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Excited state dynamics of normal dithienylethene molecules either isolated or deposited on argon cluster

Aude Lietard 1, 2 Giovanni Piani 1, 2 Rodolphe Pollet 3 Benoit Soep 1, 4, 2 Jean-Michel Mestdagh 1, 2 Lionel Poisson 1, 4, 2, * 
* Corresponding author
2 DyR - Dynamique Réactionnelle
IRAMIS - Institut Rayonnement Matière de Saclay, LIDyl - Laboratoire Interactions, Dynamiques et Lasers (ex SPAM)
3 LSDRM - Laboratoire Structure et Dynamique par Résonance Magnétique (LCF)
NIMBE UMR 3685 - Nanosciences et Innovation pour les Matériaux, la Biomédecine et l'Energie (ex SIS2M)
Abstract : Real-time dynamics of the electronically excited open-ring isomer of 1,2-bis(2-methylbenzo[b]thiophen-3-yl)perfluorocyclopentene (BTF6) and 1,2-bis(2,4-dimethyl-5-phenyl-3-thienyl)perfluorocyclopentene (PTF6) molecules was investigated using a set-up that associates a molecular beam, femtosecond lasers and a velocity map imager. The molecules were either free in the gas phase or bound to an argon cluster. DFT and TDDFT calculations were performed on BTF6. The calculated vertical excitation energies indicate an excitation by the pump laser towards a superposition of S$_5$ and S$_6$ states. The free molecule dynamics was found to follow a three wavepacket model. One describes the parallel conformer (P) of these molecules. It is unreactive with respect to the ring closure reaction which is responsible for the photochromic property of these molecules. It has no observable decay at the experiment time scale (up to 350 ps). The other two wavepackets describe the reactive antiparallel conformer (AP). They are formed by an early splitting of the wavepacket that was launched initially by the pump laser. They can be considered as generated by excitation of different, essentially uncoupled, deformation modes. They subsequently evolve along independent pathways. One is directed ballistically towards a conical intersection (CI) and decays through the CI to a potential energy surface where it can no longer be detected. The other fraction of the wavepacket decays also towards undetected states but in this case the driving mechanism is a non-adiabatic electronic relaxation within a potential well of the energy surfaces where it was launched. When BTF6 and PTF6 molecules are bound to an argon cluster, the same three wavepacket model applies. The vibronic relaxation timespan is enhanced by a factor 5 and a larger fraction of AP conformers follows this pathway. In contrast, the time constant associated with the ballistic movement is enhanced by only a factor 2.
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Submitted on : Wednesday, April 6, 2022 - 6:35:54 PM
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Aude Lietard, Giovanni Piani, Rodolphe Pollet, Benoit Soep, Jean-Michel Mestdagh, et al.. Excited state dynamics of normal dithienylethene molecules either isolated or deposited on argon cluster. Physical Chemistry Chemical Physics, Royal Society of Chemistry, 2022, 24, pp.10588-10598. ⟨10.1039/D1CP05729D⟩. ⟨cea-03633119⟩

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