Engineering circularly polarized light emission in nanostructured oligodimethylsiloxane-helicene chiral materials†

Abstract

Chiroptical properties in the bulk state can be tuned by controlling the formation of chiral ordered nanostructures. Here, we present a series of discrete oligodimethylsiloxane-helicene-pyrene block molecules with varying oDMS lengths and study the nanostructures formed in both bulk and solution, including their chiroptical properties. In bulk, ordered 2D nanostructures self-assemble, driven by phase segregation induced by the siloxane oligomers, with clear differences in the properties of the racemic and enantiopure versions. Moreover, intermolecular pyrene interactions lead to excimer emission. As a result, up to a 5-fold increase in circularly polarized luminescence is observed in the solid state as compared to the solution, accompanied by a clear influence of the pyrene excimer emission on the overall emission process. Interestingly, in the ordered lamellar packing achieved from long oDMS units, the excimer emission shows very little net circular polarization, while in the disordered state achieved from shorter oDMS units, this excimer emission displays a significant degree of circular polarization. These results demonstrate that functionalizing chiroptical building blocks with discrete oligodimethylsiloxane chains is a versatile strategy to control photophysical properties and modulate chiroptical emission in bulk. This approach advances the integration of chiroptical materials into devices, enabling diverse applications ranging from optoelectronics to communication technologies.