Synthesis, resolution and (chir)optical properties of new thia[6]helicenes and insight from a DFT investigation

An efficient and rapid synthetic approach, combining Heck coupling and classical oxidative photocyclization, was developed for the synthesis of two thiophene-based [6]helicene derivatives, providing good overall yields (57%–58%). The resulting helical species were characterized by 1H and 13C NMR, HRMS, and FT–IR spectroscopy. Enantiomeric resolution was achieved by chiral HPLC, affording the M– and P–enantiomers with high enantiomeric excesses (ee >97.5% and >99.5%, respectively). The isolated enantiomers displayed very large optical rotations (e.g., ‒2100 and ‒2400 for the M–enantiomers at λ = 589 nm) and pronounced electronic circular dichroism (ECD) signals. UV‒vis absorption and photoluminescence studies revealed notable optical properties, including intense fluorescence in the blue region of the visible spectrum. Electrochemical investigations indicated an electrochemical gap (Eg–el) in the range of 2.27–2.32 eV. Density functional theory (DFT) calculations were performed to elucidate the structure–property relationships and showed good agreement with experimental observations. The combined experimental and computational results highlight the promise of these S–heteroaromatic frameworks as organic small light-emitting molecules, particularly for their use as blue-emitting chiral dopants in OLED devices and as effective hole-transport materials