Reversible [4 + 2] Photooxygenation in Anion-Coordination-Driven-Assembled A 2 L 2 -Type Complexes.

Two bis-bis(urea) ligands ( L 1 and L 2 ) incorporating the photoactive 9,10-diphenylanthracene fragment were designed for the construction of anion-coordination-driven assemblies and subsequent oxygenation of anthracene moieties for singlet oxygen storage. The corresponding A 2 L 2 -type sulfate complexes [TEA] 4 [(SO 4 ) 2 ( L 1 ) 2 ] ( 1 ) and [TEA] 4 [(SO 4 ) 2 ( L 2 ) 2 ] ( 2 ), where TEA = tetraethylammonium, were achieved by coordinating the ligands L 1 or L 2 with sulfate anions. Both 1 and 2 were able to undergo [4 + 2] photooxygenation to form endoperoxide photoproducts 1 -EPO and 2 -EPO, which can be partially converted back to the original anthracene compounds after heating. The structures of 1 -EPO and 2 -EPO were unambiguously confirmed by X-ray crystallography, NMR and UV-vis spectroscopy, and high-resolution electrospray ionization mass spectrometry.