Visible‐Light‐Driven Halogen Bond Donor Based Molecular Switches: From Reversible Unwinding to Handedness Inversion in Self‐Organized Soft Helical Superstructures

• Published in: Angewandte Chemie International Edition 2020-02, Vol.59 (7), p.2684-2687
• Main Authors: Wang, Hao, Bisoyi, Hari Krishna, Li, Bing‐Xiang, McConney, Michael E., Bunning, Timothy J., Li, Quan
• Format: Article
• Language: English
• Subjects: Chemical bonds; chiral molecular switch; Cholesteric liquid crystals; Crystals; Electrons; halogen bond; Handedness; helical superstructure; Inversion; Irradiation; Light; Molecular machines; Phase transitions; Radiation; Superstructures; Switches; Unwinding; visible light; Wavelengths
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201913977

Visible‐light‐driven molecular switches endowing reversible modulation of the functionalities of self‐organized soft materials are currently highly sought after for fundamental scientific studies and technological applications. Reported herein are the design and synthesis of two novel halogen bond donor based chiral molecular switches that exhibit reversible photoisomerization upon exposure to visible light of different wavelengths. These chiral molecular switches induce photoresponsive helical superstructures, that is, cholesteric liquid crystals, when doped into the commercially available room‐temperature achiral liquid crystal host 5CB, which also acts as a halogen‐bond acceptor. The induced helical superstructure containing the molecular switch with terminal iodo atoms exhibits visible‐light‐driven reversible unwinding, that is, a cholesteric–nematic phase transition. Interestingly, the molecular switch with terminal bromo atoms confers reversible handedness inversion to the helical superstructure upon irradiation with visible light of different wavelengths. This visible‐light‐driven, reversible handedness inversion, enabled by a halogen bond donor molecular switch, is unprecedented. Flip a switch: An unprecedented visible‐light‐driven reversible handedness inversion has been accomplished in a photoresponsive self‐organized helical superstructure developed using a chiral halogen bond donor molecular switch. Interestingly, reversible visible‐light‐driven unwinding of a helical superstructure has also been achieved.