| Anions play significant roles in various biological, chemical, medical, catalyst, health, food and environmental processes. For example, organic or inorganic phosphates are not only biologically important targets for their pivotal roles in signal transduction and energy torage in biological systems, but also responsible for the eutrophication of waterways. Accordingly, the selective detection of anion has been a major research focus. Fluorescent chemosensors attract particular attention due to their high selectivity, sensitivity and simplicity. Currently, anion-induced molecular self-assembly is mainly used in the synthesis of helices and rotaxane structure compound, macrocyclic compounds, molecular recognition. Although selective sensing of anions driven by assembly of receptor has not attracted much attention, the sensing mechanism will be of great promising application. Based on this sensing mechanism, anion receptors can be well designed and synthesized for selectively and sensitively sensing anion. In addition, anthracene fluorophore has often been used in the design of effective chemosensors for anions because the relative proximity between anthracene moieties induces monomer and excimer emissions at considerably different wavelengths. The positive effect of amidopyridinium framework as anion binding motif has well been indentified by the authors and others. Based on these design ideas, in this paper, we taking anthracene group as signaling report group of the receptor and amidopyridinium framework as anion binding motif of the receptor, we have designed and synthesized a series of novel receptors for selectively sensing H2PO4-(Pi) and AcO-, and the specific research contents and results are as follows:1. Taking anthracene group as signaling report group of the receptor and amidopyridinium framework as anion binding motif of the receptor, we have designed and synthesized a novel and simple receptor H1. Its fluorescence behavior toward Pi was investigated. Upon addition of Pi, Pi induced the fluorescence enhancement of H1for10times and an apparent bathochromic shift of fluorescence emission with increasing intensity. This apparent bathochromic shift of fluorescence emission induced by addition of Pi was ascribed to the excimer emission between anthracene. These results show that the receptor H1can sense Pi selectively. Though fluorescence emission spectrum, UV-vis spectrum and DFT calculation, we studied the sensing mechanism of H1for Pi was ascribed to the Pi-induced assembly of H1. The assembly of H1induced the appearance of excimer emission. So the receptor H1can sense Pi selectively. 2. Based on the receptor H1, we introduced the strong electron-donating group methoxyl group and the strong electron-withdrawing group nitro-group to Hlrespectively to have designed and synthesized the receptors R1and R2. Its fluorescence behavior toward Pi was investigated. Upon addition of Pi, Pi induced the fluorescence enhancement of R1for40times and an apparent bathochromic shift of fluorescence emission with increasing intensity. This apparent bathochromic shift of fluorescence emission induced by addition of Pi was ascribed to the excimer emission between anthracene. These results show that the receptor R1can sense Pi selectively. Though fluorescence emission spectrum and UV-vis spectrum we studied the sensing mechanism of R1for Pi was ascribed to the Pi-induced assembly of R1. The assembly of R1induced the appearance of excimer emission. So the receptor R1can sense Pi selectively. However, the receptor R2containing the strong electron-withdrawing group nitro-group cannot sense Pi, which shows that electron-donating group is beneficial for the assembly of receptors and electron-withdrawing group is unbeneficial for the assembly of receptors.3. Based on the receptor H1, we exchange the position of amido-group and carbonyl group to design and synthesize the receptor L1. Fluorescent qualitative study shows that Pi cannot induce the assembly of the receptor L1, which indicates exchanging the position of recognition sites is unfavourable for the self-assembly of receptor molecule. Its UV-vis spectrum behavior toward an ion was investigated. The results of the study showed that AcO-can induce an apparent bathochromic shift of UV-vis spectrum with increasing intensity and a color change from colorless to dark yellow, which indicates that the receptor L1can selectively’naked-eyes’sense AcO-. UV-vis spectrum shows that the bonding stoichiometry between receptor L1and AcO-is1:2. The sensing mechanism is ascribed to the intramolecular charge transfer (ICT) process from the electron-rich bonding site to the electron-deficient pyridine after anions interaction with receptor through the hydrogen bonding and electrostatic interaction. For the receptor L1, Pi cannot induce the assembly of LI, which shows that exchanging the position of amido-group and carbonyl group affectes the assembly of L1. |
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