氟掺杂聚酰亚胺单体的电子结构及光学性能研究

Electron Structure and Optical Performance of Fluorine-Doped Polyimide Monomer

采用含时密度泛函理论(TD-DFT),GGA-PBE泛函在DNP 4.4基组的水平上对聚酰亚胺单体分子的紫外可见吸收光谱进行了计算,并与部分实验值进行了比较。结果显示:由于氟原子的强吸电子能力,含氟单体的总能远低于非含氟单体。非含氟单体紫外吸光系数ε为1.407 87×106L/(mol·cm);含氟单体的紫外吸光系数ε稍大,为1.533 91×106L/(mol·cm)。从二者的态密度可以看出,加氟之后,在-24 Ha处出现了较大的态密度峰值,主要来源于氟原子1s轨道的贡献;在-14 Ha处态密度不变,这是氮原子的特征能态;在-10 Ha处态密度有所减小,因为氟取代了甲基上的氢,而氟在该处不存在量子态。费米能级附近,紫外吸收对应的能量出现在这个区域中,除了费米能级以上第一个峰值外,其他峰值均有所增大,在-1 Ha处出现了两个非含氟单体中不存在的峰,因此紫外吸收能量相应增强。计算结果表明,掺氟有助于紫外吸收性能提升。

The time-dependent density functional theory （TD-DFT） and exchange-correlation function GGA-PBE, have been employed to perform a study with polyimide monomer based on basis set at the level of DNP 4. 4. The UV-vis absorption spectra were obtained and compared with some experimental values. It is shown that the total energy of fluorine-containing monomer is always much lower than that of the non-fluorine-containing counterpart, due to the strong electron withdrawing ability of fluorine atom. The ultraviolet absorption coefficient ～ of the non-fluorinated monomer is 1. 407 87×10^6L/（mol-cm）, and that of the fluorinated one is slightly larger, as 1. 533 91 ×10^6L/（mol. cm）. As can be seen from the density of states （DOS） of the two, the DOS of fluorine doped monomer has a peak at - 24 Ha, which is mainly from the contribution of fluorine ls orbit ; the peak at - 14 Ha remains unchanged, which is the characteristic of a nitrogen atom energy state. The DOS peak at - 10 Ha has been reduced, since the hydrogen was substituted by fluorine on the methyl group, and fluorine has no quantum state at -10 Ha. Most of the peaks near the Fermi level are increased, except the first peak above forbidden band. And two peaks in the fluorine doped monomer appear near- 1Ha which do not exist in the non-fluorinated monomer, therefore the ultraviolet absorption energy is enhanced.