Oxazolochlorins. 14. 8-Oxo-5,10,15,20-tetra­phenyl-7-oxa­porphyrin N(24)-oxide.

The structure of 8-oxo-5,10,15,20-tetraphenyl-7-oxaporphyrin N(24)-oxide, C43H28N4O3, (4B), shows that N-oxidation of the pyrrole opposite the oxazolidone group cants the pyrrole out of the mean plane of the chromophore. This also affects the oxazolidone group, which is also slightly canted out. This conformation is qualitatively similar to that of the parent meso-tetraphenylporphyrin N-oxide, but dissimilar to that of the porpholactone N-oxide isomer 8-oxo-5,10,15,20-tetraphenyl-7-oxaporphyrin N(22)-oxide, (4A), carrying the N-oxide at the oxazolidone group. While the degree of canting of the N-oxidized groups in both cases is comparable (and more pronounced than in the porphyrin N-oxide case), in (4A) the pyrrolic groups adjacent to the N-oxidized group are more affected than the opposing group. These differences in the conformational modes may contribute to rationalizing the distinctly different electronic properties of (4A) and (4B).