A Europium(III) Complex as an Efficient Singlet Oxygen\nLuminescence Probe

Abstract

A new europium(III) complex, [4‘-(10-methyl-9-anthryl)-2,2‘:6‘,2‘ ‘-terpyridine-6,6‘ ‘-diyl]bis(methylenenitrilo) tetrakis(acetate)−Eu³⁺, was designed and synthesized as a highly sensitive and selective time-gated luminescence probe for singlet oxygen (¹O₂). The new probe is highly water soluble with a large\nstability constant of ∼10²¹ and a wide pH available range (pH 3−10), and can specifically react with ¹O₂ to\nform its endoperoxide (EP-MTTA−Eu³⁺) with a high reaction rate constant at 10¹⁰ M^-1 s^-1, accompanied\nby the remarkable increases of luminescence quantum yield from 0.90% to 13.8% and lifetime from 0.80\nto 1.29 ms, respectively. The wide applicability of the probe was demonstrated by detection of ¹O₂ generated\nfrom a MoO₄^2-/H₂O₂ system, a photosensitization system of 5,10,15,20-tetrakis(1-methyl-4-pyridinio)porphyrin tetra(<i>p</i>-toluenesulfonate) (TMPyP), and a horseradish peroxidase catalyzed aerobic oxidation\nsystem of indole-3-acetic acid (IAA). In addition, it was found that the new probe could be easily transferred\ninto living HeLa cells by incubation with TMPyP. A time-gated luminescence imaging technique that can\nfully eliminate the short-lived background fluorescence from TMPyP and cell components has been\nsuccessfully developed for monitoring the time-dependent generation of ¹O₂ in living cells.