Strain-induced interlayer interactions can boost circularly polarized luminescence in chiral hybrid halide perovskites

The influence of pressure on the structure and circularly polarized luminescence (CPL) of the 2D chiral perovskite S-(MBA)₂PbI₄ (MBA = methylbenzylammonium) is investigated and compared to a brominated derivative, employing parallel-bias metadynamics coupled with excited-state ab initio molecular dynamics and time-dependent DFT simulations. A stepwise increase of pressure is shown to promote non-covalent interactions above the Fermi level, which in turn amplifies CPL emission, and even allows for switching its sign. We conclude that interlayer interactions can act as powerful tool to engineer chiroptical properties through external pressure or structure-induced strain (internal pressure), enabling the design of new stimuli-responsive materials or the tuning of existing ones via strain engineering.