Modulating Emission of Organic Emitters from Fluorescence to Red Afterglow through Boric Acid-Assisted Energy Transfer

Construction of red afterglow materials through a straightforward synthesis method is promising but still a challenging task. In this work, a boric acid (BA)-assisted energy transfer strategy was proposed to modulate the emission of levofloxacin (Lev) and rhodamine B (RhB) into red afterglow, with an emission lifetime of 0.54 s and a photoluminescence quantum yield of 54.1%. Detailed investigations suggested that the heat treatment process resulted in the formation of a BA matrix, accompanied by the loading of Lev and RhB. The BA matrix activated the thermally activated delayed fluorescence of Lev, and its emission intensity was promoted through reducing the molecular motion and quenching effects from environments. The red afterglow was attributed to the energy transfer from activated Lev to RhB through both singlet state to singlet state and triplet state to singlet state processes. The applications of red afterglow materials for information encryption were also demonstrated. The present results opened a door for designing red afterglow materials, which also presented a solid theory to explain the energy transfer profiles.