Photochemically colour-tuneable white fluorescence illuminants consisting of conjugated polymer nanospheres

π-Conjugated aromatic polymers have attracted much interest due to their semi-conducting and luminescent properties, and are therefore regarded as promising materials for next-generation optoelectronic devices. Especially, it is considered as one of the indispensable steps for advanced function to control the optoelectronic properties by external stimuli. Herein, we show photochemically fluorescent colour-tuneable systems consisting of photoresponsive conjugated polymer nanospheres. We design and synthesize photoresponsive conjugated polymers with red, green and blue (RGB) fluorescence by introducing photoisomeric dithienylethene moieties in the side chains. A mixture of the red-, green- and blue-fluorescent polymer nanospheres exhibits photoswitchable white fluorescence between emission and quenching by irradiating external lights in both the nanosphere solution and film state. In addition, reversible change in fluorescent colour between white and RGB is also achieved by replacing a photoresponsive polymer with a non-photoresponsive analogue in the mixture. Thus, we successfully demonstrate ‘photoresponsive polymer illuminant’ systems bearing photochemically colour-tuneable white fluorescence.