Well-defined polystyrene was successfully synthesized via atom transfer radical polymerization, using a novel coumarin derivate, 2-bromo-2-methyl-propionic acid 4-methyl-2-oxo-2H-chromen-7-yl ester (BMP), synthesized in our lab as an initiator, and CuBr/N,N,N',N',NaEuro(3)-pentamethyldiethylenetriamine (PMDETA) as the catalyst at 110 A degrees C. The kinetics of the polymerization was studied in detail. The fluorescence properties of the resultant polystyrenes were studied in N,N-dimethylformamide (DMF). It is very interesting that the adding of Fe3+ has significant effect on the fluorescence intensities, which decreased with increasing the concentration of iron in solutions. The obtained polystyrenes can be used as fluorescent probe molecules for Fe3+.