Two-step transformation of p-anisolylaminoquinoline derivatives

Significance 

Materials that exhibit emission variation in response to heat, light and mechanical action have enjoyed increased attention in industry. These materials are capable of altering their crystal structure in response to various external stimuli thus making them extremely important for application in memory and switching devices. Most notably, aminoquinoline derivatives have exhibited desired polymorphism and have been observed to undergo mechanically and thermally induced crystal phase transformations accompanied by emission color alterations. For the quinoline, six molecular structures possessing varying emission properties can be derived. These multitude of crystal structures is made possible by the existence of four rotational isomers due to the presence of quinoline and MeO-substituted benzene rings, which are also involved in numerous weak intermolecular interactions.

Researchers led by professor Satoru Karasawa at Showa Pharmaceutical University (belonging to Kyushu University by March 2017) in Japan, proposed a two-step transformation of p-anisolylaminoquinoline derivatives induced by conformation- and packing-dominated processes. They hoped to demonstrate this transformation by featuring a mechanically induced first step and subsequent self-transforming at ambient conditions. Their work is published in the research journal, Dyes & Pigments.

In their studies six polymorphs of an emissive quinoline derivative were made to undergo a two-step transformation. The team succeeded in this by ensuring that the first step was due to conformation dominated process while the second was as a result of packing dominated processes. This was confirmed by observing the changes of the corresponding emission properties and powder X-ray diffraction patterns. Eventually, the researchers ground the crystals and left them for several hours so as to undergo the spontaneous transformations in order to yield the final polymorph.

The authors observed that in the case of the mechanically induced transformations, all crystals were converted to a syn-anti isomer (2a), which was the most thermodynamically stable isomer among the four isomers. The team also noted that despite the diverse packing styles of (pseudo)polymorphs, their mechanically induced transformations reflected stability at the monomer level, proceeding through an amorphous state and resulting in a conformation-dominated process at the molecular level.

The study reported by Satoru Karasawa and his research team has aided reveal that the crystals of polymorphs 1-4 exhibit multiple transformations accompanied by emission changes, with a transformation of the metastable super-cooled liquid state being observed. This work has also shown that polymorph 3 had the highest melting point among all polymorphs, although the corresponding difference was slight. In conclusion, the mechanically induced transformation is temporary, and the resulting ground 2a (syn-anti isomer) represents a metastable state. The spontaneous self-transformation accelerated by heating is a thermodynamically controlled process, and the produced 3 (anti-syn polymorphs) corresponds to the most thermodynamically stable polymorph. These novel stimuli-responsive materials can pave a new way to develop new and more efficient memory and switching devices, changing the paradigm of information storage and retrieval.

Two-step transformation of p-anisolylaminoquinoline derivatives induced by conformation- and packing-dominated processes.. Advances in Engineering

About the author

Ryusuke Hagihara received Master’s degree at Graduate School of Pharmaceutical Sciences in Kyushu University (2016). During master course, he specialized about photo-chemistry and researched about fluorescent molecules in response to external stimulus.

He is currently working at Agrochemical Research Department in KUREHA CORPORATION (Japan) as a researcher from 2017. His current research is focused on the new fungicides and Evaluates of antibacterial activity.

About the author

Dr. Kazuteru Usui was born in Hokkaido, Japan (1981). He received his Ph.D. in 2008 from the Graduate School of Pharmaceutical Sciences, Kyushu University under the supervision of Prof. Hiroshi Suemune. He won the Japan Society for the Promotion of Science (JSPS) fellowship DC2 and PD in 2007 and 2008, respectively. During 2008-2009, he was a postdoctoral fellow in the group of Prof. Eric T. Kool at the Stanford University, USA.

In 2009, he was appointed as an assistant professor at Kyushu University. He has received Research Grant Award from UBE Industries Foundation (2016), Academic Incentive Award in the Pharmaceutical Society of Japan, Kyushu Branch (2016), Konica Minolta Award in Synthetic Organic Chemistry (2017), and Best Paper Award from the Society of Synthetic Organic Chemistry, Japan, Kyushu-Yamaguchi Branch (2017).

His current research interests include are (i) Design and synthesis of helical aromatic compounds showing specific functionality; (ii) Development of metabolically resistant carbohydrate analogs by radical reaction.

About the author

Prof. Dr. Satoru Karasawa obtained his PhD from Kyushu University (1999). He started his research career at Kyushu University in 1999 as Assistant Professor, and was promoted to Associate Professor in 2007. He also started a PRESTO researcher at JSPS from 2016. He moved to Showa Pharmaceutical University as Professor in 2018.

His current research is focused on the design and synthesis of functional molecules such as metal-free MRI contrast agent and responsive molecules by external stimuli.

Reference

Ryusuke Hagihara, Kazuteru Usui, Satoru Karasawa. Two-step transformation of p-anisolylaminoquinoline derivatives induced by conformation- and packing-dominated processes. Dyes and Pigments, volume 143 (2017) pages 401-408

 

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