A coumarin-derived multi-faceted optical material with molecular logic gate for bioimaging

Abstract

The development of stimuli-responsive, multi-faceted chromic materials has gained the interest of the material science community recently, owing to their vast range of applications in several areas simultaneously, such as viscosity, temperature, and pressure detectors. In this context, a coumarin-derived organic luminophore, HCFH, has been designed and extensively investigated for its characteristics, such as aggregation-induced emission (AIE), viscochromism, piezochromism, thermochromism, and distinguishable fluorometric detection of Zn²⁺ and Cu²⁺ ions in water. The emission intensity of HCFH amplifies 111-fold with the addition of water in tetrahydrofuran (THF), validating its aggregation-induced emission (AIE) nature. Multi-colored piezochromism is observed in the ‘crystalline’, ‘pristine’, and ‘ground’ forms of HCFH as non-emissive, weakly cyan-emissive, and bright green-emissive, respectively. Further, powder X-ray diffraction (PXRD) and differential scanning calorimetry (DSC) analyses indicate a crystalline-to-amorphous phase transition during grinding. HCFH exhibits remarkable photophysical properties, including viscosity, polarity, and temperature-dependent emissions. The probe selectively detects Zn²⁺ and Cu²⁺ ions with limits of detection (LOD) of 1.14 and 1.54 nM, respectively, employing chelation-enhanced fluorescence (CHEF) and inhibition of photo-induced electron transfer (PET) for Zn²⁺ and paramagnetic fluorescence quenching for Cu²⁺. The Job's plots indicate 1 : 2 and 1 : 1 (M : L) binding stoichiometries for Zn²⁺ and Cu²⁺, respectively, which are confirmed by their single-crystal structures. Molecular logic gates and paper strip kits are also developed utilizing their sensing capabilities. HCFH has been found highly effective in bio-imaging of Zn²⁺ and Cu²⁺ in HeLa cells. Microscopic examination of the cells indicates that the probe is localized in both the cytosol and mitochondria of the cells.