ and ZZZ, exist for [23](4,4′)azobenzenophane depending on the degree of the isomerization of three azobenzene units. These isomers are stable enough to be separated by reversed-phase liquid chromatography. The compound in methanol exists as the EEE form in the dark. Upon irradiation at 366 nm the EEE form isomerizes via the EEZ form and the EZZ form to the ZZZ form. At the photostationary state at 366 nm, 85% of the compound exists as the ZZZ form. From the photostationary state the compound thermally isomerizes gradually to the EEE form. The thermal reaction from the ZZZ form to the EEE form also proceeds in a stepwise fashion. The relative values of the quantum yields for the photoisomerization and the absolute value of the rate for the thermal isomerization have been determined for each step. Both the photo- and thermal processes in the Z→E direction show the different efficiencies (or rates) depending on the processes. These experimental results can be explained by supposing that the different degree of ring strain works for ground and (or) excited states of each isomer. In this compound, a certain isomer can be enriched by the combination of external stimuli, such as light or heat. This raises the possibility of synthesizing molecules with more than two functional states.

Triplet state electron transfer pathway for tetrabenzoporphyrin-diphenyliodonium salt photoinitiator system

Abstract A triplet state electron transfer mechanism for the photoreaction between meso -diphenyl-tetrabenzoporphyrin (P 2 TBP) metallo complexes, e.g. magnesium (1a, MgP 2 TBP), zinc (1b, ZnP 2 TBP) and cadmium (1c, CdP 2 TBP), and diphenyliodonium (DPI) salt was confirmed by the detection of the cation radicals of P 2 TBP using nanosecond laser flash photolysis equipment, as expected from the estimation of the free energy changes (ΔG T ). Rate constants ( T k q ) of the triplet state quenching of metallo P 2 TBP complexes by DPI, determined from the slopes of Stern-Volmer plots, approximately obeyed a diffusion-controlled limit in accordance with fully exothermic ΔG T values. Since the fluorescence of the magnesium and zinc complexes was quenched by DPI at high concentrations (above 10 −3 M), as previously reported, both excited states were deactivated by the onium salt, depending on its concentration. However, it was presumed that a triplet state electron transfer pathway was preferred for the cadmium complex because of its short fluorescence lifetime.

Oxidative fluorescence quenching of meso-diphenyltetrabenzoporphyrins with onium salts

Abstract The fluorescence quenching of either meso -diphenyltetrabenzoporphyrin zinc or magnesium complexes, ZnP 2 TBP and MgP 2 TBP. respectively, by onium salts has been studied in acetonitrile. The dependence of the fluorescence quenching rate constants, k q , on the free energy change, δ G , indicates that the photosensitization between these substances primarily takes place based on the photoinduced electron transfer from the singlet excited TBP molecule to the quencher.

Electroviscous effect of nematic liquid crystals in the slit-viscometer

Mechanical rubbing was applied to make a slit-viscometer. The electro-rheological effects in the slit-viscometer under AC and DC electric fields were investigated for a pure type of nematic liquid crystal (LC) in order to clarify the influence of the alignment structure. It was found that except for the magnitude of the electric field, the apparent viscosity also depends on the orientation direction of the alignment layer and the type of electric field (AC or DC). Moreover, the rubbed-surface of the alignment layer was observed using an atomic force microscope (AFM) and the orientation structures of the liquid crystals in the slit-viscometer were anticipated.

Thermo‐optic effects of 4‐alkoxy‐3‐chlorobenzoic acids in polymeric matrices

Polymer films containing 4‐alkoxy‐3‐chlorobenzoic acid heated to 140 °C showed two optically different states at room temperature depending on the cooling rate. If after heating the film cooled rapidly, it froze in the transparent state. In contrast, it reverted to the light scattering state when cooled slowly. Cycles between the two optical states were reproducible, therefore these films may offer potential as a rewritable recording material. The reversibility in the optical transmittance may be caused by a reversible change in the crystal size of the acid in the polymer matrix.

Negative resists of silicone-containing graft polymer for bilayer resist system

Abstract Photocrosslinkable silicone-containing graft polymers were synthesized using silicone-macromonomer; 0.5 μm line and space patterns were accurately fabricated by O2RIE using the graft polymers as the top layer on phenol novolak resin. TEM observation of the graft polymer indicated the phase separation of the silicone chain from the hydrocarbon chain. The phase separation enhanced the photocrosslinking efficiency of the graft polymer.

Nonlinear rheological properties of suspension of surface treated carbon black

Steady state viscosity and dynamic viscoelastic properties for the suspensions of carbon black at various surface treating stages were measured using cone and plate type rheometer. The surface modification of carbon black was performed by silane coupling agents. The relations between the degree of modification and rheological properties of the suspensions were mainly discussed by considering the alteration of flocculated network structure formed by dispersed particles. With increasing surface treating level of the particles, the apparent viscosity of the suspension decreases and shear thinning behavior is gradually diminished. The values of storage modulus decrease and the frequency dependence of them increases with surface treating. These phenomena are associated with the reducing of aggregated structures formed by dispersed particles. With proceeding the surface treating by silane coupling agent phenyl group covers the particle surface to prevent the inter-particle aggregation and fills in the nano-pore on the particle surface. Consequently, flocculated network structure is gradually reduced and the specific surface area is also reduced with increasing surface treating agent. However excess silane coupling causes inter-particle bonding and structural formation and consequently the relation between surface treating time and viscoelastic behavior becomes vague.

Laser Responsive Polymeric System Containing Iron-Arene Complex and Spectral Sensitizing Dyes

Iron-arene hexafluorophosphate was used as a radical initiator to polymerize pentaerythritol triacrylate in the presence of poly (methyl methacrylate-co-methacrylic acid) as a binder under the influence of the 488 nm argon-ion laser light source. Spectral sensitizing dyes responsive towards the region of the argon-iron laser were incorporated into the polymeric system to enhance the responsive sensitivity. The photoresponsive property of the polymeric system to the laser in term of laser sensitivity was evaluated in order to determine the appropriate spectral sensitizing dyes for the system. The roles of the iron-arene complex and the spectral sensitizing dyes to the system were also described.