Topic：Chirality Control over Polymers and Molecules by Circularly Polarized Light

Speaker：Prof. Tamaki Nakano

                  Hokkaido University

Time：2014.11.2   am 10:00-11:00

Locaton：907-1445

Abstract：Construction of helix for a polymer chain is an important goal in polymer chemistry since helical polymers find a variety of applications. Recently, we introduced a novel method of helix induction using circularly polarized light (CPL). A preferred-handed helical conformation was reversibly induced to poly(9,9-dioctylfluoren-2,7-diyl) (PDOF) in a thin film form upon irradiation by single-handed circularly polarized light. A key structural transition in this synthesis is twist-coplanar transition of biphenyl and it analogues in excited states. This transition is also known to cause helix-helix transition (racemization) of a preferred-handed helical polyacrylate. The helix induction mechanism for PDOF is proposed to be based on a photo resolution process including a predominant excitation of right- or left-handed twist conformation in the ground state into an achiral coplanar form in excited states (Fig. 1). The coplanar form is deactivated into right- and left-handed forms, resulting in enrichment of one twist form with less likelihood of excitation by the single-handed CPL than the antipode. Deactivation may tend to form a twist of which handedness is the same as single-handed twists in the vicinity that have been formed previously in earlier excitation–deactivation events. This effect should be more obvious when the difference in the populations of P- and M-twists is larger, bringing about an apparent chirality amplification. This is the first example of helix chirality induction to a main-chain conjugated polymer using CPL. Further, though chirality of polymers has been discussed mainly at the ground state so far, chirality and its change in excited states play an important role in the CPL-assisted chiral polymer synthesis described here and can also significantly contribute to extended syntheses of a wider variety of chiral polymers and small molecules by light.

Introduction to Prof. Tamaki Nakano：

Catalysis Research Center, Hokkaido University

Address: N 21, W 10, Kita-ku, Sapporo 001-0021, Japan

Phone: +81-11-706-9155 Fax: +81-11-706-9156

E-mail: tamaki.nakano@cat.hokudai.ac.jp

Education:

1982–1986 Osaka University (Profs. Yoshio Okamoto and Koichi Hatada)

1986–1988 Graduate School of Engineering Science, Osaka University

1988–1990 Graduate School of Engineering Science, Osaka University

1991 Received a PhD

Professional Career:

1990–1999 Assistant Professor, Nagoya University

1993–1994 Visiting Scientist at Cornell University

(Prof. Dotsevi Y. Sogah)

1999–2006 Associate Professor, Nara Institute of Science Technology

2006–2012 Professor at Graduate School of Engineering, Hokkaido University

2012–present Professor at Catalysis Research Center, Hokkaido University

Research Interests:

1) Polymer Synthesis Focused on Stereochemistry (Helix, Chirality, Stereospecificity)

2) Photo Physics and Chemistry of Polymers

3) Conducting Polymers

4) Catalytic Polymers