Fast synthesis and redox switching of di- and tetra-substituted bisthioxanthylidene overcrowded alkenes

Corbet, Brian P.; Wonink, Marco B. S.; Feringa, Ben L.

doi:10.1039/d1cc03098a

“…This problem is circumvented in dynamic redox (dyrex) switches, wherein two-electron redox processes are associated with significant geometric rearrangements. − This has been exploited in dyrex switches, in which reversible C–C single or CC double-bond formation/breaking via two-electron oxidations gives rise to not only significant conformational transformations but also changes in polarity, absorbance, and luminescence. − For example, we have pioneered the use of the overcrowded alkene bisthioxanthylidene ( BTX , Figure ) ,− and derivatives thereof as highly versatile redox and photoresponsive switches with multiple stable and isolable (redox) states.…”

Section: Introductionmentioning

confidence: 99%

Redox-Switchable Aromaticity in a Helically Extended Indeno[2,1-c]fluorene

Sidler,

Hein,

Doellerer

et al. 2024

J. Am. Chem. Soc.

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Molecular switches have received major attention to enable the reversible modulation of various molecular properties and have been extensively used as trigger elements in diverse fields, including molecular machines, responsive materials, and photopharmacology. Antiaromaticity is a fascinating property that has attracted not only significant fundamental interest but is also increasingly relevant in different applications, in particular organic (opto)electronics. However, designing systems in which (anti)aromaticity can be judiciously and reversibly switched ON and OFF remains challenging. Herein, we report a helicene featuring an indenofluorene-bridged bisthioxanthylidene as a novel switch wherein a simultaneous two-electron (electro)chemical redox process allows highly reversible modulation of its (anti)aromatic character. Specifically, the two thioxanthylidene rotors, attached to the initially aromatic indenofluorene scaffold via overcrowded alkenes, adopt an anti-folded structure, which upon oxidation convert to singly bonded, twisted conformations. This is not only associated with significant (chir)optical changes but importantly also results in formation of the fully conjugated, formally antiaromatic as-indacene motif in the helical core of the switch. This process proceeds without the buildup of radical cation intermediates and thus enables highly reversible switching of molecular geometry, aromaticity, absorbance, and chiral expression under ambient conditions, as evidenced by NMR, UV−vis, CD, and (spectro)electrochemical analyses, supported by DFT calculations. We expect this concept to be extendable to a wide range of robust antiaromatic−aromatic switches and to provide a basis for modulation of the structure and properties of these fascinating inherently chiral polycyclic π-scaffolds.

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A Multiresponsive Ferrocene‐Based Chiral Overcrowded Alkene Twisting Liquid Crystals

Fellert,

Hein,

Ryabchun

et al. 2024

Angewandte Chemie

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The reversible modulation of chirality has gained significant attention not only for fundamental stereochemical studies but also for numerous applications ranging from liquid crystals (LCs) to molecular motors and machines. This requires the construction of switchable molecules with (multiple) chiral elements in a highly enantioselective manner, which is often a significant synthetic challenge. Here, we show that the dimerization of an easily accessible enantiopure planar chiral ferrocene‐indanone building block affords a multi‐stimuli‐responsive dimer (FcD) with pre‐determined double bond geometry, helical chirality, and relative orientation of the two ferrocene motifs in high yield. This intrinsically planar chiral switch can not only undergo thermal or photochemical E/Z isomerization but can also be reversibly and quantitatively oxidized to both a monocationic and a dicationic state which is associated with significant changes in its (chir)optical properties. Specifically, FcD acts as a chiral dopant for cholesteric LCs with a helical twisting power (HTP) of 13 μm−1 which, upon oxidation, drops to near zero, resulting in an unprecedently large redox‐tuning of the LC reflection color by up to 84 nm. Due to the straightforward stereoselective synthesis, FcD, and related chiral switches, are envisioned to be powerful building blocks for multi‐stimuli‐responsive molecular machines and in LC‐based materials.

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A Multiresponsive Ferrocene‐Based Chiral Overcrowded Alkene Twisting Liquid Crystals

Fellert,

Hein,

Ryabchun

et al. 2024

Angew Chem Int Ed

0

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The reversible modulation of chirality has gained significant attention not only for fundamental stereochemical studies but also for numerous applications ranging from liquid crystals (LCs) to molecular motors and machines. This requires the construction of switchable molecules with (multiple) chiral elements in a highly enantioselective manner, which is often a significant synthetic challenge. Here, we show that the dimerization of an easily accessible enantiopure planar chiral ferrocene‐indanone building block affords a multi‐stimuli‐responsive dimer (FcD) with pre‐determined double bond geometry, helical chirality, and relative orientation of the two ferrocene motifs in high yield. This intrinsically planar chiral switch can not only undergo thermal or photochemical E/Z isomerization but can also be reversibly and quantitatively oxidized to both a monocationic and a dicationic state which is associated with significant changes in its (chir)optical properties. Specifically, FcD acts as a chiral dopant for cholesteric LCs with a helical twisting power (HTP) of 13 μm−1 which, upon oxidation, drops to near zero, resulting in an unprecedently large redox‐tuning of the LC reflection color by up to 84 nm. Due to the straightforward stereoselective synthesis, FcD, and related chiral switches, are envisioned to be powerful building blocks for multi‐stimuli‐responsive molecular machines and in LC‐based materials.

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Fast synthesis and redox switching of di- and tetra-substituted bisthioxanthylidene overcrowded alkenes

Abstract: A rapid and efficient method for the synthesis of overcrowded alkenes using (trimethylsilyl)diazomethane provides a range of substituted bisthioxanthylidenes. We show large conformational redox switching from folded to orthogonal states,...

Cited by 8 publications

References 35 publications

Redox-Switchable Aromaticity in a Helically Extended Indeno[2,1-c]fluorene

Redox-Switchable Aromaticity in a Helically Extended Indeno[2,1-c]fluorene

A Multiresponsive Ferrocene‐Based Chiral Overcrowded Alkene Twisting Liquid Crystals

A Multiresponsive Ferrocene‐Based Chiral Overcrowded Alkene Twisting Liquid Crystals

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