The electronic structures of polyphosphazenes and their derivatives have been studied by crystal orbital and molecular orbital methods. The substituent effects are discussed also. The calculated results show that the linear polyphosphazenes and cyclic tri-polyphosphazene are planar, the other cyclic polyphosphazenes are nestlike, and the substitute of the electron-withdrawing group may give birth to the planar structure of cyclic quad-polyphosphazenes. The results also show that these polymers are semiconductors. Although the band gap decreases for most of the substituted derivatives of polyphosphazenes, these polymers can not be conductors in intrinsic state by the substitution. Electron affinity and ionization potential of the substituted polyphosphazene chains are raised due to the substitution of electron-withdrawing substituents, while ionization potential is decreased for the electron-donating substituents. Therefore, the substitution of electron-donating group is favorable to p-type doping, while the substitution of electron-withdrawing group to n-type doping.

Key words: polyphosphazene, electronic structure, substituent effect, density functional theory