Synthesis and properties of NLO chromophores with fine-tuned gradient electronic structures
作者:Xiaohua Ma、Fei Ma、Zhenhua Zhao、Naiheng Song、Jianping Zhang
DOI:10.1039/b817789a
日期:——
A novel series of heterocycle-based NLO chromophores based on different combinations of auxiliary donor (i.e., benzene, thiophene and pyrrole) and auxiliary acceptor (i.e., thiazole with different regiochemistries) were designed and synthesized. Due to the different electron-rich and poor nature of the auxiliary donors and acceptors, respectively, the resulting NLO chromophores have systematically varied ground-state electronic structures, as evidenced by the 1H NMR, CV and UV-vis investigations. The nonlinear optical properties of the resulting NLO chromophores were studied by UV-vis spectroscopy, Hyper-Rayleigh scattering (HRS), and semi-empirical computations. All the chromophores have very large molecular hyperpolarizabilities (β1000 nm) in the range of 704–1500 × 10−30 esu (or β0, 318–768 × 10−30 esu), which showed a great sensitivity to the gradient electronic structures. Upon increasing the electron density from benzene to thiophene and to pyrrole, substantial increases in β0 were observed; significantly larger β0 values were also observed for NLO chromophores based on “matched” thiazole (C2 is connected to the acceptor) than those based on “un-matched” thiazole (C5 is connected to the acceptor). TGA investigations showed good thermal stability for the resulting NLO chromophores. However, with the increase of electron density of the auxiliary donor, a decrease in thermal and photochemical stability was observed. It is interesting to note that NLO chromophores based on triarylamine as the donor and thiazole as the auxiliary acceptor exhibited not only high thermal stability but also very large β0 values.
本研究设计并合成了一系列基于杂环的新型 NLO 发色团,这些发色团基于不同的辅助给体(即苯、噻吩和吡咯)和辅助受体(即具有不同化学结构的噻唑)组合。由于辅助供体和受体分别具有不同的富电子性和贫电子性,所得到的 NLO 发色团具有系统的不同基态电子结构,1H NMR、CV 和 UV-vis 研究证明了这一点。通过紫外-可见光谱、超雷利散射(HRS)和半经验计算研究了所得 NLO 发色团的非线性光学特性。所有发色团在 704-1500 × 10-30 esu(或 β0, 318-768 × 10-30 esu)范围内都具有非常大的分子超极化率(β1000 nm),这表明它们对梯度电子结构非常敏感。当电子密度从苯增加到噻吩和吡咯时,β0 显著增加;基于 "匹配 "噻唑(C2 连接到受体)的 NLO 发色团的β0 值也明显大于基于 "非匹配 "噻唑(C5 连接到受体)的 NLO 发色团。热重分析表明,所制备的 NLO 发色团具有良好的热稳定性。然而,随着辅助供体电子密度的增加,热稳定性和光化学稳定性都有所下降。值得注意的是,以三芳基胺为供体、噻唑为辅助受体的 NLO 发色团不仅具有很高的热稳定性,而且β0 值也非常大。