Localized orbital study on the electronic structure of phthalocyanine dimers

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The lowest excited state of lanthanide phthalocyanine dimer and {mu}-oxo silicon phthalocyanine dimer are studied by configuration interaction calculations on the localized orbital basis set obtained by a unitary transformation of semiempirical SCMOs of the dimers. The model can characterize the dimer excited states as a superposition of intraligand and interligand excitation. The higher energy component band in the Q band region of the lanthanide dimer complexes is ascribed to an excitation in the excited state essentially of the exciton coupling state, while the lower energy component band is assigned as an excitation to that of the charge resonance state, which is granted a spectral intensity from the exciton component. A rapid decrease in the splitting of the Q band of the dimers with increasing radius of the central lanthanide ion is attributable to a pronounced decrease in the difference of diagonal energies of charge transfer and local excitation configurations and the off-diagonal interaction between the two configurations. Theory can well reproduce the dimer spectra of Q band with a reduced interplanar two-electron interaction ({alpha} = 0.8). On the other hand, the dimer spectra in B band region are obtained only with an enhanced interplanar interaction ({alpha} = 1.0-1.2). Amore » broadening of the band in the Q band region of the silicon complex dimer is attributed to an internal rotation of phthalocyanine macrocycles around their C{sub 4} symmetry axis. 44 refs., 7 figs., 3 tabs.« less