The electronic structure of diblock copolymers consisting of poly (p-phenylene) and polyacetylene were studied in the framework of an inter-component coupling model. It was found that the band gaps could be tuned by the proportion of the homopolymers. The interfacial coupling between the components also affected the band gaps obviously. Localized states and hybridized states appeared in copolymers due to the interactions between the homopolymers. The doped charges accumulated in its one segment of a copolymer. The accumulation condition is discussed.

Shallow energy levels in quasi-one-dimensional MX compounds have been found firstly by considering the two-band tight-binding model. These shallow levels are situated at the band edges of the CB and VB. The electronic states of the shallow levels are localized around solitons, polarons and bipolarons. It is expected that these shallow levels could be observed in the absorption spectrum of MX compounds. Finally, the effect of e-e interactions on the shallow levels was studied. It has been found that e–e interactions will decrease the mini-gap between the shallow levels and CB and increase the mini-gap between the shallow levels and VB.

Several boundary conditions have been proposed to stabilize the dimerized structures of finite-length Peierls–Hubbard chains. The effects of different boundary conditions on the lattice structures and the electronic energy spectra have been analysed. It was found that the natural or the fixed-end boundary conditions are more suitable to describe polymer chains with very short lengths than the periodic boundary condition. The competition of electron–electron interactions with electron–phonon interactions in finite-length chains has also been studied.

In the framework of the tight-binding model, the effects of longitudinal as well as transverse coupling between polyacetylene chains with different lengths and the electron–electron interactions on excitations have been studied. A new spinless charged polaronic excitation (q=±e; s=0) was obtained due to the transverse interchain coupling, which is different from the general magnetic polaron (q=±e; s=1/2) obtained in the perfect one-dimensional model. Due to its end positioning, a polaron is more easily stimulated energetically in a longer chain than in a shorter one, and it can hop to the longer chains nearby via either transverse or longitudinal interchain coupling. In addition, the transverse coupling decreases the energy of creation of a polaron. Considering the strong electron–electron interactions and the end positioning of chains in actual materials, we concluded that the one-dimensional model of conducting polymers is fairly appropriate in certain circumstances.

The stabilities of solitons, polarons and bipolmns in divalent-doped frompolyacerylene have been shldied by considering the impurity Coulomb confinement as well as the eleetron-electron interactions in the framework of the tight-binding PeierlsHubbard model. It was found that transitions between bipolarons and solitons and between bipolarons and polarons will rake place under cert3in conditions. The calculated values of the energy msitions agree well with the experimental results in the dilute Ca2+-doped trans-polyaceiylene material. The stability of excitations with respect to the impurity confinement and the electron4edron interactions have been discussed.