“…1,4‐Diketo‐3,6‐diphenylpyrrolo[3,4‐ c ]pyrrole (DPP) and their derivatives represent an important class of high performance pigments 19–21. Recently, DPP and its derivatives have received worldwide attention as a potential class of materials in many applications, including field‐effect transistors (FETs),22 solar cells,23 organic light‐emitting diode (OLEDs),24, 25 organic photorefractive,26 and two‐photon absorption,27 due to the excellent chemical and thermal stability and high photoluminescence efficiency. The incorporation of narrow bandgap DPP20, 24, 28 in the wide bandgap fluorene‐based cationic polyelectrolytes (CPs) might form an energy donor‐acceptor molecule architectures, in which DPP units serve as an acceptor of fluorescence resonance energy transfer (FRET) and would lead to efficient intrachain FRET, which is important for colorimetric sensor.…”