Synthesis, photophysical and chiroptical properties of 9-cyano[7]helicene for OLED applications. A combined experimental and theoretical investigation

The synthesis of 9-cyano[7]helicene achieved a 62% overall yield with high purity, following a two-step procedure. Characterization was carried out using H-1, C-13, and COSY NMR spectroscopy, as well as FT-IR analysis. The racemic mixture of helicene was effectively separated into P- and M-enantiomers with exceptional optical purity (> 99% ee). This separation allowed us to showcase substantial optical rotations (+ 4800 for the P-enantiomer at lambda = 589 nm) and notable electronic circular dichroism (ECD) signals. The organic material exhibited a robust UV absorption band and emitted a vibrant blue light, resulting in a fluorescence quantum yield of 11%. Experimentally determined electronic energy levels revealed HOMO energy of - 5.86 eV and LUMO energy of - 3.25 eV, yielding an electrochemical band gap of 2.61 eV. Furthermore, an in-depth analysis of absorption and ECD spectra, along with molecular electrostatic potential (MEP) and reduced density gradient (RDG) calculations using quantum chemistry, highlighted the material's fundamental characteristics. These findings collectively suggest that this compound holds promise as a potential candidate for use in electroluminescent devices and OLED technology.