μ-Oxo Dimers of Silicon Porphyrazines and Their Interlayer Interactions

μ-Oxo dimers of octaaryl-substituted silicon porphyrazines (SiPzs) were synthesized for the first time. The steric congestion due to the peripheral aryl groups attenuated the rotation of the SiPz units around the Si-O-Si axis, resulting in the fixed D₄ symmetric conformations with the torsion angle of ∼23° at room temperature or lower, which were unambiguously elucidated by the single-crystal X-ray diffraction analysis and variable-temperature NMR studies. The interlayer molecular orbital interactions between the stacked SiPz units perturbed UV/vis absorption spectra and electrochemical properties of the dimers. In addition, the hetero-type dimer, bearing electron-donating and electron-withdrawing aryl-substituents on each SiPz unit, showed a large two-photon absorption cross-section based on the reverse saturable absorption mechanism mediated by the intramolecular charge transfer interactions.