A novel cucurbit[6]uril-based supramolecular coordination assembly as a multi-responsive luminescent sensor for Fe3+, Cr2O72− and isoquinoline antibiotics in aqueous medium

Abstract

A novel CB[6]-based supramolecular assembly: [Zn(ACA)₄]·CB[6]·[NH₂(CH₃)₂]·8H₂O (1) (where CB[6] = cucurbit[6]uril, HACA = anthracene-9-carboxylic acid) has been synthesized under solvothermal conditions, using [Zn(ACA)₄]²⁻ as a structure-directing agent. The formation of such a supramolecular assembly is attributed to the non-covalent π⋯π, C–H⋯π and hydrogen bonding interactions between the outer-surface of CB[6] and [Zn(ACA)₄]²⁻. Compound 1 exhibits good dispersibility, excellent water stability and easy regeneration ability. More importantly, 1 can be highly selective in sensing ferric ions (Fe³⁺) and dichromate ions (Cr₂O₇²⁻) ions using fluorescence quenching with a strong quenching constant (K_sv = 1.088 × 10⁴ M⁻¹ for Fe³⁺ and K_sv = 6 × 10³ M⁻¹ for Cr₂O₇²⁻). In addition, 1 can also be used as a probe for the determination of trace amounts of isoquinoline antibiotics with K_sv = 5.74 × 10⁴ M⁻¹ for palmatine and K_sv = 4.2 × 10⁴ M⁻¹ for berberine. As far as is known, this is the first example of the use of a CB[n]-based supramolecular coordination assembly for the highly efficient detection of Cr₂O₇²⁻ and antibiotics. These encouraging results indicate that 1 can act as a promising multi-responsive luminescent sensor for environmental pollutant monitoring, and also give an insight into obtaining a CB[n]-based supramolecular coordination assembly with potential applications as a luminescent sensor.