Outstanding Chiroptical Features of Thin Films of Chiral Oligothiophenes

A chiral benzo[1,2-b:4,5-b']dithiophene-based oligothiophene with the very uncommon chiroptical property of signal inversion on sample flipping was recently described. This property is due to the interference between linear dichroism and linear birefringence, called LDLB effect, which is theoretically well understood, but to date very rarely reported in the literature. Samples with very large LDLB effect lead to the unique possibility of discriminating the direction of sample illumination (i.e., from the front or back). This article presents a set of analogue compounds, in which small structural changes are introduced to uncover which factors determine the very large LDLB effect or true circular dichroism connected to supramolecular chirality. It also reveals the impact of the deposition technique, in which spin coating may exert a primary role, and results in films with outstanding chiroptical features. These features are made even more relevant due to the semiconducting properties of oligothiophenes, which are interesting for optical sensing applications.