Research on Synthesis and Properties of Hybridized System between Dihexylbithiophene and Octaethylporphyrin (OEP-DHBT-OEP) Connected with the 1,3-Diacetylene Linkages

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The extended hybridized OEP-DHBT-OEP system has been successfully synthesized by oxidative cross-coupling reactions of the corresponding terminal acetylenes under the modified Eglinton conditions. Under the same reaction conditions as for the symmetrical isomers, the more extended system describable as OEP-(DHBT)_n-OEP (n=2-5) could be simultaneously obtained as characterizable products in moderate yields, in consequence of the higher reactivity of the bis (ethynyl) DHBT than the meso-ethynyl OEP.From the ^1H NMR spectral studies of their molecular structures, it was suggested that the anisotropy by Ni-OEP ring current effect influences the Th-H located in a deshielded region within the limits of ca. 25 Å. Electronic absorption spectral properties of the OEP-DHBT-OEP system were examined, clearly proving that the orientation of DHBT plays an important role in electronic communications between the two terminal OEP rings. The HH isomer exhibited a broad Soret band, seemingly characterist … More ic of a dimeric property of the 3HTh-OEP system, while the TT isomer split Soret band into two clear bands characteristic of an intensive electronic interaction between the two terminal Ni-OEP rings. In the case of the OEP-(DHBT)_n-OEP system, it was indicated that the HH series gradually separate their electronic structures into two main components ; the diacetylene-group connected 3HTh-OEP component and the remaining (HH DHBT)_n component. On the other hand. the TT series were tentatively proposed to converge into an electronic structure hybridized between the diacetylene-group connected OEP-(TT DHBT) component and the remaining (TT DHBT)_n component, while retaining their molecular planarities. The electrochemical studies of the OEP-(DHBT)_n-OEP system showed that the compounds with n=1 exhibited the higher electron-releasing abilities with increasing the conjugation planarities of DHBT, in order of HH<HT<TT.It was proved that the electron-releasing abilities and electron-transfer processes for the compounds with more than n=2 are also determined by the extension magnitudes of the π-electronic conjugation system, reflecting both of the orientations and numbers of DHBT.It is also suggested that the OEP-DHBT-OEP system associates with each other in a highly concentrated solution, reflecting an orientation of DHBT.Continuous investigations of the self-association, however, are necessary for an elucidation of the electronic interactions betwecn the two terminal Ni-OEP rings both intra-and intermolecularly, in connection with the self-association effect on their electronic and electrochemical properties. Less