Consequences of Chirality in Directing the Pathway of Cholesteric Helix Inversion of π‐Conjugated Polymers by Light

Abstract

Control over main‐chain motion of chiral π‐conjugated polymers can lead to unexpected new functionalities. Here, it is shown that by combining photoswitchable azobenzene units in conjugation with chiral fluorene comonomers and appropriate plasticizers, the polymer organization and chiroptical properties of these alternating copolymers steered by light and its state of polarization can be dynamically controlled. The configuration of the stereogenic centers in the side chains of the fluorene units determines the handedness of the cholesteric organization in thermally annealed films, indicating cooperative behavior. The polymer alignment and helicity of the supramolecular arrangement can be switched by irradiating with linearly and circularly polarized light, respectively. Intriguingly, when switching the handedness of thermally induced cholesteric organizations by illuminating with circularly polarized light that is opposite to the handedness of the cholesteric phases, a nematic‐like intermediate state is observed during helix interconversion. By the sequence of irradiation with left and right circularly polarized light followed by thermal annealing, an asymmetric motion, reminiscent of that seen in molecular motors is observed. These findings suggest that functional conjugated polymers can exhibit emergent properties at mesoscopic scale.

Consequences of chirality on the response of materials

“…Yet no continuous rotation under illumination has been accomplished; to complete one full period also a thermal step has to be included next to the illumination stages. 123…”

Photo‐controlled alignment and helical organization in main‐chain liquid crystalline alternating polymers

“…This is due to the higher local density of photoactive moieties and the large structural reorganization induced by the cooperative motion of the azobenzenes within the polymer chains. Main‐chain azobenzene polymers offer the possibility of tuning the properties of the polymer dramatically using light 28–31 . Yet, the photo‐responsiveness of polymers containing azobenzene as part of the main chain is typically inefficient, particularly in thin film due to the restricted motion of the rigid polymer chains 32 .…”

“…Main-chain azobenzene polymers offer the possibility of tuning the properties of the polymer dramatically using light. [28][29][30][31] Yet, the photo-responsiveness of polymers containing azobenzene as part of the main chain is typically inefficient, particularly in thin film due to the restricted motion of the rigid polymer chains. 32 To overcome this issue, next to the addition of plasticizers, 31 flexible polydimethylsiloxane chains have been used to improve the segmental mobility of the main chain and facilitate the molecular reorientation of the chromophores by light.…”

“…[28][29][30][31] Yet, the photo-responsiveness of polymers containing azobenzene as part of the main chain is typically inefficient, particularly in thin film due to the restricted motion of the rigid polymer chains. 32 To overcome this issue, next to the addition of plasticizers, 31 flexible polydimethylsiloxane chains have been used to improve the segmental mobility of the main chain and facilitate the molecular reorientation of the chromophores by light. [33][34][35][36][37] However, for these materials, the nanoscale organization is limited due to the polydispersity of the polydimethylsiloxane chains, which limits the cooperative motion of the photo-switches.…”

Engineering Achiral Liquid Crystalline Polymers for Chiral Self-Recovery

“…From another point of view, good fluidity is often accompanied by poor stability and a strong dependence on chiral resources. Among the self-organized supramolecular systems, chiral liquid crystalline polymers (LCPs) represent a promising class of materials that might exhibit stable supramolecular helical organizations [ 37 , 38 ]. Usually, the induced chirality can only be temporarily stored in the achiral systems through the interactions between polymer chains but will be completely destroyed when undergoing a phase transition [ 39 ].…”