Coumarin‐based Chemosensors for Metal Ions Detection

Abstract

Coumarins, due to their intense and persistent emission of fluorescence, structural flexibility, and excellent biocompatibility, have become a popular choice in developing new fluorescent chemosensors. Coumarins have long been used for sensing anions, cations, chemically reactive nitrogen, oxygen, sulfur-containing species, and small molecules. They have also been shown to have applicability in imaging, biology, and medical research. Due to the widespread use and excellent biological activity, hundreds of such coumarin motifs have either been isolated from nature or synthesized in a laboratory. This review covers all the developments pertaining to the synthesis and use of coumarin for sensing a variety of metal ions (alkali, alkaline earth, transition, heavy, and noble metal ions). This comprehensive review includes an overview of the coumarin-based chemosensor's pH limit, detection limit, and binding mode. A brief explanation of the stoichiometric ratio between metal and chemosensor moiety and the applicability of each chemosensor is also given.

Structure–metal ion selectivity of rhodamine-based chemosensors

“…Coumarin is also a common fluorophore which was used for the construction of different chemosensors for the detection of various metal ions. 66,67 Some research groups combined coumarin with rhodamine to modulate the sensing properties. Cao et al reported a coumarin incorporated rhodamine B derivative (49) (Scheme 7) for sensing of Al 3+ and Ca 2+ in ethanol.…”

Development of Fluorescent Chemosensors for Calcium and Lead Detection

“…The wide range of chromophores and fluorophores permits fine-tuning the optical properties exhibited by the final sensor molecule. A successful case is the class of coumarins, which have been used as a fluorescence scaffold for the development of chemosensors for various relevant analytes, the vast majority of which focus on metal ions [ 3 ] ( Figure 1 ). Indeed, metal ionic species are ubiquitous in nature, and many have crucial roles for maintaining the balance of biological systems.…”

Organic Luminescent Sensor for Mercury(II) and Iron(III) Ions in Aqueous Solutions

“…While these methods are very sensitive with a wide range of linearity, still the high cost and long operation, and complicated sampling processes of such techniques increase the need of finding simpler and faster methods that provide similar results in a shorter time. Recently, chemiluminescent sensors were modified to investigate organic and inorganic analytes in biological and environmental systems [28][29][30]. This provides a simple method to detect target molecules/ions with low detection limits over a short time.…”

“…Importantly, luminescence-based sensors can be further designed to attain a wide range of signaling "antenna" when the analyte covalently binds to the luminescent probe providing opportunities to monitor the concentrations of the target within a short time. This antenna can be observed through changes in the signal's intensities, wavelength, lifetime, and chirality [28][29][30][31][32].…”

“…When the target analyte binds to the receptor, an immediate change to the emission occur where emission intensity may be enhanced or quenched making 'off-on' or 'on-off' sensors as illustrated in Scheme 1. Variations to the emission spectra may occurs through various mechanisms including PET, Ligand-tometal charge transfer (LMCT), or metal-to-ligand charge transfer (MLCT) [30][31][32][33][34]. Several studies reported that the LMCT involves electronic transitions from the localized orbitals in the conjugated linker to a metalcentered orbital and is highly sensitive to the ionic size and the coordination geometry of the linker [30][31][32][33][34][35][36][37].…”