In general, color-tunable fluorescence in polymer systems can be achieved either by direct emission spectra combination or Förster resonance energy transfer (FRET) . By modulation of energy transfer efficiency, the latter can generate more tunable emission properties, and is therefore widely used in stimuli-responsive materials , ratiometric sensors multicolor bioimaging agents , security inks , and light-harvesting systems . The precise emission tuning of FRET polymers requires careful selection of donor (D) and acceptor (A) fluorophore pairs and extensive optimization of their energy transfer efficiency that depends on the inverse 6 th power of the donor-to-acceptor separation distance .