Abstract Long-range charge transfer organic compounds are remarkable for having very large hyperpolarizabilities and thus improved nonlinear optical (NLO) properties. P-nitroaniline (pNA) is known as a classical NLO organic material. The question answered in this work is the NLO properties of pNA will be improved by introducing an extended π-conjugation chain between the phenyl ring and the two NH2/NO2 terminals. By applying the sophisticated MP2 calculations, pNA was engineered with π-conjugation of different lengths, and new derivatives of pNA were obtained. The π-conjugation is either –(CH CH)nNH2 or –(CH CH)nNO2 (n = 1–5) chain. The results indicate that introducing such chains results in smaller energy gaps and transition energies, which lead to a significant improvement in the hyperpolarizability ( β 0 ). The novel pNA derivatives exhibit larger β 0 amplitudes up to 4.67 × 104 au, which is 27-fold greater than that of pNA. Moreover, with increasing β 0 amplitude, the –(CH CH)nNO2 unit beats the –(CH CH)nNH2 unit. This study may offer assistance in designing higher performance NLO materials based on pNA.

中文翻译：

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MP2 计算 π 共轭对对硝基苯胺 (pNA) 衍生物的电子和非线性光学性质的影响

摘要 长程电荷转移有机化合物因其具有非常大的超极化率并因此改善非线性光学 (NLO) 特性而引人注目。对硝基苯胺 (pNA) 被称为经典的 NLO 有机材料。这项工作中回答的问题是 pNA 的 NLO 特性将通过在苯环和两个 NH2/NO2 末端之间引入扩展的 π 共轭链来改善。通过应用复杂的 MP2 计算，pNA 被设计为具有不同长度的 π 共轭，并获得了 pNA 的新衍生物。π 共轭是 –(CH CH)nNH2 或 –(CH CH)nNO2 (n = 1–5) 链。结果表明，引入这样的链会导致更小的能隙和跃迁能，从而显着提高超极化率（β0）。新型 pNA 衍生物表现出更大的 β 0 振幅，高达 4.67 × 104 au，比 pNA 大 27 倍。此外，随着β 0 振幅的增加，–(CH CH)nNO2 单元击败–(CH CH)nNH2 单元。这项研究可能有助于设计基于 pNA 的更高性能的 NLO 材料。