The ground and lower excited electronic singlet and triplet states of
eight macrocycles resulting from porphyrin by replacing pyrroles with
pyridines or indoles and the meso methines by nitrogens (the extended
porphyrin family) have been treated by Skala's version of the CNDO/S m
ethod in view of providing systematic reference computational data. Th
e results are especially useful for comparisons capable of throwing li
ght on the structure-property relations that make some of those macroc
ycles especially active for energy and electron transfer. A brief disc
ussion is given. The uniqueness of porphyrin stands out clearly, but s
ome of its features may be strictly related to the biochemical environ
ment of heme groups, so that other macrocycles of the family might be
better suited for technological applications simulating the in vivo be
havior of porphyrin derivatives. Hints concerning the effect of coordi
nation to metal atoms are given, pending the completion of a parallel
study on some metal complexes of the family. A few novel experimental
results from our laboratories are mentioned in the discussion.