Upper figure: the π − π ^⋆  and low energy adjustment (L + π − π ^⋆ , orange), C6 (green) and σ − σ^∗ (purple) component contributions to the imaginary part of the refractive index, k (blue line), for the optEC_(s)(a) model material with E_g(bulk) = 0.25 eV and particle radius of 3 nm (The red line shows the summed L + π − π ^⋆ , C6 and σ − σ^∗ contributions). Lower figure: the same data as in the upper figure presented as (αE)^0.5 (the blue and red lines, where the solid lines show only the summed aromatic, L + π − π ^⋆  and C6 components) but where the aromatic cluster band profiles are shown for N_R = 2,3,4, ...(thin orange line profiles right to left), the extrapolations to band gap (black lines with the band gap-determining extrapolation data points indicated by the open diamond symbols), the band gap values (thin grey vertical lines), the limiting E_g(N_R) value and the bulk material band gap or Tauc gap, E_g,Tauc. See text for details.