Abstract
The effect of the degeneracy of the molecular dipolar transitions on the properties (dispersion curves, oscillator strengths, absorption spectra) of Frenkel excitons in ordered helical and orientationally disordered columnar mesophases, characterized by strong interchromophore interactions and short stacking distance, is investigated through a model based on numerical calculations. It is shown that the degeneracy makes the optical spectra less sensitive to chromophore rotation and maintains the excitons carrying the oscillator strength quite delocalised even in the presence of complete orientational disorder.