Strain-Induced Interlayer Interactions under Hydrostatic Pressure Can Boost Circularly Polarized Luminescence in Chiral Hybrid Halide Perovskites

The influence of hydrostatic pressure on the structure and circularly polarized luminescence (CPL) of the 2D chiral perovskite S-(MBA)₂PbI₄ (MBA = methylbenzylammonium) is investigated and compared to that of a brominated derivative, employing parallel-bias metadynamics coupled with excited-state ab initio molecular dynamics and time-dependent DFT simulations. A stepwise increase in pressure is shown to promote noncovalent interactions above the Fermi level, which in turn amplifies CPL emission and even allows for switching its sign. A comparable effect can be obtained by brominating the aromatic ring of (R)- or (S)-methylbenzylammonium. Strain, arising from both intrinsic structural constraints and applied external pressure, can deform the lattice and distort the inorganic octahedra. These strain-induced distortions promote parallel stacking of the chiral ligands, resulting in a CPL response within stable free energy minima and enabling chiral memory. We conclude that interlayer interactions can act as a powerful tool for engineering chiroptical properties through external pressure or structure-induced strain (internal pressure), enabling the design of new stimulus-responsive materials or the tuning of existing ones via strain engineering.