The Fukui function is a classic descriptor of electron density in a frontier orbital, often used to describe the susceptibility of an atomic site to nucleophilic or electrophilic attack. Here, Fukui indices were calculated for stilbene derivatives, which are known to undergo photocyclization and subsequent oxidation to form helicenes, ortho-condensed polycyclic aromatics. Isomers of the [4] + [1] stilbene were analyzed via ground state and time-dependent density functional theory (TD-DFT) at the B97D/TZVP functional and basis set. The calculation of f - and f + values (normalized to 1) at the sites where ring closure would occur to form a helicene were consistent with experimental data. [4] + [1] isomers that do not form helicene products have relatively low or zero-valued f - and f + values, and the isomers that undergo ring closure have values close to unity. Calculations were also performed for stilbene derivatives of various sizes, with similar trends in reactivity found in the [4] + [1] regime. These results indicate Fukui indices may prove useful in the synthesis of higher-order helicenes and helicene functionalization.

Fukui indices as a tool to predict the reactivity of stilbene derivatives to form helicenes

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