Color Tuning of Fluorescent Polymers −Jointing Element-Blocks−

Significance 

Polymerization can be defined as the chemical reaction in which a compound is made into a polymer by the addition or condensation of smaller molecules. This process is one of the most outstanding techniques for modulating the optical properties of conjugated compounds. Amongst the various advantages ripped from this process, the most striking is that materials properties such as processability, durability and film-formability are usually improved thereby making it a hot research area. Various studies have already demonstrated on its influence on the optical properties of the conjugated polymer. Other related works have also shown the various colors and stimuli-responsiveness that can be obtained from the polymers with the same chemical components. The results from these studies have therefore instigated a hypothetical situation regarding the solid state luminescence properties of the aggregation-induced emission-active conjugated polymer controllability, by altering the connection points.

To this note, a team of researchers led by professors Kazuo Tanaka and Yoshiki Chujo from Kyoto University in Japan demonstrated the tuning of the optical properties of conjugated polymers involving the boron diiminate structure. The polymers to be utilized had aggregation-induced emission (AIE) properties, and their films presented diverse colors from green to orange depending on the type of comonomer such as fluorine and bithiophene and the connection points. Their work is currently published in the research journal, Polymer Chemistry.

The research technique employed involved the synthesis of a series of polymers by employing the fluorene and bithiophene comonomers connected to the diiminate unit at different positions. Next, optical measurements were undertaken so as to investigate the various luminescence behaviors in the film samples of the polymers. Lastly, theoretical calculations were carried out to assess the energy band gap between the energy levels of frontier orbitals significantly differed in each polymer.

The authors observed that, based on the optical measurements undertaken, the polymers possessed aggregation-induced emission properties that originated from boron diiminate. In addition, they noted that the emission color was varied from green to orange by changing the connection points in the film samples. Moreover, the mechanistic studies conducted revealed that the electron-donating and accepting abilities of the boron diiminate unit could be switched by selecting the connection points.

In a nutshell, the Kyoto University researchers’ study presented the synthesis of series of conjugated polymers involving boron diiminate with variable connection points. Generally, it was demonstrated that the charge transfer state character in the emission properties of the polymers was changed. This meant that the replacement of the connection point in the diiminate complexes could be a promising strategy not only for regulating the emission color but also for adding environmental responsiveness to the luminescence properties derived from the intrinsic characters of the charge transfer emission without changing the chemical components. Altogether, the findings presented here are versatile for designing advanced polymeric materials possessing precise function tunability according to the preprogrammed design.

Color Tuning of Fluorescent Polymers −Jointing Element-Blocks− , Advances in Engineering

About the author

Kazuo Tanaka received his Ph.D. degree in 2004 from Kyoto University, and worked in Stanford University, USA, Kyoto University, and RIKEN as a postdoctoral fellow. In 2007, he has moved to the Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University, and in 2015, he was promoted to an associate professor.

His research projects especially focus on design of new functional materials relating optics and nanotechnology based on the heteroatom-containing conjugated polymers and organic-inorganic polymer hybrids.

About the author

Yoshiki Chujo completed his Ph.D. at Kyoto University in 1980 and then joined Nagoya University as an assistant professor in 1981. In 1983, he joined the group of J. McGrath at Virginia Polytechnic Institute as a postdoctoral research fellow. He returned to Kyoto University as a lecturer in 1986 and has been Professor of Polymer Chemistry there from 1994 to 2018. He is now a professor emeritus of Kyoto University.

His research interests focus on polymer synthesis, inorganic polymers, and polymeric hybrid materials.

Reference

Madoka Yamaguchi, Shunichiro Ito, Amane Hirose, Kazuo Tanaka and Yoshiki Chujo Luminescent color tuning with polymer films composed of boron diiminate conjugated copolymers by changing the connection points to comonomers. . Polymer Chemistry, 2018, volume 9, page 1942.

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