Band Structures of Metal-Free Phthalocyanine in the β Phase

The excess electron and hole-band structures of β-metal-free phthalocyanine are calculated with the tight-binding approximation, using the Hückel molecular orbitals obtained previously by this author. The heteroatomic nature of the molecule is emphasized, and hence a new form of molecular potential, which reflects the nonuniform distribution of the pi electrons in the molecule, replaces the Goeppart–Mayer–Sklar potential used in previous band-structure calculations of hydrocarbons. The interaction between the two electron bands formed from the two nearly degenerate lowest empty molecular orbitals has also been considered. The resulting band structures are qualitatively similar to those of anthracene, but with more pronounced anisotropy in the bandwidths. The velocity tensors 〈υiυj〉 and 〈υiυj / | υ |〉, where υ is the group velocity and υi, υj are its components, associated with a particular band are computed from the band structures for different values of vibronic overlaps. The applicability of the simple band model of charge transport is discussed.