共轭CN与非共轭CF_3吸电子取代基对PPV类衍生物分子结构及光电性质的影响

Influence of Conjugated CN and Non-conjugated CF_3 Electron Withdrawing Substituents on the Molecular Structure and Photo-electricity Properties of PPV-like Derivatives

运用密度泛函DFTB3LYP/6 3 1G(d)方法对CN和CF3 吸电子基团取代的PPV类衍生物的三聚体进行了几何构型优化 ,并采用含时密度泛函TD DFTB3LYP/6 3 1G(d)方法计算了其相应化合物的紫外吸收光谱 .通过对CN和CF3 取代的PPV类衍生物的分子几何结构、前线分子轨道能级、电子云分布规律的分析 ,从理论上解释了共轭CN与非共轭CF3 吸电子取代基对其光谱性质影响的差异 :前者使相应PPV类衍生物的吸收光谱发生红移 ,后者则发生蓝移 .计算结果还表明用TD DFT方法计算该体系的紫外吸收光谱值与实验数据吻合得很好 ;另外引入CN和CF3 基团之后 ,使其相应的PPV衍生物的LUMO能级降低 ,电子亲合势增加 。

The trimer geometric structures of PPV-Iike derivatives substituted by CN and CF3 were optimized using density functional theory (DFT) at B3LYP/6-31G(d) level. The UV absorption spectra of the corresponding compounds were also calculated using time-dependent density functional theory (TD-DFT) at the same level. We analysed the molecular geometric structures, the frontier molecular orbital energy levels and the electron cloud distributing rules of the PPV-Iike derivatives substituted by CN and CF3 groups. We simultaneously interpreted the different influence of conjugated CN and non-conjugated CF3 electron withdrawing substituents on photo-electricity properties of their derivatives. The former leads to the red shift of UV absorption spectrum of the corresponding compounds, and the latter leads to the blue shift. The calculations have also shown that the UV absorption spectrum of the compounds calculated by TD-DFT method agrees well with the experimental data. In addition, the LUMO energy levels of the corresponding PPV-Iike derivatives are lowered and their electron affinities increase with the introduction of the electron withdrawing substituents CN and CF3. The PPV-Iike derivatives are all good electron transporting materials.