Enhancement of Circularly Polarized Light Detection Through <i>Ortho</i>‐Substitution in Chiral Perylene Diimides

Abstract Chiral organic small molecules are promising for circularly polarized light (CPL) detection due to their easy modifiability, strong intermolecular interactions, and straightforward manipulation of the transition dipole moments. However, they often exhibit a low absorption asymmetry factor ( g abs ) since their magnetic transition dipole moment ( m ) is overshadowed by the electric transition dipole moment ( μ ), and their alignment ( θ ) is not optimized, limiting the performance of CPL photodetectors. This study introduces an ortho ‐substitution strategy to significantly enhance CPL detection in chiral perylene diimides (PDIs) by tuning the crystal packing motif. Incorporating a cyano group at the ortho‐position markedly reduces the angle ( θ ) between m and μ within the crystal, thus amplifying the g abs . The fabricated chiral organic single‐crystal film devices of ( R )‐4CN‐PDI‐Ph demonstrated superior photodetecting performance, with a photocurrent asymmetry factor ( g ph ) of 0.362 — three times larger than that of its counterpart ( R )‐4PH‐PDI‐Ph. These findings underscore the pivotal role of ortho ‐substitution in tuning molecular stacking, enhancing CPL detection, and deepening the understanding of the structure‐performance relationship in chiral organic optoelectronics.