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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. [ABSTRACT FROM AUTHOR]

This article, titled "Front Cover: Push-Pull Bis-Norbornadienes for Solar Thermal Energy Storage," discusses the design and study of norbornadiene derivatives for molecular solar thermal energy storage. The article uses the analogy of autumn leaves swirling around a flask to represent the cyclic nature of energy storage. The absorption of these molecular switches is redshifted, similar to how leaves turn red in autumn. The ultimate goal of this research is to provide a renewable way of storing energy to protect the environment and climate. The full research article can be found in Chemistry - A European Journal. [Extracted from the article]

Towards complex coupled molecular motions, the remote handedness inversion of a helicene moiety was achieved by a rotary molecular motor. The use of a specifically engineered dynamic helicene stator in a novel overcrowded‐alkene second‐generation molecular motor based on a fluorinated dibenzofluorene fragment allows for an unprecedented control over helicity inversion. This is achieved by the mechanical coupling of the rotation of the rotor to the helicene inversion of the stator half via a remote chirality transmission process. Thus, the unidirectional rotary motion generated upon irradiation is used to invert the dynamic stereochemistry of a helicene, leading to a 6‐step cycle with eight intermediates. In this cycle, both alternation between P and M configurations of the helicene stator and dynamic thermal interconversion (paddling motion) can be achieved. In‐depth computational and spectroscopic studies were performed to support the associated mechanism. The control over coupled motion and dynamic helicity offers prospects for the development of complex responsive systems. [ABSTRACT FROM AUTHOR]

Understanding and controlling molecular motions is of pivotal importance for designing molecular machinery and functional molecular systems, capable of performing complex tasks. Herein, we report a comprehensive theoretical study to elucidate the dynamic behavior of a bis(benzoxazole)-based overcrowded alkene displaying several coupled and uncoupled molecular motions. The benzoxazole moieties give rise to 4 different stable conformers that interconvert through single-bond rotations. By performing excited- and ground-state molecular dynamics simulations, DFT calculations, and NMR studies, we found that the photochemical E-Z isomerization of the central double bond of each stable conformer is directional and leads to a mixture of metastable isomers. This transformation is analogous to the classical Feringa-type molecular motors, with the notable difference that, during the photochemical isomerization and the subsequent thermal helix inversion (THI) steps, multiple possible pathways take place that involve single-bond rotations that can be both coupled and uncoupled to the rotation of the naphthyl half of the molecule.

Invited for the cover of this issue are Ben L. Feringa and co-workers at the University of Groningen. The image depicts an autumn forest with the five molecular switches from our study cycling between their two isomers in the sunlight. Read the full text of the article at 10.1002/chem.202400482., (© 2024 Wiley-VCH GmbH.)