Nanotechnologies / Materials
Polymer materials, Organic electronic materials

Construction of new π-stacked polymers based on precise
polymerization reactions
Department of Macromolecular Science, Graduate School of Science
Assistant Professor Naoya Kanbayashi
https://researchmap.jp/naokou?lang=en

Abstract

Nanotechnologies / Materials

We have successfully synthesized a novel π-stacked polymer
based on poly(quinolylene-2,3-methylene) with amino acids derivatives as a side chain, obtained through our originally developed theliving cyclocopolymerization, which can control the length of theπ-stacked structure and terminal structures of the polymer. The
shape of the amino acid substituents on the side chain is essential
and greatly influences the formation process and stability of the π-stacked construction. When a bulky cyclohexyl alanine derivative
was used as the side chain, the π-stacked helical structure was
highly stable against high temperature and polar solvents.

achieve with the general π-stacking construction method. Therefore, based on the synthesis of our π-stack polymers, we can expect to develop new molecular designs and functions that are notbound by conventional concepts in the development of materialsfor the realization of future society by understanding the physicalproperties via the π-stack structure and systematizing these properties.

▍ Background & Results

The layered π-electron systems exhibit unique optoelectronic
properties through the π-π interactions of aromatic compounds.
However, it is still challenging to construct a stable π-stacked
structure with a well-defined number of aromatic rings.
We re p o r t s y n t h e s i z i n g a n o v e l s e r i e s o f π- s t a c k e dpoly(quinolylene-2,3-methylene)s (PQM) with amino acid derivatives bearing different substituents (Figure 1). In the resulting
polymer, the neighboring quinoline rings of the main chain forma layered structure with π–π interactions, which is stabilized byintramolecular hydrogen bonds. Additionally, the thermal stabilityof π-stacked PQM is significantly improved by packing the substituents in the space between the side chains (Figure 2). Whena bulky cyclohexyl alanine derivative was used as the side chain,the π-stacked helical structure maintained stability even in a polar
solvent and high temperatures. Stabilizing the π-stacked systemthrough the amino acid substituents resulted in a unique polymerization behavior. In the case of derivatives with leucine and cyclohexyl alanine, which form stable π-stacked helical structures,
metastable structures with entangled main chains were formedin the initial polymerization stage. These structures underwent anirreversible structural change to achieve a thermodynamically stable helical π-stacked conformation as a nucleus for subsequent
polymerization. After that, the polymerization reaction proceededwith the elongation of the π-stacked helical structure. Diﬀerencesin the stability of these systems indicated that the amino acid substituents on the side chains determine the most thermodynamicallystable π-stacked helical structure.

Figure 1 Precise Polymerization of π-staked Polymer Based on the Living Cyclocopolymerization.

▍ Significance of the research and Future perspective

π-Stacked polymers can stack aromatic rings via covalentbonds, which are attractive molecules for understanding physicalproperties and developing functions via π-π interactions. The π-stacked polymers produced in this study enable control of thelong-range π-stack structure length and design of molecules utilizing the terminal structures and side chain, which are difficult toFigure 2 Elucidation of Structural Stabilization and Formation Mechanism ofπ-Stacked Polymers.

P a t e n t
Kanbayashi, Naoya; Kataoka, Yuki; Onitsuka, Kiyotaka et al. Journal of the American Chemical Society. 2022, 144 (13), p. 6080-6090,
doi: 10.1021/jacs.2c01337
Kataoka, Yuki; Kanbayashi, Naoya; Onitsuka, Kiyotaka et al. Angewandte Chem International Edition. 2020, 59 (26), p 10286-10291,
Tr e a t i s edoi: 10.1002/anie.202002734
Kanbayashi, Naoya; Okamura, Taka-aki; Onitsuka, Kiyotaka et al. Journal of the American Chemical Society. 2019, 141 (38), p. 15307-15317,
doi: 10.1021/jacs.9b07431
UR
L https://www.chemistry.or.jp/division-topics/2022/10/post-236.html
K e y w o r d π-π-Stacking, helical polymer, living polymerization, amino acid, hydrogen bond