Abstract
Poly(1,4-phenylene-methylidynenitrilo-1,4-phenylenenitrilomethylidyne) (PPI) backbone approximated with poly(p-phenylene vinylene)like polymer composed of alternate phenylene and vinylenelike units is treated within pi electron approximation in terms of the chain composed of united atoms built up of virtual benzene and ethylene atoms. Electronic structure of the united atom is derived from interactions of benzene p and beta bands with V band of ethylene, taking into account that continuity of their pi systems results from overlap of vinylenelike highest occupied molecular orbital and lowest unoccupied molecular orbital orbitals with relevant components of benzene molecular orbitals having phase at parapositions. Electronic band structure has been derived within pi-electron approximation in a way resembling tight binding approximation usually applied to semiconductors. The proposed model is suitable to interpret UV-visible spectra of PPI with additional explaining vibronic progressions. Additionally, an expected location of lone pair related level is proposed.
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