Fe3+ Probe with Independent Signal Outputs Based

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Article Cite This: ACS Omega 2019, 4, 6597−6606

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Bifunctional Cu2+/Fe3+ Probe with Independent Signal Outputs Based on a Photochromic Diarylethene with a Dansylhydrazine Unit Yunfei Liang, Renjie Wang,* Gang Liu, and Shouzhi Pu* Jiangxi Key Laboratory of Organic Chemistry, Jiangxi Science and Technology Normal University, Nanchang 330013, P. R. China

ACS Omega 2019.4:6597-6606. Downloaded from pubs.acs.org by 193.93.193.117 on 04/10/19. For personal use only.

S Supporting Information *

ABSTRACT: A novel dual-response fluorescent sensor based on a diarylethene photoswitching unit and a dansylhydrazine functional group has been synthesized. The compound exhibited high selectivity for Fe3+ and Cu2+ with independent fluorescence signal outputs. In the presence of Fe3+, the sensor formed a 1:1 metal complex, resulting in a remarkable “turn-off” fluorescence signal. On the other hand, its fluorescence intensity was notably enhanced (turn-on) and a color change from bright yellow to bright blue was observed when the sensor interacted with Cu2+, which was due to the hydrolysis reaction of the dansyl acid dye, as confirmed by high-resolution mass spectrometry−electrospray ionization and infrared spectrum. The detection limits were 9.73 × 10−8 mol L−1 for Fe3+ and 3.49 × 10−7 mol L−1 for Cu2+, respectively. From the unimolecular platform, two molecular logic circuits were constructed using the fluorescence emission intensity at 557/494 nm (Fe3+/Cu2+) as the outputs and the combined stimuli of Fe3+/ethylenediaminetetraacetic acid, Cu2+, and UV/vis as the inputs. In addition, the sensor was successfully used to determine Fe3+ in water samples from Ganjiang River and soil samples from Nanchang fields.

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functional diarylethene fluorescent probes could be applied to detect and analyze special metal ions such as Zn2+, Cd2+, Hg2+, Cu2+, Ni2+, Fe3+, and Al3+ with high selectivity and sensitivity. As one of the most essential trace elements, Fe3+ ions play critical roles in numerous physiological and pathological processes, such as oxygen metabolism, enzymatic catalysis, oxygen uptake, electron transfer, and regulation of body temperature.14,15 However, the imbalance of the Fe3+ ion within the body could cause several diseases including various cancers, heart failure, hepatitis diabetes, and Parkinson’s disease.16,17 Additionally, as an essential trace element in the human body, Cu2+ plays a crucial role in cellular oxygen transportation/activation, energy generation, and signal transduction.18,19 However, excessive or deficient intake of Cu2+ is harmful to human health and results in serious neurodegenerative diseases including Menkes syndrome, Wilson’s disease, and Alzheimer’s.20−22 Moreover, Cu2+ and Fe3+ ions are considered as important water pollution and toxic species because of their widespread application in industry and in our

INTRODUCTION Fluorescent chemosensor molecules can change their fluorescence properties upon substrate binding or metal-induced reaction. This behavior provides an extremely sensitive optical approach for real-time monitoring of molecular interactions. These fluorescent molecules have been used as sensors in many fields such as biology, medical analysis, and environmental monitoring.1 Recently, it has been reported that dualstimuli-responsive small-molecule organic fluorescence chemosensors displayed evidently fluorescence quenching or enhancement upon excitation with multi-metal ions, photostimuli, and induced reaction. These chemosensors have attracted a great deal of attention because of their potential applications in optical devices, controlled release, erasable memory media, optical switching, molecular fluorescence probe, etc.2−7 Diarylethene derivatives were the most promising candidates as fluorescent switch units because of their fast response, excellent thermal stability, and outstanding fatigue resistance.8 During the past decade, numerous efforts had been devoted to designing and synthesizing diarylethene derivatives containing fluorophore groups with strong fluorescence, such as coumarin, naphthalimide, phenanthroline, bipyridyl, rhodamine B moieties, and so on.9−13 These © 2019 American Chemical Society

Received: November 10, 2018 Accepted: March 29, 2019 Published: April 10, 2019 6597

DOI: 10.1021/acsomega.8b03143 ACS Omega 2019, 4, 6597−6606

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mol−1 cm−1) and 556 nm (ε = 1.18 × 104 L mol−1 cm−1), and this process was accompanied by a color change from colorless to violet. This was attributed to the photocyclization reaction from the open-ring isomer to the closed-ring isomer. The photostationary state (PSS) was obtained in 10 min and a clear isosbestic point was observed at 344 nm, indicating that photoisomerization was a unimolecular process of the two species. The violet closed-ring isomer 1C could be thoroughly decolorized to colorless and the absorption spectra of the open-ring isomer 1O could be regenerated as a result of the photocycloreversion reaction upon irradiation with visible light (λ > 500 nm). The coloration−decolorization cycles of 1O could be repeated 50 times with a negligible degradation (Figure S1, Supporting Information). In addition, the thermal stability of the open-ring and closed-ring isomers of 1 was tested in methanol at 338 K in the dark for more than 7 days and no change has been observed in the UV/vis spectra and color of 1, indicating excellent thermal stability for diarylethene 1. The cyclization and cycloreversion quantum yields of 1 were determined to be 0.24 and 0.29 (Table 1), respectively, by using 1,2-bis(2-methyl-5-phenyl-3-thienyl)perfluorocyclopentene as a reference in methanol. The photoconversion ratio was 88.2% in the PSS (Figure S2, Supporting Information). The fluorescence spectrum of 1O was measured in methanol (C = 2.0 × 10−5 mol L−1) at room temperature. As shown in Figure 1B, 1O exhibited a strong fluorescence emission peak at 557 nm when excited at 338 nm. The fluorescence quantum yield of 1O was determined to be 0.045 by using an absolute PL quantum yield spectrometer QYC11347-11. Upon irradiation with 297 nm light, the fluorescence emission intensity of 1O was progressively quenched with a remarkable hypochromatic blue shift to 509 nm. An obvious concomitant color change from bright yellow to dark was observed under the excitation of 365 nm light (Figure 1B, inset), indicating the formation of the weak fluorescence closed-ring isomer 1C. The fluorescence emission intensity of 1O was quenched to ca. 55% in the PSS, and the fluorescence quantum yield of 1C was determined to be 0.027. The fluorescence peak at the 557 nm decreases because of the closed-ring isomer, which was produced by the photocyclization conversion reaction. The existence of a dansylhydrazine moiety might be responsible for the residual fluorescence in the PSS. The back irradiation with visible light (λ > 500 nm) regenerated the original emission intensity and restored to the emission peak of 1O (Table 1). Fluorescence Response to Metal Ions. The binding ability of 1O with various metal cations (5.0 equiv for Cu2+, Zn2+, Al3+, Cr3+, Co2+, Mn2+, Hg2+, Pb2+, Cd2+, K+, Ca2+, Fe3+, Mg2+, Ba2+, Sr2+, and Ni2+) were investigated by fluorescence spectroscopy. Figure 2 shows the emission spectra and fluorescence color change of 1O in methanol (C = 2.0 × 10−5 mol L−1). As shown in Figure 2A, none of these metal ions induced any significant changes in the fluorescence spectrum of 1O except Fe3+ and Cu2+. When Cu2+ was added to the solution of 1O, the fluorescence emission intensity was enhanced sharply and the emission peak hypsochromic-shifted from 557 to 494 nm with a concomitant color change from bright yellow to bright blue. In contrast, the fluorescence intensity of 1O remarkably decreased with a negligible emission peak change and a color change from bright yellow to dark when Fe3+ was applied to the solution. Consequently, diarylethene 1O could be used as a bifunctional selective fluorescence sensor for Cu2+ (turn-on) and Fe3+ (turn-off)

daily life. According to the U.S. Environmental Protection Agency (EPA) reports, the upper limits of Cu2+ and Fe3+ in drinking water or food were 1.3 ppm (∼20 μM) and 0.3 ppm (∼5.4 μM), respectively.23,24 Therefore, it is crucial to detect Cu2+ and Fe3+ in various biological and environmental systems. As transition-metal ions, both Cu2+ and Fe3+ are known to be paramagnetic and most of the reported Cu 2+ /Fe 3+ fluorescent chemosensors are “turn-off” fluorescent probes, which are not sensitive compared to the signal enhancement detection mode.25−27 Nevertheless, there were only a few cases of “turn-on” fluorescent response for Cu2+ and most of them were constructed from the Cu2+-catalyzed elimination reaction of hydrazides,28,29 esters,30,31 amide,32,33 and thiosemicarbazide group.34 Other “turn-on” fluorescent response of Cu2+ promoted by the hydrolysis reaction has also been reported. For example, Choi et al. reported a chemosensor based on dansyl-Schiff for the determination of Cu 2+ , and its fluorescence emission wavelength showed a remarkable blue shift by the Cu2+-promoted hydrolysis reaction.35 5-Dimethylamino-1-naphthalenesulfonate is a fascinating fluorophore, in which the dimethylamino moiety represents the electron donor and the naphthalene sulfonyl unit functions as the electron acceptor.36,37 The molecule has large Stokes shift, high fluorescence quantum yield, intense absorption band in the near UV region, and strong fluorescence in the visible region.38−40 These characteristics, combined with the synthesis flexibility of the sulfonic acid group, had led the dansyl fluorophore to be a core structure in many fluorescent sensors and labels. As previously mentioned, Cu2+ fluorescent enhancement sensors were rarely reported because of the paramagnetic nature of Cu2+. Particularly, a Cu2+-catalyzed hydrolysis fluorescent enhancement based on a diarylethene containing a dansylhydrazine group has not hitherto been reported. Herein, we designed and synthesized a dansyldiarylethene-based “turn-on” fluorescent probe for Cu2+ and “turn-off” fluorescent probe for Fe3+. This molecular probe showed high selectivity, low detection limit, large Stokes shift, and strong fluorescence change. The schematic illustration of photochromism is shown in Scheme 1. Scheme 1. Photochromism of Diarylethene 1O

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RESULTS AND DISCUSSION Photochromism and Fluorescence of 1O. The photochromic and fluorescence properties of 1O were studied in methanol (C = 2.0 × 10−5 mol L−1) at room temperature. 1O showed good photochromic properties and could be triggered between their colored closed-ring isomers 1C and colorless open-ring isomers 1O by alternating irradiation with UV and visible light (λ > 500 nm). The absorption spectrum changes of 1O in methanol are shown in Figure 1A. The maximum of absorption for the open-ring isomer 1O was found at 311 nm (ε = 3.85 × 104 L mol−1 cm−1) because of the π → π* transition.41,42 Upon irradiation with 297 nm UV light, two new absorption peaks appeared at 356 nm (ε = 1.59 × 104 L 6598


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Figure 1. Changes in the absorption spectrum and fluorescence of 1 upon alternating irradiation with UV and visible light in methanol (C = 2.0 × 10−5 mol L−1): (A) absorption spectral and color changes and (B) fluorescence and color changes (λex = 338 nm).

interference in the fluorescence was observed when Cu2+ was added to the solutions containing 1O and the same amount of other competitive metal ions even the paramagnetic quencher Fe3+. Additionally, there were no evident variations in the fluorescence intensity as other competitive metal ions were added to the mixed solutions containing 1O and Fe3+. The results indicated that other competitive metal ions had no obvious impact on the fluorescence of 1O. This reveals that diarylethene 1O would be a highly effective bifunctional fluorescent probe for the detection of Cu2+ and Fe3+ over other common metal ions. To further evaluate the affinities between 1O and Fe3+/Cu2+, a series of tests including fluorescence titration analysis, Job’s plot, and mass spectrometry (MS) were performed in this study. The results of the fluorescence changes by titrating Fe3+ and Cu2+ into the solution of 1O are shown in Figure 3. Upon addition of Fe3+ (0 → 3.0 equiv Figure 3A), the original fluorescence emission intensity at 557 nm dramatically

Table 1. Absorption Spectral Properties of Diarylethenes 1O and 2O in Methanol (C = 2.0 × 10−5 mol L−1) at Room Temperature λo,max/nma (ε/L mol−1 cm−1)

λc,max/nmb (ε/L mol−1 cm−1)

compound

methanol

methanol

1O 2O

311 (3.85 × 10 ) 313 (2.89 × 104) 4

556 (1.18 × 10 ) 539 (0.95 × 104) 4

Φc Φo−c

Φc−o

0.24 0.49

0.29 0.10

a

Absorption maxima of open-ring isomers. bAbsorption maxima of closed-ring isomers. cQuantum yields of cyclization (Φo−c) and cycloreversion (Φc−o), respectively.

over other competing metal ions in methanol. To estimate the specificity of 1O, competitive experiments were performed by adding Cu2+/Fe3+ (5.0 equiv) to the solution of 1O in the presence of other metal ions (5.0 equiv). As shown in Figure S3 (Supporting Information), it is clear that no obvious

Figure 2. Changes in the fluorescence of 1O induced by the addition of various metal ions (3.0 equiv) in methanol (C = 2.0 × 10−5 mol L−1): (A) emission spectral changes and (B) photos demonstrating changes in its fluorescence. 6599


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Figure 3. Changes in the fluorescence spectrum of chemosensor 1 induced by Fe3+/EDTA and Cu2+ in methanol (2.0 × 10−5 mol L−1): (A) 1O induced by Fe3+/EDTA (Inset: the fluorescence intensity curve at 557 nm with the addition of different equiv Fe3+) and (B) 1O induced by Cu2+ with sufficient response time (Inset: the fluorescence intensity curve at 494 nm with the addition of different equiv Cu2+).

Figure 4. (A) 1O induced by Cu2+ with time variation (0 → 150 min) and (B) 1C induced by Cu2+ with time variation (0 → 80 min).

intensities and the concentrations of Fe3+/Cu2+ (0 → 2.0 equiv) was obtained as shown in the inset of Figure 3. The results demonstrated that 1O could quantitatively detect Fe3+/ Cu2+ at relevant concentrations. Subsequently, the fluorescence switch properties of the complex 1O−Fe3+ and 1O + Cu2+ were performed upon irradiation with UV/vis light. The results showed that the emission intensity of 1O−Fe3+ could be further quenched to ca. 48% because of the formation of the nonfluorescence 1C−Fe3+ (Figure S4B, Supporting Information), whereas the emission intensity of the complex 1O + Cu2+ exhibited no significant change upon photoirradiation. Moreover, it was also noted that diarylethene 1 showed a timedependent fluorescence intensity to Cu2+. Upon addition of Cu2+ (4.0 equiv), the fluorescence emission peak at 557 nm quickly blue-shifted to 494 nm and the fluorescence intensity decreased slightly. The fluorescence intensity of 1O gradually increased till a certain time of 150 min and remained almost unchanged over a period of time of 30 min (Figure 4A). Just like 1O, the weak fluorescence of 1O in the PSS was also observed for a “turn-on” signal by Cu2+ (4.0 equiv) stimulation with the time-dependent fluorescence response (0 → 80 min). In comparison to the open-ring isomer 1O, the response time of the closed-ring isomer 1C to Cu2+ was much shorter, indicating that 1C had higher sensitivity toward Cu2+ than 1O. The high energy of the closed-ring 1C may be responsible for this phenomenon.44,45 Subsequently, the reversibility of 1O/ 1C toward Cu2+ was investigated and the fluorescence spectrum of 1O/1C + Cu2+ could not be restored to that of 1O/1C even when an excess amount of EDTA solution had

decreased and remained almost unchanged with further titration. Compared to 1O, the emission intensity was quenched to ca. 23% owing to the formation of a complex 1O−Fe3+. The absolute fluorescence quantum yield was determined to be 0.005. This fluorescence decay phenomenon may be ascribed to strong chelation-enhanced fluorescence quenching (CHEQ).43 It should be noted that the fluorescence of 1O could be reversibly restored by adding excess ethylenediaminetetraacetic acid (EDTA) to the complex 1O−Fe3+. This was due to the complexation−dissociation reaction between Fe3+ and EDTA. Similarly, the closed-ring isomer of 1C showed “turn-off” fluorescent response to Fe3+. When 3.0 equiv of Fe3+ was added to the solution of 1O in PSS, the emission peak was red-shifted by 30 nm with fluorescence emission intensity reduction to ca. 10% in comparison with 1O. This was due to the formation of a complex 1C−Fe3+ (Figure S4A, Supporting Information). In contrast, increased Cu2+ concentrations (0 → 4.0 equiv Figure 3B) resulted in a sharp fluorescence enhancement up to 5.5-fold around 494 nm with the notable fluorescent color change from bright yellow to bright blue. The absolute fluorescence quantum yield of 1O + Cu2+ was determined to be 0.085 using the absolute PL quantum yield spectrometer QYC11347-11. Similarly, the closed-ring isomer of 1C also showed “turn-on” fluorescent response to Cu2+. Moreover, by plotting the fluorescence intensity ratio at 557/494 and 557 nm (I557nm/I557nm for Fe3+ and I494nm/I557nm for Cu2+) as a function of Fe3+/Cu2+ concentrations, respectively, a good linear relationship between the ratio of the fluorescence 6600


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Figure 5. HRMS-ESI spectra of 1O in the presence of Cu2+ (2.0 equiv).

Scheme 2. Proposed Cu2+-Catalytic Hydrolysis Reaction Mechanism for 1O

To further confirm that the Cu2+-catalyzed hydrolysis reaction occurs, the infrared (IR) spectroscopy of 1O was conducted before and after adding Cu2+. It is clearly observed that the vibration peaks of the secondary amines ν(N−H) at 3308 and 2546 cm−1 almost disappeared after the Cu2+ addition, whereas two new vibration peaks of hydroxy ν(O−H) were observed at 3334 and 2546 cm−1 (the associating vibration peak) (Figure S5, Supporting Information). In addition, the vibration peaks of the bond (νC−N = 1053 cm−1) distinctly decreased, while the vibration peaks of νC−O = 1684 cm−1 were significantly enhanced. These results implied that diarylethene 1O was hydrolyzed in the presence of Cu2+. The fluorescence quantum yield of hydrolysate was determined to be ca. 0.085 at the saturation. On the basis of the above-mentioned facts, the hydrolysis reaction mechanism of 1O by Cu2+ was proposed as shown in Scheme 2. The limit of detection (LOD) of the probe for Cu2+ was determined to be 3.49 × 10−7 mol L−1 (Figure S6, Supporting Information). The result showed that probe 1 had excellent sensitivity for Cu2+ detection.

been added. This indicated that diarylethene 1O is a fluorescence irreversible probe for the detection of Cu2+. Considering the above results, the fluorescence enhancement effect between 1O and Cu2+ attracted more attention than the Fe3+ quenching effect. It is suspected that the Cu2+catalytic hydrolysis reaction is responsible for this phenomenon.46−49 In order to confirm the inference, the electrospray ionization (ESI) mass spectrometry (MS) tracking experiments were carried out. As shown in Figure 5, the peak at m/z = 772.1164 (calcd = 772.1173) corresponded to [1O + Na]+. When 2.0 equiv of Cu2+ was added into the solution of 1O, the original peak of 1O (m/z = 772.1164) disappeared and three new peaks were observed at m/z = 501.0248, 266.0492, and 250.0547. It was believed that these new peaks are related to compound [2O − H]− (m/zcalcd = 501.0418), compound [3 + H]+ (m/zcalcd = 266.0963), and a new strongly fluorescent dye hydrolysate 5-(dimethylamino)naphthalene-1-sulfonic acid (m/zcalcd = 250.0538), respectively. These findings suggested that diarylethene 1O was hydrolyzed upon catalysis by Cu2+. 6601


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Figure 6. (A) Job’s plot for 1O with Fe3+, (B) Hildebrand−Benesi plot based on the 1:1 ratio between 1O and Fe3+; the binding constant for 1O with Fe3+ was calculated to be 1.04 × 104 L mol−1, and (C) LOD is 9.73 × 10−8 mol L−1.

Figure 7. Concentration-dependent fluorescence signaling regression curve of Fe3+ by probe 1O in methanol. [Fe3+] = 0−1.0 × 10−5 M. (A) Content of Fe3+ in the Ganjiang river sample (Inset: the red square point was the result of upstream river water samples; the blue star point was the result of downstream river water samples), (B) content of Fe3+ in the soil sample (Inset: the purple triangular point was the result of soil samples). (C) The concentration-dependent fluorescence photographs of 1O−Fe3+.

The selectivity of 1O as a fluorescence sensor for Fe3+ was obtained through the CHEQ effect, which was different from that of Cu2+. In order to determine the binding stoichiometry

between 1O and Fe3+, Job’s method was used for fluorescence titration. As shown in Figure 6A, the inflection points were fixed at 0.5, indicating a 1:1 binding stoichiometry ratio for 1O 6602


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and Fe3+. Furthermore, the formation of a 1O−Fe3+ complex was also confirmed by the ESI mass spectra. As shown in Figure S7 (Supporting Information), the peaks at m/z = 837.0905 (calcd = 837.0523) corresponded to [1O + Fe3+ − 2H + 2OH−]+. The binding mechanism between 1O and Fe3+ is shown in Figure S8 (Supporting Information). On the basis of these findings, the association constant (Ka) was calculated to be 1.04 × 104 L mol−1 for 1O−Fe3+ with a good linear relationship (R = 0.998, Figure 6B) according to the Benesi− Hildebrand equation.50,51 Subsequently, the LOD of 1O toward Fe3+ was determined to be 9.73 × 10−8 mol L−1 by the concentration-dependent fluorescence titration experiment (Figure 6C). Compared to other Fe3+ sensors,52−54 the LOD of 1O was much lower, suggesting that diarylethene 1O could serve as a good fluorescence sensor for Fe3+ with high sensitivity and sensitivity. Determination of Fe3+ in the Real Sample. To study the practical application in the real sample, two real water samples from the Ganjiang River of Nanchang City were collected. The first sample was from upstream which was 200 m away from the city sewage outfall and the other one was from downstream. According to the reported methods,55,56 different amounts of Fe3+ were spiked into the real water samples. Table S1 (Supporting Information) shows the results obtained from the probe 1O in the presence of Fe3+. A good recovery was observed in upstream water samples, but the results showed a large deviation in downstream water. The results indicated that the detection limit of Fe3+ is low, indicating that 1O could be used to detect the content of Fe3+ in the downstream water samples. As shown in Figure 7A, a calibration curve was built within a range of 0−1.0 × 10−5 M of Fe3+ (R = 0.99352). Upon addition of 1.0 μL downstream river water sample, the concentration of Fe3+ in the sample was determined to be 4.09 × 10−6 M (0.22 ppm) with three parallel experiments, which is lower than the EPA standard. The results manifested that 1O could be served as a Fe3+ sensor for practical samples. Furthermore, solid samples (10.0 g) were collected from the rice fields of Nanchang and made into 30.0 mL solution sample by the wet digestion method.57−59 Then, upon addition of 1.0 μL sample, the Fe3+ concentration of the solid samples was determined to be 2.82 × 10−2 M in the 1.0 g soil samples (Figure 7B). Application in Logic Circuit. According to the above results, the fluorescence of 1O could be modulated independently by either light or chemical stimuli in methanol. On the basis of the findings, a combinational logic circuit was constructed (Figure 8),60,61 in which the stimulation of light irradiation (In1: 297 nm light and In2: λ > 500 nm visible light) and chemical species (In3: Fe3+ and In4: EDTA) were applied as four input signals, the changes of fluorescence intensity at 557 nm [was less than the 87% original value (turn-on)] were used as the output signal (Out1). The output signal could be treated as “on” with a Boolean value of “1” when strong fluorescence intensity was larger than 55% compared with the original value, otherwise regarded as “off” with a Boolean value of “0”. For example, when input string values were “1, 0, 0, and 0”, In1, In2, In3, and In4 were “on, off, off, and off”. Upon photoirradiation with 297 light, 1O was transformed to 1C and the fluorescence emission intensity obviously decreased. Therefore, the output signal Out1 was “on” and the output digit was “1”. Similarly, other stimulations also resulted in the same “off−on−off” fluorescence switch, and all possible logic strings of the four inputs were concluded

Figure 8. Combinational logic circuits to the truth table given in Table 2: In1 (297 nm light), In2 (λ > 500 nm visible light), In3 (Fe3+), In4 (EDTA) and Out1 (fluorescence at 557 nm).

as a combinational logic circuit (Table 2). Similarly, another logic circuit was constructed with the combination of three Table 2. Truth Table for All Possible Strings of Four BinaryInput Data and the Corresponding Output Digita input

output

In1 (UV)

In2 (vis)

In3 (Fe3+)

In4 (EDTA)

λem = 557 nm

0 1 0 0 0 1 1 1 0 0 0 1 1 1 0 1

0 0 1 0 0 1 0 0 1 1 0 1 1 0 1 1

0 0 0 1 0 0 1 0 1 0 1 1 0 1 1 1

0 0 0 0 1 0 0 1 0 1 1 0 1 1 1 1

0 1 0 1 0 0 1 1 1 0 0 1 0 1 0 0

a At 557 nm, when fluorescence is quenched to ca. 55%, the output signal is defined as “1”. Otherwise, it is “0”.

input signals (In1: 297 nm light, In2: λ > 500 nm visible light, In5: Cu2+) and one output signal (Out2: fluorescence intensity at 494 nm) (Figure S9, Supporting Information). In this logic circuit, the output signal could serve as “on” when the fluorescence intensity was larger than the original value, otherwise defined as “off”. For example, when input string values were “0, 0, and 1”, In1, In2, and In5 were “off, off, and on”. Consequently, when probe 1O was stimulated by Cu2+ and its emission intensity at 494 nm increased significantly, the output signal (Out2) was “on” and the output digit was “1”. All of the possible strings of the three inputs and their corresponding outputs are listed in Table S2 (Supporting Information).

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CONCLUSIONS In summary, a novel dual-response diarylethene fluorescence chemosensor for the detection of Cu2+ and Fe3+ was designed and successfully synthesized. Our experimental results demonstrated that diarylethene 1O was able to recognize 6603


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Scheme 3. Synthetic Routes of Diarylethene 1O

Cu2+ and Fe3+ with remarkably different fluorescence signals and distinct response mechanism. The quenching mechanism of Fe3+ was ascribed to the formation of a 1O−Fe3+ complex. While the corresponding fluorescence enhancement effect of Cu2+ was studied with HRMS-ESI and IR spectra analysis, the Cu2+-catalyzed hydrolysis reaction of 1O and the formation of a dansyl acid dye are believed to be the root cause for the enhancement effect. On the basis of the fact that the fluorescence of the diarylethene compound could be effectively modulated by stimulation with light and chemical species, two combination logic circuits were successfully designed and constructed. Furthermore, diarylethene 1O could be utilized for Fe3+ detection in real samples. In conclusion, a new approach for designing and constructing bifunctional fluorescence sensors had been demonstrated in this investigation. The sensors were based on photochromic diarylethenes, and they showed outstanding selectivity for multiple guest species of interest as shown in this report.

(3:1) as the eluent to obtain 0.30 g of the target compound 1O as a yellow solid in 55% yield. mp 134−135 °C. 1H NMR (400 MHz, DMSO-d6, ppm): δ 1.82 (s, 3H), 1.91 (s, 3H), 2.39 (s, 3H), 2.81 (s, 6H), 6.81 (s, 1H), 7.2 (d, 1H, J = 8.0 Hz), 7.55 (t, 3H, J = 8.0 Hz), 7.66 (s, 4H), 8.16 (d, 1H J = 8.0 Hz), 8.43 (q, 2H, J = 8.0 Hz), 10.16 (s, 1H), 10.64 (s, 1H); 13C NMR (100 MHz, DMSO-d6, TMS): δ 13.03, 13.17, 13.56, 29.29, 44.49, 115.09, 119.93, 122.85, 123.85, 124.25, 124.47, 125.02, 126.19, 127.81, 128.18, 130.06, 130.42, 130.80, 131.02, 134.20, 136.82, 138.48, 139.97, 140.92, 142.66, 150.73, 166.98; IR (KBr, ν, cm−1): 486, 539, 572, 631, 792, 847, 890, 899, 946, 986, 1049, 1189, 1111, 1147, 1163, 1190, 1234, 1273, 1309, 1333, 1410, 1436, 1500, 1525, 1608, 1669, 2789, 2850, 2922, 2957, 3132, 3304; HRMS-ESI (m/z): calcd for C35H29F6N3O3S3 [M + Na]+, 772.1173; found, 772.1164 m/ z for [1O + Na]+. Real Sample Analysis. The water sample was filtered through a filter paper to remove some large-size impurities. The solutions of Fe3+/Cu2+ (0.01 mol L−1) were prepared by the dissolution of Fe(NO3)3/Cu(NO3)2 in distilled water (standard solutions) and river water (sample solutions), respectively. The intensity for each of the four standard solutions was determined at 557/494 nm for the fluorescence spectrum. The results were obtained, and the working curve was prepared. The intensity of the sample solutions was determined to find out the concentration of Fe3+/Cu2+ by the working curve method.

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EXPERIMENTAL SECTION General Methods. All solvents used were of spectro-grade and purified by distillation prior to use. Expect for K1+ and Hg2+ (their counter anions were chloride ions), other metal ions were obtained by the dissolution of their respective metal nitrates (0.1 mmol) in distilled water (10 mL). EDTA was obtained by the dissolution of EDTA disodium salt (Na2EDTA) (1.0 mmol) in distilled water (10 mL).1H NMR and 13C NMR spectra were collected on a Bruker AV400 (400 MHz) spectrometer with DMSO-d6 as a solvent and tetramethylsilane (TMS) as an internal standard. UV/vis spectra were measured on an Agilent 8453 UV/vis spectrophotometer. Fluorescence spectra were recorded with a Hitachi F-4600 fluorescence spectrophotometer. The fluorescence quantum yield was measured with an absolute PL quantum yield spectrometer QY C11347-11. IR spectra were collected on a Bruker Vertex-70 spectrometer. MS analysis was performed on an Agilent 1100 ion trap MSD spectrometer. Melting point was measured using a WRS-1B melting point apparatus. Photoirradiation experiments were performed using an SHG-200 UV lamp, Cx-21 ultraviolet fluorescence analysis cabinet, and a BMH-250 visible lamp. Synthesis of diarylethene 1O is shown in Scheme 3. Synthesis of 1-(2,5-Dimethyl-3-thienyl)-2-[2-methyl5-(dansyl-4-benzoylhydrazino)-3-thienyl]perfluorocyclopentene (1O). A mixture of compound 2O (0.50 g, 1 mmol) was added dropwise to isobutyl chloroformate (0.16 g, 1.2 mmol) and triethylamine (0.10 g, 1.0 mmol) in anhydrous tetrahydrofuran under stirring at 0 °C for 0.5 h. Then, compound 3 (0.32 g, 1.2 mmol) was added to the reaction mixture at 70 °C and stirred 5 h. The reaction mixture was cooled, the solvent was under reduced pressure, and then the mixture was extracted with dichloromethane. The organic layer was washed with water, dried over anhydrous Na2SO4, and evaporated. The crude product was purified by column chromatography using petroleum ether/ethyl acetate

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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/acsomega.8b03143. Absorption spectra, fluorescence spectrum, 1H NMR and IR spectra, HRMS-ESI spectra, competition experiment, LOD, and logic circuits of diarylethene 1O (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (R.W.). *E-mail: [email protected]. Phone: +86 791 83831996 (S.P.). ORCID

Renjie Wang: 0000-0002-2715-8831 Gang Liu: 0000-0001-7269-9859 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors are grateful for the financial support from the Natural Science Foundation of China (41867053) and the Science Funds of Natural Science Foundation of Jiangxi Province (20171ACB20025). The authors were also grateful for the “5511” Science and Technology Innovation Talent 6604


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Project of Jiangxi Province (20165BCB18015), the Project of the Science Funds of Jiangxi Education Office (GJJ180614), and the Jiangxi Science & Technology Normal University Doctoral Research Startup fund (2018BSQD021).

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