Application of a distinctly bent, trinuclear, end-to-end azide bridged, mixed valence cobalt(iii/ii/iii) complex in the fabrication of photosensitive Schottky barrier diodes.

A mixed-valence trinuclear cobalt(iii)-cobalt(ii)-cobalt(iii) complex, [(µ-1,3-N3)Co3L(N3)3]·MeOH has been synthesized using a tetradentate N2O2 donor 'reduced Schiff base' ligand, H2L {1,3-bis(2-hydroxybenzylamino)2,2-dimethylpropane} and azide as anionic co-ligand. The complex has been characterised by elemental analysis, IR, UV-vis spectroscopy and single-crystal X-ray diffraction studies etc. The cobalt(iii)-cobalt(ii)-cobalt(iii) skeleton in the complex is non-linear and non-centrosymmetric. The redox behavior of the complex was studied by using Cyclic Voltammetry (CV). The complex is found to be a semiconductor material as confirmed by determining the band gap of this complex by experimental as well as theoretical studies. The band gap in the solid state has been determined experimentally. The conductivity of the synthesized complex based device improves considerably in illumination conditions from the non-illuminated conditions. The complex has also been used to fabricate Schottky barrier diodes.

Combined Experimental and Theoretical Studies on the Rubbing-Induced Fluorescence Behavior of a Luminophore in the Solid State.

It is intricate to break and make chemical bonds in solid states compared to their solution states, so it is imperative to ascertain green proficient approaches by regulating the solid-state structures and their related material properties. Here, the rubbing-induced photoluminescence behavior of a luminophore (RIL) of the benzimidazole family in the solid state has been accomplished. Interestingly, upon gentle rubbing or mere scratching, solid-state fluorescence from the nonemissive pristine RIL was observed due to the aggregation-induced emission (AIE) phenomenon in the solid state, for which the phenolic moiety is present in the molecule and is accountable. The structure-property relationship of RIL and the mechanism responsible for this solid-state fluorescence characteristics have been explained with the help of experimental (using the single-crystal structure, powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) images, etc.) and theoretical (by DFT and TDDFT) studies. The crystal arrangements with different stacking interactions and the SEM images after being rubbed revealed that the mechanical force- or pressure-induced slight deformation in the crystal arrangement notably facilitated the strong emission in the solid state. This rubbing-induced solid-state fluorescence in a new luminophore (RIL) through stacking of layers restricting the molecular motion has been developed here for the first time, and it can be explicitly employed in steganography techniques for data security. This present study will open up a new insight into the use of this RIL as a solid-state smart material for data security in coding devices in the future, and this developed approach may be helpful to ameliorate the design of new-generation smart materials by modifying the structure to attain other characteristics.

Two rhodamine-azo based fluorescent probes for recognition of trivalent metal ions: crystal structure elucidation and biological applications.

Two rhodamine and azo based chemosensors (HL1 = (3',6'-bis(ethylamino)-2-((2-hydroxy-3-methoxy-5-(phenyldiazenyl)benzylidene)amino)-2',7'-dimethylspiro[isoindoline-1,9'-xanthen]-3-one) and HL2 = (3',6'-bis(ethylamino)-2-(((2-hydroxy-3-methoxy-5-(p-tolyldiazenyl)benzylidene)amino)-2',7'-dimethylspiro[isoindoline-1,9'-xanthen]-3-one) have been synthesized for colorimetric and fluorometric detection of three trivalent metal ions, Al3+, Cr3+ and Fe3+. The chemosensors have been thoroughly characterized by different spectroscopic techniques and X-ray crystallography. They are non-fluorescent due to the presence of a spirolactam ring. The trivalent metal ions initiate an opening of the spirolactam ring when excited at 490 nm in Britton-Robinson buffer solution (H2O/MeOH 1 : 9 v/v; pH 7.4). The opening of the spirolactam ring increases conjugation within the probe, which is supported by an intense fluorescent pinkish-yellow colouration and an enhancement of the fluorescence intensity of the chemosensors by ∼400 times in the presence of Al3+ and Cr3+ ions and by ∼100 times in the presence of Fe3+ ions. Such a type of enormous fluorescence enhancement is rarely observed in other chemosensors for the detection of trivalent metal ions. A 2 : 1 binding stoichiometry of the probes with the respective ions has been confirmed by Job's plot analysis. Elucidation of the crystal structures of the Al3+ bound chemosensors (1 and 4) also justifies the 2 : 1 binding stoichiometry and the presence of an open spirolactam ring within the chemosensor framework. The limit of detection (LOD) values for both the chemosensors towards the respective metal ions are in the order of ∼10-9 M which supports their application in the biological field. The biocompatibility of the ligands has been studied with the help of the MTT assay. The results show that no significant toxicity was observed up to 100 µM of chemosensor concentration. The capability of our synthesized chemosensors to detect intracellular Al3+, Cr3+ and Fe3+ ions in the cervical cancer cell line HeLa was evaluated with the aid of fluorescence imaging.

Phenoxo-bridged dinuclear mixed valence cobalt(III/II) complexes with reduced Schiff base ligands: synthesis, characterization, band gap measurements and fabrication of Schottky barrier diodes.

Two homometallic class-I dinuclear mixed valence cobalt complexes, [(N3)CoIIIL1(µ-C6H4(NO2)CO2)CoII(N3)] (1) and [(N3)CoIIIL2(µ-C6H4(NO2)CO2)CoII(N3)] (2), have been synthesized using multisite N2O4 coordination ligands, H2L1 {where H2L1 = (2,2-dimethyl-1,3-propanediyl)bis(iminomethylene)bis(6-methoxyphenol) and H2L2 = (2,2-dimethyl-1,3-propanediyl)bis(iminomethylene)bis(6-ethoxyphenol)}. Each complex has been structurally characterized by single crystal X-ray diffraction and spectral analysis. Both the cobalt centers in these dinuclear complexes adopt a distorted-octahedral geometry, where the cobalt(iii) center resides at the inner N2O2 cavity and the cobalt(ii) center resides at the outer O4 cavity of the reduced Schiff base. Both of them show good electrical conductivity, which has been rationalized by band gap measurements. The band gap in the solid state has been determined by experimental and DFT calculations and it confirms that each of the two complexes behaves as a semiconductor. The space-charge-limited current (SCLC) theory is employed to evaluate the charge transport parameters such as effective carrier mobility and transit time for both complexes. The difference in the conductivity values of the complexes may be correlated with the strengths of extended supramolecular interactions in the complexes. Bader's quantum theory of atoms-in-molecules (QTAIM) is applied extensively to get quantitative and qualitative insights into the physical nature of weak non-covalent interactions. In addition, the non-covalent interaction reduced density gradient (NCI-RDG) methods well support the presence of such non-covalent intermolecular interactions.

An insight into the interaction between α-ketoamide- based inhibitor and coronavirus main protease: A detailed in silico study.

The search for therapeutic drugs that can neutralize the effects of COVID-2019 (SARS-CoV-2) infection is the main focus of current research. The coronavirus main protease (Mpro) is an attractive target for anti-coronavirus drug design. Further, α-ketoamide is proved to be very effective as a reversible covalent-inhibitor against cysteine proteases. Herein, we report on the non-covalent to the covalent adduct formation mechanism of α-ketoamide-based inhibitor with the enzyme active site amino acids by QM/SQM model (QM = quantum mechanical, SQM = semi-empirical QM). To uncover the mechanism, we focused on two approaches: a concerted and a stepwise fashion. The concerted pathway proceeds via deprotonation of the thiol of cysteine (here, Cys145 SγH) and simultaneous reversible nucleophilic attack of sulfur onto the α-ketoamide warhead. In this work, we propose three plausible concerted pathways. On the contrary, in a traditional two-stage pathway, the first step is proton transfer from Cys145 SγH to His41 Nδ forming an ion pair, and consecutively, in the second step, the thiolate ion attacks the α-keto group to form a thiohemiketal. In this reaction, we find that the stability of the tetrahedral intermediate oxyanion/hydroxyl group plays an important role. Moreover, as the α-keto group has two faces Si or Re for the nucleophilic attack, we considered both possibilities of attack leading to S- and R-thiohemiketal. We computed the structural, electronic, and energetic parameters of all stationary points including transition states via ONIOM and pure DFT method. Additionally, to characterize covalent, weak noncovalent interaction (NCI) and hydrogen-bonds, we applied NCI-reduced density gradient (NCI-RDG) methods along with Bader's Quantum Theory of Atoms-in-Molecules (QTAIM) and natural bonding orbital (NBO) analysis.

Field-induced single molecule magnet behavior of a dinuclear cobalt(II) complex: a combined experimental and theoretical study.

Two dinuclear cobalt(ii) complexes, [(dmso)CoIIL1(µ-(m-NO2)C6H4COO)CoII(NCS)] (1) and [(dmso)CoIIL2(µ-(m-NO2)C6H4COO)CoII(NCS)] (2) [dmso = dimethylsulfoxide, H2L1 = (2,2-dimethyl-1,3-propanediyl)bis(iminomethylene)bis(6-methoxyphenol) and H2L2 = (2,2-dimethyl-1,3-propanediyl)bis(iminomethylene)bis(6-ethoxyphenol)] have been synthesized and structurally characterized by single-crystal X-ray diffraction, magnetic-susceptibility measurements and various spectroscopic techniques. Each complex contains a cobalt(ii) center with a slightly distorted octahedral geometry and a second cobalt(ii) center with a distorted trigonal prismatic one. To obtain insight into the physical nature of weak non-covalent interactions, we have extensively used the Bader's quantum theory of atoms-in-molecules (QTAIM). In addition, the non-covalent interaction reduced density gradient (NCI-RDG) methods established the presence of such non-covalent intermolecular interactions. Variable temperature magnetic susceptibility measurements show that both cobalt centers in each complex are in the high spin state (S = 3/2) and both complexes show weak ferromagnetic couplings through the double phenoxido bridges (J = 3.36(3) cm-1 in 1 and 4.56(2) cm-1 in 2). The magnetic properties of both complexes can be fitted to a Co(ii) dimer model including similar orbital reduction factors (α = -0.94(1) for 1 and -0.85(1) for 2) although different zero field splitting parameters D(1) = 11.0(4) cm-1 and D(2) = 19.5(4) cm-1 in 1 and D(1) = 8.2(4) cm-1 and D(2) = -1.3(4) cm-1 in 2. AC magnetic measurements reveal that the CoII2 unit in complex 2 exhibits field-induced slow relaxation of the magnetization at low temperatures and high frequencies.

Effect of Main Versus Ancillary Ligand Substitution on the Photophysical Properties of a Series of Ir(III) Complexes: A Detailed Theoretical Investigation.

Herein, we report the effects of different electron-withdrawing groups (EWG) (-F) and electron-donating groups (EDG) (-OMe and -NH2) on main ligands (ppy) and ancillary (acac) of [Ir(ppy)2(acac)] [ppy = 2-phenylpyridine; acac = acetylacetonato] using seven complexes by DFT and TDDFT calculations. We find that irrespective of the substituents, absorption of ppy-substituted complexes is blue-shifted, while for the acac-substituted complexes, it is red-shifted. The calculations also show that the substitution of EWGs causes an overall drop in the frontier molecular orbital energy levels; however, we observed a reverse effect for EDGs. To calculate the radiative rate kr, we considered the spin-orbit coupling matrix element (SOCME) (⟨T1|HSOC|Sn⟩) between Sn (n = 1, 2, etc.) excited state and T1, transition dipole moment (µ(Sn)), and the energy difference between excited singlet states Sn and T1 state (ΔE(Sn - T1)). To compare the temperature-independent nonradiative process, we considered SOC between T1 and S0 (⟨T1|HSOC|S0⟩) and the energy gap between optimized T1 and S0 states. Furthermore, to formulate the temperature-dependent nonradiative rate, we computed the activation barrier (E1) for the metal-to-ligand state (3MLCT) to a metal-centered state (3MC) conversion. The emission peaks show that the changes of triplet state T1 from 3MLCT → 3MC via transition states (3TS) and 3MLCT → 1GS (GS = ground state) via the 3MC/1GS minimum energy crossing point are not much affected by the nature of substituents in the ancillary and the main ligand. The order of E1 for the investigated complexes indicates that electron-donating substituents -OMe at both ppy and acac ligands can cause a decrease in nonradiative rate constants. Natural transition orbitals of the complexes show that they are mainly localized on the main ligand ppy and the Ir atoms and hardly on the ancillary ligand acac.

Synthesis of Biocompatible Aliphatic Terpolymers via In Situ Fluorescent Monomers for Three-in-One Applications: Polymerization of Hydrophobic Monomers in Water.

Biocompatible, nonconventional, multifunctional, purely aliphatic, light-emitting terpolymers, i.e., acrylonitrile-co-3-(N-isopropylacrylamido)propanenitrile-co-N-isopropylacrylamide (AN-co-NIPAMPN-co-NIPA, 1) and acrylonitrile-co-3-(N-hydroxymethylacrylamido)propanenitrile-co-N-hydroxymethylacrylamide (AN-co-NHMAMPN-co-NHMA, 2), were designed and synthesized via N-H-functionalized C-C + N-C-coupled in situ protrusions/grafting of fluorophore monomers, i.e., NIPAMPN and NHMAMPN, by solution polymerization of two highly hydrophobic nonemissive monomers in water. These scalable and reusable 1 and 2 were suitable for high-performance three-in-one applications, such as Fe(III) sensors, imaging of Madin-Darby canine kidney (MDCK) and human lung cancer (A549) cells, and security inks. The structures of 1 and 2, N-C-coupled in situ attachments/grafting of third fluorophore monomers, grafting events, and aggregation-enhanced emissions (AEEs), were analyzed by 1H and 13C NMR spectroscopy, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, ultraviolet-visible (UV-vis) spectroscopy, thermogravimetric (TG) analysis, high-resolution transmission electron microscopy (HRTEM), dynamic light scattering (DLS), fluorescence imaging, and fluorescence lifetime. The geometries, electronic structures, and absorption/emission properties of 1 and 2 at optimized compositions were examined by density functional theory (DFT), time-dependent DFT (TDDFT), and natural transition orbital (NTO) analyses. The limits of detection were 3.20 × 10-7 and 1.37 × 10-7 M for 1 and 2, respectively. The excellent biocompatibility of 1 and 2 was confirmed by >95% retention of MDCK and A549 cell morphologies.

Light-Emitting Multifunctional Maleic Acid-co-2-(N-(hydroxymethyl)acrylamido)succinic Acid-co-N-(hydroxymethyl)acrylamide for Fe(III) Sensing, Removal, and Cell Imaging.

The intrinsically fluorescent highly hydrophilic multifunctional aliphatic terpolymer, maleic acid (MA)-co-2-(N-(hydroxymethyl)acrylamido)succinic acid (NHASA)-co-N-(hydroxymethyl)acrylamide (NHMA), that is, 1, was designed and synthesized via C-C/N-C-coupled in situ allocation of a fluorophore monomer, that is, NHASA, composed of amido and carboxylic acid functionalities in the polymerization of two nonemissive MA and NHMA. The scalable and reusable intrinsically fluorescent biocompatible 1 was suitable for sensing and high-performance adsorptive exclusion of Fe(III), along with the imaging of Madin-Darby canine kidney cells. The structure of 1, in situ fluorophore monomer, aggregation-induced enhanced emission, cell-imaging ability, and superadsorption mechanism were studied via microstructural analyses using 1H/13C NMR, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, atomic absorption spectroscopy, ultraviolet-visible spectroscopy, thermogravimetric analysis, dynamic light scattering, high-resolution transmission electron microscopy, solid-state fluorescence, fluorescence lifetime, and fluorescence imaging, along with measuring kinetics, isotherms, and thermodynamic parameters. The location, electronic structures, and geometries of the fluorophore and absorption and emission properties of 1 were investigated using density functional theory and natural transition orbital analyses. The limit of detection and the maximum adsorption capacity were 2.45 × 10-7 M and 542.81 mg g-1, respectively.

Fluorescent Terpolymers Using Two Non-Emissive Monomers for Cr(III) Sensors, Removal, and Bio-Imaging.

The nonconventional purely aliphatic intrinsically fluorescent multifunctional terpolymers, such as 2-acrylamido-2-methylpropane sulfonic acid-co-2-(3-acrylamidopropylamido)-2-methylpropane sulfonic acid-co-acrylamide (AMPS-co-APMPS-co-AM, 1), acrylic acid-co-3-acrylamidopropanoic acid-co-acrylamide (AA-co-APA-co-AM, 2), and methacrylic acid-co-3-acrylamido-2-methyl propanoic acid-co-acrylamide (MAA-co-AMPA-co-AM, 3), were synthesized via N-H functionalized multi-C-C/N-C coupled in situ attachments of fluorophore monomers, that is, APMPS, APA, and AMPA, in solution polymerization of two non-fluorescent monomers. These terpolymers were suitable for selective Cr(III) sensors, high-performance exclusions of Cr(III), and fluorescence imaging of human osteosarcoma cancer cells. The structures of 1, 2, and 3, in situ attachments of fluorescent amino acid monomers, locations of fluorophores, aggregation-induced enhanced emissions, and the superadsorption mechanism were understood via microstructural analyses. The geometries, electronic structures, and the low-lying singlet-singlet absorption and emission of 1, 2, and 3 were explored using density functional theory (DFT), time-dependent DFT, and natural transition orbital analyses. The ionic and variable interactions of 1, 2, and 3 with Cr(III) were envisaged via analyses of adsorbed microstructures, fitting of kinetics data to a pseudo-second-order model, and the measurements of activation energies. For 1/2/3, limit of detection values and adsorption capacities were 1.88 × 10-7/3.75 × 10-7/1.25 × 10-7 M and 1316.35/1431.40/1372.18 mg g-1, respectively, at pHi = 7.0, 303 K, and 1000 ppm. The better overall properties made 3 to be more suitable in sensing and cell imaging.

Fluorescent Guar Gum-g-Terpolymer via In Situ Acrylamido-Acid Fluorophore-Monomer in Cell Imaging, Pb(II) Sensor, and Security Ink.

The nonconventional purely aliphatic scalable and reusable fluorescent guar gum (GRGM)-grafted-acrylic acid-co-3-(N-isopropylacrylamido)propanoic acid (NIPAPA)-co-N-isopropylacrylamide (GRGM-grafted-1, i.e., 2), was synthesized via grafting of the optimum amount of GRGM and N-H functionalized in situ protrusion of acrylamido-acid fluorophore-monomer, i.e., NIPAPA, in multi C-C/N-C/O-C coupled solution polymerization of two non-emissive monomers in water. The intrinsically fluorescent noncytotoxic 2 envisaged the excellent potentials in sensing and removal of Pb(II), security ink, logic function, and imaging of both cancer and normal cells. The emission intensities of 2 elevated in concentrated solutions and solid state because of concentration-enhanced emission and aggregation-induced enhanced emission (AIEE) characteristics of 2. Additionally, the emission efficiency of 2 elevated considerably with increasing GRGM contents and temperatures. The structure of 2, in situ attached fluorophore-monomer, AIEE, cell-imaging ability, and the superadsorption mechanism were studied employing 1H/13C NMR, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy, atomic absorption spectroscopy, thermogravimetric analysis, differential scanning calorimetry, X-ray diffraction, dynamic light scattering, high-resolution transmission electron microscopy, fluorescence imaging, and fluorescence lifetime, along with measuring isotherms, kinetics, and thermodynamic parameters. The location, geometries, and electronic-structures of fluorophore, along with absorption and emission properties, of 2 were explored via density functional theory (DFT), time-dependent DFT, and natural transition orbital analyses. In solution, cyan light-emitting 2 envisaged an average 1.22 ns lifetime in CHCl3. The limit of detection and the maximum adsorption capacity were 2.94 × 10-7 M and 1100.25 mg g-1 at pH 7.0, 303 K, and 1000 ppm, respectively.

Multi-C-C/C-N-Coupled Light-Emitting Aliphatic Terpolymers: N-H-Functionalized Fluorophore Monomers and High-Performance Applications.

To circumvent costly fluorescent labeling, five nonconventional, multifunctional, intrinsically fluorescent aliphatic terpolymers (1-5) have been synthesized by C-C/C-N-coupled, solution polymerization of two non-emissive monomers with protrusions of fluorophore monomers generated in situ. These scalable terpolymers were suitable for sensing and high-performance exclusion of CuII , logic function, and bioimaging. The structures of the terpolymers, in situ attachment of fluorescent monomers, aggregation-induced enhanced emission, bioimaging ability, and super adsorption were investigated by 1 H and 13 C NMR, EPR, FTIR, X-ray photoelectron, UV/Vis, and atomic absorption spectroscopy, thermogravimetric analysis, high-resolution transmission electron microscopy, dynamic light scattering, solid-state fluorescence, fluorescence imaging, and fluorescence lifetime measurements, as well as by isotherm, kinetics, and thermodynamic studies. The geometries and electronic structures of the fluorophores and the absorption and emission properties of the terpolymers were examined by DFT, time-dependent DFT, and natural transition orbital analyses. For 1, 2, and 5, the limits of detection were determined to be 1.03×10-7 , 1.65×10-7 , and 1.77×10-7 m, respectively, and the maximum adsorption capacities are 1575.21, 1433.70, and 1472.21 mg g-1 , respectively.

Magnetic Properties of End-to-End Azide-Bridged Tetranuclear Mixed-Valence Cobalt(III)/Cobalt(II) Complexes with Reduced Schiff Base Blocking Ligands and DFT Study.

Two tetranuclear mixed-valence cobalt(III/II) complexes having the general formula [(µ1,3-N3){CoII(L n )(µ-O2CC6H4NO2)CoIII(N3)}2]PF6 (where H2L1 and H2L2 are two reduced Schiff base ligands) have been synthesized and characterized. The structures of both complexes show cobalt(II) and cobalt(III) centers with a distorted octahedral geometry with cobalt(III) and cobalt(II) centers located at the inner N2O2 and outer O4 cavities of the reduced Schiff base ligands, respectively. The oxidation states of both cobalt centers have been confirmed by bond valence sum (BVS) calculations. The magnetic properties show that both compounds behave as cobalt(II) dimers connected through an end-to-end azido bridging ligand and show moderate antiferromagnetic Co(II)-Co(II) couplings of -11.0 and -14.4 cm-1 for 1 and 2, respectively, as also corroborated by DFT calculations, J theo = -13.07 cm-1 for 1 and -12.49 cm-1 for 2. The calculated spin densities of both complexes at the cobalt(II) centers are -2.75 and +2.75, respectively, clearly supporting that they are the magnetic centers.

Fluorescent Terpolymers via In Situ Allocation of Aliphatic Fluorophore Monomers: Fe(III) Sensor, High-Performance Removals, and Bioimaging.

Herein, purely aliphatic intrinsically fluorescent terpolymers, i.e., 1 and 2, are synthesized through one-pot solution polymerization via N-H functionalized and multi C-C/C-N coupled in situ protrusion of fluorescent monomers using two nonemissive monomers. These scalable terpolymers are suitable for highly selective Fe(III) sensing, high-performance exclusion of Fe(III), logic function and the imaging of normal mammalian Madin-Darby canine kidney and human osteosarcoma cancer cell lines. The structures of terpolymers, in situ attachment of fluorescent monomers, clusteroluminescence, adsorption-mechanism, and cell-imaging abilities are understood via unadsorbed and/or adsorbed microstructural analyses using 1 H/13 C NMR, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, UV-vis spectroscopy, atomic absorption spectroscopy, thermogravimetric analysis, high-resolution transmission electron microscopy, dynamic light scattering, fluorescence imaging, and fluorescence lifetime. The geometries, electronic structures, location of fluorophores, and singlet-singlet absorption and emission of terpolymers are examined using density functional theory (DFT) and time-dependent DFT. For the precise identification of fluorophores, transition from occupied natural transition orbitals (NTOs) to unoccupied NTOs is computed. For 1/2, limit of detection (LOD) values and adsorption capacities are 6.0 × 10-7 /8.0 × 10-7 m and 147.82/120.56 mg g-1 at pHi = 7.0 and 303 K, respectively. The overall properties of 1 are more advantageous compared to 2 in sensing, cell imaging, and adsorptive exclusion of Fe(III).

A napthelene-pyrazol conjugate: Al(III) ion-selective blue shifting chemosensor applicable as biomarker in aqueous solution.

A newly synthesized and crystalographically characterized napthelene­pyrazol conjugate, 1-[(5-phenyl-1H-pyrazole-3-ylimino)-methyl]-naphthalen-2-ol (HL) behaves as an Al(III) ion-selective chemosensor through internal charge transfer (ICT)-chelation-enhanced fluorescence (CHEF) processes in 100 mM HEPES buffer (water­DMSO 5:1, v/v) at biological pH with almost no interference of other competitive ions. This mechanism is readily studied from electronic, fluorimetric and (1)H NMR titration. The probe (HL) behaved as a highly selective fluorescent sensor for Al(III) ions as low as 31.78 nM within a very short response time (15­20 s). The sensor (HL), which has no cytotoxicity, is also efficient in detecting the distribution of Al(III) ions in HeLa cells via image development under fluorescence microscope.