Naked-Eye Detection of C1–C4 Alcohols Based on Ground-State Intramolecular Proton Transfer

Experimental and theoretical investigation of ground state intramolecular proton transfer (GSIPT) in salicylideneaniline Schiff base derivatives in polar protic medium

Ground state intramolecular proton transfer process has been comprehensively investigated in three salicylideneaniline Schiff base derivatives (SB1, SB2, and SB3) using experimental and theoretical methods. It has been confirmed that all the three Schiff base molecules in the ground electronic state exist in the enol form in non-polar and polar aprotic solvents. Keto form is being populated by the polar protic solvent through ground state intramolecular proton transfer (GSIPT) process. Ground state equilibrium between the enol and keto tautomers for SB1 and SB3 is mainly governed by the proton donating ability of the solvent. Ground state equilibria between the enol and keto tautomers of SB2 which is a positional isomer of SB3 is governed by the polarity and proton donating ability of the solvents. Excited state intramolecular proton transfer (ESIPT) process is also evidenced in all the three Schiff base molecules. Theoretical calculations at the B3LYP/cc-pVDZ level in the gas phase and in different solvents using polarisable continuum model (PCM) have failed to establish the GSIPT process. Microsolvation of individual enol and keto conformers has been investigated considering upto three solvent molecules. The energetics of the individual conformers together with the corresponding transition state have been calculated. It has been confirmed that the keto conformer is more stable compared to the enol conformer in microsolvated cluster of three methanol molecules. Lowering of activation energy for the enol to keto tautomerisation in the presence of methanol also supports the experimental observation for GSIPT process. TDDFT/B3LYP/cc-pVDZ single point calculations for microsolvated clusters of enol and keto form of the Schiff base molecules exhibit an excellent agreement with the experimentally obtained absorption spectra. Difference in spectral nature of the Schiff base molecules has been explained using natural bond orbital (NBO) analysis. Quantum theory of atoms in molecules (QTAIM) has also been utilised to understand the GSIPT process in detail.

A naked-eye colorimetric sensor for methanol and ‘turn-on’ fluorescence detection of Al3+

A multifunctional Schiff base compound, NRSB, having a rhodanine scaffold was fabricated by a simple and cost-effective protocol.

Mitochondria-targeted ratiometric fluorescent detection of hydrazine with a fast response time

A fluorescent hydrazine-probe was synthesized, which exhibited high sensitivity, excellent selectivity and anti-interference ability.

Intramolecular versus intermolecular hydrogen bonds in a novel conjugated dimethylamino-benzylidene-amino-2-naphthoic acid Schiff base

A new compound based on the D-π-A concept, where D = dimethylamino-phenyl and A = naphthoic acid, separated by an imine motif, was designed, synthesized and characterized. The spectral, energetics, and structural characteristics of the compound were studied thoroughly theoretically by density functional theory (DFT) in the gas and aqueous phases and experimentally (steady-state absorption) in aqueous media with various degrees of polarity and hydrogen bonding ability. This compound shows high sensitivity to the polarity, basicity and proton affinity of the environment. Based on DFT, TD-DFT and NBO analysis, the compound exists in the ground-state with both intermolecular and intramolecular hydrogen bond conformations in association with the -COOH, with latter isomer calculated to be more stable. Furthermore, structural changes via intermolecular solute-solvent interactions, dictate electronic modifications and spectral changes. Graphical abstract Acidic and basic sites in DMAMN involved in protonation/deprotonation.

Ratiometric Fluorescent Probe for Lysosomal pH Measurement and Imaging in Living Cells Using Single-Wavelength Excitation

A novel lysosome-targeting ratiometric fluorescent probe (CQ-Lyso) based on the chromenoquinoline chromorphore has been developed for the selective and sensitive detection of intracellular pH in living cells. In acidic media, the protonation of the quinoline ring of CQ-Lyso induces an enhanced intramolecular charge transfer (ICT) process, which results in large red-shifts in both the absorption (104 nm) and emission (53 nm) spectra which forms the basis of a new ratiometric fluorescence pH sensor. This probe efficiently stains lysosomes with high Pearson's colocalization coefficients using LysoTrackerDeep Red (0.97) and LysoTrackerBlue DND-22 (0.95) as references. Importantly, we show that CQ-Lyso quantitatively measures and images lysosomal pH values in a ratiometric manner using single-wavelength excitation.

High-throughput and ultratrace naked-eye colorimetric detection of Au3+ based on the gold amalgam-stimulated peroxidase mimetic activity in aqueous solutions

Herein, we present a catalysis-based, label-free, and efficient strategy for a rapid, high-throughput, highly selective and ultrasensitive naked-eye colorimetric assay of Au³⁺ in aqueous solutions, based on the gold amalgam-stimulated peroxidase mimetic activity.

A new near-infrared ratiometric fluorescent probe for hydrazine

Under mild conditions, a novel near-infrared ratiometric and on–off fluorescent probe was synthesized, which can detect hydrazine with high selectivity and anti-interference over other amines, biological species, anions and metal ions.

Ratiometric luminescence detection of hydrazine with a carbon dots–hemicyanine nanohybrid system

Under mild conditions, a novel ratiometric fluorescent probe containing CDs and a hemicyanine derivative was fabricated for reliable, selective, and sensitive sensing of hydrazine.

Nanomolar colorimetric quantitative detection of Fe³⁺ and PPi with high selectivity

A novel rhodamine and 8-hydroxyquinoline-based derivative was synthesized, which is shown to act as a colorimetric chemosensor for Fe(3+) in aqueous solution with high selectivity over various environmentally and biologically relevant metal ions and anions with a distinct color change from colorless to pink in very fast response time (<1 min). Fe(3+) can be detected quantitatively in the concentration range from 6.7 to 16 μM and the detection limit (LOD) on UV-vis response of the sensor can be as low as 15 nM. The 'in situ' prepared Fe(3+) complex (1⋅Fe) showed high selectivity toward PPi against many common anions, and sensitivity (the LOD can be as low as 71 nM). In addition, both the chemosensor and the 'in situ' prepared Fe(3+) complex are reusable for the detection of Fe(3+) and PPi respectively.

A radical approach for fluorescent turn ‘on’ detection, differentiation and bioimaging of methanol

A Schiff base (RC) is presented herein as a smart fluorescent material for the selective detection and bioimaging of methanol. The key step behind same involves methanol induced opening of the cyclic control unit ofRCresulting in the formation of a highly fluorescent moiety,RO.

Naked-eye and fluorescence detection of basic pH and F−with a 1,8-naphthalimide-based multifunctional probe

A novel multifunctional colorimetric and fluorescent 1,8-naphthalimide-based probe toward basic pH and F⁻has been developed.

Naked-eye detection and thermochromic properties of Cu(ii)-3,3′-thiodipropionate complexes with benzimidazole

Two novel coordination complexes were synthesized and characterized. Solvent sensing and their thermochromic properties were studied. Complex 1 can be used as a naked-eye sensor for methanol. Complex 2 may be used as a DMF sensor. The thermochromic behaviors of complexes 1 and 2 were investigated.

Naked-eye-based selective detection of pyrophosphate with a Zn2+ complex in aqueous solution and electrospun nanofibers

Based on keto–enol transformation process, a zinc complex as a naked-eye-based chemosensor for pyrophosphate in aqueous solution and electrospun nanofibers has been developed.