Polymer Science Unit, Indian Association for the Cultivation of Science, Jadavpur, Kolkata-, 700 032, India.
Chemistry. 2018 Apr 11;24(21):5591-5600. doi: 10.1002/chem.201705782. Epub 2018 Mar 9.
Detection of nitroaromatics at ultralow concentration is a major security concern in defense, forensics, and environmental science. To this end, a new triarylamine-cored dendritic gelator (OGR) was synthesized, which produced thermoreversible, thixotropic, and fluorescent gels in n-octanol. On gelation, both π-π* transitions and the emission peak of the gelator show redshifts with a 4.5-fold increase of fluorescence intensity in the gel state indicating J-aggregation. The nitrogen lone-pair electrons of OGR make it a donor, and electron transfer occurs to acceptor nitroaromatics causing fluorescence quenching, which is further promoted due to its acidity. The Stern-Volmer rate constants measured for different nitroaromatics showed that it senses picric acid (PA) best. The contact-mode technique with OGR-treated paper strips can allow naked-eye detection of PA under UV light down to 10 m concentration within 30 s. Reusability of the gel is achieved by treating OGR@PA with NaOH solution. Impedance spectroscopic results indicated a decrease of both charge-transport resistance and Warburg impedance on successive addition of PA. The limits of detection of PA determined from fluorescence and impedance measurements match well. Thus, the OGR gel is a reusable, low-cost, specific sensor for PA by naked-eye colorimetric, fluorescence, and impedance techniques.
超痕量检测硝基芳香族化合物是国防、法庭科学和环境科学的主要安全关注点。为此，合成了一种新型的三芳胺核树枝状凝胶剂（OGR），它在正辛醇中产生热可逆、触变和荧光凝胶。在凝胶化过程中，OGR 的π-π*跃迁和凝胶剂的发射峰都发生红移，荧光强度在凝胶态下增加了 4.5 倍，表明发生了 J 聚集。OGR 的氮孤对电子使其成为供体，电子转移到接受体硝基芳香族化合物上，导致荧光猝灭，由于其酸性，这种猝灭作用进一步增强。测量不同硝基芳香族化合物的 Stern-Volmer 速率常数表明，它对苦味酸（PA）的检测效果最佳。使用 OGR 处理的纸带的接触式技术可以在 30 秒内，在紫外光下，以低至 10 μM 的浓度肉眼检测到 PA。通过用 NaOH 溶液处理 OGR@PA，可以实现凝胶的重复使用。连续加入 PA 后，阻抗光谱结果表明电荷传输电阻和 Warburg 阻抗都降低了。荧光和阻抗测量法确定的 PA 检测限吻合得很好。因此，OGR 凝胶是一种可重复使用、成本低、对 PA 具有特异性的传感器，可通过肉眼比色、荧光和阻抗技术进行检测。
