Aggregation‐Controlled Triplet Exciton Regulation Enables Single‐Emitter Color‐Evolving Afterglow

ABSTRACT Aggregation plays a crucial role in regulating excited‐state processes in organic luminescent materials, yet the simultaneous control of delayed fluorescence (DF) and room‐temperature phosphorescence (RTP) remains challenging. Herein, a series of dithienopyrrole‐based luminophores (DTP‐R) are developed as a single‐emitter system to investigate aggregation‐regulated excited‐state dynamics. By tuning the doping concentration in poly(methyl methacrylate) (PMMA), the emission evolves from monomer‐like to aggregate‐dominated states, accompanied by a continuous red shift of both prompt fluorescence (PF) and DF, as well as the coexistence of DF and RTP in the delayed spectra. Structural analysis reveals that aggregation is governed by cooperative weak intermolecular interactions, particularly S⋯π interaction, rather than conventional π‐π stacking. Theoretical calculations suggest that aggregation induces intermolecular charge separation, reduces the singlet‐triplet energy gap (ΔE ST ), and provides more accessible triplet states, thereby favoring thermally activated RISC‐related DF. Temperature‐dependent delayed emission and ultralow‐concentration system DF further support a RISC‐mediated DF process. BPBr‐based host‐guest system regulates triplet‐exciton distribution through TTET, enhancing the phosphorescence contribution. As a single‐emitter system with concentration‐tunable color‐evolving afterglow, this system enables spatiotemporal information storage and dynamic anti‐counterfeiting, providing a strategy for designing organic afterglow materials with tunable excited‐state dynamics.