Light-Powered Dissipative Assembly of Diazocine Coordination Cages

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 [Pd n cis -L 2 n ], the less stable trans -isomer yields a defined [Pd 2 trans -L 4 ] cage that reversibly converts back to the cis -system by irradiation at 530 nm or thermal relaxation. The [Pd n cis -L 2 n ] species do not bind a given guest; however, [Pd 2 trans -L 4 ] 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.

Linear and Nonlinear Optical Properties of Azobenzene Derivatives Modified with an (Amino)naphthalene Moiety

“… 18 The physicochemical and structural changes accompanying their E – Z photoisomerization, i.e., the photochromic effect, have been widely exploited to provide the strategy for material modification by means of light stimulation. 19 , 20 Up to now, azo compounds have been used to modulate the properties of supramolecular systems, 21 − 23 biomolecules (DNA, protein), 24 , 25 ion channels and receptors, 26 , 27 polymers, 28 and liquid crystals, 29 , 30 in solution as well as on surfaces and bulk materials, transferring effects from the molecular level to the macroscopic scale. 31 In general, the E – Z isomerization is induced by UV irradiation and the return to the initial state can be achieved either by visible light or thermally.…”

Visible-light-responsive self-assembled complexes: improved photoswitching properties by metal ion coordination

“…Cages formed by bridged azobenzenes (diazocines) and palladium(II) ions can be isomerized to around 65% of the metastable isomer using visible light, essentially identical to the behavior of the free ligand. [25] We recently reported the first example of self-assembled cages that were switchable with visible light. [26] ortho-Tetrafluoroazobenzene [27,28] -based ligands with appended pyridyl groups were assembled with palladium(II) ions to form a dynamic mixture of two species (trimer and tetramer).…”

Visible-light-responsive self-assembled complexes: improved photoswitching properties by metal ion coordination

“…Cages formed by bridged azobenzenes (diazocines) and palladium(II) ions can be isomerized to around 65% of the metastable isomer using visible light, essentially identical to the behavior of the free ligand. [23] We recently reported the first example of self-assembled cages that were switchable with visible light. [24] ortho-Tetrafluoroazobenzene [25][26] -based ligands with appended pyridyl groups were assembled with palladium(II) ions to form a dynamic mixture of two species (trimer and tetramer).…”