中心对称的对氨基苯甲酸尿素超分子晶体的SHG效应

The SHG Effect on Centrosymmetric Supermolecular Crystal of p-Aminobenzonic Acid/Urea

利用分子组装方法获得了对氨基苯甲酸 /尿素超分子晶体 .经X衍射单晶结构测定 ,晶体为中心对称结构 ,空间群为Pnab ;经Nd :YAG皮秒激光器测试晶体粉末 ,以KDP粉末为参比 ,超分子晶体粉末的绿色倍频光的相对强度和积分值分别为 80 .2 0 (KDP ,176 .4 0 )和 181.0 (KDP ,4 2 3.98) .在超分子晶格中 ,尿素分子受到共存的对氨基苯甲酸分子的相互作用 ,改变了尿素分子在晶格中的彼此间的距离或取向 ,使中心对称的基态偶极矩的相互作用偏离最佳状态 ,能够部分地保持各自独立的超极化分张量 ,而呈现SHG效应 .

Centrosymmetric Supermolecular crystal is obtained by molecular assembly with urea and p aminobenzonic acid. The results determined by x ray single crystal diffraction show that the supermolecular crystal is a centrosymmetric structure with a space group Pnab. The relative intensity and integral value of the green light from the crystal powder compared to that of KDP powder sample, which were measured by pico second Nd:YAG laser, are 85.47 (KDP: 183.4) and 181.0 (KDP: 423.98), respectively. In the supermolecular crystal, centrosymmetric urea molecules are restricted by coexisting p aminobenzonic acid, thus change molecular distance and molecular orientation to each other. Therefore, the interaction between ground state dipole moment of centrosymmetric molecules depart from the optimal state, keep partial hyperpolarizability tensor component independently, and exhibit SHG effect.