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

Abstract

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.

Helix Inversion Controlled by Molecular Motors in Multistate Liquid Crystals

“…[ 13 ] Therefore, liquid crystals constitute an effective host medium for molecular motors and switches. [ 14–16 ] Chiral molecular switches can drive dynamic helix inversion in liquid crystals, [ 17–24 ] and artificial molecular motors also induce the formation of chiral nematic liquid crystals that respond to light with large changes in pitch and in the orientation of the helical axis, usually also with chiral inversion at the photostationary state. [ 25,26 ] Motor‐doped cholesteric liquid crystals have supported the discovery of rotating surfaces, [ 27–29 ] supramolecular vortices, [ 30 ] swimming [ 31 ] and reconfigurable chiral droplets, [ 32 ] and adaptive optical materials.…”

Proton‐Gated Ring‐Closure of a Negative Photochromic Azulene‐Based Diarylethene

“…Stimuli‐responsive molecules are the basis of information processing in biological as well as synthetic complex systems. Among them, photochromic molecules are particularly attractive for the ability to convert between (at least) two states by noninvasive and rapid optical stimuli with a potential of high spatial and temporal resolution . Additionally, multiple photochromic molecules have been developed, which in addition to light respond to a secondary stimulus, such as the presence of ions, oxidants/reductants, or acids/bases .…”

Protonenvermittelter Ringschluss eines negativ photochromen, Azulen‐basierten Diarylethens

“…Auf Stimuli reagierende Moleküle sind die Grundlage der Informationsverarbeitung in biologischen wie auch synthetischen, komplexen Systemen. Unter ihnen sind photochrome Moleküle aufgrund ihrer Fähigkeit zur Umwandlung zwischen (mindestens) zwei Zuständen durch nicht‐invasive und schnelle optische Stimuli bei gleichzeitig potentiell hoher räumlicher und zeitlicher Auflösung besonders attraktiv . Darüber hinaus wurden photochrome Moleküle entwickelt, die zusätzlich zu Licht auf einen sekundären Stimulus reagieren, beispielsweise auf die Anwesenheit von Ionen, Oxidations‐/Reduktionsmitteln, oder Säuren/Basen .…”