Bis[1,1'-N,N'-(2-picolyl)aminomethyl]ferrocene as a redox sensor for transition metal ions

The compound bis[1,1'-N,N'-(2-picolyl)aminomethyl]ferrocene, L(1), was synthesized. The protonation constants of this ligand and the stability constants of its complexes with Ni(2+), Cu(2+), Zn(2+), Cd(2+) and Pb(2+) were determined in aqueous solution by potentiometric methods at 25 degrees C and at ionic strength 0.10 mol dm(-3) in KNO(3). The compound L(1) forms only 1:1 (M:L) complexes with Pb(2+) and Cd(2+) while with Ni(2+) and Cu(2+) species of 2 [ratio] 1 ratio were also found. The complexing behaviour of L(1) is regulated by the constraint imposed by the ferrocene in its backbone, leading to lower values of stability constants for complexes of the divalent first row transition metals when compared with related ligands. However, the differences in stability are smaller for the larger metal ions. The structure of the copper complex with L(1) was determined by single-crystal X-ray diffraction and shows that a species of 2:2 ratio is formed. The two copper centres display distorted octahedral geometries and are linked through the two L(1) bridges at a long distance of 8.781(10) Angstrom. The electrochemical behaviour of L(1) was studied in the presence of Ni(2+), Cu(2+), Zn(2+), Cd(2+) and Pb(2+), showing that upon complexation the ferrocene-ferrocenium half-wave potential shifts anodically in relation to that of the free ligand. The maximum electrochemical shift ([capital Delta]E(1/2)) of 268 mV was found in the presence of Pb(2+), followed by Cu(2+)(218 mV), Ni(2+)(152 mV), Zn(2+)(111 mV) and Cd(2+)(110 mV). Moreover, L(1) is able to electrochemically and selectively sense Cu(2+) in the presence of a large excess of the other transition metal cations studied.     

Synthesis, electrochemical, and optical properties of linear homo- and heterometallocene triads

The synthesis, electrochemical, and optical properties of homo- (5, 8, 9, and 12) and heterometallic (6, 7, 10, and 11) ferrocene-ruthenocene triads, are presented. Triferrocenyl derivatives 5 and 9 form the mixed-valence species 5*+ and 92+ by partial oxidation, which show intramolecular electro-transfer phenomena. Interestingly, spectroelectrochemical studies of compound 11, bearing two peripheral ferrocene units and one central ruthenocene moiety, revealed the presence of low-energy bands in the near-infrared (NIR) region, which indicate a rather unusual intramolecular charge-transfer between the ferrocene and ruthenocene units. The value of the electronic coupling parameter V(ab) = 150 cm(-1) calculated by deconvolution of the observed Fe(II)-Fe(III) IVCT transition in the mixed-valence compound 11*+, (d(Fe(II)-Fe(III)) = 18.617 A), indicates the ability of the ruthenocene system to promote a long distance intervalence electron-transfer. Moreover, the reported triads show selective cation sensing properties. Triads 5, 9, and 11 behave as dual redox and optical chemosensors for Zn(2+), Hg(2+), and Pb(2+). Their oxidation redox peaks are anodically shifted (up to 130 mV), and their low-energy (LE) bands of the absorption spectra are red-shifted (up to 115 nm) upon complexation with these metal cations. These changes in the absorption spectra are accompanied by dramatic color changes which allow the potential for "naked eye" detection.     

Aldimines generated from aza-Wittig reaction between bis(iminophosphoranes) derived from 1,1'-diazidoferrocene and aromatic or heteroaromatic aldehydes: electrochemical and optical behaviour towards metal cations

Aldimine 4 bearing a 2-quinolyl group was prepared by aza-Wittig reaction between the triphenyliminophosphorane derived from the 1,1'-diazidoferrocene and 2-formylquinoline. However, aldimine 5, bearing a pyrene ring, was prepared using the most reactive tributyliminophosphorane derivative and the corresponding 1-formylpyrene. On the other hand, formation of aldimine 8 involves a tandem process, Staudinger reaction/intramolecular aza-Wittig reaction, by using directly 1,1'-diazidoferrocene and 2-(diphenylphosphonyl)benzaldehyde. Aldimine 4 behaves as chemosensor molecule for Ni(2+), Zn(2+), Cd(2+), Hg(2+) and Pb(2+) cations through two different channels: electrochemical (ΔE(1/2) = 222-361 mV) and chromogenic (Δλ = 122-153 nm), which can be used for the "naked eye" detection of these metal cations. Aldimine 5 behaves as a highly selective redox (in CH(3)CN) and fluorescent (in CH(3)Cl-DMF) probe for Hg(2+) metal cations even in the presence of a large excess of the other metal cations tested. Aldimine 8 displays electrochemical affinity (ΔE(1/2) = 60-288 mV) to Li(+), Ca(2+), Mg(2+), Zn(2+) and Pb(2+) metal cations, with the phosphorus oxide functionality as a binding site. From the (1)H NMR titration data as well as DFT calculations, different tentative binding modes have been established, for these structurally related ferrocenyl derivatives.     

Metal complexes with a new N(4)O(3) amine pendant-armed macrocyclic ligand: synthesis, characterization, crystal structures, and fluorescence studies

The synthesis of a new oxaaza macrocyclic ligand, L, derived from O(1),O(7)-bis(2-formylphenyl)-1,4,7-trioxaheptane and tren containing an amine terminal pendant arm, and its metal complexation with alkaline earth (M = Ca(2+), Sr(2+), Ba(2+)), transition (M = Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+)), post-transition (M = Pb(2+)), and Y(3+) and lanthanide (M = La(3+), Er(3+)) metal ions are reported. Crystal structures of [H(2)L](ClO(4))(2).3H(2)O, [PbL](ClO(4))(2), and [ZnLCl](ClO(4)).H(2)O are also reported. In the [PbL] complex, the metal ion is located inside the macrocyclic cavity coordinated by all N(4)O(3) donor atoms while, in the [ZnLCl] complex, the metal ion is encapsulated only by the nitrogen atoms present in the ligand. pi-pi interactions in the [H(2)L](ClO(4))(2).3H(2)O and [PbL](ClO(4))(2) structures are observed. Protonation and Zn(2+), Cd(2+), and Cu(2+) complexation were studied by means of potentiometric, UV-vis, and fluorescent emission measurements. The 10-fold fluorescence emission increase observed in the pH range 7-9 in the presence of Zn(2+) leads to L as a good sensor for this biological metal in water solution.     

Functionalized BODIPY with various sensory units - a versatile colorimetric and luminescent probe for pH and ions

A series of BODIPY (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) derivatives containing ion- and pH-sensory units have been successfully designed and synthesized. One of the compounds was structurally characterized by X-ray crystallography. Owing to the presence of an ICT absorption band, one of the compounds was found to show pronounced solvatochromic behavior in different organic solvents. Their emission energies in various solvents show a linear dependence on the Lippert solvent parameter. The cation-binding properties of the complexes with different metal ions (alkali metal, alkaline earth metal and transition metal ions) have been studied using UV-vis and emission spectroscopies. A 1?:?1 complexation to metal ions (Li(+), Na(+), Mg(2+), Ba(2+), Zn(2+), Cd(2+)) was found for the compound with one azacrown moiety in acetonitrile while another one with two azacrown moieties was shown to form 1?:?2 complexes with Zn(2+) and Mg(2+) cations. Their stability constants have been determined by both UV-vis and emission spectrophotometric methods. By introducing triarylborane moieties into the meso position and the 2-position of the BODIPY skeleton, different electronic absorption spectral changes together with an emission diminution were observed in response to fluoride ions. Ditopic binding study of 5, which was functionalized with both azacrown and triarylborane moieties, showed emission enhancement in the presence of Mg(2+) and F(-). These findings suggest that these BODIPY derivatives are capable of serving as versatile colorimetric and luminescence probes for pH, cations and F(-).     

Interactions of metal ions with monoaza crown ethers A15C5 and A18C6 carrying dansyl fluorophore as pendant in acetonitrile solution

The influence of metal cations Li(+), Na(+), K(+), Cs(+), Mg(2+), Ca(2+), Sr(2+), Ba(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Pb(2+) and Al(3+) on the spectroscopic properties of the dansyl (1-dimethylaminonaphthalene-5-sulfonyl) group covalently linked to monoaza crown ethers 1-aza-15-crown-5 (1,4,7,10,-tetraoxa-13-azacyclopentadecane) (A15C5) and 1-aza-crown-6 (1,4,7,10,13-pentaoxa-16-azacyclooctadecane) (A18C6) was investigated by means of absorption and emission spectrophotometry. Interaction of the alkali metal ions with both fluoroionophores is weak, while alkaline earth metal ions interact strongly causing 50 and 85% quenching of dansyl fluorescence of N-(5-dimethylamine-1-naphthalenesulfonylo)-1,4,7,10,-tetraoxa-13-azacyclopentadecane (A15C5-Dns) and N-(5-dimethylamine-1-naphthalenesulfonylo)-1,4,7,10,13-pentaoxa-16-azacyclooctadecane (A18C6-Dns), respectively. The Cu(2+), Pb(2+) and Al(3+) cations interact very strongly with dansyl chromophore, causing a major change in absorption spectrum of the chromophore and forming non-fluorescent complexes. The Co(2+), Ni(2+), Zn(2+), Mg(2+) cations interact moderately with both fluoroionophores causing quenching of dansyl fluorescence by several percent only.     

Complexes of bivalent metal cations in electrospray mass spectra of common organic compounds

In the standard electrospray ionization mass spectra of many common, low molecular mass organic compounds dissolved in methanol, peaks corresponding to ions with formula [3M + Met](2+) (M = organic molecule, Met = bivalent metal cation) are observed, sometimes with significant abundances. The most common are ions containing Mg(2+), Ca(2+) and Fe(2+). Their presence can be easily rationalized on the basis of typical organic reaction work-up procedures. The formation of [3M + Met](2+) ions has been studied using N-FMOC-proline methyl ester as a model organic ligand and Mg(2+), Ca(2+), Sr(2+), Ba(2+), Fe(2+), Ni(2+), Mn(2+), Co(2+) and Zn(2+) chlorides or acetates as the sources of bivalent cation. It was found that all ions studied form [3M + Met](2+) complexes with N-FMOC-proline methyl ester, some of them at very low concentrations. Transition metal cations generally show higher complexation activity in comparison with alkaline earth metal cations. They are also more specific in the formation of [3M + Met](2+) complexes. In the case of alkaline earth metal cations [2M + Met](2+) and [4M + Met](2+) complex ions are also observed. It has been found that [3M + Met](2+) complex ions undergo specific fragmentation at relatively low energy, yielding fluorenylmethyl cation as a major product. [M + Na](+) ions are much more stable and their fragmentation is not as specific.     

Ferrocene-based small molecules for dual-channel sensing of heavy- and transition-metal cations

The synthesis, electrochemical, optical, and cation-sensing properties of ferrocene-pentakis(phenylthio)benzene dyads, linked through a putative cation-binding 2-azadiene bridge, are presented. Dyad 5 behaves as a highly selective dual-redox and chromogenic chemosensor molecule for Pb(2+) cations; the oxidation redox peak is anodically shifted (DeltaE(1/2) = 125 mV), and the low energy band of the absorption spectrum is red-shifted (Delta lambda = 119 nm) upon complexation with this metal cation. Linear sweep voltammetry and spectroelectrochemical studies revealed that Cu(2+) and Hg(2+) metal cations induced oxidation of the ferrocene unit. The isomeric dyad 7, in which the nitrogen atom and the ferrocene unit are in closer proximity, has shown its ability for sensing both Pb(2+) and Hg(2+) ions; the oxidation redox peak is anodically higher shifted (DeltaE(1/2) = 340 mV), and the low energy band of the absorption spectrum is lower red-shifted (Delta lambda = 61 nm) that those found for dyad 5. The changes in the absorption spectra are accompanied by dramatic color changes which allow the potential for "naked eye" detection. A further exciting property of dyad 7 is that it behaves as an electrochemically induced switchable chemosensor for Pb(2+) and Hg(2+) because of the low metal-ion affinity of the oxidized 7(*+) species for these metal cations. The experimental data and conclusions about the ion-sensing properties are supported by DFT calculations.     

Lead-selective poly(vinyl chloride) membrane electrodes based on acyclic dibenzopolyether diamides

Lipophilic acyclic dibenzopolyether diamides, 12 kinds, have been designed to prepare solvent polymeric membrane ion-selective electrodes (ISEs) for Pb(2+). The ionophores include 1,5-bis[2-(N,N-dialkylcarbamoylmethoxy)phenoxy]-3-oxapentanes1-4, 1,5-bis[2-(N,N-dialkylcarbamoylpentadecyloxy)phenoxy]-3-oxapentanes 5-8, and 1,2-bis[2-(2'-N,N-dialkylcarbamoylpentadecyloxy)phenoxy]ethanes 9-12. Linear response concentration range of the ISE based on 9 is 3 x 10(-2) - 1 x 10(-6) M of Pb(2+) (average slope = 28.5 mV decade(-1)). Potentiometric selectivities of the ISEs based on 1-12 for Pb(2+) over other heavy metal cations, alkali metal cations, and alkaline earth metal cations have been assessed. These ISEs exhibit remarkably high selectivities for Pb(2+) relative to heavy metal cations, such as Cu(2+), Fe(2+), and Ni(2+), the selectivity coefficients (K(Pot)(Pb,Cu)) being 5 x 10(-5) - 6 x 10(-5) for 1-4 and ca. 6 x 10(-4) for 9. For the Pb(2+) selectivities over alkali metal cations, such as Na(+) and K(+), 9 which has an ethylene glycol spacer and a N,N-diethyl group is superior to other dibenzopolyether diamide ionophores 1-8 and 10-12.     

Multichannel recognition of hydrogen sulphate anion by a Zn(II)–triazole–pyridine complex bearing a ferrocenyl pendant

Receptors ferrocene–triazole–pyridine triads assembled with Zn(II) or Cd(II) metal cations behave as chemosensor molecules for HSO₄ ^?  anions through electrochemical and optical channels: the redox peak of the ferrocene/ferrocenium redox couple is shifted cathodically by 72–53 mV, and a new absorption band appeared in the UV–vis spectrum upon complexation with the HSO₄ ^?  anion. Association constants, detection limits and stoichiometries of the recognition processes have been determined, whereas ¹H NMR experiments and density functional theory calculations are used to suggest the plausible binding mode taking place in the new supramolecular assembly formed.     

Incorporation of triazole into a quinoline-rhodamine conjugate imparts iron(iii) selective complexation permitting detection at nanomolar levels

Two new rhodamine based probes 1 and 2 for the detection of Fe(3+) were synthesized and their selectivity towards Fe(3+) ions in the presence of other competitive metal ions tested. The probe 1 formed a coloured complex with Fe(3+) as well as Cu(2+) ions and revealed the lack of adequate number of coordination sites for selective complexation with Fe(3+). Incorporation of a triazole unit to the chelating moiety of 1 resulted in the probe 2, that displayed Fe(3+) selective complex formation even in the presence of other competitive metal ions like Li(+), Na(+), K(+), Cu(2+), Mg(2+), Ca(2+), Sr(2+), Cr(3+), Mn(2+), Fe(2+), Co(2+), Ni(2+), Zn(2+), Cd(2+), Hg(2+) and Pb(2+). The observed limit of detection of Fe(3+) ions (5 × 10(-8) M) confirmed the very high sensitivity of 2. The excellent stability of 2 in physiological pH conditions, non-interference of amino acids, blood serum and bovine serum albumin (BSA) in the detection process, and the remarkable selectivity for Fe(3+) ions permitted the use of 2 in the imaging of live fibroblast cells treated with Fe(3+) ions.     

Bi-1,10-phenanthrolines and their mononuclear Ru(II) complexes

A series of four biphen (phen = 1,10-phenanthroline) ligands, 2,2'-biphen (1), 3,3'-biphen (2), 2,2'-dimethylene-3,3'-biphen (3), and 2,3'-dimethylene-3,2'-biphen (4), is prepared by coupling and Friedl?nder methodology. The corresponding mononuclear Ru(II) complexes, [Ru(1-4)(Mebpy)(2)](2+) where Mebpy = 4,4'-dimethyl-2,2'-bipyridine, are prepared. These complexes show long wavelength electronic absorptions at 441-452 nm and emissions at 622-641 nm. Metal-based oxidations occur in the range 1.18-1.21 V, and ligand-based reductions, at -1.20 to -1.30 V. The addition of Zn(2+), Cd(2+), or Hg(2+) ions results in a strong enhancement and red shift of the luminescence of complex Ru-3. Alkali and alkaline earth metal ions barely affect the luminescence of Ru-3 while transition metal ions such as Co(2+), Cu(2+), Ni(2+), and Mn(2+) lead to efficient quenching of the Ru-3 luminescence. The luminescence of Ru-2 and Ru-4 is quenched in the presence of Zn(2+) because of a conformationally induced reduction in electronic communication between the two phen halves of the ligand. The addition of Zn(2+) has only a slight effect on the luminescence of Ru-1 because of steric hindrance toward complexation.     

A novel fluorescent sensor for metal cations and protons based of bis-1,8-naphthalimide

A newly synthesized bis-1,8-naphthalimide aimed to increase its fluorescence intensity in the presence of protons or metal cations has been investigated. Its spectral photophysical characteristics in acetonitrile and chloroform solutions are described. The influence of metal cations (Zn(2+), Ni(2+), Ce(3+), Co(2+), Cu(2+) and Ag(+)) and protons on the fluorescence intensity has been investigate with regard to obtain fluorescence sensors for this ions in the environment.     

A new Schiff base system bearing two naphthalene groups as fluorescent chemodosimeter for Zn2+ ion and its logic gate behavior

1-((E)-(2-((2-nitrobenzyl)(2-((E)-(2-hydroxynaphthalen-1-yl)methyleneamino)ethyl)amino)ethylimino)methyl)naphthalen-2-ol (H(2)L), The new compound featuring two naphthalene units was synthesized and characterized. We find that H(2)L has high selectivity and sensitivity to detect Zn(2+) ion over other metal ions such as Na(+), Ag(+), Cd(2+), Co(2+), Cr(3+), Cu(2+), Hg(2+), Mn(2+), Ni(2+), Fe(3+), and the sensitivity is about 10(-7)M. The fluorescent changes of H(2)L upon the addition of cations Zn(2+) and triethylamine is utilized as an AND logic gate at the molecular level, using Zn(2+) and triethylamine as chemical inputs and the fluorescence intensity signal as output.     

Salt effects on the conformational behavior of 5-carboxy- and 5-hydroxy-1,3-dioxane

The varied and essential involvement of metal ions and inorganic salts in biological and chemical processes motivated the present study where 5-carboxy- and 5-hydroxy-1,3-dioxanes are used as model frameworks for the evaluation of the conformational behavior of oxygen-containing receptors in the presence of Li(+), Na(+), K(+), Ag(+), Mg(2+), Ca(2+), Ba(2+), and Zn(2+). Thus, the position of equilibria, established by means of BF(3), between diastereomeric cis- and trans-5-substituted-2-phenyl-1,3-dioxanes, in solvent THF and in the presence of 0, 1, and 5 equiv of salt, has been determined. The observed Delta G(o) degrees values for the conformational equilibria of 5-carboxy-1,3-dioxane show that Ag(+), Li(+), and Ca(2+) complexation leads to increased stability of the axial isomer. In the case of the 5-hydroxy-1,3-dioxane, Mg(2+), Ag(+), and Zn(2+) are the metal ions that stabilize the axial conformer of the heterocycle upon association. Interpretation of the experimental observations was based on DFT molecular modeling studies at the Becke3LYP/6-31G* and Becke3LYP/6-31+G** levels of theory. Although gas-phase calculations give Delta E values that are too large when modeling equilibria involving ionic species in polar solution, the computational results confirm the structural and energetic consequences of metal cation coordination to the oxygen atom in carbonyls or ethers. The results derived from the present study contribute to our understanding of the chemical processes involved in molecular recognition and physiological events.     

Spectrophotometric study of cobalt, nickel, copper, zinc, cadmium and lead complexes with murexide in dimethylsulphoxide solution

The complexation reactions between murexide and Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+) and Pb(2+) ions have been studied spectrophotometrically in dimethylsulphoxide solution at 25 degrees . The stoichiometry of the complexes was found to be 1:1. The stability constants of the complexes were determined, and found to follow the Irving-Williams rule for the cations of the first transition series. In dimethylsulphoxide solution, the complexes are much more stable than those in aqueous solution.     

Colorimetric test kit for Cu2+ detection

A coumarin-based colorimetric chemosensor 1 was designed and synthesized. It exhibits good sensitivity and selectivity for the copper cation over other cations such as Zn(2+), Cd(2+), Pb(2+), Co(2+), Fe(2+), Ni(2+), Ag(+), and alkali and alkaline earth metal cations both in aqueous solution and on paper-made test kits. The change in color is very easily observed by the naked eye in the presence of Cu(2+) cation, whereas other metal cations do not induce such a change. The quantitative detection of Cu(2+) was preliminarily examined.     

The significance of the alkene size and the nature of the metal ion in metal-alkene complexes: a theoretical study

Cation interactions with π-systems are a problem of outstanding contemporary interest and the nature of these interactions seems to be quite different for transition and main group metal ions. In this paper, we have systematically analyzed the contrast in the bonding of Cu(+) and main group metal ions. The molecular structures and energetics of the complexes formed by various alkenes (A = C(n)H(2n), n = 2-6; C(n)H(2n- 2), n = 3-8 and C(n)H(2n + 2), n = 5-10) and metal ions (M = Li(+), Na(+), K(+), Ca(2+), Mg(2+), Cu(+) and Zn(2+)) are investigated by employing ab initio post Hartree-Fock (MP2/6-311++G**) calculations and are reported in the current study. The study, which also aims to evaluate the effect of the size of the alkyl portion attached to the π-system on the complexation energy, indicates a linear relationship between the two. The decreasing order of complexation energy with various metal ion-alkene complexes follows the order Zn(2+)-A > Mg(2+)-A > Ca(2+)-A > Cu(+)-A > Li(+)-A > Na(+)-A > K(+)-A. The increased charge transfer and the electron density at (3,-1) intermolecular bond critical point corroborates well with the size of the π-system and the complexation energy. The observed deviation from the linear dependency of the Cu(+)-A complexes is attributed to the dπ→π* back bonding interaction. An energy decomposition analysis via the reduced variational space (RVS) procedure was also carried out to analyze which component among polarization, charge transfer, coulomb and exchange repulsion contributes to the increase in the complexation energy. The RVS results suggest that the polarization component significantly contributes to the increase in the complexation energy when the alkene size increases.     

Determination of nickel by anodic adsorptive stripping voltammetry with a cation exchanger-modified carbon paste electrode

The behavior of a modified carbon paste electrode (CPE) for nickel determination by anodic adsorptive stripping voltammetry (AAdsSV) was studied. The electrode was built incorporating the Dowex 50W x 12 (H(+) form) ion exchanger to a Nujol-graphite base paste. Ni(2+) was preconcentrated on the electrode surface in open circuit conditions, with the reduction (-1300 mV)/reoxidation step carried out in HCl solution (pH 3). During deposition time (5 min), the hydrogen evolution did not present obstacle in the quantification of nickel. For 12 min of accumulation and 5 min of deposition, nickel can be quantified up to 600 mug l(-1). The detection limit was 0.005 mug l(-1) at a linear potential scan rate of 200 mV s(-1). Interferences from Hg(2+) and Ag(2+) up to a concentration of 1 and 0.6 mg l(-1), respectively, were eliminated with the aid of the anion exchanger Dowex-2 (mesh 200-400) which was added to the sample in the preconcentration step. The tolerance for some metal ions such as Cu(2+), Cd(2+), Fe(3+), Zn(2+), Co(2+) and Pb(2+) was improved in the same way. The method was applied for the determination of nickel in samples of tap and mineral water. At the concentration level of 50 mug l(-1) of Ni (2+), the results were in good agreement with those obtained using Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). For a Ni(2+) concentration of 5 mug l(-1), the results obtained showed better accuracy than those obtained by ICP-AES.     

Selective colorimetric sensing of Cu2+ using triazolyl monoazo derivative

Although the high sensitivity, high selectivity and fast response make emission (fluorescence) based technique as one of the most promising tool for developing the chemosensors for metal ions, the past few years have witnessed a demand for the absorption based chemosensors for paramagnetic heavy metal ions, especially Cu(2+). Being paramagnetic, Cu(2+) leads to the low signal outputs ("turn-off") caused by decreased emission which may sometimes give false positive response, rendering the emission based technique less reliable for analytical purposes. Herein, we report synthesis and characterization of a hetarylazo derivative, characterized by a strong charge-transfer band which gets attenuated convincingly in the presence of Cu(2+) leading to distinct naked-eye color change (yellow to purple), and to a lesser extent in the presence of Cd(2+), Zn(2+), Co(2+), Pb(2+), Fe(2+), Ni(2+), Fe(3+) and Hg(2+) for which the naked eye sensitivity was comparatively (w.r.t. Cu(2+)) much less. No response was observed for the other metal ions including Li(+), Na(+), K(+), Mg(2+), Ca(2+), Ba(2+), Mn(2+), Ag(+), Zn(2+), Cd(2+), Pb(2+), and lanthanides Ce(3+), La(3+), Pr(3+), Eu(3+), Nd(3+), Lu(3+), Yb(3+), Tb(3+), Sm(3+), Gd(3+). The proposed sensing mechanism has been ascribed to the stabilization of LUMO after complexation with Cu(2+) and a 1:1 stoichiometry has been deduced.