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Ultrafast Nonadiabatic Dynamics of Tetraphenyl-substituted Nitrogen-Based Heterocycles
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DOI:10.1002/sstr.70567.png)
Abstract
En 中文
Tetraphenylpyrazine (TPP) and 2,3,4,5-tetraphenyl-1H-pyrrole (TePP) are closely related heterocycles bearing four phenyl substituents, whose structural similarity makes them a useful pair for comparing how intramolecular flexibility influences excited-state relaxation and emission in the gas phase and in the solid state. TPP is a prototypical solid-state luminescence enhancement emitter, exhibiting a markedly increased quantum yield upon molecular aggregation. In contrast, TePP displays similar quantum yields in solution and solid state, a characteristic of dual-state emission. This behavior indicates that intramolecular rotations are already significantly hindered in the isolated-molecule regime, consistent with our previous observations for TPP and other solid-state emitters (Hernández-Rodríguez et al., ChemPhysChem, 2024, 25, e202400563). To unravel the excited-state dynamics underlying this contrasting behavior, we performed mixed quantum–classical trajectory simulations on a single molecule of TPP and TePP employing the surface-hopping method. Twelve singlet states were included at the TD-B3LYP-D3/def2-SVP level, which were previously benchmarked against coupled-cluster methods. Simulated observables, such as gas-phase ultrafast electron diffraction and time-resolved fluorescence signals, allow us to dissect the distinct deactivation pathways operating in both systems in the gas phase, while also providing mechanistic insight into how these pathways are expected to evolve in solution and solid-state environments.
Keywords:
dynamics
electron diffraction
fluorescence
luminescent materials
nonadiabatic
ultrafast
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