Acenaphthoporphyrins are a class of porphyrins in which a one or more naphthalene moieties are fused to the pyrrole units of the macrocyclic ring. It is expected that the extension of the conjugation via naphthalene fusion will have an effect in the photophysical properties of the porphyrins. Here we present photophysical studies on the mono- and di-substituted tetraphenyl acenaphthoporphyrins. Both photoacoustic calorimetry and emission spectroscopy have been used to quantify the formation of both singlet and triplet states, and singlet oxygen. The compounds show fluorescence yields comparable to those of tetraphenyl porphyrin (~0.10-0.15). Photoacoustic calorimetry reveals a triplet state and singlet oxygen yields of ~ 0.3, with slight differences between the compounds. Production of singlet oxygen has been confirmed via near infrared emission at 1270 nm.