A highly selective chemosensor for Al3+ based on 2-oxo-quinoline-3-carbaldehyde Schiff-base

A new highly selective “off–on” typical chemosensor of Al3+, 1-((Z)-((E)-(3,5-dichloro-2-hydroxybenzylidene)hydrazono)methyl) naphthalene-2-ol, an experimental and in silico study

A new promising fluorescent chemosensor based on a 2-hydroxynaphthaldehyde skeleton was successfully synthesized through double imine formation as a yellow solid with an overall chemical yield of 63%. The compound showed UV/Visible maxima of at 394 nm in DMSO. Based on spectroscopic data of FTIR, ToF-HRMS, ¹H-NMR, and ¹³C-NMR, the product was characterized as 1-((Z)-((E)-(3,5-dichloro-2-hydroxybenzilydine)hydrazono)methyl)naphthalene-2-ol. Upon experimental study, the compound was confirmed as a highly selective and reversible off–on typical chemosensor against Al³⁺ with an emission quantum yield of 0.203 ± 0.009. The Job's plot analysis revealed that a highly stable 1:1 complex was formed with an association constant of 8.73 × 10⁵ M⁻¹. A pH-dependent study showed that the sensor was potentially applicable at physiological conditions (pH 7–8) in a mixture of DMSO : H₂O (99 : 1, v/v). The LoD and LoQ of the chemosensor towards Al³⁺ in DMSO were found to be 0.04 and 0.14 μM respectively. Based on DFT and TD-DFT calculation (B3LYP hybrid method/basis set of 6-311+G(d,p)), the sensing mechanism of the chemosensor to the ion was discovered as inhibition of excited-state intramolecular proton transfer (ESIPT).

A new promising fluorescent chemosensor of Al³⁺ based on a 2-hydroxynaphthaldehyde skeleton was successfully synthesized through double imine formation and demonstrated excellent sensing properties through the ESIPT inhibition mechanism.

Hydrazone-Based Small-Molecule Chemosensors

The hydrazone functional group is widely applied in several fields. The versatility and large use of this chemotype are attributed to its easy and straightforward synthesis and unique structural characteristics which is useful for different chemical and biological purposes. Recently hydrazone scaffold has been widely adopted in the design of small-molecule fluorescent and colorimetric chemosensors for detecting metals and anions because of its corresponding non-covalent interactions. This chapter provides an overview of hydrazone-based fluorescent and colorimetric chemosensors for anions and metals of biological interest, with their representative rational designs in the last 15 years. We hope this chapter inspires the development of novel and powerful fluorescent and colorimetric chemosensors for a broad range of applications.

Synthesis, photophysical properties and theoretical studies of new bis-quinolin curcuminoid BF2-complexes and their decomplexed derivatives

This paper presents the synthesis and characterization of two series of new bis-quinolin curcuminoid BF₂-complexes 11 and their respective decomplexed bis-quinolin curcuminoid derivatives 12, in an attempt to understand their optical properties. The synthesized compounds showed interesting fluorescent characteristics in both solution and in solid-state. The characteristic of the electronic transitions involved in these systems were measured via Uv-vis spectroscopy and fluorescence spectroscopy. Results revealed that the absorption and emission bands are dependent of the structure of compounds 11 and 12 but also of the type of substituent, even showing a push-pull behavior in those derivatives substituted with methyl group. These findings were also confirmed through computational calculations at DFT level via simulations of the Uv-vis spectra and determining the topology of the border orbitals responsible for light absorption.

Highly selective CHEF-type chemosensor for lutetium (III) recognition in semi-aqueous media

A simple phosphoryl quinolone (L) based sensor has been synthesized for the selective recognition of Lu³⁺ by spectrofluorimetric method. In methanol-water (1:1, v/v), the ligand L exhibits a weak emission peak at 400 nm upon excitation at 280 nm. Upon interaction with various f-metal and other selected metals from s, p, and d-block elements, the fluorescence of L is selectively enhanced in the presence of Lu³⁺ due to the chelation enhanced fluorescence (CHEF) effects. The quantum yield (φ) of L (φ = 0.063) is enhanced to φ = 0.118 upon chelation with Lu³⁺ ion. From the titration experiment, the limit of detection (LOD) of sensor L to recognize Lu³⁺ is estimated down to 24.2 nM, which is much lower than the WHO guidelines (76 μM) in drinking water. The formation of host-guest complexation between L and Lu³⁺ in 2:1 binding stoichiometry is studied by Job's method and the binding constant is estimated by band fit analysis (logK_f = 5.1). Further, the coordination behaviour between L and Lu³⁺ is well supported by FT-IR, ¹H NMR, ¹³C NMR, ³¹P NMR, ESI mass spectral data and the theoretical results.

A selective diaminomaleonitrile-based dual channel emissive probe for Al3+ and its application in living cell imaging

A selective diaminomaleonitrile-based fluorescent probe for Al³⁺(L) has been synthesized and characterized. The sensing behavior of L towards different metal ions was investigated by fluorescent spectra and competition experiment. The results showed that L exhibited a dual channel emission (λ_em 522 & 558 nm) with yellow fluorescence in the presence of Al³⁺ over other metal ions in EtOH solution. The probe L was bound to Al³⁺ in a 1:2 stoichiometric manner as supported by Job's plot analysis. The binding constant was 9.55 × 10⁸ M^-2 with the detection limit of 10.3 nM. The turn-on response was attributed to the inhibition of PET and CN isomerization after binding with Al³⁺ while the dual emissions were due to ESIPT and ICT processes. In addition, the application of L for imaging Al³⁺ in living Hela cells was achieved.

A novel crown ether-acylhydrazone turn-on fluorescent chemosensor for Al3+ ion

A novel fluorescent chemosensor based on crown ether-acylhydrazone (L) was synthesized and characterized. The sensor L exhibited high selectivity and sensitive recognition towards Al³⁺ through a significant "turn-on" fluorescence response at 444 nm in methanol solution. While, other competitive ions had no such significant effects on the fluorescence emission. The associated spectra behavior might be attributed to the formation of 2:1 L-Al³⁺ complex and the proposed binding mode of L-Al³⁺ was demonstrated by the fluorescence titration profiles, Job's plot, ESI-MS spectrometry, ¹H NMR titration and the IR analysis. Besides the high reproducibility of the optical signals, very low detection limit of 0.24 μM was calculated. The association constant (K_s) for L-Al³⁺ complex was about 5.56 × 10⁹ ± 8.19 × 10⁷ M^-2. The results of various experiments showed the sensor L followed a turn-on mechanism via of the suppression of CN isomerization and excited state intramolecular proton transfer (ESIPT) process and the activation of chelation-enhanced fluorescence (CHEF). Theoretical calculations using DFT/B3LYP method was also used to get insight into the sensing mechanism and electronic structure of L. The sensor L could be conceived as an effective and practical fluorescent chemosensor for determination of Al³⁺.

A highly selective and sensitive acylhydrazone-based turn-on optical sensor for Al3+

The fluorescence turn-on probing of Al³⁺ in ethanol was realized by the utilization of a type of conjugated acylhydrazone-based compound.