Coupled Molecular and Framework Descriptors for Band-Edge Spin Splitting in Chiral Hybrid Organic-Inorganic...

Chiral hybrid organic-inorganic perovskites offer a chemically tunable platform in which inversion-asymmetric crystal fields and strong spin-orbit coupling generate spin-split band edges, yet the mechanisms through which the chiral molecules and the inorganic framework interact to produce spin splitting are not well understood. Here we use the electronic chirality measure─a wave function-based metric─to quantify molecular chirality across three substitution series of chiral metal halides derived from methylbenzylammonium ligands. We find that halogen functionalization increases the valence-band spin splitting from 6.6 meV in the parent system to 64.8 meV in the benzylic-halogenated (S-MBA)X series and up to 110.0 meV in the side-chain-halogenated (S-MBA)CH2X series (X = H, F, Cl, Br). In contrast, for the pnictogen-substituted (S-MBA)Y series (Y = P, As, Sb, Bi), the splitting remains in the few-meV regime. The electronic chirality measure captures changes in the chiral electronic structure and provides a useful molecular descriptor for comparison with parity-violating energy differences, but it does not alone determine the band-edge splitting. The largest splittings emerge when electronic chirality, intrinsic cation dipoles, and inorganic-framework distortion act cooperatively. Within the present substitution series, larger intrinsic cation dipoles are associated with smaller spin splitting energies. Large band-edge splitting occurs only when molecular chirality is efficiently converted into the induced chiral Pb/I framework mode. We identify the chirality transfer efficiency (CTE), a descriptor introduced in this work, together with the cation electrostatic environment, as key parameters governing chirality transfer.