基于共掺杂调控C32多极矩的二阶非线性光学响应

Second-order nonlinear optical response based on codoped C32 multipole moments modulation

  • 摘要: 基于密度泛函(DFT)理论,采用CAM-B3LYP方法,以C32分子为多极矩构建骨架,设计了两类替位式共掺杂的富勒烯衍生物C28B2N2和C28B2P2,共16种同分异构体,并对它们的电子性质、线性极化率α和一阶超极化率β进行研究。结果表明,掺杂后分子的HOMO-LUMO能隙变小,C28B2P2αβ值均大于C28B2N2系列。其中偶极分子具有大的β值,八极分子则有较小的β值,筛选出具有优异的二阶非线性光学(NLO)响应特性的结构。含时密度泛函理论(TD-DFT)的结果表明,与C32相比,掺杂后所有结构的吸收光谱的响应范围变宽,最大吸收强度减弱,且最大吸收波长的位置发生红移或蓝移。基于完全态求和(SOS)方法,分别用二能级或三能级公式解释了两类共掺杂结构中β值最大的来源,并且证明了与之有关的电子激发类型为π→π*激发。

     

    Abstract: Using C32 molecule as the skeleton of multipole moments, two types of substitutional co-doped fullerene derivatives C28B2N2 and C28B2P2 were designed with 16 isomers. The electronic properties, linear polarizability α and first hyperpolarizability β were studied by CAM-B3LYP method of density functional theory (DFT). The results show that the HOMO-LUMO gap of the doped molecules becomes smaller, and the values of α and β of C28B2P2 are larger than those of C28B2P2. Additionally, dipole molecules in these molecules have large β, while the octapolar molecules have smaller β. The structure with excellent second-order nonlinear optical (NLO) response characteristics is selected. The calculation results of time-dependent density functional theory (TD-DFT) method show that, compared with C32, the response range of absorption spectra of all doped structures becomes wider, the maximum intensity becomes weaker, and the position of the maximum absorption wavelength may be red-shifted or blue-shifted. Based on the sum-over-states (SOS) method, the two-level or three-level formulas are used to explain the origin of large β in two co-doped structures, and verify the related electronic excitation type is π→π* excitation.

     

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