Inversion of Circular Dichroism Signals in Chiral Polythiophene Films Induced by End-On-Oriented Surface-Segregated Monolayers

Fanji Wang; Kyohei Nakano; Hiroshi Segawa; Keisuke Tajima

doi:10.1021/acsami.0c22099

Inversion of Circular Dichroism Signals in Chiral Polythiophene Films Induced by End-On-Oriented Surface-Segregated Monolayers

ACS Appl Mater Interfaces. 2021 Feb 17;13(6):7510-7516. doi: 10.1021/acsami.0c22099. Epub 2021 Feb 4.

Authors

Fanji Wang^{1

2}, Kyohei Nakano¹, Hiroshi Segawa^{3

4}, Keisuke Tajima¹

Affiliations

¹ RIKEN Center for Emergent Matter Science (CEMS), 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
² Department of Applied Chemistry, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
³ Research Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan.
⁴ Department of General Systems Studies, Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan.

PMID: 33539070
DOI: 10.1021/acsami.0c22099

Abstract

A chiral polythiophene surfactant based on poly(3-(S)-2-methylbutylthiophene) ((S)-P3MBT) with a semifluoroalkyl group at one end of the main chain was synthesized and used to form surface-segregated monolayers (SSMs). Films of pure (S)-P3MBT mainly adopted the edge-on orientation, whereas (S)-P3MBT films with a SSM of the polymer surfactant (S)-P3MBT-F₁₇ contained a large proportion of end-on-oriented polythiophene, both at the surface and inside the films. The thin films with the SSM showed circular dichroism signals, with the sign opposite to those observed in (S)-P3MBT films. These findings suggest that the orientation-controlled SSM layers induced changes in the packing of the polymer aggregates in the films, resulting in a dramatic change in the excitonic interactions of the chiral semiconducting polymers.

Keywords: circular dichroism; molecular chirality; optical anisotropy; organic semiconductor thin-film; polymer chain orientation; surface-segregated monolayer.