Radiationless deactivation pathways versus H-atom elimination from the N-H bond photodissociation in PhNH 2 -(Py) n (n = 1,2) complexes.

Autor: Esboui M; LSAMA, Department of Physics, Faculty of Sciences, University of Tunis El-Manar, 2092, Tunis, Tunisia. mounir.esboui@fst.rnu.tn., Trabelsi J; High Institute of Environmental Sciences and Technologies of Borj Cedria, University of Carthage, Tunis, Tunisia.
Jazyk: angličtina
Zdroj: Photochemical & photobiological sciences : Official journal of the European Photochemistry Association and the European Society for Photobiology [Photochem Photobiol Sci] 2023 Jan; Vol. 22 (1), pp. 33-45. Date of Electronic Publication: 2022 Sep 07.
DOI: 10.1007/s43630-022-00295-z
Abstrakt: Minimum energy structures of the ground and lowest excited states of aniline (PhNH 2 ) solvated by pyridine (Py) show that the clusters formed are stabilized by hydrogen bonds in which only one or both hydrogen atoms of the NH 2 group take part. Two different N-H bonds photodissociation in PhNH 2 -(Py) n (n = 1,2) complexes, free and hydrogen bonded have been studied by analyzing excited state potential energy surfaces. In the first one, only N-H bonds engaged in hydrogen bonding in these complexes are considered. RICC2 calculations of potential energy (PE) profiles indicate that all photochemical reaction paths along N-H stretching occur mainly via the proton-coupled electron transfer (PCET) mechanism. The repulsive charge transfer 1 ππ*(CT) state dominates the PE profiles, leading to low-lying 1 ππ*(CT)/S 0 conical intersections and thus provide channels for ultrafast radiationless deactivation of the electronic excitation or stabilization to biradical complexes. The second photoreaction consists of a direct dissociation along the free N-H bond of the NH 2 group. It has been shown that this process is played by excited singlet states of 1 πσ* character having repulsive potential energy profiles with respect to the stretching of N-H bond, which dissociates over an exit barrier about 0.5 eV giving rise to the formation of a 1 πσ*/S 0 conical intersection. This may cause an internal conversion to the ground state or may lead to H-atom elimination. This photophysical process is the same in both planar and T-shaped conformers of the PhNH 2 -Py monomer complex. Our findings reveal that there is no single dominating path in the photodissociation of N-H bonds in PhNH 2 -(Py) n complexes, but rather a variety of paths involving H-atom elimination and several quenching mechanisms.
(© 2022. The Author(s), under exclusive licence to European Photochemistry Association, European Society for Photobiology.)
Databáze: MEDLINE
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