Phenyl 4-((5 00-hexyl-2,2 0-bithienyl)methyl)aminobenzoate (M1), phenyl 4-((5 00-hexyl-2,2 0-bithienyl)propyl)aminobenzoate (M2) and phenyl 4-((5-hexyl-2,2 0 :5 0 ,2 00-terthienyl)propyl)aminobenzoate (M3), each having oligothiophene on the nitrogen atom through the use of an alkylene spacer, were synthesized using a method in which the oligothiophene group was introduced by the reductive amination (M1) or the nucleophilic substitution (M2 and M3). The condensation polymerization was performed by adding the monomer and 4 0-nitrophenyl 4-methylbenzoate to lithium bis(trimethylsilyl)amide and N,N,N 0 ,N 0-tetramethylethylenediamine (Method A). Poly(p-benzamide)s with number-averaged molecular weights ranging from 4400-7300 were obtained in high yields (B80%). From the gel permeation chromatography profiles and the 1 H-nuclear magnetic resonance spectra, the polymerization was found to proceed in a controlled manner. The C ¼ O stretching vibration signal in the infrared spectra indicated the cis conformation of the amide group in the polymer backbone. However, the direct polycondensation of 4-((5 00-hexyl-2,2 0-bithienyl)methyl)aminobenzoic acid using PPh 3 and hexachloroethane in pyridine produced a cyclic trimer, that is, p-calix[3]amide (Method B). In contrast to polyM2 and p-calix[3]amide, a broad emission peak at B480 nm was observed for polyM1, indicating the p-stacked interaction between the bithiophene chromophores. As polyM3 (having the terthiophene) also exhibited a redshift of the emission maxima, the wide conjugated system was found to be susceptible to the strong p-stacked interaction at the polymer side chain.
An optically active oligo(m‐benzamide) (OBA1), with a chiral alkyl group on the amide nitrogen and a bithiophene chromophore on the benzene ring by the chain‐growth polymerization of methyl 3‐((S)‐2′‐methylbutylamino)‐5‐(2′′‐(5′′,2′′′‐bithienyl)) benzoate are prepared. In addition, unimer to trimer model compounds (M1, M2, and M3) are synthesized by the iterative ester hydrolysis and dehydration condensation. An optically active oligo(m‐benzamide) with a chiral methoxyethoxyethoxy group (OBA2) is likewise synthesized. On the basis of electronic circular dichroism (CD), UV–vis, and fluorescence spectra, the chiral arrangement of bithiophene chromophores is discussed. By converting the carbonyl group in OBA1 into the methylene group using LiAlH4/AlCl3, a bisignate Cotton effect is collapsed, indicating the importance of the aromatic tertiary amide skeleton for the chiral arrangement of chromophores. The chain conformation of OBA1 is further investigated by means of theoretical CD calculations to figure out that two neighboring bithiophene units are preferentially rotated in a counterclockwise direction.
We developed a new seven-beam heterodyne receiver “7BEE” in the 72–116 GHz band for the Nobeyama 45 m telescope to investigate the early stage of star formation by deriving the deuterium fraction of dense cores. The optics for the receiver employs wideband corrugated horns covering the 72–116 GHz band and dielectric lenses to couple the incoming radiation from the antenna on to the feeds. One of the important aspects in the lens design is the anti-reflection (AR) structure to mitigate the reflections on the lens surfaces. Triangular grooves, which gradually change the effective refractive index from air to dielectric, were adopted as a basic AR design since the return loss can be in the order of 20 dB or better. The main goal of this study is to compare the radio frequency (RF) characteristics of the lenses with different patterns and sizes of AR grooving structures. We confirmed that concentric grooves degraded beam symmetry, cross-polarization characteristics, and aperture efficiency due to the birefringence of the grooves, which gave rise to wavefront distortions. Straight grooves of two different gap widths, 1.2 mm and 1.7 mm, were compared and showed similar good performance in terms of beam patterns and noise contribution. However, the latter showed a few percent higher aperture efficiency. Therefore, the straight grooves with 1.7 mm gap width were adopted as the AR structure of our lens.
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