We report a new method to generate families of organic fluorophores with any desirable emission wavelengths based upon the controlled oxidation of the light-emitting conjugated polymer, poly[2-methoxy-5-(2́- efhylhexyloxy)-p-phenylenevinylene] (MEH-PPV), with weta-chloroperbenzoic acid (m-CPBA). In this method, m-CPBA reacts with ethylene moieties along the MEH-PPV backbone to create conjugation breaks, which gives rise to a gradual and controllable change in the emission wavelength. By simply adjusting the reaction time, light-emitting polymers possessing emission wavelengths spanning a 470-555 nm wavelength range can be easily prepared. Significantly, fluorescence quantum yields (QYs) of the oxidized polymers were comparable to or greater than that of the pristine polymer, contrary to the products typically resulting from oxidation of MEH-PPV by dioxygen. This new method should provide a simple way to generate color- tunable organic fluorophores with high QYs in a time- and cost-effective manner.