Strain-Induced Interlayer Interactions under Hydrostatic Pressure Can Boost Circularly Polarized Luminescence in...

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.