Photooxidation pathway providing 15-bromo-7-cyano[6]helicene. Chiroptical and photophysical properties and theoretical investigation

Abstract 15-bromo-7-cyano[6]helicene has been prepared, in good yield and purity, through a two step-sequence starting from 2-bromobenzo[c]phenanthrene-6-carbonitrile and making use of palladium-catalyzed Heck coupling and oxidative photocyclization. Enantiomeric separation of the helicene was achieved by chiral HPLC, affording enantiomers in >96.5% ee. The aim of this work was to evaluate experimental chiroptical and photophysical properties of the new helicene. Thus, the organic material is showing an emission in the blue region, and HOMO and LUMO levels were estimated experimentally, demonstrating an electrochemical band gap of 2.36 eV. Quantum chemical investigations based essentially on DFT and TD-DFT are discussed to more exploit the geometrical and electronic properties of the new helicene. Obtained results in this study were found to be helpful for explaining the interest of the new π-conjugated system as a good candidate to be used in optoelectronic applications.