Optical Anisotropies and Frenkel/Charge-Transfer Exciton Admixtures in Perylene Diimide Films: A Stokes Spectropolarimetric Study

This work demonstrates that perylene diimide (PDI) hJ hybrid aggregates originating from competing Coulomb and charge-transfer interactions constitute effective building blocks for film formation and explores the influence of such interactions in the emergence of film optical anisotropy. The anisotropic optical properties, linear dichroism (LD), and optical retardance (Φ) of hJ aggregates are shown to be controllable through processing parameters, including the film deposition method, thermal treatment, and imide-position functionalization. These two observables are intrinsically linked through Kramers–Kronig relations. While conventional techniques typically provide macroscopic observables, often measuring either LD or Φ separately, or rely on experimentally complex and costly instrumentation, here, both quantities are simultaneously determined using rotating-sample transmission Stokes spectropolarimetry.