Boosting Excited‐State Energy Transfer by Anchoring Dipole Orientation in Binary Thermally Activated Delayed Fluorescence/J‐Aggregate Assemblies

Förster resonance energy transfer (FRET) has been widely applied in fluorescence imaging, sensing and so on, while developing useful strategy of boosting FRET efficiency becomes a key issue that limits the application. Except optimizing spectral properties, promoting orientation factor (κ2) has been well discussed but rarely utilized for boosting FRET. Herein, we constructed binary nano‐assembling of two thermally activated delayed fluorescence (TADF) emitters (2CzPN and DMAC‐DPS) with J‐type aggregate of cyanine dye (C8S4) as doping films by taking advantage of their electrostatic interactions. Time‐resolved spectroscopic measurements indicated that 2CzPN/Cy‐J films exhibit an order of magnitude higher kFRET than DMAC‐DPS/Cy‐J films. Further quantitative analysing on kFRET and kDET indicated higher orientation factor (κ2) in 2CzPN/Cy‐J films play a key role for achieving fast kFRET, which was subsequently confirmed by anisotropic measurements. Corresponding DFT/TDDFT calculation revealed strong “two‐point” electrostatic anchoring in 2CzPN/Cy‐J films that is responsible for highly orientated transitions. We provide a new strategy for boosting FRET in nano‐assemblies, which might be inspired for designing FRET‐based devices of sensing, imaging and information encryption.