Chemical probe compounds that become fluorescent upon reduction, and methods for their use

A method of monitoring change in the oxidation state of a non-biological system, the method comprising:

• providing a non-biological system;
• contacting the non-biological system with at least one chemical compound to form a test system, wherein the chemical compound has the structure FU-RQU or FU-L-RQU;
• where FU is a fluorophore unit, RQU is a reducible quenching unit, and L is a linker unit;
• determining the fluorescence of the test system at a first time point to provide a first fluorescence;
• determining the fluorescence of the test system at a second time point to provide a second fluorescence;
• determining the difference between the first fluorescence and the second fluorescence to monitor change in the oxidation state of the non-biological system.