Donor−acceptor complexes of porphyrins and semiconducting single-walled carbon nanotubes (SWCNTs) are noncovalently assembled using oligonucleotide DNA, and their photophysical interactions are studied for light-harvesting. Five cationic 5,10,15,20-tetrakis(N-methylpyridynium-4yl)porphyrins with a free-base (H 2 T4) or metal ions at the core (MT4, M = Zn 2+ , Pt 2+ , Pd 2+ , and Cu 2+ ) are explored as donor chromophores as they exhibit species-unique optical signatures, such as fluorescence, phosphorescence, or both. These porphyrins are examined for their abilities to interact with semiconducting carbon nanotubes after photoexcitation. We find that carbon nanotubes efficiently quench the emission properties of porphyrins via charge transfer, which is confirmed by the quenching of singlet oxygen emission generated by porphyrins. Phosphorescence lifetime measurements reveal that the lifetime in the triplet states is largely constant in porphyrins interacting with both DNA alone and DNA-coated SWCNTs, suggesting that photoexcited electrons are transferred to carbon nanotubes from the low-lying singlet state before an intersystem crossing to the triplet state. We demonstrate that the DNA-assembled porphyrin−SWCNT complexes in a photoelectrochemical cell produce stable anodic photocurrents with a conversion efficiency of approximately 1.5%.