Reversible [4+2] Photooxygenation in Anion-Coordination-Driven-Assembled A2L2-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)[(SO4)(2)(L-1)(2)] (1) and [TEA](4)[(SO4)(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.

Automated summary

In this study, two photoactive ligands were designed and used to construct sulfate complexes. These complexes can undergo oxygenation reactions under light, storing singlet oxygen, and partially recover the original structures after heating.