Cyclo[6]aramide-Tropylium Charge Transfer Complex as a Colorimetric Chemosensor for Differentiation of Intimate and Loose Ion Pairs.

Shape-persistent iso-C16-cyclo[6]aramide (1) was found to form a charge-transfer (CT) complex with aromatic carbonium tropylium (Tr(+)). The resulting CT complex was evidenced by both experimental results and theoretical calculations. Particularly, dibutylammonium salt with PF6(-) as the counterion can extrude Tr(+) from the CT complex, but it cannot do so with Cl(-), thereby offering a visual approach to identify organic intimate ion pairs and loose ion pairs.