几种芳香类NLO材料中非对位取代基团的作用

The Roles of the Non-centrosymmetrically Substituted Groups in Several Aromatic NLO Materials

计算了几种芳香烃类二阶非线性光学材料的分子二阶非线性光学系数 β值 ,研究了这些化合物中非对位取代基团 CH3,Cl,Br和 NHCOCH3等的作用 .结果表明 ,它们对材料的分子内电荷转移和β的影响很小 ,但是对化合物的晶体结构却有很大影响 。

The molecular second\|order nonlinear optical(NLO) polarizabilities \%β\% of several aromatic NLO materials were calculated and the roles of the non\|centrosymmetrically substituted groups in these compounds were studied. The results showed that the strong donor\|acceptor(such as nitro and amino group etc.) \%para\%\|disubstituted compounds usually crystallized in a centrosymmetric crystal structure and therefore had no SHG(second harmonic generation) effect. However, they would show very strong SHG effect when the groups CH\-3, Cl, Br or NHCOCH\-3 were non\|centrosymmetrically attached to these molecules. The intromolecular charge transfer and the molecular polarizabilities were hardly dependent on these substituents. But they played an important role in forming the non\|centrosymmetric crystal structures and therefore the second harmonic generation response. So such non\|centrosymmetrically substituted groups were important in designing effective organic second\|order NLO materials.