A short and simple synthetic route for thiophene-fused aromatic compounds
Thiophene-fused polycyclic aromatic hydrocarbons (PAHs) are known to be useful as organic semiconductors due to their high charge transport properties. Scientists at Nagoya University have developed a short route to form various thiophene-fused PAHs by simply heating mono-functionalized PAHs with sulfur. This new method is expected to contribute towards the efficient development of novel thiophene-based electronic materials.
About the research:
Nagoya, Japan – Dr. Lingkui Meng, Dr. Yasutomo Segawa, Professor Kenichiro Itami of the JST-ERATO Itami Molecular Nanocarbon Project, Institute of Transformative Bio-Molecules (ITbM) of Nagoya University and Integrated Research Consortium on Chemical Sciences, and their colleagues have reported in the Journal of the American Chemical Society, on the development of a simple and effective method for the synthesis of thiophene-fused PAHs.
Thienannulation (thiophene-annulation) reactions, a transformation that makes new thiophene rings via cyclization, leads to various thiophene-fused PAHs. Most conventional thienannulation methods require the introduction of two functional groups adjacent to each other to form two reactive sites on PAHs before the cyclization can take place (Figure 2). Thus, multiple steps are required for the preparation of the substrates. As a consequence, a more simple method to access thiophene-fused PAHs is desirable.
A team led by Yasutomo Segawa, a group leader of the JST-ERATO project, and Kenichiro Itami, the director of the JST-ERATO project and the center director of ITbM, has succeeded in developing a simple and effective method for the formation of various thiophene-fused PAHs. They have managed to start from PAHs that have only one functional group, which saves the effort of installing another functional group, and have performed the thienannulation reactions using elemental sulfur, a readily available low cost reagent (Figure 3). The reactions can be carried out on a multigram scale and can be conducted in a one-pot two-step reaction sequence starting from an unfunctionalized PAH. This new approach can also generate multiple thiophene moieties in a single reaction. Hence, this method has the advantage of offering a significant reduction in the number of required steps and in the reagent costs for thiophene-fused PAH synthesis compared to conventional methods.
The researchers have shown that upon heating and stirring the dimethylformamide solution of arylethynyl group-substituted PAHs and elemental sulfur in air, they were able to obtain the corresponding thiophene-fused PAHs. The arylethynyl group consists of an alkyne (a moiety with a carbon-carbon triple bond) bonded to an aromatic ring. The reaction proceeds via a carbon-hydrogen (C-H) bond cleavage at the position next to the arylethynyl group (called the ortho-position) on PAHs, in the presence of sulfur. As the ortho-C-H bond on the PAH can be cleaved under the reaction conditions, prior functionalization (installation of a functional group) becomes unnecessary.
Arylethynyl-substituted PAHs are readily accessible by the Sonogashira coupling, which is a cross-coupling reaction to form carbon-carbon bonds between an alkyne and a halogen-substituted aromatic compound. The synthesis of thiophene-fused PAHs can also be carried out in one-pot, in which PAHs are subjected to a Sonogashira coupling to form arylethynyl-substituted PAHs, followed by direct treatment of the alkyne with elemental sulfur to induce thienannulation.
“Actually, we coincidentally discovered this reaction when we were testing different chemical reactions to synthesize a new molecule for the Itami ERATO project,” says Yasutomo Segawa, one of the leaders of this study. “At first, most members including myself felt that the reaction may have already been reported because it is indeed a very simple reaction. Therefore, the most difficult part of this research was to clarify the novelty of this reaction. We put in a significant amount of effort to investigate previous reports, including textbooks from more than 50 years ago as well as various Internet sources, to make sure that our reaction conditions had not been disclosed before,” he continues.
The team succeeded in synthesizing more than 20 thiophene-fused PAHs (Figure 4). They also revealed that multiple formations of thiophene rings of PAHs substituted with multiple arylethynyl groups could be carried out all at once. Multiple thiophene-fused PAHs were generated from three-fold and five-fold thienannulations, which generated triple thiahelicene (containing three thiophenes) and pentathienocorannulene (containing five thiophenes, top right of Figure 4), respectively. The pentathienocorannulene was an unprecedented molecule that was synthesized for the first time.
“I was extremely happy when I was able to obtain the propeller-shaped triple thiahelicene and hat-shaped pentathienocorannulene, because I have always been aiming to synthesize exciting new molecules since I joined Professor Itami’s group,” says Lingkui Meng, a postdoctoral researcher who mainly conducted the experiments. “We had some problems in purifying the compounds but we were delighted when we obtained the crystal structures of the thiophene compounds, which proved that the desired reactions had taken place.”
“The best part of this research for me is to discover that our C-H functionalization strategy on PAHs could be applied to synthesize structurally beautiful molecules with high functionalities,” says Segawa. “The successful synthesis of a known high-performance organic semiconductive molecule, (2,6-bis(4-n-octylphenyl)- dithieno[3,2-b:2′,3′-d]thiophene (the lower right of Figure 4), from a relatively cheap substrate opens doors to access useful thiophene compounds in a rapid and cost-effective manner.”
“We hope that ongoing advances in our method may lead to the development of new organic electronic devices, including semiconductor and luminescent materials,” say Segawa and Itami. “We are considering the possibilities to make this reaction applicable for making useful thiophene-fused PAHs, which would lead to the rapid discovery and optimization of key molecules that would advance the field of materials science.”
Being able to determine magnetic properties of materials with sub-nanometer precision would greatly simplify development of magnetic nano-structures for future spintronic devices. In an article published in Nature Communications Uppsala physicists make a big step towards this goal – they propose and demonstrate a new measurement method capable to detect magnetism from areas as small as 0.5 nm2.
Due to the ever-growing demand for more powerful electronic devices the next generation spintronic components must have functional units that are only a few nanometers large. It is easier to build a new spintronic device, if we can see it in a sufficient detail. This becomes more and more tricky with the rapid advance of nano-technologies, especially when we need not only an overall picture “how the thing looks”, but also know its physical properties at nano-scale. One of instruments capable of such detailed look is a transmission electron microscope.
Electron microscope is a unique experimental tool offering to scientists and engineers a wealth of information about all kinds of materials. Differently from optical microscopes, it uses electrons to study the materials, and thanks to that it achieves an enormous magnification. For example, in crystals one can even observe individual columns of atoms. Electron microscopes routinely provide information about structure, composition and chemistry of materials. Recently researchers found ways to use electron microscopes also for measuring magnetic properties. There, however, atomic resolution has not been reached so far.
A team of three physicists from Uppsala University – Ján Rusz, Jakob Spiegelberg and Peter Oppeneer, together with colleagues from Nagoya University (Japan) and Forschungszentrum Jülich (Germany) have developed and experimentally proven a new method, which allows to detect magnetism from individual atomic planes. The area of the sample, from which a magnetic signal was detected, is about a trillion (1012) times smaller than that of an average grain of sand.
‘The discovery of this method came from an unexpected result obtained from computer simulations. It was a surprise, which made us dig deeper into it. Thanks to the international collaboration our curious theoretical observation was soon after followed by an experimental confirmation’, says Ján Rusz.
A significant advantage of this new method is its ease of application. Modern transmission electron microscopes can apply the method right away, without any need of modifications or special equipment.
Nagoya University (名古屋大学 Nagoya daigaku?), abbreviated to Meidai (名大?), is a Japanese national university headquartered in Chikusa-ku, Nagoya.
It is the last Imperial University in Japan and among the National Seven Universities. It is the 4th best ranked higher education institution in Japan.
As of 2014, six faculty and alumni of the university have won the Nobel Prize in science.
Nagoya is one of the top research institutions in Japan. According to Thomson Reuters, Nagoya is the 5th best research university in Japan. Its research standard is especially high in Physics (6th in Japan, 61st in the world), Chemistry (7th in Japan, 43rd in the world), and Biology & Biochemistry (5th in Japan, 97th in the world).
Weekly Diamond reported that Nagoya has the 6th highest research standard in Japan in research funding per researchers in COE Program. In the same article, it’s also ranked 6th in terms of the quality of education by GP funds per student.
In addition, Nikkei Shimbun on 16 February 2004 surveyed the research standards in Engineering studies based on Thomson Reuters, Grants in Aid for Scientific Research and questionnaires to heads of 93 leading Japanese research centers, and Nagoya was placed 9th (research planning ability 5th//informative ability of research outcome 9th/ability of business-academia collaboration 6th) in this ranking.
Furthermore, Nagoya had the 8th highest number of patents accepted (108) in 2009 among Japanese universities.
It has a high research standard in Social Science & Humanities. Asahi Shimbun summarized the amount of academic papers in Japanese major legal journals by university, and Nagoya University was ranked 4th during 2005-2009. RePEc in January 2011 ranked Nagoya’s Economic department as Japan’s 13th best economic research university.
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