Light-powered dissipative assembly of diazocine coordination cages
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Date
2022-01-26
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Abstract
Stimuli-responsive coordination cages allow reversible control over guest binding and release, relevant for adaptive receptors, carriers, catalysts, and complex systems. Light serves as an
advantageous stimulus, as it can be applied with precise spatial and
temporal resolution without producing chemical waste products. We
report the first Pd-mediated coordination cage based on ligands
embedding a diazocine photoswitch. While the thermodynamically
more stable cis-photoisomer sloppily assembles to a mixture of
species with general formula [Pdncis-L2n], the less stable trans-isomer
yields a defined [Pd 2trans-L4] cage that reversibly converts back to
the cis-system by irradiation at 530 nm or thermal relaxation. The
[Pdncis-L2n] species do not bind a given guest; however, [Pd2trans-
L4] is able to encapsulate a bis-sulfonate as long as it is kept
assembled, requiring continuous irradiation at 385 nm. In the absence of UV light, thermal relaxation results in back-switching and
guest release. Assembly and properties of the system were characterized by a combination of NMR, ion mobility ESI-MS, single-
crystal X-ray diffraction, and UV−vis absorption studies.
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Keywords
Supramolecular chemistry, Pd, Guest binding, Control, Light stimulus, Stimuli responsive coordination cage, Photoswitch, Dissipative assembly, Out of equilibrium