Functional monomers and polymers. LXXXVI. Photochemical reactions on synthetic polymers with pendant thymine bases: Effect of solvents

Photodimerization of thymine bases present on the side chain of acryloyl and methacryloyl-type polymers was studied in dimethyl sulfoxide, dimethylformamide, and dimethyl sulfoxide—ethylene glycol mixture. Quantum efficiencies for photodimerization and quenching with isoprene were influenced by the solvents. The self-association of thymine bases estimated from their ultraviolet (UV) spectra and intrinsic viscosity were related to the effect of solvent on the photodimerization.     

Enhancement of resolution and quality of nano-hole structure on GaN substrates using the second-harmonic beam of near-infrared femtosecond laser

By using a second harmonic of near infrared femtosecond (fs) laser (λ=387 nm, 150 fs) with high NA objective lens, fabrication resolution has been greatly improved in nano-fabrication of wide band-gap semiconductor gallium nitride (GaN). We have carried out a wet-chemical-assisted fs laser ablation method, in which the laser beam is focused onto a single-crystal GaN substrate immersed in a concentrated hydrochloric (HCl) acid solution. A two-step processing involving irradiation with a fs laser beam in air followed by wet chemical treatment is also performed for comparison. In the wet-chemical-assisted ablation, theoretical diameters of ablation craters are calculated as a function of pulse energy by assuming that the reaction is based on two-photon absorption. In lower energy, the calculated curve is close to the experimental value, while the actual measured diameters in the region of higher energy are larger than calculated values. In the condition of the highest fabrication resolution, we obtained ablation craters smaller than 200 nm at full width at half maximum. We have also demonstrated the fabrication of two-dimensional (2D) periodic nanostructures on surface of a GaN substrate using the second harmonic single fs-laser pulse. Uniform ablation craters with the size as small as 410 nm in diameter are arranged with a periodicity of 1 μm. Such structures are applicable to 2D photonic crystals which improve the light extraction efficiency for blue LEDs in the near future.     

Synthetic study of azaspiracid-1: synthesis of the EFGHI-ring fragment

Here, we report a synthesis of the lower half C21-C40 fragment of the shellfish toxin, azaspiracid-1. The C28-C40 fragment was synthesized by a coupling between the C28-C35 epoxide and the C36-C40 dithioacetal anion, followed by the HI-ring spiroaminal formation. An aldehyde corresponding to the C28-C40 fragment was then coupled with the C21-C27 allylic stannane by using InCl3. Finally, the FG-ring was constructed by HF.pyridine to accomplish the synthesis of the suitably protected C21-C40 fragment.     

Mechanism study of femtosecond laser induced selective metallization (FLISM) on glass surfaces

We investigate the mechanism of selective metallization on glass surfaces with the assistance of femtosecond laser irradiation followed by electroless plating. Irradiation of femtosecond laser makes it possible to selectively deposit copper microstructures in the irradiated area on glass surfaces coated with silver nitrate films. The energy-dispersive X-ray (EDX) analyses reveal that silver atoms are produced on the surface of grooves formed by laser ablation, which serve as catalysis seeds for subsequent electroless copper plating.     

Convenient asymmetric synthesis of beta-substituted alpha,alpha-difluoro-beta-amino acids via Reformatsky reaction between Davis' N-sulfinylimines and ethyl bromodifluoroacetate

The enantiopure Davis' N-sulfinylimines were found to be efficient as chiral imine equivalents in the high-temperature Reformatsky-type additions with BrZnCF(2)COOEt affording an efficient approach to the enantiomerically pure alpha,alpha-difluoro-beta-amino acids. High chemical and stereochemical yields (drs > 9:1, and as high as 99:1) render this method immediately useful for preparing the target amino acids.     

Preparation and some reactions of 3,5:8,10-di-1,3-benzo[8](3,4)-1,2,5-thiadiazolocyclophane

Titled 1,2,5-thiadiazolometacyclophane 1 was prepared via thia[2.3]cyclophane 5 which was obtained by the reaction of di(bromomethyl) 2 with sodium sulfide under phase-transfer-catalyzed conditions. Cyclophane 1 gave the corresponding pyrene derivatives by the oxidative transannular reaction in the reaction with brominating reagent. Reduction of 1 with lithium aluminum hydride followed by acetylation with acetic anhydride gave a 4:l-mixture of cis- and trans-diamide 11 and 12 with a trace amount of cyclophane-ring-cleaved product 13 . On the other hand, 13 was obtained as a major product in the reduction with metal sodium and diisobutylaluminum hydride.     

Functional monomers and polymers. XCIII. Photochemical reactions on the acrylic and methacrylic copolymers containing thymine bases

Photodimerization of Polyacrylic and polymethacrylic derivatives with different pendant thymine unit content was studied in dimethylformamide solution. The quantum efficiency of thymine base for the photodimerization increased with increasing thymine content in the copolymers. The quenching study, which used isoprene as the quencher, revealed that the photodimerization resulted from excited singlet state increases with increasing thymine content. The photochemical results were discussed in terms of self-association of thymine bases in the polymer chain.     

High-quality and high-efficiency machining of glass materials by laser-induced plasma-assisted ablation using conventional nanosecond UV, visible, and infrared lasers

This paper reports the micromachining of fused quartz and Pyrex glass by laser-induced plasma-assisted ablation (LIPAA) using a conventional nanosecond laser at wavelengths 266 nm, 532 nm, and 1064 nm, respectively. High-quality surface structuring can be achieved at each of these wavelengths. The micrograting formed has periods of 14 7m at 266 nm, 20 7m at 532 nm, and 30 7m at 1064 nm, respectively. The ablation rate using a 266 nm laser is much larger than that at longer wavelengths. The ablation thresholds of laser fluence are 0.7 J/cm² for 266 nm, 1.5 J/cm² for 532 nm and 3.7 J/cm² for 1064 nm, respectively. The 532 nm and 1064 nm lasers enable hole drilling in 0.5 and 2.0-mm thick fused quartz and Pyrex glass substrates of about 0.7-0.8 mm in diameter. However, the less destructive through channel can be only formed in Pyrex glass by using a 532 nm laser.     

Rapid fabrication of optical volume gratings in Foturan glass by femtosecond laser micromachining

We report on rapid fabrication of optical volume gratings in Foturan glass using a modulated femtosecond laser focused with cylindrical lenses. An optical volume grating with an area of 2 mm ×3 mm and ∼2 mm thickness can be achieved within 10 min by use of this method. Optical micrography confirms the volume nature of the gratings and shows that they consist of 10 μm-thickness planes with a period of 15 μm. The diffraction efficiency is examined to be ∼56%. The limitations and future implementations of the fabricated volume gratings are discussed.