A double helicene with a spiro-Si linker (4) was synthesized by four successive nucleophilic substitutions on SiCl4 . Its (P,P), (M,M) and (P,M) isomers were isolated and characterized by single crystal X-ray analysis. Due to the central spirosilabi[fluorene] moiety, the two helicene units in 4 are symmetrically and nearly perpendicularly arranged. (P,P)-4 and (M,M)-4 exhibit unique optical properties attributable to the LUMO spiro-conjugation between the two sila[7]helicene units.
Keywords: chirality; double helicenes; helicenes; siloles; spiro compounds.
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