Picosecond excited-state lifetimes of protonated indazole and benzimidazole: The role of the N–N bond

Certain chemical groups give rise to characteristic excited-state deactivation mechanisms. Here, we target the role of a protonated N–N chemical group in the excited-state deactivation of protonated indazole by comparison to its isomer that lacks this group, protonated benzimidazole. Gas-phase proto...

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Veröffentlicht in:The Journal of chemical physics 2021-11, Vol.155 (18)
Hauptverfasser: Marlton, Samuel J. P., McKinnon, Benjamin I., Greißel, Phillip, Shiels, Oisin J., Ucur, Boris, Trevitt, Adam J.
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Sprache:eng
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Zusammenfassung:Certain chemical groups give rise to characteristic excited-state deactivation mechanisms. Here, we target the role of a protonated N–N chemical group in the excited-state deactivation of protonated indazole by comparison to its isomer that lacks this group, protonated benzimidazole. Gas-phase protonated indazole and protonated benzimidazole ions are investigated at room temperature using picosecond laser pump–probe photodissociation experiments in a linear ion-trap. Excited state lifetimes are measured across a range of pump energies (4.0–5.4 eV). The 1ππ* lifetimes of protonated indazole range from 390 ± 70 ps using 4.0 eV pump energy to ≤18 ps using 4.6 eV pump energy. The 1ππ* lifetimes of protonated benzimidazole are systematically longer, ranging from 3700 ± 1100 ps at 4.6 eV pump energy to 400 ± 200 ps at 5.4 eV. Based on these experimental results and accompanying quantum chemical calculations and potential energy surfaces, the shorter lifetimes of protonated indazole are attributed to πσ* state mediated elongation of the protonated N–N bond.
ISSN:0021-9606
1089-7690
DOI:10.1063/5.0071847