Supramolecular Aggregate of Cadmium (II)-Based One-Dimensional

Article Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

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Supramolecular Aggregate of Cadmium(II)-Based One-Dimensional Coordination Polymer for Device Fabrication and Sensor Application Basudeb Dutta,† Rajkumar Jana,‡ Anup Kumar Bhanja,§ Partha Pratim Ray,*,‡ Chittaranjan Sinha,*,§ and Mohammad Hedayetullah Mir*,† †

Department of Chemistry, Aliah University, New Town, Kolkata 700 156, India Department of Physics, Jadavpur University, Jadavpur, Kolkata 700 032, India § Department of Chemistry, Jadavpur University, Jadavpur, Kolkata 700 032, India

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‡

S Supporting Information *

ABSTRACT: A novel mixed ligand one-dimensional coordination polymer (1D CP), {[Cd2(adc)2(4-nvp)6]·(MeOH)· (H2O)}n (1; H2adc = 9,10-anthracenedicarboxylic acid, and 4nvp = 4-(1-naphthylvinyl)pyridine), has been synthesized and structurally characterized by single crystal X-ray crystallography. The 1D polymer undergoes supramolecular aggregation via hydrogen bonding, C−H···π, and π···π interactions. Interestingly, compound 1 shows increasing conductivity upon irradiation of light. Therefore, it has the potential to be used in optoelectronic devices. Moreover, the supramolecular assembly of 1 specifically detects Cr3+ cation in the presence of other competitive analytes. Most importantly, compound 1 exhibits fascinating turn-on Cr3+ sensing, which seems to be an ornament in the field of sensing application.

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INTRODUCTION

On the other hand, a large number of CPs have been studied for sensor applications.29−32 CPs are more attractive in the field of sensing application due to their higher stability as well as recyclability and easy synthetic procedure. In this regard, a gadget detecting Cr(III) is significant.33−36 Cr(III) appears at trace levels in the human body, and the recommended intake for adults is 50−200 μg/day. In the human body, the action of insulin is also regulated by Cr(III) activating certain enzymes and alleviating nucleic acids and proteins. Insufficiency of this element shows various types of disorders. Again, the preeminent levels of Cr(III) may even lead to cancer. Therefore, there is an essential need for developing a material that specifically detects Cr(III). Estimation of Cr(III) is performed by various methods: titrimetry, chromatography, flame atomic absorption spectrometry, inductively coupled plasma−atomic emission spectroscopy, potentiometry, fluorimetry, fluorescence spectrometry, X-ray fluorescence spectrometry, and spectrophotometry, etc. However, fluorescence spectrometry is one of the advantageous methods because of high selectivity, enhanced sensitivity, high sampling frequency, low cost of equipment, operational simplicity, and direct visual perception. Although there are few reports in the literature,33−36 there is still an urge to design a suitable CP for the improvement of detection selectivity of Cr(III). We have a keen interest in developing CPs with selectivity and sensitivity for probing Cr(III). For this purpose, CPs have to be made of organic

Over the past few decades, the interest in supramolecular chemistry has been awe inspiring due to their functions beyond the molecule.1−3 From the eternal concept of chemistry, there is a relation between the structure and property of a molecule. Since the Nobel prize in supramolecular chemistry was received in 1987, the sciences of secondary interactions have demanded an active place in the study of material science. Taking advantage of such interactions, many desired coordination polymers (CPs) have been synthesized. The polymeric entity of coordination compounds is known as CPs;4−8 composed of hybrid components (inorganic metal ions and organic ligands). Diversity in the view of structural dimensionality transforms the materials for various potential applications: sorption and separation of gases, drug delivery, catalysis, dye degradation, energy strategy, device fabrication, magnetism in variable temperature, and ion replacing.9−23 However, fabrication of electronic devices using this class of materials is still a challenge because of their low conductivity. This lower value of conductivity concerns the designing of these materials from redox inactive organic ligands and hard metal ions. Nevertheless, the judicious selection of components of CPs brands them as device applicable materials. Not only their structural stability but also their thermal and chemical stability make them desirable for researchers working in the field of materials chemistry. Our group is able to design a number of CPs for application in device fabrication and electrical conductivity.24−28 © XXXX American Chemical Society

Received: November 26, 2018

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DOI: 10.1021/acs.inorgchem.8b03294 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

Figure 1. (a) Coordination environment of Cd(II) in 1. (b) View of 1D chain of 1. (c) View of 2D supramolecular aggregate of 1 by hydrogen bonding and C−H···π interactions. Hydrogen atoms are not shown for the clarity.

linkers containing an electron rich moiety for fluorescence sensitivity and free coordination sites for interactions with Cr3+. Herein, we report an electron rich 9,10-anthracenedicarboxylate (adc)-based one-dimensional (1D) CP {[Cd2(adc)2(4-nvp)6]·(MeOH)·(H2O)}n (1; 4-nvp = 4-(1naphthylvinyl)pyridine), which is found to be a selective chemosensor for Cr3+. Moreover, compound 1 shows turn-on Cr3+ sensing through enhancement mechanism, which is fascinating and seems to be not very available. Meanwhile, compound 1 behaves as a semiconducting material and shows better conductivity upon light irradiation, which can be used as a photosensitive electronic device. Thus, the simultaneous presence of turn-on Cr3+ sensing and photosensitive electrical conductivity properties in a single CP makes it novel and inspires one to move further for the exploration of new multifunctional smart materials.

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Synthesis. Compound 1 was synthesized by slow diffusion method. A methanolic solution (2 mL) of 4-nvp (0.046 g, 0.2 mmol) was carefully added to an aqueous solution (2 mL) of Cd(NO3)2·4H2O (0.062 g, 0.2 mmol), using 2 mL of a 1:1 (v/v) buffer solution of MeOH and H2O. Then an ethanolic solution (2 mL) of H2adc (0.0308 g, 0.2 mmol) neutralized with Et3N (0.010 g, 0.1 mmol) was layered upon it. After 3 days, yellow color needle shaped crystals of {[Cd2(adc)2(4-nvp)6]·(MeOH)·(H2O)}n (1) appeared in 65% yield (0.284 g). Elem. Anal. (%) Calcd for C135H101Cd2N6O10: C, 73.97; H, 4.79; N, 3.81. Found: C, 74.10; H, 4.65; N, 4.01. Crystallographic Data Collection and Refinement. The crystal data of a properly shaped single crystal of compound 1 were collected on a Bruker SMART APEX II diffractometer attached with a graphite-monochromated Mo Kα radiation source (λ = 0.71073 Å). The structure was solved by using the SHELX-97 package,37 and full matrix least-squares refinement was carried out on F2 for nonhydrogen atoms with anisotropic displacement parameters. All of the hydrogen atoms were fixed geometrically at their proper positions by HFIX command. The crystallographic data of compound 1 are depicted in Supporting Information Table S1. The selected bond lengths and bond angles around the coordination atmosphere of the metal ion are also given in Table S2. Methodology of Density Functional Theory Computation. Molecular structure of the compound has been optimized via density functional theory (DFT) computation and, subsequently, timedependent DFT (TD-DFT) also performed by using the GAUSSIAN-09 program package38 for the certification of experimental band gap. DFT-B3LYP hybrid functional39 has been executed throughout the calculation process. To analyze the fractional involvement of metal molecular orbital and ligand molecular orbital, a Gauss sum40 was used. Device Fabrication and Characterization. To construct the Al/compound 1/ITO structure, first indium tin oxide (ITO) coated glass is taken. The ITO coated glass is then cleaned using acetone, ethanol, and distilled water with the help of an ultrasonication bath. The synthesized compound is dispersed in DMF medium. The well dispersed solution of the compound is spun onto the ITO coated glass with the help of a SCU2700 spin coating 3unit at a spin rate of

EXPERIMENTAL SECTION

Materials and Physical Measurements. Metal salt, dicarboxylic acid, and all other chemicals were procured from different commercial resources in reagent grade and were used as received. The elemental analysis (C, H, and N) was performed using a Perkin-Elmer 240C elemental analyzer. The FT-IR spectrum in KBr (500−4500 cm−1) was taken on a Perkin-Elmer FT-IR RX1 spectrometer. For thermogravimetric analysis (TGA), a Perkin-Elmer Pyris Diamond TG/DTA instrument was used. The TGA experiment was carried out in the temperature range 30−600 °C under a nitrogen gas flow with a heating rate of 12 °C min−1. The powder X-ray diffraction (PXRD) data collections were performed in Bruker D8 Advance X-ray diffractometer using Cu Kα radiation source (λ = 1.548 Å) at room temperature. The solid-state UV−vis spectrum was recorded on a Perkin-Elmer Lambda 25 spectrophotometer, and the solid-state fluorescence measurements were performed using a Perkin-Elmer spectrofluorimeter model LS55 at room temperature. Luminescence lifetime measurements were performed using a Horiba Jobin Yvon fluorescence spectrophotometer. B


Article

Inorganic Chemistry 2000 rpm for 2 min. The prepared thin film of thickness 1 μm is then placed in vacuum desiccators for overnight to remove the solvent from the as-deposited film. Here, aluminum (Al) is taken to make the metal contact as an electrode. The Al is deposited onto the dry thin film by using vacuum coating unit 12A4D of HINDHIVAC under a pressure of 10−6 Torr. The effective diode area is maintained as 7.065 × 10−6 m2.

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RESULTS AND DISCUSSION Structural Descriptions of {[Cd 2 (adc) 2 (4-nvp) 6 ]· (MeOH)·(H2O)}n (1). The needle shaped yellow colored crystals of compound 1 have been obtained by layering of alcoholic solution of mixed ligand 4-nvp and adc over the aqueous solution of Cd(NO3)2·4H2O. X-ray crystallographic experiment reveals that compound 1 crystallizes in the triclinic space group P1̅ with Z = 1. In 1, {[Cd2(adc)2(4-nvp)6]· (MeOH)·(H2O)}n, each Cd(II) center has a distorted pentagonal bipyramidal geometry and it is ligated to four O atoms from two adc anions in chelating fashion and three N atoms from three 4-nvp ligands (Figure 1a). The asymmetric unit further contains a lattice MeOH molecule and a H2O. The chelating adc ligands link Cd(II) centers into a 1D zigzag chain (Figure 1b). In the solid-state crystal structure, the presence of water molecules helps 1D chains undergo supramolecular association to generate a two-dimensional (2D) network. The water molecule constructs hydrogen bonding with O atom (O3) of the adc anion where O···O separation is 2.85 Å. In addition, there exists a nonclassical hydrogen bonding between H atom (H2) of the nvp moiety and O atom of the aqua molecule with C···O distance of 3.24 Å (Figure 1c). Moreover, the accumulation of 1D chains is also supported by C−H···π interactions among the 4-nvp ligands between adjacent chains with edge-to-face distances in the range of 2.92−3.39 Å (Figure 1c). This 2D network further undergoes π···π interactions to create three-dimensional (3D) supramolecular assembly (Figure S1). TGA and PXRD Analysis. The phase purity and stability of compound 1 were verified by powder X-ray diffraction (PXRD) and thermogravimetric analysis (TGA) study, respectively. The PXRD pattern of compound 1 was essentially in accordance with the simulated pattern obtained from single crystal data, indicating a pure sample of 1 (Figure S2). To check the framework stability, PXRD of 1 was also performed with the sample used in photoconductivity measurement. The PXRD pattern shows almost identical pick of positions with their corresponding pattern obtained from as-synthesized 1 (Figure S2). TGA plot shows a small amount of initial weight loss due to the presence of solvent molecules; otherwise the compound is stable up to 240 °C (Figure S3). Therefore, the compound seems to be an appropriate candidate for material applications. Optical Study. The optical property of compound 1 is studied by recording the UV−vis absorption spectra in the wavelength range of 250−800 nm. The absorption spectrum of the compound is recorded in dimethylformamide (DMF) medium. Figure 2 portrays the absorption spectrum of the compound along with the Tauc plot (inset). The absorption spectrum of the compound reveals that the maximum energy of absorption is found to be in the visible region at ∼432 nm. The optical band gap can be calculated using the following equation41 αhυ = A(hυ − Eg )1/2

Figure 2. UV−vis absorption spectrum of the compound 1 (inset: Tauc’s plot).

Here α is the absorption coefficient, A is an energy-dependent constant, hυ is the photon energy, and Eg is the οptical band gap of the compound. The band gap of compound 1 from the Tauc plot is estimated as 2.87 eV, which belongs to the class of a wide band gap semiconductor. Theoretical Study. Here, lattice matching and deformation potentials have been utilized to attain the Schottky electrical contact. The deformation normally denotes the energy difference between conduction and valence bands, which is indeed the difference between HOMO and LUMO (ΔE = ELUMO − EHOMO, eV). The band gap of the hybrid material can be resolute by using absolute deformation potentials (ADPs).42 Here, the calculated HOMO and LUMO energy values are −5.29 and −2.43 eV, respectively (Figure 3). Therefore, the theoretical energy difference (ΔE) is 2.86 eV, which is consistent with the experimental band gap attained from the Tauc plot. Electrical Study. To observe current voltage (I−V) characteristic of compound 1 based Schottky barrier diode (SBD, a bias voltage varying from −2 V to +2 V is applied between Al and ITO. The measurement is performed at room temperature under dark and illumination conditions, respectively. The I vs V curve of the SBD is portrayed in Figure 4 along with the plot of I (log scale) vs V in the inset. It has been observed from Figure 4 that the compound 1 based device shows good rectifying behavior which is the indication of the SBD. The on/off of the diode is found to be 47 and 69 under dark and light conditions, respectively. This result indicates that the rectifying property of the diode is highly influenced by the illumination. In addition, we have estimated the room temperature conductivity. Under dark condition, the measured conductivity is (6.91 ± 0.03) × 10−4 Sm−1, whereas after the soaking of light the value changes to (13.90 ± 0.36) × 10−4 Sm−1, which is nearly two times larger than the value in dark condition. In order to realize the electrical properties of the Al/ compound 1/ITO based SBD, the I−V characteristics have been investigated by introducing the thermionic emission (TE) theory. The current−voltage relation for a SBD can be written as the following equations43

(1) C


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Inorganic Chemistry

height of the SBD and Richardson constant, respectively. The value of A* is assumed to be 32 A K−1 cm−2 for the diode. It is observed from Figure 4 that the I vs V graph is almost linear at the low bias voltage and deviates from the linearity as the bias voltage increases. Here, the deviation of this graph at higher voltage suggests the existence of series resistance in the device.44 To determine the value of the ideality factor (η), barrier height (ΦB) and series resistance (Rs) of the device based on compound 1, we have employed the following equations45 ηkT dV = + IR s d ln I q

Figure 4. I−V characteristics of compound 1 under dark and light conditions (inset: plot of current in log scale vs voltage (where, for example, 1E-3 represents 1 × 10−3)).

i −qΦB yz zz I0 = AA*T 2 expjjjj z k ηkT {

H(I ) = IR s + ηϕb

(6)

(5)

The plots of dV/(d ln I) vs I and the H(I) vs I curve of the SBD are presented in Figure 5a,b, respectively. Ideality factor (η) and series resistance (Rs) of the diode can be determined from the y-axis intercept and the slope of dV/(d lnI) vs I graph, respectively (Figure 5a). The estimated values of the ideality factor (η) are 2.47 and 1.52 under dark and illumination conditions, respectively. The deviation of the ideality factor from the unity indicates that the metal−semiconductor (MS) junction is not perfectly ideal. This type of property of the SBD arises due to the presence of barrier inhomogeneities, the existence of interface states, and series resistance at the MS interface.46 In addition, we have calculated the barrier height (ΦB) of the SBD from the y-axis intercept of the H(I) vs I graph (Figure 5b). We can also determine the value of series resistance from the slope of the H(I) vs I plot, which is quite similar to the value calculated from the dV/(d ln I) vs I graph. The barrier height of the SBD is estimated as 0.55 and 0.49 eV under dark and light conditions, respectively. The values of ideality factor, barrier height, and series resistance of the device are summarized in Table 1. The semiconducting feature of compound 1 has been possibly attributed to the charge delocalization due to the close proximity of adjacent polymeric chains forming supramolecular assembly. The charge might move through covalent bonds and subsequent noncovalent supramolecular contacts via so-called “hopping transport”.47 In the metal−organic polymeric system, the highly ordered molecules produce a unitary cell-like arrangement, while, with illumination, these cells are assembled together via various secondary interactions to generate a high surface area for the collection of photons. Here, monodented 4-nvp ligands projected on both sides of the 1D polymeric chain behave as antenna. During the illumination, these ligands absorb light and energize the charge carriers (Figure S4), resulting in the increase in mobility and enhancement of conductivity. To understand the charge transport properties of the Al/ compound 1 junction, we have plotted the I−V characteristics in log−log scale (Figure 6a). The charge transport mechanism can be explained by the power law (I ∝ Vm), where m is the slope of the log−log representation of I−V curve. As observed in Figure 6a, the graph consists of two regions with different values of m, suggesting the possibilities of a different conduction mechanism in different regions. In region I, the value of m is nearly equal to 1, which suggests an ohmic nature, whereas, in region II, the m value is equal to or greater than 2,

Figure 3. DFT computed energy of MOs and the energy difference (ΔE) between HOMO and LUMO of 1.

É Ä i qV yzÅÅÅÅ i yÑÑÑ zzÅÅ1 − expjjj −qV zzzÑÑÑ I = I0 expjjjj zÅ j ηkT zÑÑ k ηkT {ÅÅÅÇ k {ÑÑÖ

ij ηkT yz i I y zz H(I ) = V − jjj zz lnjj j q zz jk AA*T 2 z{ k {

(4)

(2)

(3)

where q, I, k, T, η, A, and I0 are the electronic charge, current at forward bias voltage V, Boltzmann constant, temperature in Kelvin, ideality factor, effective diode area and the saturation current, respectively. Here, ΦB and A* are referred to as barrier D


Article

Inorganic Chemistry

Figure 5. (a) dV/(d ln I) vs I and (b) H(I) vs I graph of the compound under dark and light condtions, respectively.

Table 1. Schottky Diode Parameters of Al/Compound 1/ITO Structure Rs (Ω)b sample

condition

on/off ratio

ηa

dV/d(ln I) vs I

H(I) vs I

ΦB (eV)c

compound 1

dark light

47 69

2.47 1.52

135 76

134 77

0.55 0.49

η = ideality factor. bRs = series resistance. cΦB = barrier height.

a

Figure 6. (a) Current vs voltage graph (log−log scale (where, for example, 1E-3 represents 1 × 10−3)) of the compound under dark and light conditions. (b) Capacitance vs frequency graph of 1.

governed by the influence of barrier inhomogeneities. However, in the higher frequency region, the movement of charge carriers contributing to the dielectric constant is administrated by hopping mechanism. At higher frequency, the charge carrier hopping is unable to follow the applied field and, thus, the dielectric constant gets reduced and becomes saturated. At the saturation level, the relative permittivity of compound 1 has been evaluated using eq 8. Moreover, transit time (τ) and diffusion length (LD) can be calculated by employing the following equations51

indicating the space charge limited current (SCLC) theory. At low forward voltage region (region I), the current−voltage relationship can be written as I ∝ V, where m ∼ 1 and the I−V characteristics can be attributed to the TE theory.48−50 In the higher bias region (region II), the estimated value of m is 2. It indicates that the I−V characteristic obeys the power law I ∝ V2 and the current conduction mechanism of the MS junction is governed by the popular SCLC theory.51 The effective carrier mobility (μeff) can be determined with the help of the Mott−Gurney space SCLC equation52,53 I=

9μeff ε0εr A ij V 2 yz jj zz j d3 z 8 k {

τ= (7)

where ε0 and A are the permittivity in free space and the effective area of the device, respectively. The term εr stands for the dielectric constant, and it can be calculated from the following equation54 εr =

1 Cd ε0 A

9ε0εr A ij V yz jj zz 8d k I {

LD =

2Dτ

(9) (10)

Here D represents the diffusion coefficient. The value of D can be determined from the Einstein− Smoluchowski equation51

(8)

μeff =

Here C is the capacitance at saturation, which can be obtained from the capacitance vs frequency curve (Figure 6b). As shown in Figure 6b, the room temperature capacitance is frequencydependent and decreases with increasing frequency. In the lower frequency region, the charge transport mechanism is

qD kT

(11)

where T and k are the temperature in kelvin and the Boltzmann constant, respectively. In this regard, the charge carrier concentration (ND) has been evaluated by introducing the following equation51 E


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Inorganic Chemistry Table 2. Characteristic Parameters of Compound 1 Based on SBD in the SCLC region sample

condition

μeff × 10−4 (m2 V−1 s−1)

τ × 10−10 (S)

μeffτ × 10−13 (m2 V−1)

ND × 10−19 (eV m−3)

D × 10−5 (SI)

LD × 10−7 (m)

compound 1

dark light

9.25 18.12

2.96 1.62

2.74 2.93

4.34 5.09

2.38 4.66

1.18 1.29

Figure 7. (a) Fluorescence spectra of 1 in the presence of different metal ions and Cr3+ in CH3CN/H2O (v/v, 1:1) [inset: emission change of 1 and Cr3+ with 1 under illumination in a UV chamber]. (b) Change of fluorescence intensity of 1 upon addition of Cr3+ at an emission slit of 3 nm [inset: time-dependent changes of fluorescence intensity ratio I456 nm/I416 nm; all spectra were acquired at room temperature at excitation slit 340 nm].

ND =

σ qμeff

(12)

We have calculated effective charge carrier mobility (μeff), transit time (τ), diffusion length (LD), and carrier concentration (ND) of the compound 1 based device by employing SCLC theory, listed in Table 2. The value of effective charge carrier mobility (μeff) is measured as 9.25 × 10−4 m2 V−1 s−1 under dark condition, while it is increased to 18.12 × 10−4 m2 V−1 s−1 under illumination. The enhancement of the charge carrier mobility under light condition indicates that compound 1 based SBD shows good photoresponse property. In addition, the values of carrier concentration (ND) are estimated as 4.34 × 10−19 eand 5.09 × 10−19 eV m−3 under dark and light conditions, respectively. The improvement of the charge carrier concentration under influence of illumination also contributed to the enhanced photoresponse. Moreover, it is seen from Table 2 that the value of LD is higher in light condition than the dark condition which may also be responsible for better photoresponse. Sensor Application. The presence of delocalized systems such as naphthyl and anthranyl rings causes the emission of compound 1, which prompted us to investigate the sensor application. To assess the sensor application, fluorescence spectra of compound 1 with several cations (Na+, Al3+, Cu2+, Cd2+, Co2+, Mn2+, Fe3+, Pb2+, K+, Ba2+, Ni2+, Zn2+, Pd2+, Ca2+, and Cr3+) using their chloride, acetate, and nitrate salts in CH3CN−H2O (1:1, v/v) solution have been examined on excitation at 340 nm (Figure 7a), and the turn-on emission is observed in the presence of Cr3+ at room temperature. On increasing [Cr3+] to the solution of 1, the fluorescence intensity decreases at 417 nm and increases at 456 nm (Figure 7b). Selectivity toward a metal ion target is the most important parameter for a fluorescent moiety. Here, the detection of Cr3+ by the fluorescent probe has not been perturbed by biologically accessible metal ions such as Na+, K+, Ca2+, Cu2+, and Zn2+, while other metal ions such as Cd2+, Co2+, Mn2+, Pb2+, Ni2+, Ba2+, Al3+, and Fe3+ do not interfere with fluorescence intensity change (Figure 8). The same observation is also obtained upon addition of 5 equiv of aforesaid interfering metal ions. It should

Figure 8. Fluorescence intensity of 1, its intensity change profile with various competing ions and intensity diagram with Cr3+ along with competing ions in CH3CN/H2O (v/v, 1:1) medium.

be mentioned that the fluorescence intensity of 1 is quenched a little for Al3+ and Fe3+ (Figure 8). However, the quenching is insignificant in terms of sensing application. The dramatic shifting in fluorescence enhancement response to the binding of 1 to Cr3+ may be ascribed due to the intramolecular charge transfer (ICT). The titration of Cr3+ in the solution of 1 results in a remarkable decrease in emission at 417 nm and increases at 456 nm (Figure 7b). Importantly, the ratio of emission intensities (I456 nm/I416 nm) is increased by a good linear correlation with the amount of Cr3+. Here, the fluorescence of 1 has been enhanced with a red shift in the presence of Cr3+. The π-electron cloud of bigger conjugated fused aromatic systems in the supramolecular aggregate creates a favorable interaction environment toward Cr3+, which imparts rigidity in the flexible supramolecular assembly (Figure S9). This causes ICT and fluorescence enhancement as fluorescence is more F


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Inorganic Chemistry commonly favored in molecules with rigid structures associated with π−π* transition. In addition, bigger conjugated fused aromatic systems are able to move the π−π* transition band toward longer wavelength and, simultaneously, the fluorescence intensity is also enhanced. The 1H NMR titration also supports the proposed mechanism as the aromatic protons of naphthyl and anthranyl rings undergo shifting in the presence of Cr3+ ions (Figure 9).

DFT table, conductivity measurements and comparison, and LOD calculation and comparison (PDF) Accession Codes

CCDC 1872458 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (P.P.R.). *E-mail: [email protected] (C.S.). *E-mail: [email protected] (M.H.M.). ORCID

Partha Pratim Ray: 0000-0003-4616-2577 Chittaranjan Sinha: 0000-0002-4537-0609 Mohammad Hedayetullah Mir: 0000-0002-2765-6830 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by SERB, India (Grant No. SB/FT/ CS-185/2012, dated Jul. 30, 2014). B.D. thanks the DST, Government of India for an INSPIRE fellowship. Single crystal X-ray diffraction data were collected at the DBT-funded CEIB program (Project No. BT/01/CEIB/11/V/13) awarded to the Department of Organic Chemistry, IACS, Kolkata.

Figure 9. Partial 1H NMR spectra (400 MHz, DMSO-d6) of compound 1 and the compound 1 with Cr3+.

It can be seen from Figure 9 that the peaks have been broaden and peak positions have been shifted toward lower δ values on addition of Cr3+ ion. Besides, most of the CPs used for Cr3+ sensing application are found to be quenching type in the literature.33−35 However, fabrication of turn-on type Cr3+ sensors with low LOD are still challenging. Here, the turnon sensor with the limit of detection (LOD) of Cr3+ has been determined by 3σ/m method54 and found to be as low as 0.31 μM (Figure S10).

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CONCLUSION In summary, we have synthesized a new Cd(II)-based 1D CP which has multidimensional applications. It can be used as a potential aspirant in the fabrication of an optoelectronic device, and on the other hand, it has high selectivity toward Cr3+ ion sensing over other interfering anions. Most importantly, our reported compound shows turn-on Cr3+ sensing, which is innovative and seems to be elusive. In the field of sensor application, fluorescence enhancement or turn-on sensing is a challenging task and also an ornament for the respective field. In this energy crisis period, the synthesized material will be useful for reviving from the condition. From an analytical point of view, sensing of Cr3+ is highly relevant for its essence as a trace element for human health. Therefore, both applications of the material have a great donation toward civilization.

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REFERENCES

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.8b03294. 3D supramolecular assembly of 1, PXRD patterns, TGA plot, charge transport diagram, fluorescence spectra, LOD curve, lifetime measurement, crystallographic data, bond lengths and bond angles, bonding interactions, G


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