Amplification of fluorescence quenching of a polythiophene is optically triggered by converting pendant dithienylethene (DTE) photoswitches to their ring-closed isomers using UV light. The effect can be reversed with visible light, which regenerates the original DTE isomer. Amplification attributed to the high mobility of electronic excited states in conjugated polymers, which facilitates energy transfer to a ring-closed DTE.