The high photothermal conversion efficiencies observed are encouraging, as these materials were previously found to show high molar absorptivity and low photoluminescence (Table ). This suggests a strong preference for nonradiative decay pathways, such as singlet oxygen and heat production following photoexcitation. Indeed, moderate singlet oxygen quantum yields were previously reported for some of these materials in 9:1 solutions of EtOH/THF, ranging from 28 -40% when excited at 405 nm. The presence of a saturated carbon within the isoporphyrinoid macrocycles presumably leads to increased flexibility, allowing for energy dissipation as heat via low-frequency molecular vibrations, in contrast to stronger photoluminescence typically observed for fully conjugated porphyrin-type molecules. Thus, it has been shown both experimentally and computationally that metallophlorins exhibit a ruffled structure with a low inversion barrier. Such a large-amplitude motion is expected to result in more facile nonradiative decay in metallophlorins relative to their aromatic counterparts. In fact, a similar effect was recently exploited by Stache and coworkers, who showed that corrins derived from vitamin B12, which are highly saturated natural counterparts of corroles, can be used as photothermal photocatalysts for atom transfer radical polymerization. While these materials were shown to exhibit moderate singlet oxygen quantum yields in solution, unfortunately this effect was not observed in the nanoparticles. This could be due to the reduced permeability of oxygen through the DSPE-PEG2k surfactant or quenching of the emitters within the hydrophobic core. Further investigations are therefore necessary to evaluate if the photothermal and photodynamic effects can be simultaneously observed for dual phototherapy.