Conjugated polymers have received ever-increasing attention as fluorescent materials. They have many advantages compared with small-molecular fluorescent materials. As materials, conjugated polymers can be fabricated into different forms, such as thin films by spinning coating or drop casting, nano-/micro- fibers by electrospinning, nano-/micro- spheres, and micelle/vesicle/microtubule/nanoparticles by self-assembly. The great flexibility of conjugated polymers in processing makes it possible for them to meet the demands of different applications. With regard to the photophysics, the broader absorption allows conjugated polymers to be excited by different light sources. In addition, the high resistance to the photobleaching, or photostability, guarantees a long lifetime when conjugated polymers in real applications. These advantages allow conjugated polymers to be used in different fields, ranging from fluorescent bioimaging and sensors, to optical encoding and photoelectric displays. Some applications, such as encoding and display, require that the fluorescent materials have various emission colors. Thus fluorescent color tuning is very important and also very challenging for realization of these applications. This article gives some detailed discussion about the main mechanisms for the color tuning, based on the adjustment of the band gap of the single emission specie, or based on the chromaticity diagram advanced by International Commission on Illumination (CIE) for blending different emission species. The different methods for the color tuning are also discussed, such as physical blending of several emission species, copolymerization of different monomers, varying the substituent or the backbone of conjugated polymers, and changing the state of aggregation. Detailed examples with different chemical structures of polymers are provided to make clear illustrations about these mechanisms/methods.
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