In the CBN_2-m ribbons, very small positive singlet-triplet gaps of ≈ 0.05 eV can be realized together with oscillator strengths larger than 1.0. Another notable property of the CBN ribbons is their rigidity, which results in narrow absorption and emission bands and thus high color purity. Moreover, the rigidity is expected to result in a low radiationless relaxation rate of the S1 state and therefore a favourable fluorescence quantum yield.