An efficient circularly polarized luminescence probe base on anthryl-modified Eu(III)-helicates for the detection and imaging singlet oxygen in living cells.

Singlet oxygen (O) is the main active ingredient in photodynamic therapy (PDT). However, an excess O can cause unnecessary toxicity. Therefore, it is of great importance to develop reliable and sensitive methods or probes for detecting O in biological systems. In this study, a pair of anthryl-modified Eu(III) binaphthol-bis-β-diketones helicates, (NEt)[Eu(L)] are designed, synthesized and characterized. Initially, the complexes display faint luminescence. Upon reacting with O to create endoperoxides of the anthracene framework, the long-lived luminescence of the Eu(III) complexes is activated. Notably, the high luminescence dissymmetry factor, g of the D → F transition (595 nm) shows an obvious increase from -1.21 to -1.29 before and after oxidation. The complex exhibits a highly selective luminescent response to the O generated by 5-aminolevulinic acid (ALA) loaded 4 T1 cells during photodynamic processes. To the best of we knowledge, this is the first example of O detection based on circularly polarized luminescence (CPL) probe. The design of the lanthanide CPL probe provides a practical way for the sensitive detection of O in the future.