A multifunctional coumarin-based probe for distinguishable detection of Cu2+ and Zn2+: its piezochromic, viscochromic and AIE behavior with real sample analysis and bio-imaging applications

Abstract

A multifunctional coumarin based organic luminophore, CTH, has been synthesized and its fluorescence properties are investigated. The probe displays the properties of aggregation-induced emission (AIE), viscochromism, piezochromism and distinguishable flourometric sensing of Cu²⁺ and Zn²⁺ ions. The molecular structure of the probe has been determined by FT-IR, UV-Vis, NMR, and HRMS spectral studies. Powder XRD, dynamic light scattering (DLS), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and density functional theory (DFT) calculations have been carried out to explore the photo-physical properties of the synthesized probe. CTH is non-emissive in ethanol, but upon adding water its emission intensity increases by 8-fold and fluorescence quantum yield increases from Φ = 1.19 × 10⁻³ (f_w = 70%) to Φ= 8.50 × 10⁻³ (f_w = 99%), indicating typical AIE behaviour. The probe demonstrates excellent viscochromism with increasing glycerol fraction in EtOH. Upon grinding, the probe exhibits piezochromic properties and shows an emissive color change from blue to bright green along with a bathochromic shift of 83 nm. In addition to the aforementioned properties, the probe selectively discriminates Cu²⁺ and Zn²⁺ from a pool of different metal ions in DMF : H₂O (3 : 7, v/v, pH 7.4) HEPES buffer. CTH detects Cu²⁺ and Zn²⁺ ions via paramagnetic fluorescence quenching and CHEF induced fluorescence enhancement, respectively. Job's plots suggest 1 : 1 binding stoichiometry for both CTH–Cu²⁺ and CTH–Zn²⁺ complexes. Significant low detection limits (LODs) of 6.75 nM for Cu²⁺ and 2.97 nM for Zn²⁺ have been observed and molecular logic gates have also been constructed. The probe has been effectively utilized in the bio-imaging of Cu²⁺ and Zn²⁺ in the gut tissue of Drosophila and in the quantification of Cu²⁺ and Zn²⁺ in real water samples.