Synthesis of Symmetrical Tetraaryltetranaphtho[2,3]porphyrins

A new method of synthesis of meso-tetraaryltetranaphtho[2,3]porphyrins (Ar4TNP) has been
developed. Ar4TNPs with peripheral functional groups are obtained by oxidative aromatization of
meso-tetraarylporphyrins in which pyrrole units are fused with either octahydro- or dihydronaphthalene moieties. These precursor porphyrins are synthesized in four to five steps from readily
available starting materials, such as naphthalene or 1,4-benzoquinone. The pathway originating
in dihydronaphthalene, i.e., the “dialine” route, was found to be superior to the alternative “octaline”
route in that it (1) enables the shortening of the overall reaction sequence, (2) has a broader scope
in terms of the peripheral substitution in Ar4TNPs, and (3) affords higher yields of the target
porphyrins. Pd complexes of the synthesized Ar4TNPs exhibit remarkably strong absorption bands
at 710−720 nm (ε ∼ 200 000 M-1 cm-1) and phosphoresce at room temperature with moderate
quantum yields (φ = 2−3%, λmax = 900−1000 nm). The absorption maxima of naphthoporphyrins
substituted with eight methoxy groups (Ar4TNP(OMe)8) were found to be about 15−20 nm red
shifted compared to the corresponding maxima of unsubstituted Ar4TNPs. The X-ray crystallographic
data suggest that these spectral shifts are caused not by the differences in nonplanar distortions
of the macrocycles but by the purely electronic effects of the substituents.