Abstract
Here we introduce a new class of ratiometric O2 sensors for hypoxic environments. Two-component structures composed of phosphorescent cyclometalated Ir(iii) complexes and the well-known organic fluorophore BODIPY have been prepared by the 1 : 1 reaction of bis-cyclometalated iridium synthons with pyridyl-substituted BODIPY compounds. Two different cyclometalating ligands are used, which determine the relative energies of the iridium-centered and BODIPY-centered excited states, and the nature of the linker between iridium and BODIPY also has a small influence on the photoluminescence. Some of the conjugates exhibit dual emission, with significant phosphorescence from the iridium site and fluorescence from the BODIPY, and thus function as ratiometric oxygen sensors. Oxygen quenching experiments demonstrate that as O2 is added the phosphorescence is quenched while the fluorescence is unaffected, with dynamic ranges that are well suited for hypoxic sensing (pO2 < 160 mmHg).
Highlights
Molecular oxygen plays a major role in a large range of chemical and biochemical reactions essential to aerobic metabolism.[1,2,3] As hypoxia is associated with a variety of diseases in our daily lives and found in tumor cells,[4] many researchers have worked to develop reliable methods for sensing triplet oxygen in the past several years.[5,6,7,8,9,10] Accurate O2 sensors are especially important in cancer biology, where the O2 level in tumor cells can be used to determine the tumor's metabolic state and guide therapeutic protocols
Two-component structures composed of phosphorescent cyclometalated Ir(III) complexes and the well-known organic fluorophore BODIPY have been prepared by the 1 : 1 reaction of bis-cyclometalated iridium synthons with pyridyl-substituted BODIPY compounds
Recently reported designs for ratiometric O2 sensors include quantum dots decorated with phosphorescent metal complexes,[12] metal–organic frameworks with both uorescent and phosphorescent linkers,[13] uorescent polymers with covalently linked cyclometalated iridium complexes,[14] and University of Houston, Department of Chemistry, 3585 Cullen Blvd., Room 112, Houston, TX 77204-5003, USA
Summary
Molecular oxygen plays a major role in a large range of chemical and biochemical reactions essential to aerobic metabolism.[1,2,3] As hypoxia is associated with a variety of diseases in our daily lives and found in tumor cells,[4] many researchers have worked to develop reliable methods for sensing triplet oxygen in the past several years.[5,6,7,8,9,10] Accurate O2 sensors are especially important in cancer biology, where the O2 level in tumor cells can be used to determine the tumor's metabolic state and guide therapeutic protocols. There are some known constructs which combine bis-cyclometalated iridium complexes with BODIPY uorophores,[53,54,55,56,57,58] offering the advantages of BODIPY's high uorescence quantum yields and biological compatibility,[59,60,61,62] but these have not been developed as ratiometric oxygen sensors.
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