Scientific article
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Ovalene Photophysics Revisited

First online date2026-02-25
Abstract

Herein, we reinvestigate the photophysics of ovalene, a prototypical nanographene for which conflicting spectroscopic results have been reported. Owing to its structural similarity and its identical D2h point-group symmetry, ovalene can essentially be viewed as a larger pyrene. We show that its optical transitions can be understood using the same model that is invoked to explain the excited states of pyrene. Absorption and (polarized)-emission measurements reveal that the S1 ← S0 (1B3u1Ag ) transition is forbidden, whereas the first prominent absorption band can be assigned to the allowed S2 ← S0 (1B2u1Ag ) transition, in contrast to recent reassignments. Temperature and time-dependent spectroscopic measurements show that the S1 and S2 states quickly establish a thermal pre-equilibrium, giving rise to thermally activated S2 → S0 emission at room-temperature. As a result, the fluorescence lifetime of ovalene decreases with increasing temperature while its fluorescence quantum yield increases. Contrary to the frequently cited small energy gap of ∼400 cm-1 , our measurements reveal a significantly larger S2 -S1 gap of approximately 1200 cm-1.

Keywords
  • Aromatic compounds
  • Fluorescence
  • Hydrocarbons
  • Thermodynamic properties
Research groups
Citation (ISO format)
WEGA, Johannes, VAUTHEY, Eric. Ovalene Photophysics Revisited. In: The journal of physical chemistry. A, 2026. doi: 10.1021/acs.jpca.5c08602
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Article (Published version)
Identifiers
Additional URL for this publicationhttps://pubs.acs.org/doi/10.1021/acs.jpca.5c08602
Journal ISSN1089-5639
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