Molecular properties controlling chirality transfer to halide perovskite: computational insights

Interfacing chiral molecules with achiral semiconductor nanomaterials has been shown to induce chiroptical (i.e., preferential absorption of circularly polarized light) signatures. This chirality transfer phenomena is attractive for enhancing the functionality of nanomaterials by making them sensitive to the circular polarization states of photons, and attractive for selective optical sensing applications. Chirality transfer via interfacing chiral molecules with nanomaterial surfaces generally gives small sensitivities as determined by anisotropy factors, the ratio of polarized and linear absorption. Here we use atomistic time-dependent density functional theory simulations to investigate the molecular properties which influence the chiroptical signatures of a lead-halide perovskite cluster. First, we find that for chiral molecules that contain aryl groups, such as (R/S)-methylbenzylamine and (R/S)-methylphenyl acetic acid, modulating their molecular dipole via meso functionalization with strong withdrawing groups, such as NO₂, can enhance intensities of chiroptical signatures. Second, using the lactic acid series ((S)-lactic, (S)-malic, and (S,S) tartaric acid) we average over conformations of these molecules on the cluster surface. We find that limited conformational flexibility of lactic acid provides the largest chiroptical intensities while signal from tartaric acid quenches after conformational average. These results demonstrate an importance of chemical functionalization leading to a polarized chiral system. Altogether, either through acid-base equilibrium or strategic functionalization, and limited conformationally degrees of freedom are important for obtaining high-intensity nanomaterial chiroptical signatures through chirality transfer.