Multiple-responsive ionic complex luminogen of quinine and camphorsulfonic acid with aggregation-induced emission

Abstract

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.