Nitrile grafted thia[5]Helicenes through a photocyclization pathway of styrylnaphtho[2,1-b]thiophenes: Synthesis and photophysical properties

Abstract

Six nitrile grafted pentacyclic π-conjugated systems have been designed and synthesized, in 44–68% overall yields, through a photochemical route under mild conditions and using a suitable phenanthrene-like derivative as a basic molecular skeleton. Their structural characterization has been performed using various spectroscopic techniques among them X-ray diffraction, which indicated the presence of pair of P and M helical enantiomers in the crystal structure. These helical compounds were found readily soluble in a variety of organic solvents and exhibit a good thermal stability. The UV–vis absorption and photoluminescence properties of these π-conjugated helical scaffolds have been experimentally examined indicating an absorption maxima around 281–284 nm and a remarkable dual emissions in the blue region as their characteristic. All compounds exhibited irreversible redox-active characteristics. HOMO and LUMO energy level have been evaluated experimentally by cyclic voltammetry showing an electrochemical band gap (Eg-el) ranging from 2.87 eV to 3.01 eV.