Synthesis, Characterization, and Photochemistry of a Ga2L3 Coordination Cage with Dithienylethene-Catecholate Ligands

Two new photoswitchable dithienylethene (DTE)-catechol ligands, specifically designed for group 13 metal coordination, were synthesized via Suzuki coupling reactions from a dichloro-DTE building block, each with varying longitudinal extensions. The shorter DTE-catechol ligand did not efficiently assemble with Ga3+ metal ions; however, elongation with a phenylene-amide spacer group enabled the successful formation of a novel triply DTE-functionalized coordination [Ga2L3]6– cage. This cage represents a unique example of integrating DTE photoswitches with main group metals in a supramolecular coordination framework. The [Ga2L3]6– cage was thoroughly characterized by NMR spectroscopy, including DOSY hydrodynamic volumetric analyses, high-resolution mass spectrometry, computational DFT, and photochemical analyses. The DFT studies highlighted the structural integrity and dynamic interplay within the helicate and mesocate isomeric forms of the [Ga2L3]6– cage upon photoswitching. While the free ligands exhibited all-photonic reversible switching at up to mM concentrations upon alternating irradiation at 365 and >495 nm, the [Ga2L3]6– cage demonstrated these capabilities under dilute μM conditions, albeit with lower efficiency and fatigue resistance. This behavior highlights the intricate relationship between rigid coordination with main group metals and the flexibility of the photoswitchable DTE ligands within the [Ga2L3]6– cage.