Novel bis-nitrile grafted [6]Helicenes through a photochemical pathway: Chiroptical and photophysical properties

Abstract

New suitably nitrile grafted [6]Helicene derivatives have been synthesized, in 36%-54% over all yields, through a UV-light photochemical pathway making use of inexpensive materials and mild experimental conditions. The target hexacylic helicenes have been characterized by 1H and 13C NMR and FT-IR spectroscopies. The enantiomeric separation of these helical compounds was accomplished by chiral HPLC leading to (P)- and (M)-enantiomers with high optical purity (94.3–100% ee) demonstrating a large optical rotatory dispersion and significant electronic circular dichroism (ECD) signals. UV–vis absorption and photoluminescence of these helical compounds have been evaluated showing a notable behavior and a strong fluorescence in the blue region of the visible spectrum making them promising candidates for applications in electronic and optoelectronic devices. Their electrochemical behavior was also experimentally examined revealing an important charge transfer interaction owing to their π-conjugated electronic system. These helicenes were found to be potential donor materials for polymer solar cells, with broad electrochemical band gap in the range of 2.63–2.80 eV.