Impacts of heteroatom substitution on the excited state dynamics of π-extended helicenes.

Benzo-annulated aza[9]helicene ([9]AH) and thia[9]helicene ([9]TH) were prepared as novel π-extended heterohelicenes. [9]TH showed a quite short fluorescence lifetime of ∼0.3 ns and intense phosphorescence at low temperature that were attributed to its larger spin-orbit coupling and faster intersystem crossing between pseudo-degenerate S 1/2 and triplet states.