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

O 95 : 5 with an unusual interlocked host selectivity for acetate and dihydrogenphosphate 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.