Bay-Substituted Thiaza[5]helicenes: Synthesis and Implications on Structural and Spectroscopic Properties

A series of bay-substituted thiaza[5]­helicenes was synthesized to investigate the effect of different substituents on the properties of these helicenes. These thiaza[5]­helicenes with different substituents were prepared in a straightforward manner through indole- and benzo­[b]­thiophene synthesis, palladium-catalyzed Suzuki coupling, oxidative cyclization, and functional group interconversion reactions. We investigated the impact of these different bay area substituents compared to the unsubstituted thiaza[5]­helicene on the structural parameters and studied the steady-state electronic spectroscopy of these thiaza[5]­helicenes in toluene and acetonitrile. We found that different functional groups influence the solid state structure and spectroscopic properties, but a single substituent in the bay area of a thiaza[5]­helicene was not enough to prevent enantiomerization at room temperature.