English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

We present numerical studies of one- and two-photon excited states orderingin a number of polycyclic aromatic hydrocarbon molecules: coronene,hexa-peri-hexabenzocoronene and circumcoronene, all possessing $D_{6h}$ pointgroup symmetry versus ovalene with $D_{2h}$ symmetry, within thePariser-Parr-Pople model of interacting $\pi$-electrons. The calculatedenergies of the two-photon states as well as their relative two-photonabsorption cross-sections within the interacting model are qualitativelydifferent from single-particle descriptions. More remarkably, a peculiar roleof molecular geometry is found. The consequence of electron correlations is farstronger for ovalene, where the lowest spin-singlet two-photon state is aquantum superposition of pairs of lowest spin triplet states, as in the linearpolyenes. The same is not true for $D_{6h}$ group hydrocarbons. Our workindicates significant covalent character, in valence bond language, of theground state, the lowest spin triplet state and a few of the lowest two-photonstates in $D_{2h}$ ovalene but not in those with $D_{6h}$ symmetry.

Electron Correlations and Two-Photon States in Polycyclic Aromatic Hydrocarbon Molecules: A Peculiar Role of Geometry