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    Area of Science:

    • Photochemistry
    • Materials Science
    • Computational Chemistry

    Background:

    • Understanding excited-state dynamics is crucial for designing luminescent materials.
    • The interplay between molecular structure and phase influences photophysical properties.
    • 1-NH2 molecule's fluorescence behavior requires detailed investigation.

    Purpose of the Study:

    • To elucidate the phase-dependent excited-state relaxation pathways and fluorescence mechanisms of the 1-NH2 molecule.
    • To investigate the roles of excited-state intramolecular proton transfer (ESIPT) and twisted intramolecular charge transfer (TICT) in fluorescence.
    • To provide theoretical guidance for developing novel luminescent materials.

    Main Methods:

    • Quantum chemical simulations were employed to model the 1-NH2 molecule.
    • Analysis of excited-state relaxation pathways and fluorescence mechanisms was performed.
    • Reorganization energy analysis was utilized to understand emission properties.

    Main Results:

    • In the liquid phase, synergistic coupling of ESIPT and TICT leads to nonradiative decay and quenched Keto* fluorescence.
    • In the solid phase, restricted rotation blocks nonradiative decay, promoting ESIPT and strong Keto* emission in the near-infrared (NIR) region.
    • Reorganization energy analysis explains the origin of redshifted emission in the solid phase.

    Conclusions:

    • A novel, phase-dependent fluorescence switching mechanism in 1-NH2 was revealed.
    • The study highlights the critical role of phase in controlling photophysical properties.
    • Findings offer valuable theoretical insights for the design of smart luminescent materials.