偏光依存赤外分光でMOF薄膜の配向を明らかに！　～X線を使わない結晶配向解析

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偏光依存赤外分光でMOF薄膜の配向を明らかに！　～X線を使わない結晶配向解析

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第333回のスポットライトリサーチは、大阪府立大学大学院工学研究科高橋研究室でJSPS外国人特別研究員をされていたBettina Baumgartnerさんにお願いしました。

高橋研究室では、分子/ナノレベルでの有機物質と無機物質の複合化により、様々な機能性材料を次々に創出されています。高橋雅英教授には、昨年は第8回ケムステVシンポ「有機無機ハイブリッド」でもご登壇いただきました。

今回ご紹介いただける成果は、最先端の金属-有機フレームワーク（Metal-Organic Framework：MOF）材料の解析に関するものです。通常薄膜中の結晶の配向を解析するとなるとX線を使った解析が一般的ですが、有機分子を含むといった特徴を利用して赤外分光から配向の情報を得る装置を開発されたという研究です。簡便に評価・解析できるため価値の高い成果となっています。Chem. Sci.誌に原著論文として公開され、プレスリリースも公開されています。

“Infrared Crystallography for Framework and Linker Orientation in Metal-Organic Framework Films”
Bettina Baumgartner, Ken Ikigaki, Kenji Okada and Masahide Takahashi, Chem. Sci. 2021, 12, 9298-9308. DOI: 10.1039/D1SC02370E

研究室を主宰されている高橋雅英教授から、Bettinaさんについて以下のコメントを頂いています。

Currently, I host Bettina as a postdoctoral JSPS fellow in my group in the Department of Materials Science at Osaka Prefecture University. I met Bettina at a material chemistry summer school in 2018 and again at the international Sol-Gel conference in 2019, where she stood out with here innovative way of combining IR spectroscopy with porous materials and was awarded the best poster prize. During this conference, she approached me with the idea of combining oriented MOF films developed in my group with her IR spectroscopic approach. I saw great scientific value in that idea and I encouraged her to apply for the prestigious JSPS fellowship, which she was awarded. Within the first months, Bettina established ATR spectroscopy in combination with gas sorption in my group and assembled the required optical setup and gas handling devices independently. Additionally, she substantially contributed to the implementation of polarized IR spectroscopy for determining the degree of orientation in MOF films. She is an efficient scientist and she demonstrated great skills in material synthesis, material characterization and in-depth data analysis.

Bettinaさんからは、英語でインタビューに答えていただきました。お楽しみください！

Q1. 今回プレスリリースとなったのはどんな研究ですか？簡単にご説明ください。

Material development and utilization constantly demand for new experimental tools to contribute to the understanding of structure-function relationships. Metal-organic framework (MOF) films consist of organic linkers and metal-containing units that form porous materials with great variety and multiplicity regarding constituents’ geometry, pore size and functionality. Their fields of applications are equally manifold and include photonics, energy-related, catalysis, gas and fuel storage, or (bio-)sensing. The structure-function relationship of MOFs largely relies on pore alignment and linker orientation.
The use of highly oriented 2D and 3D Cu-based MOF films allowed us to proof that polarization-dependent IR spectroscopy is well suited to study the orientation of thin films in all three crystallographic axes. While the framework orientation is accessible via diffraction methods and allowed us to validate our method against X-ray diffraction, IR crystallography revealed following points for the first time for MOF films:
• The aromatic linker is aligned perpendicular to the carboxylate plane in the Cu-paddle wheel subunit
• The degree of orientation of ultra-thin MOF can be determined
• Polarization-dependent IR spectra can give extra information on MOF structures if XRD patterns are ambiguous

Q2. 本研究テーマについて、自分なりに工夫したところ、思い入れがあるところを教えてください。

I really enjoyed that I could combine cutting-edge materials synthesized in Prof. Takahashi’s group with the well-established technique of FTIR spectroscopy and teaching this “old dog” a new trick. This project illustrates nicely how fruitful interdisciplinary cooperation can be. I believe that we will be able to explore further relevant structure-function properties with the combination of ATR spectroscopy and functional films. The potential of IR crystallography has yet to be fully exploited, allowing to fill the information gap left by diffraction techniques and giving access to key information of hybrid material structures.

Q3. 研究テーマの難しかったところはどこですか？またそれをどのように乗り越えましたか？

Explaining the polarization-dependent IR spectra with theory was the most challenging but most rewarding part of this project. Although, Harrick already laid out the theoretical fundament of ATR spectroscopy in the 1960s, their application to MOF thin films and formulation for other MOF films was demanding and were discussed vividly. The same holds true for the strength and limits of X-ray diffraction and polarization-dependent IR spectroscopy that we looked at in very detail to explain our results.

Q4. 将来は化学とどう関わっていきたいですか？

MOF films and ATR spectroscopy are a very powerful couple that I want to further exploit. I am particularly interested to combine the presented experimental setup to study adsorption phenomena and catalytic reactions within the MOF pores in situ. These would not just allow to investigate the orientation of the MOF itself but the alignment of guest molecules during the adsorption process. Insights into the orientation and adsorption site of the probe molecules will deepen the understanding of interactions between adsorbent and adsorbate, which is key to exploit the full potential of MOF films.

Q5. 最後に、読者の皆さんにメッセージをお願いします。

The presented principles are not limited to MOF films but can be easily translated to other thin film, e.g. inorganic, organic and inorganic-organic hybrid thin films.
If you are interested in the topic, please feel free to contact us or follow our updates on this topic on twitter: @bettinabaumgar3, @KenjiOkada_nano and @MasaGroup_OPU!

研究者の略歴

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Bettina Baumgartner

Bettina Baumgartner is currently FWF Schrödinger fellow at Utrecht University, Netherlands. She was a JSPS research fellow at Osaka Prefecture University in the group of Prof. Takahashi, where she worked on the project “In Situ Infrared Spectroscopic Studies on Metal-Organic-Framework Films”. In 2019, she obtained her PhD in the field of analytical chemistry from TU Wien, Austria. Bettina’s research interests are the combination of porous materials with spectroscopic techniques to gain insights into material growth and function.