Chirality-Controlled Triplet Generation in π-Stacked Cocrystals: A Spin-Adapted Frenkel–Holstein Framework

Chirality-induced spin selectivity (CISS) is widely reported in organic materials, yet how molecular chirality modulates triplet yield in π-stacked co-crystals remains unresolved. We develop a spin-adapted Frenkel– Holstein framework in a configuration-state-function basis for Frenkel singlets and triplet excitons, coupled to a charge-transfer (CT) states. The intra-pair energy detuning and chiral-induced coupling offsets in the electron and hole hopping integrals encode helical electrostatic fields and generate singlet-triplet parity breaking. The CT states then mediate forbidden S–T mixing, enhancing triplet formation without requiring a static magnetic field. Phonon dressing and weak dephasing select an optimal spectral window for CISS-enhanced yield. The theory predicts chirality-dependent changes in delayed fluorescence and triplet signatures and identifies regimes where inter- and intra-pair contributions cancel or reinforce, explaining material-dependent outcomes. These results provide design rules for chiral side-chains and stacking geometries to control triplet yield in organic co-crystals.