Beilstein Arch. 2025, 202562. https://doi.org/10.3762/bxiv.2025.62.v1
Published 12 Nov 2025
A twisted D-π-A molecule, PI-Cz, was designed and synthesized using phthalimide as the acceptor, carbazole as the donor, and a phenylene bridge. Single-crystal X-ray diffraction reveals a markedly noncoplanar 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, PI-Cz 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. Correlating temperature-dependent lifetimes with phase characterization indicates that, in amorphous environments lacking ordered π-π stacking and rigid confinement, the small ΔEST 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.
Keywords: room-temperature phosphorescence; thermally activated delayed fluorescence; π-π stacking; imide; carbazole
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Wang, R.; Wu, Y. Beilstein Arch. 2025, 202562. doi:10.3762/bxiv.2025.62.v1
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© 2025 Wang and Wu; licensee Beilstein-Institut.
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