Figure 3.

Exciton coupling mechanism in its degenerate (top) and non-degenerate version (bottom). a) Chirality defined by transition moments located on the two chromophores. A positive chirality corresponds to a clockwise direction when rotating the transition dipole in the front onto that in the back. b) Splitting of excited states due to exciton coupling. Notice the stronger effect in the degenerate case. c) ECD couplet originating from exciton coupling. The sign of the couplet (i.e., of its long-wavelength branch) is the same of the chirality (exciton chirality rule). In the degenerate case, the couplet is centered in correspondence of the chromophore transition at λ₀. In the non-degenerate case, each band is localized close to one chromophore transition (λ₀₁ and λ₀₂). d) Absorption spectra originating from exciton coupling. The wavelength splitting Δλ is related to the energy splitting ΔE.