Abstract: Potential energy of poly(m-phenylene)(PMP, P1) and the related derivatives (P2,P3) as a function of torsion angles(f) were constructed by using molecular mechanics method based on force field(Drieding 2.11). It is found that there are four minima in potential energy curve, which correspond to four torsion angles (f ≈－135°, －45°, 135°, 45°) respectively. Furthermore, all constructed PMP and derivatives are minimized by molecular force field, and four main conformations are found. For PMP, two helical conformations have minimal energy, and they have preponderant population. Under the real conditions, PMP and derivatives polymer chain may consist of above stable conformation segments with an equilibrium ratio, which depends on polymer surroundings. The electronic structure (HOMO-LUMO gap) prediction depending on torsion angles was calculated by GGA-DFT method using Dmol3 program. The AM1 method was used to investigate geometry optimization, and the optimized conformations are basically consistent with that simulated by molecular mechanics. In order to get more accurate HOMO-LUMO gap of above optimized geometries, the hybrid functional B3LYP was adopted at the level of 6-31G basis set using Gaussian98 software. At last, it is found that the twist extent of torsion angle between phenyl rings is the main factor that affects HOMO-LUMO gap of PMP and its derivatives.

Key words: PMP, 　Conformation, 　Electronic structure, 　Molecular simulation