Control of Linearly and Circularly Polarized Fluorescences on Photoresponsive Liquid Crystalline and Chiral Conjugated Polymer

Abstract

A photoresponsive chiral substituent consisting of dithienylethene moiety and chiral center was introduced into the side chain of bithienylene-phenylene copolymer. Reversible photoisomerization of the dithienylethene moiety was observed in both in CHCh solution and in cast film. Fluorescence of the polymer was quenched when the photochromic moiety changed from an open form to a closed one upon an irradiation of ultraviolet light. The quenched fluorescence was recovered through the reverse photoisomerization using visible light. Polarizing optical microscope demonstrated that the polymer has a main chain type liquid crystallinity. The polymer aligned by a rubbing technique exhibited a linearly polarized fluorescence (LPF). The cast film of the polymer showed Cotton effects in the region of 1t -n* transition of main chain in both circularly dichroism (CD) and circularly polarized fluorescence (CPF) spectra. The anisotropic fluorescence was controlled by the photochemical switching.

Particle dispersion system consisting of helically assembled liquid crystalline poly(para-phenylene)derivatives with reproducible chiroptical properties

“…Polymers can also be used to facilitate the fabrication of devices used in organic light emitting diodes and solar batteries. Thus far, we have used various approaches to synthesize conjugated polymers bearing CPL functions, i.e., (i) synthesis of aromatic conjugated polymers with side chains bearing chiral moieties, [5][6][7][8][9] (ii) exploitation of intermolecular electrostatic interactions to construct a helically stacked assembly between achiral conjugated polymers bearing ionic side chains and counterionic chiral compounds, 10,11 (iii) synthesis of liquid crystalline di-substituted polyacetylene derivatives with chiral side chains, 12 and (iv) exploitation of selective reflection/transmission functions of chiral nematic liquid crystals to amplify the CPL for chiral fluorescent conjugated polymers and even control the CPL helicity by temperature change. 13,14 It is highly interesting that (iii) and (iv) afford CPLs with a high dissymmetry factors (g lum ) on the order of 10 À1 and 10 0 , respectively.…”