A chiral self-sorting photoresponsive coordination cage based on overcrowded alkenes

Abstract

In recent years, increasing efforts have been devoted to designing new functional stimuli-responsive supramolecular assemblies. Here, we present three isomeric supramolecular coordination complexes consisting of a Pd2L4 stoichiometry. As shown by NMR, CD and X-ray studies, as well as DFT calculations, these complexes form cage-like structures by chiral self-sorting. Photochromic ligands derived from first generation molecular motors enable light-driven interconversion between the three isomers. Two of the isomers were able to form host–guest complexes opening up new prospects toward stimuli-controlled substrate binding and release.

Increasing structural and functional complexity in self-assembled coordination cages

“…For example, Wezenberg and Feringa presented a photo-responsive coordination cage based on Pd II cations and bidentate bis-pyridyl ligands with an overcrowded alkene as backbone. 118 This motif is similar to their famous molecular motors 119 and can be switched reversibly by irradiation. Irradiating the Z -enantiomer of the ligand (or cage) with 312 nm light at −78 °C, and then slowly warming up to room temperature, leads to a switch to the E -enantiomer.…”

Integrative Assembly of Heteroleptic Tetrahedra Controlled by Backbone Steric Bulk

“…The dynamic nature of many transition metal–ligand interactions, characterized by precise geometry and directionality, combined with a polytopic ligand structure, allow us to design and self-assemble a plethora of compounds with different shapes, sizes, and properties. Embedded functions, depending on either individual building blocks or their synergistic interaction, − may involve host–guest interactions, − photoswitching, , chirality, − chromophore effects, − or catalysis, − just to name a few.…”

Recent Advances of Photoresponsive Supramolecular Switches

“…Feringa and co-workers reported another photoresponsive molecular cage based on overcrowded alkenes, which is able to bring about the lightcontrolled transformation between three isomers. [32] Two of the larger isomers could bind a tosylate anion in acetonitrile solution, showing similar binding strengths (around 10 3 M À 1 ). This series of work displayed the potential of light-controlled molecular cages for information processing on a molecular scale.…”

“…Meanwhile, when these metallacycles were alternately exposed to UV (302±20 nm) and visible light (>480 nm), chirality of the metallacycle would undergo reversible transformation. Feringa and co‐workers reported another photoresponsive molecular cage based on overcrowded alkenes, which is able to bring about the light‐controlled transformation between three isomers [32] . Two of the larger isomers could bind a tosylate anion in acetonitrile solution, showing similar binding strengths (around 10 3 M −1 ).…”