Synthesis and properties of novel second-order NLO chromophores containing pyrrole as an auxiliary electron donor
作者:Xiaohua Ma、Ran Liang、Fan Yang、Zhenhua Zhao、Aixin Zhang、Naiheng Song、Qifeng Zhou、Jianping Zhang
DOI:10.1039/b720023d
日期:——
A novel series of second-order NLO chromophores containing pyrrole as an auxiliary electron donor was synthesized via Knoevenagel reactions between 5-aminated N-methylpyrrole-2-carbaldehydes and different electron-accepting groups, i.e., malononitrile, picolinium tosylate and 2-dicyanomethylene-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran (TCF). Their corresponding NLO chromophores containing thiophene in the place of pyrrole were also prepared for comparison. The resulting NLO chromophores showed good solubility in common organic solvents such as CHCl3, THF and DMF, except for TTCF containing thiophene and TCF, which is soluble in polar aprotic solvents but poorly soluble in less polar solvents. NMR studies of these chromophores showed that, in comparison with thiophene rings in the same type of NLO chromophores, pyrrole rings had higher electron density, as evidenced by the up-field chemical shifts of pyrrole protons. TGA investigations showed good thermal stability of these chromophores in nitrogen with the onset weight loss temperatures in the range of 203 to 296 °C. Positive solvatochromism of 10–44 nm from dioxane to chloroform were found for these chromophores, and moderate to very large molecular static hyperpolarizabilities (β0) of 57–1490 × 10−30 esu were revealed by hyper-Rayleigh scattering measurements. For chemical bonding to polymer chains, hydroxyl-containing NLO chromophores were also prepared and characterized for their linear and nonlinear optical properties.
通过 5-氨基 N-甲基吡咯-2-羰基醛与不同电子接受基团(即丙二腈、吡啶对甲苯磺酸盐和 2-二氰基亚甲基-3-氰基-4,5,5-三甲基-2,5-二氢呋喃 (TCF))之间的 Knoevenagel 反应,合成了一系列含有吡咯作为辅助电子供体的新型二阶 NLO 发色团。为了进行比较,还制备了含有噻吩而非吡咯的相应 NLO 发色团。所制备的 NLO 发色团在 CHCl3、THF 和 DMF 等常见有机溶剂中具有良好的溶解性,但含有噻吩的 TTCF 和 TCF 除外,它们在极性非丙烷溶剂中的溶解性较好,但在极性较弱的溶剂中的溶解性较差。对这些发色团进行的核磁共振研究表明,与同类 NLO 发色团中的噻吩环相比,吡咯环的电子密度更高,这一点可以从吡咯质子的上场化学位移得到证明。TGA 研究表明,这些发色团在氮气中具有良好的热稳定性,开始失重的温度在 203 至 296 °C 之间。通过超瑞利散射测量发现,这些发色团从二氧六环到氯仿的正溶解色度为 10-44 nm,分子静态超极化率(β0)为 57-1490 × 10-30 esu。为了与聚合物链进行化学键合,还制备了含羟基的 NLO 发色团,并对其线性和非线性光学特性进行了表征。