The B,N-substituted GRs investigated in the present work represent a novel class of materials with spectroscopic properties which appear promising for optoelectronic applications. The characteristic spectroscopic features are low-lying electronic excitation energies, exceptionally small (or negative) singlet-triplet energy gaps and appreciable oscillator strengths of the S1-S0 transition. These properties can be systematically tuned in a two-dimensional parameter space: (i) the distribution of the B and N heteroatoms in the GRs and (ii) the length of the GRs.