Synthesis and properties of ethylene-, vinylene-, and diacetylene-groups connected porphyrin hexamer

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Oligornerization of the pai-electronic conjugated cyclic system which have wide area and thus highly respond to outside stimulations is a very important methodology for the development of new functional organic materials. Among the pai-electronic conjugated cyclic systems, porphyrin ring system is particularly promising as seen in an example of a special dimer in a photo-synthesis reaction center. Therefore, oligomerization of porphyrin ring with various linkages has been demonstrated to achieve a wide variety of purposive functions such as photocurrent (PC) and electroluminescence (EL). We also previously reported the synthesis of vinylene-group connected octaethylporphyrin trimer, (OEP)3, and studied its electronic property, proving that the electron releasing ability, for instance, outstandingly enhances in order of (OEP) <<(OEP) 2 <<<(OEP)3.Successively to this result, in the present research stint, dimerization of the (OEP)3 component by connecting with ethylene linkage was planne … More d in cider to examine the electronic properties of ethylene- and vinylene-groups connected OEP hexamer, (OEP)6. After several examinations, we were successful in introducing the functional groups such as formyl (CHO) and alcohol (CH2OH) onto the central OEP ring of (OEP)3 selectively. And, both Mcmurry coupling of the CHO derivative and acid-catalyzed coupling of the CH2OH derivative were examined to lead to the corresponding (OEP)6 derivatives. From the former reaction, the all-vinylene-group cannected (OEP)6 derivative was not obtained at all, only affording the insoluble materials. On the other hand, from the latter reaction, the ethylene- and vinylene-groups connected (OEP)6 derivative was successfully isolated, the molecular structure of which was fully determined by means of MS, PMR and electronic absorption spectra. It was proved that the present (OEP)6 derivative substantially possesses the electronic properties of the vinylene-group connected (OEP)3 derivative and thus is regarded as a dime is structure of the vinylene-group connected (OEP)3 simply connected with ethylene linkage.On the way of the present research, an unsymmetrical molecular motion was observed in the CHO and CH2OH derivatives of vinylene-group connected (OEP)3, probably due to the steric repulsion between those substituents and the peripheral ethyl substituents. In other words, these (OEP)3 derivatives were found to possess the unsymmetric molecular structure at room temperature, where both three OEP rings and two vinylene linkages are different from each other, respectively.Furthermore, in relation with these properties of oligomeric (OEP)n derivatives, the diacetylene- and ethylene-group connected (OEP)4 derivative with symmetrical molecular structure has been preliminarily proved to be a host molecule which forms inclusion complexes with various guest molecules. If a guest molecule has a chirality, such an inclusion complex should be chiral. In practice, the diacetylene- and ethylene-group connected (OEP)4 derivative showed an active circuler dichroism (CD) spectral behavior, by forming the corresponding inclusion complexes with optically active substances like (R)- or (S)-2-alkanols. Thus, at present, the preparation of a large quantity of the ethylene-and vinylene-group connected (OEP)6 derivatives is underway to examine its CD spectral behavior. Less