Construction of Helical Structures with Multiple Fused Anthracenes: Structures and Properties of Long Expanded Helicenes

Polycyclic aromatic compounds consisting of four or five fused anthracene units were synthesized by PtCl2-catalyzed cycloisomerization as novel long expanded helicenes. These compounds have helical structures with significant stacking of the terminal anthracene moieties at 0.33 nm interlayer distance. In the UV-vis and fluorescence spectra, the absorption and emission bands were red-shifted as the number of fused anthracene units was increased. The characteristic broad and long-lived emission bands of the long analogues are explained by the excimer-like stabilization of the excited state. These photophysical data as well as their cyclic voltammetric data are discussed on the basis of the pi-conjugation and interlayer pi...pi interactions in the molecular structures and the molecular orbitals. The barrier and mechanism of helical inversion are also reported.

Automated summary

Polycyclic aromatic compounds, synthesized by PtCl2-catalyzed cycloisomerization, have helical structures with significant stacking between the terminal anthracene moieties. As the number of fused anthracene units increases, the absorption and emission bands are red-shifted. The long-lived emission bands of the long analogues are explained by the excimer-like stabilization of the excited state.