To provide additional insights on the role of N-heteroatoms in CBN ribbons, calculations of vertical excitation energies and oscillator strengths were performed for the ribbons CBN_3-m and CBN_4-m (see Scheme 1 and Scheme S2). The ADC(2) results are shown in Fig. . The spectroscopic properties of the CBN_3-m and CBN_4-m ribbons are qualitatively similar to those of the CBN_1-m and CBN_2m series. The S1, T1 energies are inverted for the CBN_3-m ribbons, but not for the CBN_4-m ribbons (with the exception of m = 1). The energy-level structure of the CBN ribbons is thus rather robust. However, the oscillator strengths of the less nitrogen-rich CBN_3-m and CBN_4-m series are significantly lower than those of the CBN_1-m and CBN_2-m series. The asymmetric distribution of the B,N heteroatoms perpendicular to the main axis apparently is crucial for the enhancement of the oscillator strength.