1. Non-Kasha fluorescence of pyrene emerges from a dynamic equilibrium between excited states
- Author
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Braun, Gabriel, Borges, Itamar, Aquino, Adélia J. A., Lischka, Hans, Plasser, Felix, do Monte, Silmar A., Ventura, Elizete, Mukherjee, Saikat, Barbatti, Mario, Instituto Militar de Engenharia=Military Institute of Engineering (IME), Texas Tech University [Lubbock] (TTU), Loughborough University, Federal University of Paraíba (UFPB), Institut de Chimie Radicalaire (ICR), Aix Marseille Université (AMU)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), Institut Universitaire de France (IUF), Ministère de l'Education nationale, de l’Enseignement supérieur et de la Recherche (M.E.N.E.S.R.), and European Project: 832237,SubNano
- Subjects
[CHIM.THEO]Chemical Sciences/Theoretical and/or physical chemistry - Abstract
International audience; Pyrene fluorescence after a high-energy electronic excitation exhibits a prominent band shoulder not present after excitation at low energies. The standard assignment of this shoulder as a non-Kasha emission from the second-excited state (S2 ) has been recently questioned. To elucidate this issue, we simulated the fluorescence of pyrene using two different theoretical approaches based on the vertical convolution and nonadiabatic dynamics with nuclear ensemble approaches. To conduct the necessary nonadiabatic dynamics simulations with high-lying electronic states and deal with fluorescence timescales of about 100 ns of this large molecule, we developed new computational protocols. The results from both approaches confirm that the band shoulder is, in fact, due to S2 emission. We show that the non-Kasha behavior is a dynamic-equilibrium effect, not caused by a metastable S2 minimum. However, it requires considerable vibrational energy, which can only be achieved in collisionless regimes after transitions into highly excited states. This strict condition explains why the S2 emission was not observed in some experiments.
- Published
- 2022