As our final example, we present results for a single-walled carbon nanotube (SWCNT) system (∼1000 atoms, see Computational Details) which has been the subject of recent experimental interest. Semi-conducting SWCNTs are known to be ''dark" to emission due to low-lying optically inactive states below the so-called band-edge E 11 exciton. Fig. provides the transition dipole matrix for the pristine (6,5) SWCNT system, showing a sparse matrix with only the ground-to-E 11 (i.e., the sixth bare molecular transition) transition to be optically allowed with a large dipole moment of ∼ 28 a.u. with minimal dipole coupling between excited states. This is in strong contrast to previous molecules studied in this work (see Fig. , Fig. , Fig. , and Fig. ). The E 11 transition is just below 2.0 eV, which agrees with previous theoretical calculations of the E 11 excitonic energy. See above Fig. for the real-space projected transition density of the E 11 ground-to-E 11 exciton showcasing its delocalized character. Semiconducting SWCNTs, when functionalized with covalent adducts forming a hybridization defect, exhibit bright emission features due to the addition of a defect-associated exciton below the band edge, which have been the subject of much experimental and theoretical work over the last decade for their use as single-photon light sources and for their tunable emission at low-energy telecommunications wavelengths. The simplicity of this system's dipole matrix will lead to simple results and a new pathway toward the tunable manipulation of SWCNT without the need for chemical functionalization.