Cooperative Recognition of a Copper Cation and Anion by a Calix[4]arene Substituted at the Lower Rim by a β‐Amino‐α,β‐Unsaturated Ketone

Chemodosimeter: Upon titration with CuII, the fluorescence of 1 showed strong fluorescence enhancement because the metal ion helps to lock the conformation of the fluorophores. CuII was reduced to CuI by the free phenolic OH group of 1, the phenol was then oxidised by CuII and assisted in the trapping of CuI. Ditopic behaviour was observed for 1⋅CuI, which showed further enhancement of its fluorescence intensity upon complexation with anions (as depicted, A−=CH3COO− or F−). magnified image We report herein a new ditopic calix[4]arene receptor 25,27‐bis‐{[4‐amino‐4‐(1‐naphthyl)‐2‐oxo‐3‐butenyl]oxy}‐26,28‐dihydroxycalix[4]arene (2) for the simultaneous complexation of anionic and cationic species. The host molecule 25,27‐bis{[3‐(1‐naphthyl)‐5‐isoxazolyl]methoxy}‐26,28‐dihydroxycalix[4]arene (1) was synthesised first and was followed by a [Mo(CO)6]‐mediated ring‐opening reaction to give the target receptor 2. The binding properties of ligands 1 and 2 towards metal ions in CH3CN were investigated by UV/Vis and fluorescence spectroscopies. The results showed that both ligands 1 and 2 were highly selective for CuII ions. Upon titration with CuII, the fluorescence of 1 was severely quenched, whereas 2 showed strong fluorescence enhancement because the metal ions help to lock the conformation of the fluorophores. During the complexation of 2 with CuII, the CuII was reduced to CuI by the free phenolic OH of 2, whereas the phenol was oxidised by CuII, after which it assisted in the trapping of CuI. Ditopic behaviour was observed for the complex 2⋅CuI, which showed further enhancement of its fluorescence intensity upon complexation with anions such as acetate or fluoride.