Active metal template synthesis of a neutral indolocarbazole-containing [2]rotaxane host system for selective oxoanion recognition

An active metal template strategy was used to synthesise a neutral indolocarbazole containing [2]rotaxane anion host system. H-1 NMR anion binding investigations reveal that the [2]rotaxane recognises a range of monoanions in acetone-d(5):D2O 95:5 with an unusual interlocked host selectivity for acetate and di-hydrogenphosphate oxoanions over halides. The rotaxane displays an overall selectivity for the sulfate dianion, favouring a 2 : 1 host : guest binding stoichiometry at low sulfate concentration and a 1 : 1 stoichiometry in the presence of excess sulfate. Fluorescence titration demonstrates that the [2] rotaxane is also capable of sensing guest anions via significant changes in its emission spectrum.