Comparing the frontier molecular orbitals of the donor scaffolds, all of our selected AQ derivatives bear delocalized singly occupied molecular orbital (SOMO) in their triplet state, as presented in Figure . The molecules in Group A present a smaller singlet-triplet energy gap of the donor where ΔG varies from -13.3 to 3.6 kcal/mol. This small energy gap is due to the biased position of electron-donating groups and the resulting localized highest occupied molecular orbital (HOMO), which leads to a relatively unstable singlet ground state. The consequence is dramatic for the deprotonated Ali and Pur (ΔG of 3.6 kcal/mol and -0.1 kcal/mol, respectively) possessing phenolate moieties with a strong electron-donating character at neutral pH. In contrast to Group A, the compounds in Group B retain symmetrically positioned hydroxyl groups with delocalized HOMO in the singlet ground state maintaining the singlet-triplet energy gap to a range of -16.2 to -14.7 kcal/mol.