Intermixing of Chirality and Local Structure in the Second Harmonic Generation Response of Dibenzo[c]acridine Helicene-Like Molecule Thin Films

Enantiopure and racemic films of dibenzo[c]acridine helicene-like molecules were elaborated by laser pulsed deposition (PLD) and their quadratic nonlinear optical properties determined by Second Harmonic Generation (SHG). The SHG intensity was measured as a function of the incident fundamental and outgoing harmonic wave polarization angles. For the enantiopure films, the polarization analysis highlights a nonlinear optical signature due to the presence of chiral molecules. These films also exhibit a remarkable in-plane homogeneity. A close inspection also reveals the formation of domains, especially in the case of the racemic film. The underlying molecular structure of the films is also discussed. The combination of the SHG technique and optical microscopy provides a deeper insight into the film morphology. For the racemic film, differences in the local structure with respect to the enantiopure ones were shown and segregation in domains was observed.