Effects Of Next-nearest-neighbor Hopping In Pernigraniline-base Polymer

In recent years Polyanilines have attracted a great deal of attention due to its novel physical and chemical properties in the past decade as a new class of organic conducting materials. The conduction mechanism of them is different from metals or inorganic semiconductors. Carriers in them are made up of solitons, polarons and bipolarons what are nonlinear excitations in the polymer. In theoretical research, it has put forward a Ginder-Epstein(GE) model and the Baranowski-Büttner-Voit (BBV) model. Both the GE and BBV models take the tight-binding approximation into consideration, only the nearest-neighbor hopping term appears in their model Hamiltonian. Due to the"zigzag"configuration of the nitrogen atoms existing in the main chain, the wave function of the next-nearest-neighbor sites might be overlapped. Thus hopping between the next-nearest-neighbor sites might be possible.On the basis of BBV model, we considered the effects of next-nearest-neighbor hopping on the energy structure, the lattice configuration and the charge density of the positive and negative solitons in pernigranine-base polymer. And on this basis, PNB polaron excited states were studied.we calculated the effects of next-nearest-neighbor hopping on the energy structure , the lattice configuration and the charge density of the positive and negative solitons in pernigranine-base polymer, in the framework of the Baranowski-Büttner-Voit model. The numerical results showed: For the two kinds of solitons,the increase of the next-nearest-neighbor coupling strength led to the valence band(VB) expanded to a larger range while the conduction band(CB) acted to the contrary, as well as the transition energy of electrons increased gradually;the width of the two kinds of the solitons varied slightly;The oscillation of charge density of the negative solitons would enhance, while the oscillation of charge density of the positive solitons would weaken. Be that the experiment go along provided a reference.Furthermore, we investigated the effects of next-nearest-neighbor hopping on the electronic structure and the lattice configuration of the positive and negative polarons on the basis of Baranowski-Büttner-Voit model. For the two kinds of polarons,it is founded that the increase of the next-nearest-neighbor coupling strength led to the valence band(VB) expanded to a larger range while the conduction band(CB) acted to the contrary, as well as the transition energy from the lower gap state to the higher one decreased gradually. Our numerical results also showed that the width of the negative polarons decreased obviously while that of the positive polarons varied slightly.We suggested the next-nearest-neighbor coupling strength takeβ< 0.08 by comparing with the experimental data of Leng J M et al.Calculated absorption spectra of the PNB polarons were given out: two types of polaronsπ-π* absorbance with increasingβhad a slight blue-shift phenomenon, which could be used as proof of the previous theoretical work.