Syntheses of 5,6-Benzocoumarin Derivatives and the Studies of Their Ion-Sensing Properties
篩選結果顯示DPA延伸碳鏈使分子彈性增加，又螢光基團苯駢香豆素上少了推電子基團幫助，導致化合物與金屬離子螯合後螢光強度變化差異小，此系列化合物對金屬離子選擇性低。我們選擇鋅、鎘離子與化合物16、17、20進行詳細的1H NMR、UV□vis及螢光光譜的滴定，結果發現分子辨識單元經碳鏈延伸之化合物16均以1:1（16:ion）方式與鋅、鎘離子錯合，使用改良版Benesi-Hildebrand plot計算錯合常數分別為3.4 × 104及3.9 × 104 M-1；化合物17以1:1（17:Cd2+）方式與鎘離子錯合，其錯合常數為1.8 × 105 M-1。碳鏈未經延伸之化合物20與鎘離子以1:2（20:Cd2+）方式與鎘離子錯合，其錯合常數為1.3 × 109 M-2。
In this work, a series of novel fluoroionophores 16□20 were synthesized. The structures of 16□20 featured 5,6-benzocoumarin moiety as the fluorophore and di-2-picolylamino (DPA) group as the ionophore for metal ions. The photophysical and ion-sensing properties of these compounds were examined in acetonitrile. The results showed that 5,6-benzocoumarin based sensors had a longer absorption wavelength than that of 7-methoxycoumarin derivatives by 20 nm. The extended chain length of DPA made the carbonyl group on amide at the same plane with 5,6-benzocoumarin, and also elongated the absorption wavelength. However, the absorption wavelength of these compounds still do not fall into the visible range. The extended chain length of DPA increased the flexibility of the molecule. However, lacking of an electron-donating group on the 5,6-benzocoumarin skeletons resulted in a smaller difference in the fluorescence spectra in the absence and presence of metal ions. The metal ions selectivity of these benzocoumarin-based fluoroionophores 16□20 was poor. We selected Cd2+and Zn2+ to do detailed 1H NMR, UV-vis, and fluorescence titrations spectroscopy with compounds 16, 17 and 20. Compound 16 with extended DPA formed a 1:1 complex with Cd2+and Zn2+ respectively. We used modified Benesi-Hildebrand plot to calculate the binding constant between 16 and Cd2+, which was 3.4 × 104 M-1. The binding constant between 16 and Zn2+ was determined to be 3.9 × 104 M-1. Compound 17 with extended DPA formed a 1:1 complex with Cd2+ and its binding constant was determined to be 1.8 × 105 M-1. Hill plot was used to analyze the complexation behavior between compound 20 and Cd2+. Compound 20 without extended DPA formed 1:2 complex with Cd2+, and its binding constant was determined to be 1.3 × 109 M-2. Finally, compounds 16, 17 and 18 with amide group were selected for anion screening. The results revealed that compounds 16, 17 and 18 had a high selectivity toward fluoride ion. The high selectivity of these amide-containing hosts 16, 17 and 18 toward fluoride ion was resulted from the H-bonding interaction between fluoride ion and the amide hydrogen as evidenced by their 1H-NMR titration results.
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