Laterally patterning the emission color of polymer light-emitting devices is one of the current technological challenges for their commercialization. Photopatterning is one of the most convenient approaches for the production of closely spaced, differently colored pixels, other than direct-writing approaches such as ink-jet printing. The photo-induced addition of thiols to C=C bonds (the thiol-ene) reaction is here utilized to achieve photobleaching of poly (phenylenevinylene)-type polymers. By exploiting the chemical selectivity of the UV-induced thiol-ene reaction, the emission color in a guest-host system is tuned from that of the guest to that of the host. It is demonstrated that the presented method can be applied for numerous energy-transfer systems.