The ground-state equilibrium geometries of all compounds were pre-optimized with density functional theory (DFT) employing the B3LYP functional and using Grimme's D3 dispersion correction. The geometry optimizations were performed with C2v symmetry constraint. It was verified by the computation of the Hessian that the stationary points represent energy minima. The ground-state equilibrium geometries were re-optimized with the second-order Møller-Plesset (MP2) method, using the DFT equilibrium geometries as initial guesses. The vertical excitation energies of the S1 and T1 excited states were calculated with the ADC(2) method as well as with the CC2 method. The correlation-consistent polarized valence double-zeta (cc-pVDZ) basis set and the resolution-of-the identity (RI) approximation were employed. All calculations were performed with version 7.3 of the TURBOMOLE program package. Recent extensive benchmark studies of vertical excitation energies confirmed the remarkable accuracy of the computationally efficient ADC(2) and CC2 methods for the lowest singlet and triplet states of organic molecules. Root mean square (rms) errors of the order of 0.2 eV for the S1 and T1 energies and of the order of 0.1 eV for the S1-T1 energy gap were reported. For the present investigation of relatively large CBN ribbons, the use of the ADC(2) and CC2 methods represents a pragmatic compromise between accuracy and computational cost.