Bulky camphorsulfonic acid (CSA) was used to complex with quinine (Qu) to impose restricted intramolecular rotation (RIR) required for aggregation-induced emission (AIE) properties. After complexation with two equivalents of CSA, the non-emissive quinine (Qu) base can be protonated to produce an ionic complex Qu(CSA)2 with AIE properties. The ionic bonds in the complex Qu(CSA)2 are sensitive to various external stimuli, which allows its use as a luminescent sensor for pH values and different metal ions. Moreover, the ionic Qu(CSA)2 can be a denaturant and biological sensor for the blood protein of bovine serum albumin (BSA); through the use of Qu(CSA)2, the unfolding process of the BSA chains was evaluated. Theoretical and practical aspects of this ionic Qu(CSA)2 complex are discussed in this study.
