MIND THE SINGLET-TRIPLET GAP: PHOTOELECTRON SPECTROSCOPY OF 1,3,4,6,9B-PENTAAZAPHENALENE

Wilson, Kenneth

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Title

MIND THE SINGLET-TRIPLET GAP: PHOTOELECTRON SPECTROSCOPY OF 1,3,4,6,9B-PENTAAZAPHENALENE

Author(s)

Wilson, Kenneth

Contributor(s)

Garand, Etienne

Issue Date

2023-06-19

Keyword(s)

Mini-symposium: Spectroscopy with Cryogenic Ion Traps

Abstract

The vast majority of closed-shell organic molecules follow Hund’s rule, namely: their first excited triplet state (T₁) lies energetically below their first excited singlet state (S₁). Recent computational studies, however, suggest that energetic inversion of these states is possible in a family of closed-shell species known as azaphenalenes. The phenomenon is believed to arise from (i) minimal overlap between highest-occupied and lowest-unoccupied molecular orbitals, and (ii) stabilization of the S₁ state via coupling to higher-excited electronic configurations. Despite experimental efforts to confirm S₁-T₁ inversion in an azaphenalene species using optical techniques (1), quantification of the T₁ energy–and thus the S₁-T₁ gap–is precluded by the spin selection rule. Using photoelectron spectroscopy, which circumvents the spin selection rule, we report a S₁-T₁ gap for 1,3,4,6,9b-pentaazaphenalene of either 374 cm−¹ or -374 cm−¹ (± 46 meV), pending definitive assignment of the S state. Once confirmed, these results will have important implications in the fields of organic light-king for high-level quantum chemical calculations of electronically excited states.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

Text

Language

eng

Handle URL

https://hdl.handle.net/2142/122606

DOI

https://doi.org/10.15278/isms.2023.7115

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