Thiazolidine based differential chromo-fluorescent

Journal of Luminescence 180 (2016) 292–300

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Journal of Luminescence journal homepage: www.elsevier.com/locate/jlumin

Thiazolidine based differential chromo-fluorescent sensor for Cu2 þ and CN ions: Elaboration as logic devices Richa Rani, Gulshan Kumar, Kamaldeep Paul, Vijay Luxami n School of Chemistry and Biochemistry, Thapar University, Patiala 147004, India

art ic l e i nf o

a b s t r a c t

Article history: Received 22 January 2016 Received in revised form 8 August 2016 Accepted 17 August 2016 Available online 26 August 2016

Thiazolidine based probe 1 has been synthesized for selective estimation of Cu2 þ ions amongst other metal ions viz., Zn2 þ , Co2 þ , Ca2 þ , K þ , Ni2 þ , Mn2 þ , Fe2 þ , Hg2 þ , Na þ , Pb2 þ , Ba2 þ , Fe3 þ , Al3 þ , Cr3 þ . The probe 1 has opened new absorption channels at 300 nm and 500 nm in the presence of Cu2 þ ions. The ratiometric response has been observed in the presence of Cu2 þ ions due to emission quenching at 425 nm and enhancement at 485 nm that resulted in “ON–OFF–ON” type sensing. The probe 1 has been used to estimate Cu2 þ ions between 50 nM and 15 mM, which is much lower than recommended by WHO in drinking water (30 mM). The probe 1 has also shown selective ratiometric absorption behavior towards CN ions in CH3CN: H2O: 1:1. The ratiometric behavior of the probe 1 in the presence of Cu2 þ and CN ions has mimicked as XOR logic function at λem 485 nm and YES logic gate at λabs 300 nm. The sensing mechanisms of the probe 1 toward Cu2 þ and CN ions have been theoretically supported by DFT and TD-DFT calculations. Probe 1 has been used for its practical aplicability to sense Cu2 þ and CN through dip coating method. & 2016 Elsevier B.V. All rights reserved.

Keywords: Thiazolidine Chemosensor Logic gates DFT-calculations

1. Introduction The fluorescent chemosensor is considered as a useful analytical tool, with the advantage of good selectivity, high sensitivity, quick response time and low response consistency. The development of fluorescent chemosensor for the detection of cations and anions, harmful to the environment or human health, is an area of emerging interest [1]. Presently, numbers of organic molecules have been designed and used as fluorescent chemosensors for different metal ions [2–4] and anions [5–7]. Some of metal ions or anions are responsible for the dysfunction in biological systems, creating challenge to detect such analytes [8]. Among the different metal ions, Cu2 þ is the third most abundant metal and plays an important role in various physiological processes, but excess of Cu2 þ ions responsible for the damage of central nervous system, affect kidneys, liver, lungs, blood composition and other parts of human body. So, detection of such toxic metal ion such as Cu2 þ ions selectivity becomes an important area of research [9]. On the other, cyanide anion, a toxic, hazardous pollutant, is widely spread in the environment due to its use in industries. Cyanide ions inhibit cellular respiration in mammals and also absorb through the lungs, gastrointestinal track, skin and responsible for vomiting, convulsions, loss of consciousness or n

Corresponding author. Fax: þ91 175 236 4498. E-mail address: [email protected] (V. Luxami).

http://dx.doi.org/10.1016/j.jlumin.2016.08.041 0022-2313/& 2016 Elsevier B.V. All rights reserved.

death. So, expedition towards designing of such chemosensor, which can sense cations and anion simultaneously are in major demand to the chemists [10]. Thiazolidine derivatives have attracted continuing attention in the last few years, because of having well-known scaffolds in medicinal chemistry [11,12]. The thiazolidine ring has been used as a novel class of anticancer agent with broad spectrum of cytotoxicity [13]. Thiazolidine and its analogues have also found a prominent place in drug development for the treatment of various diseases. They are known as inhibitors of bacterial enzyme, COX-I inhibitors, non nucleoside inhibitors of HIV, antihistaminic agents [14,15] and the treatment of type II diabetes [16,17]. In recent years, analogues of thiazolidine have attracted great attention as chemosensors [18,19]. Thiazolidine heterocycle provides a diverse range of molecular structure due to the presence of heteroatoms like N, S and O, that gives the opportunity to behave as good chemosensor [20–23]. According to the best of our knowledge, there is no report in the literature where thiazolidine moiety has been used as a sensor for cations and anions. In the present manuscript, we have synthesized thiazolidine based compound as a chromofluorescent sensors for Cu2 þ and CN ions. The probe 1 opened a dual absorption channels at 300 nm and 500 nm in the presence of Cu2 þ in acetonitrile solution. Probe 1 has also behaved as selective sensor for cyanide ions in the mixed aqueous system and opened a new absorption channel at 415 nm and emission channel at 560 nm. The binding properties of the probe 1 towards Cu2 þ and CN ions have been

R. Rani et al. / Journal of Luminescence 180 (2016) 292–300

O

CHO

S +

HN

OH

CH3COOH NH4OAc

O

O

hS

293

e

a

b c

d HN g f O HO

1 Scheme 1. Synthesis of Probe 1.

studied through 1H NMR titrations and further supported with theoretical studies. The optical outputs in the presence of Cu2 þ and CN ions have also been used for elaboration of molecular logic gates.

binding stoichiometry of the probe 1 with different ions for which binding constant being calculated and C is the concentration of ions. 2.2. Theoretical studies

2. Experimental section 2.1. General procedure All the solvents and reagents used for synthesis or analytical purpose were purchased from Sigma-Aldrich or spectrochemicals and were used as received. TLC analysis was performed on silica gel plates. 1H NMR and 13C NMR measurements were performed on a JEOL ECS 400 MHz and 100 MHz respectively, in CDCl3 and DMSO-d6 as solvents. Chemical shifts were recorded in ppm relative to the TMS as an internal reference and J values are given in Hz. Electrospray ionization mass spectra (ESI-MS) were recorded on Brucker MicroToff/QII. UV–vis spectra were recorded at 25 °C using Champion UV/Vis spectrometer. Fluorescence measurements were performed on a Varian Cary Eclipse fluorescence spectrometer. The stock solutions of metals and anions of concentration 1 10 1 molL 1 were prepared from their corresponding salts, viz., Al(ClO4)3 9H2O, Ba(ClO4)2, Ca(NO3)2 4H2O, Co(ClO4)2 6H2O, Fe(ClO4)2 xH2O, Hg(ClO4)2.xH2O, Ni(ClO4)2 6H2O, Fe(ClO4)3 H2O, Pb(ClO4)2 3H2O, Zn(ClO4)2 6H2O, Cu(ClO4)2 6H2O, (n-Bu)4NOAc, (n-Bu)4NBr, (n-Bu)4NCl, (n-Bu)4NClO4, (n-Bu)4NCN, (nBu)4NF xH2O, (n-Bu)4NH2PO4, (n-Bu)4NHSO4 and (n-Bu)4NI. A stock solution of the probe 1 was prepared in 10 3 M concentration in distilled CH3CN. Solution of the probe 1 was 20 mM for UV– vis and fluorescence studies and further diluted with CH3CN:H2O in a ratio of 1:1. In titrations, metal ions were added using a micropipette to a solution of probe 1. 1H NMR titrations were performed in deuterated solvents viz., CD3CN-d3 for fluoride ions and CD3CN-d3:D2O:1:1 for cyanide ions. For NMR titrations, the concentration of the probe 1 was 5 10 3 M in respective solvents. The detection limit was calculated based on the fluorescence titration. To determine the S/N ratio, the emission intensity of the probe 1 (20 mM) was measured 5 times and the standard deviation of blank measurements was determined. The detection limit was then calculated using the equation: Detection limit ¼ 3σ bi=m where σbi is the standard deviation of blank measurements; m is the slope of intensity versus sample concentration. The detection limit was measured to be 1 mM at S/N ¼ 3. Stability constants were calculated by Benesi–Hildebrand Eq. (1) [24]. 1=ðI I 0 Þ ¼ 1= K ðI max –I 0 ÞC n þ1=ðI max –I 0 Þ ð1Þ where I 0 is the absorbance or emission intensity of the probe 1 at absorbance or emission maximum, I is the observed intensity at a particular wavelength in the presence of a certain concentration of ions, I max is the intensity where complete titration is observed. K is the binding constant (M 1 ), n is the

In order to confirm the absorption properties of the probe 1 and its complexes with Cu2 þ and CN ions, theoretical calculations were performed using density functional theory (DFT) and time dependent-density functional theory (TD-DFT) using Gaussian 03 W package [25]. The ground state of probe 1 was optimized for minimum energy by using DFT and B3LYP/6-31G (d, p) levels of basis set and TD-DFT calculations were performed at the same basis set to examine the excited state. All the calculations were done in acetonitrile using the integral equation formalism variant (IEFPCM) method. Density functional theory (DFT) and time dependent-density function theory (TD-DFT) calculations were performed to probe 1 and its complexes with CN and Cu2 þ with Gaussian 03 program [25] by using various basis set B3LYP/631G (d, p). In case of Cu2 þ , calculations were performed by using basis set B3LYP/6-31G(d,p). The optimizations were confirmed by frequency calculations. The HOMO and LUMO were generated from the Gauss View 4.0 program. 2.3. Synthesis of probe 1 Thiazolidine-2,4-dione has been synthesized (Scheme 1) via modified reported method [26]. A mixture of thiazolidine-2,4dione (8.5 mmol), 2-hydroxy-benzaldehyde (8.5 mmol), sodium acetate (8.5 mmol) and glacial acetic acid (1 ml) were heated to the temperature of 140 °C for 6 h. After the completion of the reaction (TLC), the reaction mixture was poured into dilute HCl. The solid was separated out, filtered and dried to get the pure product. Yield 90%; M.pt.¼235–237 °C; IR (KBr, cm 1): 3412.1 (OH), 3131.4 (NH), 3013.3 (CH), 1721.4, 1668.3 (C ¼O), 1H NMR (DMSO-d6, 400 MHz, ppm): δ 12.50 (s, 1 H, OH), 10.51 (s, 1H, NH), 8.00 (s, 1H, CHe), 7.32–7.26 (m, 2H, ArHa,c), 6.95–6.90 (m, 2 H, ArHb, 13 C NMR (CDCl3 þDMSO-d6, 100 MHz): δ 168.4 (C ¼O), 167.7 d); (C ¼O), 157.5 (C ¼ C), 132.2 (C–O), 128.4, 127.6, 121.8, 120.2, 119.6, 116.2 (ArH). ESI-MS: m/z 222.1 (M þ þ H); Anal. Calcd. For C10H7NO3S: C, 54.29; H, 3.19; N, 6.33%, Found: C, 54.99; H, 3.34; N, 6.33% (Figs S1–S6).

3. Results and discussion 3.1. Photophysical behavior of probe 1 towards metal ions The probe 1 (20 mM, CH3CN) showed absorption maxima at 347 nm. With the addition of various metal ions like Zn2 þ , Co2 þ , Ca2 þ , K þ , Ni2 þ , Mn2 þ , Fe2 þ , Hg2 þ , Na þ , Pb2 þ , Ba2 þ , Fe3 þ , Al3 þ , Cr3 þ etc., no significant change was detected. But, in the presence of Cu2 þ ions, a new absorption band at 300 nm associated with discharge of yellow color was observed (Fig. S7). The incremental addition of 35 mM of Cu2 þ ions to probe 1 caused a decrease in

294


Fig. 1. Effect of addition of Cu2 þ ion (a) 0 35 mM; (b) 35–800 mM on absorption spectrum of probe 1 (20 mM, CH3CN).

Fig. 2. Effect of incremental addition of Cu2 þ ions on the emission spectrum of the probe 1 (20 mM, CH3CN); and inset showing a ratiometric plot of emission changes at 485 nm and 425 nm vs. concentration of Cu2 þ ions.

ions like Zn2 þ , Co2 þ , Ca2 þ , K þ , Ni2 þ , Mn2 þ , Fe2 þ , Hg2 þ , Na þ , Pb2 þ , Ba2 þ , Fe3 þ , Al3 þ , Cr3 þ etc., no significant change was observed except Cu2 þ ions (Fig. S8). The presence of Cu2 þ ions showed the formation of the new emission band at 485 nm. The incremental addition of Cu2 þ into probe 1, caused quenching of the emission band at 425 nm and formation of new red shifted emission band at 485 nm. As emission at 425 nm was switched “OFF” and emission at 485 nm (Fig. 2) was switched “ON” so, this switching “ON–OFF” phenomenon provided the opportunity for ratiometric estimation of Cu2 þ ions which is very rare in the literature [27,28] due to the paramagnetic effect of Cu2 þ ions. The emission bands at 425 nm and 485 nm linearly decreased and increased respectively, and were used to estimate 50 nM–15 mM of Cu2 þ ions (Fig. 2 inset). The binding constant was 6.37 105 M 1, calculated through Benesi–Hildebrand equation (Fig. S9). To check the practical applicability of the probe 1 as a Cu 2 þ selective sensor, we carried out various metal ion competition experiment. Probe 1 was mixed with 1 equiv. Cu 2 þ ions in the presence of 100 equiv. of other metal ions. As shown in Fig. 3, other metal ions had no interference with Cu 2 þ ions estimation. Hence, these results suggested that the probe 1 could be an effective and selective sensor for Cu 2 þ ions. Job's plot analysis of the probe 1 showed formation of 2:1 (probe 1: Cu 2 þ ) complex with Cu 2 þ ions (Fig. S10). The mass spectrum of the probe 1.Cu 2 þ complex also clearly predicted the 2:1 stoichiometry (Fig. S11). 3.2. Photophysical behavior of probe 1 towards anions

Fig. 3. The blue bars represent the selectivity of the probe 1 towards Cu2 þ ions (20 mM) upon addition of different metal ions in CH3CN and the red bars show the competitive binding of the probe 1 in the presence of interfering metal ions.

absorption intensity at 347 nm with concomitant bathochromically shift to new absorption band between 400 nm and 500 nm (Fig. 1a). Further addition of Cu2 þ ions between 35 and 800 mM caused the formation of new absorption band at 300 nm (Fig. 1b). The complexation constant of Cu2 þ ions with probe 1 was 5.1 105 M 1, calculated through Benesi–Hildebrand equation. Probe 1 (20 mM, CH3CN) on excitation at 350 nm showed an emission maximum at 425 nm. The addition of various metal

On addition of various anions like Cl , Br , I , OAc , H2PO4 , NO3 , SCN , HSO4 and CN etc, to probe 1 (20 mM, CH3CN), no significant change was observed except in the presence of F ions (Fig. S12). The presence of fluoride ions caused the formation of new absorption band at 420 nm. The incremental addition of fluoride ions caused a decrease in absorption intensity of the band at 340 nm with concomitant formation of new bathochromically shifted absorption band at 420 nm. Bathochromic shift was associated with a visible color change from colorless to bright yellow. The probe 1 showed a clear isobestic point at 355 nm (Fig. 4) which indicating no stepwise complexation and formation of single complexed species. Job's


295

Fig. 4. (a) Effect of incremental addition of fluoride ions on absorption spectrum of probe 1 (20 mM, CH3CN); (b) Ratiometric plot of absorption changes at 420 nm and 347 nm vs concentration of F ions.lu.

Fig. 5. (a) Effect of various anions on absorption spectrum of probe 1 (20 mM CH3CN: H2O: 1:1); (b) Effect of incremental addition of cyanide ions on absorption spectrum of probe 1 (20 mM CH3CN: H2O: 1:1, buffer, pH ¼7.2).

plot analysis of the probe 1 also showed formation of 1:1 complex with fluoride ions (Fig. S13). Emission changes of the probe 1 were recorded in the presence of various anions viz., F , Cl , Br , I , OAc , H2PO4 , HSO4 and CN . Presence of F , OAc , H2PO4 , and CN ions showed the formation of the new emission band at longer wavelength and no selectivity of ions was observed (Fig. S14). In order to achieve the selectivity, we studied anions binding in different solvents as a handy method to control anion nucleophilicity and sensing response. As it is well known that the nucleophilic character of different species is solvent dependent and protic solvent decreases the anion nucleophilicity by hydrogen bonding to the nucleophile's lone pairs (solvation effects). As stated above, in CH3CN solutions, the probe 1 induced the changes with anions like F , AcO , H2PO4 and CN but 50% vol. in water was enough to avoid completely the reaction of the probe 1 with F , AcO and H2PO4 . Thus, in the presence of various anions like F , Cl , Br , I , OAc , H2PO4 , NO3 , SCN , HSO4 and CN etc., probe 1 (20 mM,

CH3CN: H2O: 1:1, pH ¼7.2) did not affect the absorption spectrum except cyanide ions (Fig. 5a). The incremental addition of cyanide ions to probe 1 (20 mM, CH3CN: H2O: 1:1, pH ¼ 7.2) caused a decrease in absorption intensity at 345 nm with concomitantly formation of new red shifted absorption band at 415 nm (Fig. 5b). The probe showed a clear isobestic point at 360 nm, indicating no stepwise complexation and formation of single complexed species. To check the practical applicability of the probe 1 as CN selective sensor, we carried out anion competition experiments. Probe 1 was mixed with 10 equiv. of CN ions in the presence of 100 equiv. of other anions like F , Cl , Br , I , OAc , H2PO4 , NO3 , SCN , HSO4 and CN etc. (Fig. S15). No significant variation was observed in absorbance by the addition of interfering anions. On excitation of the probe 1 (20 mM, CH3CN: H2O: 1:1) at 350 nm, emission maxima at 420 nm was observed. The presence of various anions did not affect the emission spectrum of the probe 1 except cyanide ions (Fig. 6a). The presence of cyanide ions

296


Fig. 6. (a) Effect of various anions on emission spectrum of probe 1 (20 mM CH3CN: H2O: 1:1); (b) Effect of incremental addition of cyanide ions on emission spectrum of probe 1 (20 mM, CH3CN: H2O: 1:1, buffer, pH¼ 7.2).

Fig. 7. 1H NMR titrations of probe 1 with TBACN in CD3CN-d3: D2O: 1:1.

caused the formation of the new emission band at 560 nM. On incremental addition of cyanide ions to probe 1 (20 mM, CH3CN: H2O: 1:1), did not affect the emission band at 420 nm but lead to formation red shifted band (Δλ ¼ 140 nm) at 560 nm (Fig. 6b). Job's plot analysis of the probe 1 also showed formation of 1:1 complex with cyanide ions (Fig. S16). The complexation constant was determined to be 8.2 104 M 1 (Fig. S17). The lowest detection limit for CN was calculated using 3σ/slope method and was found to be 1 μM. 3.3. Effects of pH on absorption and emission changes Since the pH variation effects the charge distribution on a molecule, it can change the absorbance and fluorescence response of the probe. To check the versatility of this probe in different pH, the effects of pH on probe 1 and complex of the probe 1 with cyanide in 1:1 CH3CN: H2O in UV–Visible and fluorescence were also studied. The results revealed that the probe 1 and its complex with cyanide ion are stable at pH range of 1.5–9.4 (Fig. S18, S19).

3.4. NMR titrations To understand the binding of cyanide with probe 1, 1H NMR titrations were performed in CD3CN-d3: D2O: 1:1. The hydroxyl proton signal of the probe 1 was not observed due to D2O exchange. On addition of cyanide ions up to 1.5 equivalents, singlet of alkene H-6 upfield shifted by 0.29 ppm from 8.07 ppm to 7.78 ppm and H-3a proton of phenyl ring downfield shifted from 7.39 to 7.44 ppm. Protons H-4a and H-5a upfield shifted from 7.31 ppm to 7.15 ppm (Δδ ¼0.16 ppm) and 6.99 ppm to 6.96 ppm respectively. The NMR titrations clearly predicted the deprotonation of hydroxyl proton induced intramolecular charge transfer. Thus, due to charge density variations, shifts in proton signals were observed (Fig. 7). 3.5. Logic gates In the era of molecular computing, the progress of molecular logic gates [29,30] has been achieved with great importance. Basic logic gate that is programmed in single molecular switch, has


implicated in the electronic and photonic devices [31–34]. On the basis of chemical information about inputs and outputs of Cu2 þ and CN in the absorption and emission channels, XOR and YES logic gates have been fabricated. It is always difficult to achieve XOR logic gate chemically because for XOR gate (0-0), two inputs (1-1) should have same spectroscopic properties for low signal output. In contrast, when there is a single input (0-1 and 1-0 states), there should have a high signal output. Chemical inputs for Cu2 þ and CN have been represented as “1” for the presence and “0” for their absence. The output signal for probe 1 was measured at 485 nm in case of emission spectroscopy and at 300 nm in the case of absorption spectroscopy. For fluorescence emission, output is considered as “1” when intensity is above 40 a.u (threshold value) and “0” when intensity is below this value. While in case of absorption spectroscopy, output is considered as “1” when absorption intensity is above 0.3 a.u (threshold value) and “0” when intensity is below this value. The inputs and outputs of Cu2 þ and CN corresponding to fluorescence and UV–Visible responses are given in Table 1. The emission at 485 nm is in ‘ON’ state when either of the two inputs (Cu2 þ and CN ) are present and in ‘OFF’ state when neither is present or both are present. This behavior provided the elaboration of XOR logic

Table 1 Truthtable for the sequential logic circuits XOR and YES gate, where 0 ¼ Off and 1¼ On.

297

function. The outputs at λab ¼300 nm in the presence of chemical inputs Cu2 þ and CN activated YES gate (Fig. 8). 3.6. Theoretical studies Theoretical calculations (DFT) have also been carried out on probe 1 to gain a better understanding of the binding interactions with Cu2 þ and CN ions. Two stable conformations MODEL 1 and MODEL 2 were observed with optimization of the probe 1 in a solvent system (Fig. 9). Potential energy surface (PES) using a dihedral scan (atoms labeled C9, C8, C6, and C5) showed that MODEL 1 is 4.21 kJmol 1 more stable than MODEL 2. TD-DFT calculations were performed on both MODEL 1 and 2 in solvent phase to conclude conformation of probe 1. The simulated UV–vis spectra of both the conformations (MODEL 1 and MODEL 2) have been summarized in Table 2. MODEL 1 was found to be in close agreement with experimental data. So, further calculations were performed with MODEL 1. TD-DFT calculations to probe 1 showed the absorption maximum (λmax) at 352 nm corresponding to transitions from HOMO - LUMO and HOMO-1 - LUMO with orbital contributions, 90.8% and 9.2% respectively. An analysis of frontier molecular orbital, these transitions showed that HOMO is located at the π cloud of phenyl ring containing hydroxyl, sulfur and ketone part. LUMO is distributed over π* cloud of phenyl ring containing hydroxyl, sulfur, ketone part of the thiazolidine ring along with a small contribution of nitrogen atom that clearly predicted π-π* transitions (Fig. 10, Table 2). The structure of probe 1.CN was optimized using the same protocol as probe 1. The optimized structure resulted in planar keto conformation at the phenyl ring by deprotonation of hydroxyl hydrogen and led to formation of HCN molecule (Fig. 9). TD-DFT studies revealed that HOMO was distributed over the whole molecule except nitrogen atom, whereas LUMO was distributed over the whole molecule except sulfur atom with opposite charge densities. The electronic transition can be considered as π-π* transition with a smaller energy gap that caused red shift in a spectrum which is in close agreement with the experimental results (from 352 nm to 438 nm). The electronic transition was contributed from HOMO-LUMO only. The structure optimization of probe 1.Cu2 þ complex showed the dimeric structure with slightly distorted square planar geometry.

Fig. 8. Bar diagram of the logic circuits (a) XOR gate in emission spectroscopy at 485 nm; (b) YES gate in absorption spectroscopy at 300 nm, where 0 ¼ Off and 1¼ On.

298


Fig. 9. DFT optimized structure of probe 1 and their complexes with CN and Cu2 þ ions.

Table 2 Calculated contribution of orbital in excitations.

Probe1

Theoretical λ (nm)

Observed λ (nm)

f

Energy (eV)

Orbital

Orbital contribution %

Model 1: 352

347

0.2313

3.5188

0.4045

3.4156

0.3352 0.0801 0.2936

2.8255 2.6388 3.8985

H-L H-1-L H-L H-1-L H-L H-7 (B) -L (B) H-5 (B) -L (B) H (B) -L (B) H (A) -L þ1 (A) H-2 (B) -Lþ 1 (B) H-1 (B) -Lþ 1 (B)

90.8 9.2 93.5 6.5 100 5.7 93.0 1.3 42.9 10.0 36.3

Model 2: 363 Probe1.CN Probe1.Cu2 þ

438 469 318

415 450 (b) 300

In complex, Cu2 þ symmetrically coordinates through a sulfur atom of thiazolidine moiety and oxygen atom of hydroxyl phenyl (E ¼1547.26 au). The probe 1.Cu2 þ complex was stabilized through symmetrically strong hydrogen bonding interaction between phenolic hydrogen and thiazolidine oxygen. The selected bond lengths and bond angles have been shown in Fig. S20. A TD-DFT calculation on the optimized geometry of complex showed that the energy difference between HOMO and LUMO was small as compared to probe 1, resulted in red shift in absorption spectra. Electronic transitions were mainly due to HOMO to LUMO and HOMO to LUMO þ1 of π-π* with a small contribution of ligand to metal charge transfer (Table 2).

check the contamination through contact mode. We prepared different samples of solution coated strips and checked their fluorescence response towards Cu2 þ ions and CN ions in contact mode and solution phase. Solutions of different concentration of Cu2 þ and CN ions were placed over coated strips for 10 s for Cu2 þ ions and 1–2 min for CN ions. Upon illumination with UV-lamp, blue spots were observed in the contact area in case of Cu2 þ ions and bright yellow in case of CN ions. The minimum amount of Cu2 þ ions that can be detected with the naked eye was 10 μM (Figs. 11 and 12).

4. Conclusion 3.7. Practical application of probe 1 towards Cu2 þ ions and CN ion To check the practical applicability of probe 1 toward Cu2 þ and CN ions, TLC strips were coated with 20 μM solution of probe 1 by dip-coating, followed by drying under vacuum to

We have synthesized a fluorescent probe 1 for the selective recognition of Cu2 þ and CN ions. Probe 1 has been shown ratiometric “ON–OFF–ON” type of emission response in the presence of Cu2 þ ions and used to estimate Cu2 þ between the


299

Fig. 10. Frontier molecular orbital of probe 1 and its complexes (MO with highest contribution are shown).

Fig. 11. Photographs of a test strips coated (upper) with probe 1 (10 3 M 1) and its color changes (in circle) in the presence of different concentrations of Cu2 þ ions.

detection limit of 50 nM–15 mM. On the other hand, probe 1 was used to estimate cyanide ions between 4 mM and 200 mM in CH3CN: H2O: 1:1. The binding behavior and optical response

achieved in the presence of Cu2 þ and CN ions have been confirmed through DFT calculations. The probe 1 also mimicked the XOR and YES logic function by using Cu2 þ and CN- ions chemical

300


Fig. 12. Photographs of a test strips coated (upper) with probe 1 (10 3 M 1) and its color changes (in circle) in the presence of different concentrations of CN ions.

inputs. Probe 1 has also been used for its practical aplicability to sense Cu2 þ and CN through dip coating method.

Acknowledgment

[11] [12] [13] [14]

We thank DST-INSPIRE (IFA12-CH-59), New Delhi for fellowship and financial assistance. We also thank to SAIF, Panjab University, Chandigarh for mass analysis and SAI Labs, Thapar University, Patiala for NMR facility. We thank Ms. Charanpreet Kaur (M.Sc. Project student) for her initial support for this work.

Appendix A. Supporting information Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.jlumin.2016.08.041.

[15] [16] [17] [18] [19] [20] [21] [22] [23]

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