Theoretical Studies On The Conducting Macromolecule With σ-π Conjugated System

Since MacDiarmid, Heeger and Shirakawa discovered that the doped polyethyne has high conductivity, the organic conducting polymer materials have been regarded by material scientists, chemists and physical scientists all along, because of light, unique properties on optical, superconduction and so on and the potential application prospects of molecular apparatus, composite materials and other fields. It becomes the forefront topic in materials science field. There are many theory studies onÏ€-conjugated conducting polymer at present, but few other literatures have been reported on the charge-dopedσ-Ï€conjugated conducting polymer especially the doped PSi and its ramification. So a systematical study on a series ofσ-Ï€conjugated conducting polymer is needed. We wish this work would provide a guiding principle toward a molecular design of novel Si-based functional materials.The geometric and the electronic structures of organosilicon oligomers nSi_x^L(C=C)_y, nSi_xR(C=C)_y, and R-nSi_x(C=C)_y are studied using the density functional theory. It is found that the extension of theÏ€-conjugation plays an important role in tuning the geometric and electronic structures. The band gap tends to be decreased and the hole injection rate and hole transfer rate tend to be increased with the enlongation of theÏ€-conjugated units. There exists an effectiveσ-Ï€conjugation between the silanylene moiety and the ethenylene moiety, which is significantly operative for the polymers with a rather smallÏ€-electron moiety. There exists an even/odd effect of the silanylene number x on the band gap. Charge-doping could remarkably lower the excitation energies. The interchain hole hoppings mainly occur between theÏ€-conjugated units. A doped nSi_x^L(C=C)_y⁺, nSi_xR(C=C)_y⁺, or R-nSi_x(C=C)_y⁺ (x≥2) oligomer could convert from a unrearrangement conformation to a rearrangement one except nSi₄^R(C=C)_y⁺. The simulated UV/vis absorption peak of the rearrangement structure locates at higher energy region related to the unrearrangement one. The hole transfer rate is significantly decreased if a doped unrearrangement molecule changes to a rearrangement one. These results are in good agreement with the experimental observations.