Another potentially relevant advantage of the CBN_n-m ribbons compared with the BxNy compounds of Pu et al. is the higher rigidity of the former. It can be seen by a comparison of Tables and that the vibrational stabilization energy of B2N1 is larger by a factor of 1.7 and the difference of absorption and emission energies (the Stokes shift) is larger by a factor of 2.1 The emission band of B2N1 therefore is broader (lower color purity). Due to the torsional flexibility of the two phenyl groups, the S1 state of B2N1 is expected to exhibit a higher radiationless decay rate and thus lower fluorescence quantum yield than the S1 state of CBN_2-2.