Gadolinium(III) Porpholactones as Efficient and Robust Singlet Oxygen Photosensitizers

Construction of Gd-III photosensitizers is important for designing theranostic agents owing to the unique properties arising from seven unpaired f electrons of the Gd3+ ion. Combining these with the advantages of porpholactones with tunable NIR absorption, we herein report the synthesis of Gd-III complexes Gd-1-4 (1, porphyrin; 2, porpholactone; 3 and 4, cis- and trans-porphodilactone, respectively) and investigated their function as singlet oxygen (O-1(2)) photosensitizers. These Gd complexes displayed O-1(2) quantum yields (Phi(Delta)s) from 0.64-0.99 with the order Gd-1< Gd-2< Gd-3< Gd-4. The gradually enhanced O-1(2) sensitization after beta-oxazolone moiety replacement was ascribed to the narrowing of the energy gap (Delta E) between the lowest triplet states (T-1) of the ligand and the energy level of the (1)Delta(g) -> (3)Sigma(g) transition of O-1(2). In particular, Gd-4 is capable of excitation in the visible to NIR region (400-700 nm) with a quantum yield near unity. These Gd complexes were first demonstrated as efficient photosensitizers in photocatalysis such as oxidative C-H bond functionalization of secondary or tertiary amines, and the oxygenation of the natural product cholesterol. Finally, after glycosylation, these water-soluble Gd complexes showed potential applications in photodynamic therapy (PDT) in HeLa cells. This work revealed that Gd-III complexes of "bioinspired" beta-modified porpholactones are efficient NIR photosensitizers and form a chemical basis to construct appealing photocatalysts and theranostic agents based on lanthanides.National Key Basic Research Support Foundation of China (NKBRSFC) [2015CB856301]; NSFC [20971007, 21101169, 21571007, 21271013, 21321001, 21425313]SCI(E)EIPubMedARTICLEzhangjunlong@pku.edu.cn289676-96862