Phthalocyanine-C₆₀ fused conjugates exhibiting molecular orbital interactions depending on the solvent polarity

New covalently C₆₀-connected zinc phthalocyanine (ZnPc) derivatives have been synthesized by utilizing successive cycloaddition reactions of C₆₀ with a ZnPc derivative containing a pyridazine moiety employing Komatsu's method in reaction of C₆₀ with phthalazine. The UV/Vis absorption spectrum of the fused conjugate (5) shows red shifts from the corresponding absorption of ZnPc derivative (8), indicating interactions between the ZnPc and C₆₀ moieties. The DFT calculations under non-polar medium predict that the HOMO and LUMO of 5 localize on the ZnPc moiety, whereas LUMO+1 localizes on the C₆₀ moiety, which reasonably explain the magnetic circular dichroism (MCD) and absorption spectra in toluene. Electrochemical redox potentials of 5 in polar solvents indicate the first-oxidation potential arises from the ZnPc moiety, whereas the first reduction potential is associated with the C₆₀ moiety, suggesting the LUMO localizes on the C₆₀ moiety in polar solvent. This reversal of the LUMO is supported by the ZnPc-fluorescence quenching with a nearby C ₆₀ moiety in benzonitrile, which leads to the charge-separation via the excited singlet state of the ZnPc moiety. In toluene on the other hand, such a ZnPc-fluorescence quenching owing to the photoinduced charge separation is not observed as predicted by the DFT-calculated LUMO on the ZnPc moiety.