Synthesis and electronic properties of trimeric octaethylporphyrin (OEP) derivative connected with diacetylene linkage. A comparative study with vinylene-group connected OEP trimer

A new trimeric octaethylporphyrin (OEP) derivative was synthesized, in which each porphyrin ring is connected with diacetylene linkage. Its electronic absorption spectrum was examined, proving that the diacetylene linkage induces splitting of Soret band of OEP into two main bands with clear maxima at 429 and 481 nm and more bathochromic shift of Q band to appear in such a longer wavelength region at λmax=670 nm in chloroform, in contrast with that of the corresponding vinylene-group connected OEP trimer. It was shown that the spectrum of the present diacetylene-group connected OEP derivative drastically changed in pyridine, suggesting a coordination of pyridine molecule as the fifth ligand onto Ni(II) metal of the central ring. Furthermore, Vilsmeier formylation, a typical electrophilic substitution on the aromatic compounds, was examined for further oligomerization of OEP, proving that it takes place at the central ring exclusively.