Macroscopic Change in Luminescent Color by Thermally Driven Sliding Motion in [3]Rotaxanes

[3]Foldarotaxane-mediated synthesis of an improbable [2]rotaxane

The wrapping of an aromatic oligoamide helix around an active ester-containing [2]rotaxane enforced the sliding and the sequestration of the surrounding macrocycle around a part of the axle for which it has no formal affinity. The foldamer-mediated compartmentalization of the [2]rotaxane shuttle was subsequently used to prepare an improbable rotaxane.

Dibenzosuberenone-Based Photo- and Thermochromic Switches, a Transformation: Rearrangement of Dibenzosuberenones to Spiro Anthrones

In this study, a new class of photo- and thermochromic compounds was discovered. Fluorescent dihydropyridazine-appended dibenzosuberenone derivatives with central seven-membered rings were converted to colorless spiro anthrones with central six-membered rings by thermal isomerization or visible-light (420 nm) irradiation. Under UV light (350 nm), the spiro anthrones converted back to benzosuberenones. The chemical structures of the spiro anthrones were determined by NMR, UV-vis spectroscopy, and HRMS analyses. It was also observed that the dibenzosuberenone derivatives were oxidized on exposure to UV irradiation for a long time.

Chemically Induced Mismatch of Rings and Stations in [3]Rotaxanes

The mechanical interlocking of molecular components can lead to the appearance of novel and unconventional properties and processes, with potential relevance for applications in nanoscience, sensing, catalysis, and materials science. We describe a [3]rotaxane in which the number of recognition sites available on the axle component can be changed by acid–base inputs, encompassing cases in which this number is larger, equal to, or smaller than the number of interlocked macrocycles. These species exhibit very different properties and give rise to a unique network of acid–base reactions that leads to a fine pK_a tuning of chemically equivalent acidic sites. The rotaxane where only one station is available for two rings exhibits a rich coconformational dynamics, unveiled by an integrated experimental and computational approach. In this compound, the two crown ethers compete for the sole recognition site, but can also come together to share it, driven by the need to minimize free energy without evident inter-ring interactions.

Interplay between a Foldamer Helix and a Macrocycle in a Foldarotaxane Architecture

The design and synthesis of a novel rotaxane/foldaxane hybrid architecture is reported. The winding of an aromatic oligoamide helix host around a dumbbell-shaped thread-like guest, or axle, already surrounded by a macrocycle was evidenced by NMR spectroscopy and X-ray crystallography. The process proved to depend on the position of the macrocycle along the axle and the associated steric hindrance. The macrocycle thus behaves as a switchable shield that modulates the affinity of the helix for the axle. Reciprocally, the foldamer helix acts as a supramolecular auxiliary that compartmentalizes the axle. In some cases, the macrocycle is forced to move along the axle to allow the foldamer to reach its best recognition site.

Recent advances in higher order rotaxane architectures

Despite dramatic advances in the template-directed synthesis of archetypal [2]rotaxanes, higher order rotaxanes with multiple molecular components (rings or dumbbells) are relatively daunting subjects owing to their synthetic challenges. With unique interlocked architectures, higher order rotaxanes have found applications in artificial molecular machines. In this feature article, we will focus on the recent advances in higher order rotaxanes with well-defined structures. Different types of rotaxane architectures will be described, and their synthetic approaches will be highlighted. Moreover, the stimuli-responsive molecular motion with increasing complexity in these diverse architectures will also be discussed.