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

Abstract

Two new photoswitchable dithienylethene (DTE)-catechol ligands, specifically designed for group 13 metalcoordination, were synthesized via Suzuki coupling reactions froma dichloro-DTE building block, each with varying longitudinalextensions. The shorter DTE-catechol ligand did not efficientlyassemble with Ga3+ metal ions; however, elongation with aphenylene-amide spacer group enabled the successful formationof a novel triply DTE-functionalized coordination [Ga2L3]6− cage.This cage represents a unique example of integrating DTEphotoswitches with main group metals in a supramolecularcoordination framework. The [Ga2L3]6− cage was thoroughlycharacterized by NMR spectroscopy, including DOSY hydro-dynamic volumetric analyses, high-resolution mass spectrometry, computational DFT, and photochemical analyses. The DFT studieshighlighted the structural integrity and dynamic interplay within the helicate and mesocate isomeric forms of the [Ga2L3]6− cageupon photoswitching. While the free ligands exhibited all-photonic reversible switching at up to mM concentrations upon alternatingirradiation at 365 and >495 nm, the [Ga2L3]6− cage demonstrated these capabilities under dilute μM conditions, albeit with lowerefficiency and fatigue resistance. This behavior highlights the intricate relationship between rigid coordination with main groupmetals and the flexibility of the photoswitchable DTE ligands within the [Ga2L3]6− cage