It is also important to recall that most of these reported results are in a single-mode cavity and, in principle, only represent the θ = 0 special incident angle in a FP cavity (see Fig. and Sec. 2.6). Fig. -b presents the polariton transition density when coupling matter to an optical cavity. The molecular transition density indicates the electron and hole overlap in real space and provides information regarding the localization of the exciton and on molecules, which may provide useful insights into possible reactive bonding sites upon photo-activation. Fig. showcases the polaritonic ground-to-excited transition density 189 (see Eq. 145) for three defected hexagonal boron nitride quantum dots: (left) carbon substitution at a boron site CH B , (middle) carbon substitutions at meta-boron sites C B -C B , and (right) carbon substitution and adjacent nitrogen vacancy C B -V N . Outside of the cavity (top row), these defects each have a unique low-lying exciton of varied localization character. The nitrogen vacancy C B -V N (right) presents the most localized features in the transition density (where the electron and hole are strongly overlapped only in this region near the defect). When coupling the system inside a cavity (bottom row), the transition density for all species becomes mostly delocalized. This delocalization in the transition density facilitates an increase in polaritonic dipole moment and hence the increase in the lowest absorption peak in all species. Here, the tun-ability over the bright, low-lying transition in defected boron nitride quantum dots has been achieved through cavity QED.