Photoluminescence of H-GQD and H-GNR in aqueous surfactant solutions is very weak, as evident from the spectra presented in Figures and. Since it is known that -stacking causes a significant increase in excited-state nonradiative decay rates in aromatic chromophores, we hypothesize that the use of aqueous surfactants results in solubilization of -stacked aggregates of H-GQD and H-GNR, rather than fully dissolved isolated molecular species. Therefore, we attribute the steady-state spectroscopic signatures of H-GQD and H-GNR in Figure to aggregates. To decrease -stacking and improve solubilization of nanographenes, we utilized the chlorination methodology previously shown by Müllen and co-workers to be an effective strategy for functionalization of nanographene edges. The effect of chlorination on the nanographene structure is best observed when comparing the DFT-calculated structures of H-GQD and Cl-GQD (Figure ). While H-GQD is a planar molecule, the steric repulsion between chlorine atoms in Cl-GQD results in significant non-planarity. The chlorination of our model compounds significantly improved their solubility in organic solvents, such as toluene and trichlorobenzene, indicating reduced -stacking interactions. Interestingly, the chlorination results in surprisingly small changes in the calculated UV-vis absorption spectra (Figure ). Cl-GQD exhibits a modest bathochromic and hyperchromic shift relative to H-GQD, while the calculated difference density plots indicate that the lowest-energy transitions of both GQD derivatives are of the charge-transfer character (with bipyrimidine moieties acting as charge accepting sites). The experimental UV-vis absorption spectra are consistent with calculated predictions: H-terminated nanographenes H-GQD and H-GNR exhibit absorption spectra with absorption maxima located at similar energies as the spectra of Cl-GQD and Cl-GNR, respectively (Figures and), with slightly red-shifted absorption maxima. However, the effect of chlorination is more drastic when the photoluminescence spectra are compared. While H-GQD and H-GNR exhibit almost negligible emission, relatively strong emission peaks are observed for Cl-GQD and Cl-GNR in the visible range (quantum yields are 1% and 15%, respectively. See Section S2 for more detail). The emission is assigned to the fluorescence from singlet excited states of Cl-GQD and Cl-GNR, based on their insensitivity to oxygen (Figure ). Steady-state excitation/emission spectroscopy provides some evidence for sample aggregation, even for nanographenes with chlorinated edges. Figure shows 2D emission/excitation maps for Cl-GQD and Cl-GNR, along with excitation and emission spectra at selected wavelengths. In the case of Cl-GQD, this effect is best observed in normalized emission spectra in Figure , which show that the excitation at 360 nm gives rise to an emission spectrum dominated by the sharp feature maximum at 490 nm and a weak contribution from the broad features at 625 nm.