Configuration-packing synergy enabling integrated crystalline-state RTP and amorphous-state TADF

A twisted D-π-A molecule, PI-Cz 1, was designed and synthesized using phthalimide as the acceptor, carbazole as the donor, and a phenylene bridge. Single-crystal X-ray diffraction revealed a markedly non-coplanar skeleton. Calculations based on the crystallographic geometry and frontier-orbital analysis indicate that the HOMO and LUMO are localized on the carbazole and phthalimide fragments, respectively, affording a small singlet-triplet energy gap. In the solid state, compound 1 exhibits pronounced phase dependence: powder samples display room-temperature delayed emission with principal bands at 550/600 nm and a lifetime of ≈0.39 s that undergoes strong thermal quenching, diagnostic of room-temperature phosphorescence. In contrast, amorphous films show no RTP; their delayed component grows with temperature and shares the same peak position as the prompt emission, consistent with thermally activated delayed fluorescence (TADF). Correlating temperature-dependent lifetimes with phase characterization indicate that, in amorphous environments lacking ordered π-π stacking and rigid confinement, the small ΔE _ST promotes reverse intersystem crossing, yielding delayed fluorescence; whereas in powder states, intermolecular interactions enhance spin-orbit coupling and crystallinity suppresses nonradiative decay, thereby activating RTP. This work achieves an integrated "crystalline-state RTP-amorphous-state TADF" regulation within a single molecule.