Calculated UV spectra of CL-20 (a), CSi5H6N12O12 (b) and C4Si2H6N12F12 (c) cages. Black and grey lines correspond to the monomers and dimers, respectively. Gauss broadening of spectral lines with σ = 10 nm is applied. Transitions energies and oscillators’ strengths are also available in Supplementary Materials.