Recent developments on heteroarene–based organic semiconductors applicable to high–performance, air–stable thin–film p–channel transistors are described. First, a molecular design strategy for effectively using chalcogen atoms (sulfur or selenium), where molecular orbital calculations play an important role, was proposed, which was followed by the syntheses of target molecules, including development of new synthetic methods. Then, new molecules thus developed, i.e. benzo[1,2–b:4,5–b’]chalcogenophenes (BDXs), benzochalcogenopheno[3,2–b]benzochalcogenophenes (BXBXs), and dinaphtho[2,3–b:2’,3’–f]chalcogenopheno[3,2–b]chalcogenophenes (DNXXs), were evaluated as an active semiconducting materials of organic thin film transistors (OTFTs). In the present work, molecular factors (molecular structures, energy levels and shapes of HOMO, molecular arrangements in the thin film) and the device performances were correlated and discussed to understand a structure–properties relationship. As a consequence of this approach, several air–stable and high–performance semiconductors for the OTFTs were successfully developed. For example, vapor–processable DNTT and solution–processable alkylated–BTBTs showing field–effect mobility as high as 3.0 cm2 V–1 s–1 and with 2.8 cm2 V–1 s–1, respectively, are among the best for recently developed new materials.
In this review article, we introduce our recent studies based on the self–assembly of functional dyes through multiple hydrogen bonding interactions. Functional dyes have received a great deal of attention owing to their diverse optical and electronic properties that are appreciably favorable for application as functional materials. Combination of their π–stacking propensity with other noncovalent interactions enables the creation of diverse functional supramolecular assemblies. Multiple hydrogen bonds are highly directional noncovalent interactions, allowing a creation of oligomeric functional dye assemblies with well–defined supramolecular architectures. Such supramolecular species exhibit unique stimuli–responsive hierarchical organization processes. Furthermore, diversification of materials morphologies and local chromophore packing are possible by changing one of the supramolecular building blocks.
The three–dimensional structure and the dynamic behavior of a molecule is important issue for regulating the molecular function or biological activity. Recently the development of functional molecular devices that undergo reversible conformational interconversion between two or more stable states when exposed to an external stimulus, such as light, electricity or a chemical reaction, has received much attention. In our investigations on the cis conformational preference of aromatic N–methylated amides, we found several aromatic amides altered the stable conformations depending on the external stimulus. Namely, 3,5–bis (dimethylamino) –N–methylacetanilide (6) existed in cis form in CD2Cl2, while the addition of TFA–d caused the conformational alteration into trans form. Similarly, N– (2,5–dihydroxyphenyl) –N–phenylacetanilide (8) and N–phenylbenzohydroxamic acid (12) changed the amide conformation by redox reaction or solvent properties, respectively. N–Methylated pyridylamide also showed unique conformational properties. The stable conformation of the diamide 16 is solvent–dependent, and the acceptor number of the solvent seems to be significant. These pyridylamides and the oligomers changed the conformation by addition of acid. Further, we demonstrated the conformational change of the amide molecules could be detected by fluorescence spectra. These properties of the aromatic amides would be applied to the molecular switch or fluorescent sensors towards some external stimulus.
Ladder–shaped polyether (LSP) toxins are thought to bind to transmembrane (TM) proteins. To elucidate the interactions of LSPs with TM proteins, artificial ladder–shaped polyethers (ALPs) possessing simple iterative structure with different number of rings were synthesized based on the convergent method via α–cyano ethers. The interaction of these ALPs with TM proteins was evaluated, and we found that the difference of activities among the ALPs can be accounted for by the concept of “hydrophobic matching” i. e. lengths of the hydrophobic region including the side chains of ALPs are ca. 25 Å, which match the lengths of the hydrophobic region of α–helical TM proteins. The partial structure corresponding to the WXYZA’B’C’ ring system of maitotoxin (MTX) was synthesized based on the convergent method via α–cyano ethers, and we found that hemolysis of human red blood cells induced by MTX was blocked by the fragment. The hydrophobic portion of MTX is expected to be promising molecular probes for identifying the target proteins of MTX.
Photoreactivities of 5–bromouracil– or 5–iodouracil–containing DNA have widely been used as DNA–protein photocrosslinking to investigate their interface. We have accumulated the photoreactivities of 5–bromouracil or 5–iodouracil in various DNA local structures. It was found that hydrogen abstraction by uracil–5–yl radical is highly conformation–dependent to provide unique oxidative damage sites. The results suggest that this photochemical method can be used to detect DNA local structures. Recently, 5–bromouracil– or 5–iodouracil–containing DNA has also been used as probe of DNA charge transfer, since one–electron reduction is necessary for the formation of uracil–5–yl from 5–bromouracil–containing DNA. In this review, we discuss specific hydrogen abstraction by uracil–5–yl radical in various DNA local structures and electron transfer processes along DNA strand in B– and Z–form as well as between DNA–protein interface.
We found the interesting results that alkylation of carboxylic acids with methyl iodide using strontium metal proceeded smoothly to afford the corresponding monomethylated ketones, rather than the dimethylated alcohols, preferentially in moderate to good yields. Using the carboxylic acid sodium salt, the yield decreases slightly, but the reaction controls the over–addition of methyla-ting agent to give the dramatically improvement with high selectivities. Next, when benzoic acid reacted with metallic strontium and alkyl iodides, the unexpected reactions occurred to give p–alkylated products of the aromatic ring of benzoic acid in a trace amount. We were interested in the p–allylated product because this allylation reaction is unusual in these conditions and there are only a few reports of the p–alkylation of aromatic carbonyl compounds. As the results of various investigations, the p–alkylated products were obtained predominantly in good yields. Furthermore, it was found that the convenient bulky tert–benzylic alcohol benzoates were prepared by the dialkylation of methyl benzoate with methyl or i–butyl iodide in the presence of metallic strontium, followed by the addition of benzoyl chloride, benzoic anhydride or acetic anhydride as two portions.
Cucurbit[n]urils (CB[n]) are macrocyclic hosts synthesized by the acid-catalyzed condensation of glycoluril and formaldehyde. Although the synthesis of CB was first reported by Behrend et al. in 1905, its structure and chemical nature had not been known until 1981, when full characterization was reported by Mock et al. This review will focus on the recent development of structurally interesting CB[n] derivatives and analogues.
Primary anilines are versatile intermediates, while the direct syntheses from aryl halides using NH3 as nitrogen source remain difficult. However, in recent years, catalytic direct synthetic methods of primary anilines under mild conditions have been reported by some groups. In this short review, recent advances of direct synthesis of primary aniline using metal catalysts (Pd, Cu) without high pressure, high temperature and long reaction time are described.