Anisotropic Artifacts Coupled with Light-Scattering Generating “Non-Reciprocal-Like” CD/CPL Signals in Polyurethane Films

Linear dichroism/linear birefringence (LDLB) effect enables chiroptical nonreciprocity in achiral materials, leading to chiral inversion without chiral sources. However, in the burgeoning field of polymer-based nonreciprocity system, certain samples generate severe artifact signals during measurements, significantly interfering with CD/CPL (circular dichroism/circularly polarized luminescence) data interpretation. Thus, distinguishing true signals from artifacts is crucial, particularly for nonreciprocity studies. Herein, we report a polyurethane (PU) system exhibiting apparent “non-reciprocal” CD signals. Rigorous analysis reveals that these signals do not originate from intrinsic chirality or LDLB effects but are instead from artifacts driven by the synergistic interplay of anisotropic microstructures and light scattering. Specifically, by incorporating polylactic acid (PLA) stereocomplex crystals, we effectively controlled artifact generation and intensity through tuning crystallinity, domain orientation, and surface morphology. Moreover, by systematically dissecting the contributions of material properties and measurement conditions, we identified key influencing factors governing artifact intensity. Critically, similar artifacts were also found in CPL measurements in these films. This work provides mechanistic understanding of artifact generation in multiphase polymers, establishes approaches for their detection and reduction, and serves as a vital caution for researchers investigating chiroptical nonreciprocity to thoroughly eliminate artifact interference