Optical spectroscopic data on triply protonated H2[TA3PyP] clearly indicate a very strong hyperporphyrin effect. The magnitude of the hyperporphyrin effect is most simply indicated by the lowest-energy absorption maximum and its extinction coefficient. For comparison, a simple free-base porphyrin such as meso-tetraphenylporphyrin is a normal porphyrin that continues to follow the four-orbital model upon diprotonation; the lowest energy band at 646 nm shifts marginally to 657 nm upon diprotonation with little change in extinction coefficient. Diprotonation of H2[TAPP], in contrast, results in a spectral shift from 669 nm to 813 nm, along with an increase in the extinction coefficient from 11 to 89 mM -1 cm -1 ; 16 this is the most powerful hyperporphyrin effect in a free-base porphyrin that we are aware of. Triprotonated H2[TA3PyP] shows nearly as large an effect, with the lowest-energy band shifting from 664 nm to 781 nm, with an increase in the extinction coefficient from 12 to 84 mM -1 cm -1 (Figure ). Although we do not address the point in this study, it has been noted that the pyridinium N-H in protonated H2[TA3PyP] might serve as a hydride donor, leading to an oxidized porphyrin. Recently, we have reported ground-state and time-dependent density functional theory calculations to elucidate the hyperporphyrin spectra engendered upon protonation of H2[TAPP] and O-deprotonation of H2[THPP]. These studies revealed significant orbital interactions between the porphyrin core and the meso-aryl substituents, which raise the energy level of the HOMO and shrink the HOMO-LUMO gap. In this study, we use the same techniques to evaluate the nature of the unique Type D porphyrin-aryl interactions in triply protonated