Molecular Pincers Using a Combination of N-H and C-H Donors for Anion Binding.

A naphthalene imide () and a naphthalene () bearing two pyrrole units have been synthesized, respectively, as anion receptors. It was revealed by H NMR spectral studies carried out in CDCN that receptors and bind various anions via hydrogen bonds using both C-H and N-H donors. Compared with receptor , receptor shows higher affinity for the test anions because of the enhanced acidity of its pyrrole NH and naphthalene CH hydrogens by the electron-withdrawing imide substituent. Molecular mechanics computations demonstrate that the receptors contact the halide anions via only one of the two respective available N-H and C-H donors whereas they use all four donors for binding of the oxyanions such as dihydrogen phosphate and hydrogen pyrophosphate. Receptor , a push-pull conjugated system, displays a strong fluorescence centered at 625 nm, while receptor exhibits an emission with a maximum peak at 408 nm. In contrast, upon exposure of receptors and to the anions in question, their fluorescence was noticeably quenched particularly with relatively basic anions including F, HPO, HPO, and HCO.