S-Shaped Helical Singlet Diradicaloid and Its Transformation to Circumchrysene via a Two-Stage Cyclization

Abstract

Polycyclic hydrocarbons with diradical and polyradical characters usually display unique reactivities in ring-cyclization reactions. However, such reactions are rarely used to construct π-extended polycyclic aromatic hydrocarbons. Here, we describe the synthesis of an S-shaped doubly helical singlet diradicaloid compound and its facile transformation into an unprecedented circumchrysene via a two-stage ring cyclization, which includes: (1) an eletrocylization from diradicaloid precursor and (2) a Scholl reaction. The reaction mechanism was investigated through in situ spectroscopic studies, assisted by theoretical calculations. This reaction sequence yields an optically resolved π-extended [5]helicene derivative with a fluorescence quantum yield up to 85% and a circularly polarized luminescence brightness up to 6.05 M^-1 cm^-1 in the far-red to near-infrared regions. This sequence also yielded a highly delocalized circumchrysene molecule, exhibiting large electron delocalization, moderate fluorescence quantum yield, and multistage redox properties.