Synthesis, Characterization, and Chiroptical Properties of [6]Helicene-Containing Nanographenes from the Modification of Axially Chiral Arenes

Two π-extended [6]helicenes 7 and 10a have been successfully synthesized through the modification of their corresponding axially chiral precursors, which were verified by single crystal X-ray diffraction analysis. The (P)- and (M)-enantiomers of compounds 7 and 10a were resolved via chiral high-performance liquid chromatography (HPLC). However, the enantiomers of the axially chiral arenes 2, 3, and 4 could not be resolved by chiral HPLC due to their susceptibility to racemization at room temperature. The as-prepared arenes were characterized using UV-vis absorption and fluorescence spectroscopy, cyclic voltammetry, circular dichroism (CD) spectroscopy, and circularly polarized luminescence (CPL) spectroscopy. The CD and CPL spectra of 7 and 10a exhibit opposite Cotton effect and fluorescence signals, rendering them promising ingredients for CPL emitters.