Structure-Response Relationships in Rigid C2-Symmetric Excitonic Systems: Principles, Modulation, and Functional Design Strategies.

Exciton coupling model provides one of the most intuitive and powerful frameworks to directly connect molecular structure with chiroptical responses. This review focuses on rigid architectures with C2 symmetry, in which conformational rigidity, symmetry constraints, and independent chromophores allow for direct correlations among molecular geometry, Davydov splitting, and electronic circular dichroism intensity. After introducing the theoretical basis of exciton coupling and its crucial role in absolute configuration assignment, we analyze how molecular design strategies control the conformational space, as well as how the electron transition dipole moments of interacting chromophores enable the modulation of dissymmetry factors (g-factors). Next, we expand these principles from isolated molecules to supramolecular assemblies, thin films, and polymers, where cooperative effects and new structural constraints can come into play to amplify or distort excitonic signatures. Overall, this review compiles transferable design principles to guide the development of next-generation chiroptical materials with broad relevance for sensing, optoelectronic, and spintronic applications.