Ethylenedithio-Tetrathiafulvalene-Helicenes: Electroactive Helical Precursors with Switchable Chiroptical Properties

Electroactive fused ethylenedithiotetrathiafulvalene[4]helicene and -[6]helicenes have been synthesized through a strategy that involved the preparation of 2,3-dibromo-helicene derivatives as intermediates. The dihedral angles between the terminal helicenes, as determined by single-crystal X-ray analysis, are 22.7 degrees and 50.7 degrees for the [4]helicene and [6]helicene, respectively. Their solid-state architectures show interplay between SS and intermolecular interactions. The chiroptical properties of the enantiopure EDTTTF[6]helicene derivatives have been investigated and supported by TDDFT calculations. Remarkable redox switching of the circular dichroism (CD) signal between the neutral and radical-cation species has been achieved.