Article pubs.acs.org/JPCB

Highly Sensitive and Selective Fluorescent Sensor for Zinc Ion Based on a New Diarylethene with a Thiocarbamide Unit Congcong Zhang, Shouzhi Pu,* Zhiyuan Sun, Congbin Fan, and Gang Liu Jiangxi Key Laboratory of Organic Chemistry, Jiangxi Science & Technology Normal University, Nanchang 330013, P. R. China ABSTRACT: A new photochromic diarylethene has been synthesized by using thiocarbamide as a functional group and perfluordiarylethene as photoswitching trigger via a salicylidene Schiff base linkage. The diarylethene could be used as a multicontrollable fluorescence switch when triggered by base/ acid, light, and metal ions. The results showed that the absorption and fluorescence characteristics of the diarylethene exhibited sequence-dependent responses through efficient interaction of specific salicylidene Schiff base-linked thiocarbamide unit with tetrabutylammonium hydroxide/trifluoroacetic acid and photoirradiation. Moreover, the diarylethene was highly selective toward Zn2+ ion with obvious fluorescence change from light blue to bright yellow in acetonitrile. The deprotonated form of the diarylethene had typical photochromism, but it showed an irreversible photocyclization reaction after binding with Zn2+. Finally, two logic circuits were constructed by using the fluorescence intensity as the output signal with the inputs of the combinational stimuli of light and chemical species.

1. INTRODUCTION Over the past several decades, an increasing number of photochromic compounds have been synthesized because of their potential applications in optoelectronic devices, such as photoresponsive self-assemblies,1,2 molecular switches,3−6 information manipulation,7−9 logic gates,10−13 and fluorescent chemosensors.14,15 To date, several types of thermally irreversible photochromic compounds, such as furylfulgides,16 phenoxynaphthacenequinones,17 and diarylethenes,6,18 have been studied. Among all photochromic compounds, organic diarylethenes were regarded as one of the most attractive candidates for practical applications owing to their excellent thermal stability, remarkable fatigue resistance, high sensitivity, and rapid response.6,18−21 In recent years, the design and synthesis of diarylethenes derivatives with high selectivity and sensitivity for cations, especially transition-metal ions, have received much attention.22−24 Among the various transition-metal ions, Zn2+ is an essential one which plays a vital role in many cellular processes, such as control of gene transcription and metalloenzyme functions, DNA synthesis, cell apoptosis, and structural motifs maintenance in proteins.25−30 In contrast, the soil microbial activity may be reduced by Zn2+, a common contaminant in agricultural and food wastes.31,32 Therefore, it is valuable to design a highly selective fluorescent sensor for Zn2+. However, the reported fluorescent sensors for Zn2+ were poorly selective due to the interference of Cd2+ with similar electron configuration.33−35 For example, Samit Majumder and co© XXXX American Chemical Society

workers synthesized a tetraiminodiphenol macrocyclic ligand and found that it could be coordinated with Cd2+ and Zn2+. Meanwhile, its fluorescence could be effectively modulated by stimulation of the two metal ions.34 In order to make full use of optical methods for the detection of Zn2+, various new dyes and fluorophores have been developed, and the results obtained have contributed to understand the mechanism of Zn2+ detection.36−42 Thiocarbamide is an excellent candidate for constructing sensing system because of its high biological characteristics for resisting zymad and its special structure (−HN−CS−NH−) having multiple hydrogen-bonding interaction sites such as N and S atom.43,44 To date, thiocarbamide derivatives have drawn great attention due to their important applications in ion sensors,45−47 medical science,48 bioorganic chemistry,44,49 supramolecular chemistry,50 and asymmetric synthesis.51,52 In addition, thiourea-based molecular systems have been widely used to make the components of machinery and electronics down to molecular level.53,54 For example, Norio Teramae et al. constructed a highly selective chromoionophore for the recognition of MeCO2− by using thiourea-based chromoionophore/didecyldimethylammonium bromide complexes in water.55 Tian He and co-workers reported a selective ratiometric chemosensor based on a 1,8-naphthalimide Received: February 10, 2015 Revised: March 4, 2015

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DOI: 10.1021/acs.jpcb.5b01390 J. Phys. Chem. B XXXX, XXX, XXX−XXX

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The Journal of Physical Chemistry B Scheme 1. Synthetic Method and Photochromism of Diarylethene 1O

Figure 1. Changes in the absorption spectrum and fluorescence of 1O upon alternating irradiation with UV and visible light in acetonitrile: (A) absorption spectral change (2.0 × 10−5 mol L−1); (B) fluorescence change (5.0 × 10−5 mol L−1), excited at 380 nm.

derivative for Hg2+ with high selectivity in aqueous solution.56 The results obtained have contributed to a broad understanding of the recognition mechanism for anions and cations with thiourea-based compounds. However, fluorescent chemosensors for special ions of interest based on thiocarbamidecontaining photochromic diarylethenes have rarely been reported. In this work, a new fluorescent chemosensor for Zn2+ with high selectivity based on a diarylethene with a thiocarbamide unit was constructed, and its multifunctional fluorescent switching characteristics induced by tetrabutylammonium hydroxide/trifluoroacetic acid, light, and Zn2+ were systematically studied and discussed. The schematic illustration of photochromism is shown in Scheme 1.

Mass spectra were obtained on a Bruker AmaZon SL spectrometer. Elemental analysis was measured with a PE CHN 2400 analyzer. The solutions of metal ions (0.1 mol L−1) were prepared by the dissolution of their respective metal nitrates in methyl alcohol, except for Mn2+, Hg2+, K+, and Pd2+ (all of their counterions were chloride ions). 2.2. Synthesis of the Target Compound. The synthesis route to diarylethene 1O is shown in Scheme 1. Compound 2 was synthesized by the reported method.40 Synthesis of 1-(2,5-dimethyl-3-thienyl)-2-[2-methyl-5-(3formyl-4-hydroxylphenyl)-3-thienyl]perfluorocyclopentene (3). Compound 2 (1.55 g, 3.0 mmol) dissolved in anhydrous CH2Cl2 was added to BBr3 (6.0 mL) at 195 K under an argon atmosphere. After stirring for 0.5 h at this temperature, the mixture was warmed to room temperature and stirred for 2 h. Then reaction was quenched with water, and the organic layer was extracted with dichloromethane and washed with plenty of water. The organic layer was dried over MgSO4, filtrated, and evaporated. The crude product was purified by column chromatography on silica gel using petroleum ether/ethyl acetate (10:1) as the eluent to give compound 3 (0.46 g, 31%) as a light yellow solid. 1H NMR (CDCl3, 400 MHz), δ (ppm): 1.80 (s, 3H, −CH3), 1.85 (s, 3H, −CH3), 2.36 (s, 3H, −CH3), 6.67 (d, 1H, J = 8.0 Hz, phenyl−H), 6.97 (s, 1H, thienyl−H), 7.12 (s, 1H, thienyl−H), 7.62 (m, 2H, phenyl−H), 9.89 (s, 1H, −CHO), 10.96 (s, 1H, −OH). MS (m/z): 501.0 [M − H]+. Synthesis of 1-(2,5-dimethyl-3-thienyl)-2-{2-methyl-5-[4hydroxyl-3-(2-methyleneaminophenylthioureayl)phenyl]-3-

2. EXPERIMENTS 2.1. General Methods. All solvents were spectroscopic grade and were purified by distillation before use. Other reagents were used without further purification. NMR spectra were recorded on a Bruker AV400 (400 MHz) spectrometer with CDCl3 as the solvent and tetramethylsilane as an internal standard. Infrared spectra (IR) were recorded on a Bruker Vertex-70 spectrometer. Melting point was measured on a WRS-1B melting point apparatus. Absorption spectra were measured using an Agilent 8453 UV/vis spectrophotometer. Photoirradiation was carried out using an MUΛ-165 UV lamp and a MVL-210 visible lamp. The required wavelength was isolated by the use of appropriate filters. Fluorescence spectra were measured using a Hitachi F-4500 spectrophotometer. B

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The Journal of Physical Chemistry B Scheme 2. Photochromism, Color, and Fluorescence Changes of 1 Induced by TBAH/TFA and UV/vis

thienyl}perfluorocyclopentene (1O). To a stirred solution of compound 4 (0.083 g, 0.5 mmol) in refluxing ethanol, equimolar quantities of compound 3 (0.25 g, 0.5 mmol) were added and continued stirred for 12 h. Then the crude product was purified by recrystallization. Diarylethene 1O (0.25 g) was obtained in 77% yield as a pale yellow solid. 1H NMR (CDCl3, 400 MHz), δ (ppm): 1.80 (s, 3H, −CH3), 1.84 (s, 3H, −CH3), 2.35 (s, 3H, −CH3), 6.67 (s, 1H, thienyl−H), 6.97 (d, 1H, J = 8.0 Hz, phenyl−H), 7.10 (s, 1H, thienyl−H), 7.26 (m, 1H, phenyl−H), 7.37 (m, 3H, phenyl−H), 7.46 (m, 1H, phenyl− H), 7.51 (m, 2H, phenyl−H), 8.01 (s, 1H, −OH), 8.30 (s, 1H, −CHN), 9.37 (s, 1H, −NH), 9.63 (s, 1H, −NH). 13C NMR (CDCl3, 100 MHz), δ (ppm): 14.4, 14.8, 15.3, 117.3, 117.7, 122.1, 124.7, 125.0, 126.4, 127.0, 128.4, 129.1, 130.0, 137.3, 137.8, 139.7, 140.6, 140.8, 146.5, 157.0, 175.8. IR (KBr, υ, cm−1): 1084 (CS), 1655 (CN), 3344 (N−H), 3666 (O− H). MS (m/z): 650.1 [M − H] + . Anal. Calcd for C30H23F6N3O2S3: C, 55.29; H, 3.56; F, 17.49; N, 6.45. Found: C, 55.31; H, 3.57; N, 6.47.

and at 353 K, and the results showed that the two isomers of 1 had good thermal stability at both temperatures. In photostationary state (PSS), the photoconversion ratio from the openring isomer 1O to the closed-ring isomer 1C was determined as 50% by HPLC analysis. By using 1,2-bis(2-methyl-5-phenyl-3thienyl)perfluorocyclopentene as a reference compound,58 the cyclization and cycloreversion quantum yields of 1 were measured to be 0.026 and 0.014, respectively. Figure 1B shows the emission spectral changes of 1O upon photoirradiation when excited at 380 nm. The emission peak of 1O was observed at 472 nm in acetonitrile. Upon irradiation with 297 nm UV light, the photocyclization reaction occurred, and the emission peak of 1O decreased notably, accompanied by an obvious color change from light blue to dark. In photostationary state, the emission intensity of 1O was quenched to ca. 29%. The residual fluorescence in photostationary state may be attributed to the incomplete cyclization reaction and the existence of open-ring isomer with parallel conformation.59 3.2. Changes in Absorption and Fluorescence by Base/Acid Stimuli. The dual-controllable photoswitching behaviors of 1O were investigated by the stimulation of base/ acid as shown in Scheme 2. The absorption spectral changes of 1O induced by tetrabutylammonium hydroxide (TBAH) and trifluoroacetic acid (TFA) in acetonitrile at room temperature are shown in Figure 2A. When 2.0 equiv of TBAH (1.2 μL, 0.1 mol L−1) was added to the colorless solution of 1O, a new visible band centered at 386 nm (ε = 3.99 × 104 mol−1 L cm−1) was observed, and the solution color turned pale yellow due to the formation of deprotonated diarylethene 1O′. The deprotonated 1O′ could return to 1O by neutralization with 2.0 equiv of TFA (1.2 μL, 0.1 mol L−1). Moreover, 1O′ could undergo photoisomerization (Figure 2B). Upon irradiation with 297 nm light, the pale yellow solution of 1O′ turned dark blue with concomitant appearance of a new visible absorption band centered at 584 nm (ε = 1.67 × 104 mol−1 L cm−1) due to the formation of the closed-ring isomer 1C′. The dark blue solution changed to pale yellow when irradiated with visible light (λ > 450 nm), indicating that 1C′ returned to its initial form 1O′. In addition, the reversible transformation between

3. RESULTS AND DISCUSSION 3.1. Photochromic and Fluorescent Properties. Figure 1 shows the absorption spectrum and fluorescence changes of 1O upon alternating irradiation with UV and visible light in acetonitrile (2.0 × 10−5 mol L−1) at room temperature. As shown in Figure 1A, the absorption maximum of 1O in acetonitrile was observed at 307 nm (ε = 4.19 × 104 mol−1 L cm−1) due to a π → π* transition.57 Upon irradiation with 297 nm light, a new absorption band centered at 554 nm (ε = 1.06 × 104 mol−1 L cm−1) emerged due to the formation of the closed-ring isomer 1C with larger π-electron delocalization in the molecule, accompanied by a color change from colorless to purple. Alternatively, the absorption spectrum recovered to the initial state and the purple color returned colorless when the solution of 1C was irradiated with visible light. The coloration− decoloration cycles between 1O and 1C could be repeated for more than 10 times, and no remarkable decomposition was observed by UV/vis spectral analysis. The thermal stability of 1O and 1C was checked in acetonitrile at room temperature C

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Figure 3. Changes in the fluorescence of 1 induced by TBAH/TFA and light stimuli in acetonitrile (5.0 × 10−5 mol L−1): (A) 1O induced by TBAH/TFA; (B) 1O′ induced by photoirradiation; (C) 1C induced by TBAH/TFA.

Figure 2. Changes in the absorption spectrum and color of 1 induced by TBAH/TFA and light stimuli in acetonitrile (2.0 × 10−5 mol L−1): (A) 1O induced by TBAH/TFA; (B) 1O′ induced by photoirradiation; (C) 1C′ induced by TFA/TBAH.

fluorescence switch by photoirradiation in acetonitrile at room temperature (Figure 3B). Upon irradiation with 297 nm UV light, the photocyclization reaction took place and produced the weakly fluorescent closed-ring isomer 1C′. In photostationary state, the emission intensity of 1C′ was quenched to ca. 22% with a concomitant color change from bright yellow to dark yellow. In addition, the fluorescence change between 1C and 1C′ could be circulated by the stimulation of TBAH and TFA (Figure 3C). When 2.0 equiv of TBAH (1.2 μL, 0.1 mol L−1) was added to the solution of 1C, the fluorescence intensity was enhanced by 1.7-fold, and the peak shifted from 463 to 553 nm due to the formation of 1C′. After addition of 2.0 equiv of TFA (1.2 μL, 0.1 mol L−1), 1C′ returned to its initial form 1C and its fluorescence restored to the initial state. The results indicated that both absorption and fluorescence of the diarylethene could be effectively modulated by the stimulation of base/acid and photoirradiation. 3.3. Changes in Absorption and Fluorescence Induced by Zn2+. The photoswitching behaviors of 1O were studied with the stimulation of Zn2+ and light irradiation

1C′ and 1C could be realized by the stimulation of TBAH and TFA (Figure 2C). After adding 2.0 equiv of TFA (1.2 μL, 0.1 mol L−1) to the solution of 1C′, the dark blue solution immediately changed to purple with a notable blue-shift from 584 to 554 nm due to the formation of 1C. Reversely, 1C could return to 1C′ when 2.0 equiv of TBAH (1.2 μL, 0.1 mol L−1) was added. Figure 3 shows the fluorescence changes of 1 induced by TBAH/TFA and light in acetonitrile (5.0 × 10−5 mol L−1) at room temperature. As described previously, 1O showed weak fluorescence at 472 nm. However, its fluorescence was significantly enhanced by the addition of 2.0 equiv of TBAH (1.2 μL, 0.1 mol L−1). A new peak centered at 566 nm emerged due to the formation of the deprotonated 1O′ (Figure 3A). The new emission peak at 566 nm has a 2.5 times intensity. Compared to that of 1O, the emission peak 1O′ was red-shifted by 94 nm with a notable color change from light blue to bright yellow. This result was in agreement with the previous reports on the enhanced fluorescence of salicylidene Schiff bases upon deprotonation.40 Diarylethene 1O′ exhibited a notable D

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The Journal of Physical Chemistry B Scheme 3. Photochromism, Color, and Fluorescence Changes of 1 induced by Zn2+/EDTA and UV/vis

Figure 4. Changes in the absorption spectrum and color of 1 induced by Zn2+/EDTA and light stimuli in acetonitrile (2.0 × 10−5 mol L−1): (A) 1O induced by Zn2+/EDTA; (B) 1O″ upon irradiation with UV light; (C) 1C induced by Zn2+/EDTA; (D) 1C″ upon irradiation with visible light.

E

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Figure 5. Changes in the fluorescence of 1O induced by the addition of various metal ions (5 equiv) in acetonitrile (5.0 × 10−5 mol L−1): (A) emission spectral changes; (B) emission intensity changes; (C) photos demonstrating changes in its fluorescence.

Figure 6. Changes in the fluorescence and color of 1 induced by Zn2+/EDTA and light stimuli in acetonitrile (5.0 × 10−5 mol L−1): (A) 1O induced by Zn2+; (B) 1O″ upon irradiation with UV light; (C) 1C induced by Zn2+; (D) 1C″ upon irradiation with visible light; (E) photos demonstrating changes in its fluorescence.

acetonitrile (2.0 × 10−5 mol L−1) at room temperature are shown in Figure 4. When 5.0 equiv of Zn2+ (3.0 μL, 0.1 mol

as shown in Scheme 3. The absorption spectral and color changes of 1 induced by Zn2+/EDTA and UV/vis stimuli in F

DOI: 10.1021/acs.jpcb.5b01390 J. Phys. Chem. B XXXX, XXX, XXX−XXX

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The Journal of Physical Chemistry B L−1) was added to the solution of 1O, the initial absorption peak at 307 nm decreased and a new absorption band centered around 425 nm emerged due to the formation of complex 1O″ (Figure 4A). Upon irradiation with 297 nm UV light, the light yellow solution of 1O″ turned purple, accompanied by the appearance of a new absorption band centered at 567 nm (ε = 1.37 × 104 mol−1 L cm−1) due to the formation of the closedring isomer 1C″ (Figure 4B). 1C″ could be formed by reacting 1C with Zn2+ (Figure 4C). It was noticed that the absorption properties of 1O and 1C could not be restored by adding excess EDTA to the solutions containing 1O″ and 1C″, respectively. The results elucidated that both of the two isomers bound to Zn2+ much more tightly than EDTA to Zn2+. In addition, the experimental results revealed that 1C″ could not entirely return to 1O″ upon irradiation with appropriate visible light (Figure 4D). Enough long time exposure of 1C″ under visible light could not bleach the purple solution of 1C″. Its absorbance only decreased slightly to 77% of the initial value. Under the same experimental conditions, the fluorescence changes of 1O was tested by the addition of various metal ions, including Mn2+, Al3+, Ni2+, K+, Cd2+, Ca2+, Cu2+, Ba2+, Pb2+, Cr3+, Co2+, Sr2+, Mg2+, Sn2+, Hg2+, Fe3+, and Zn2+. Figure 5 shows the fluorescence and color changes of 1O induced by metal ions in acetonitrile (5.0 × 10−5 mol L−1) at room temperature. The results clearly showed that the fluorescence and color dramatically changed only when 5.0 equiv of Zn2+ was added to the solution of 1O. Compared with that of 1O, the emission intensity of the binding complex 1O″ was enhanced by 5-fold at 549 nm, and its peak showed a notable red-shift of 77 nm, accompanied by a remarkable fluorescence color change from light blue to bright yellow. It is noteworthy that the individual addition of Ni2+, Cu2+, Co2+, Fe3+, and Sr2+ also resulted in very tiny fluorescence change, but the change is negligible and its fluorescence color is unobservable. The stimulation with other metal ions induced no obvious changes in the fluorescence and color of 1O. Therefore, the diarylethene could serve as a naked-eye chemosensor for detection of Zn2+ with high selectivity. To further elucidate the responsive fluorescence of 1O induced by Zn2+ and UV/vis irradiation, the fluorescence titration tests were performed in acetonitrile (5.0 × 10−5 mol L−1) at room temperature as shown in Figure 6. When Zn2+ was gradually added to the solution of 1O, an increase in fluorescence intensity at 549 nm was observed, accompanied by a notable fluorescent color change from light blue to bright yellow. The maximum intensity was reached when 5.0 equiv of Zn2+ was added, followed by a plateau with further titration (Figure 6A). Compared to 1O, the emission peak of 1O″ was red-shifted by 77 nm with an enhanced intensity of 5-fold at the plateau. The inset of Figure 6A depicts the effect of Zn2+ concentration on the emission intensity at 549 nm. The result indicated that there existed a linear relationship between the fluorescence intensity and the Zn2+ concentration in the range of 0−40 μM, suggesting that the diarylethene could be potentially used as a colorimetric fluorescent probe for Zn2+.24 Upon irradiation with 297 nm UV light, the fluorescence intensity of 1O″ was quenched dramatically with a concomitant color change from bright yellow to dark due to the formation of the closed-ring isomer 1C″ (Figure 6B). The quenched fluorescence intensity reached ca. 15% in photostationary state. Furthermore, a fluorometric titration of 1C by Zn2+ was tested in acetonitrile at room temperature as shown in Figure 6C. The result showed that the maximum intensity of

1C″ was reached by adding 5.0 equiv of Zn2+ to the solution of 1C. Compared to 1C, the emission peak of 1C″ was red-shifted by 66 nm with an enhanced intensity of 2.7-fold. As observed for the absorption property of 1O″, the fluorescence of 1C″ could not return to 1O″ upon irradiation with visible light (Figure 6D). Enough long time exposure of 1C″ under visible light enhanced the fluorescence intensity by 2.2-fold. This phenomenon can be applied in nondestructive readout.9,60 The fluorescence color changes between 1 and 1″ are shown in Figure 6E. The result also indicated that the fluorescent properties of 1O and 1C could not be restored by adding excess EDTA to the solutions containing 1O″ and 1C″, respectively. In order to calculate the binding ratio between 1O and Zn2+, the Job’s plot experiment was performed according to the reported method.40,61 As shown in Figure 7, the

Figure 7. Job’s plot showing the 2:1 complex of 1O and Zn2+.

concentration of the complex 1O″ approached the maximum value when the molar fraction of [Zn2+]/([Zn2+] + [1O]) was ca. 0.33, indicating that 1O bound to Zn2+ with a binding stoichiometry of 2:1. 3.4. Application in Logic Circuits. On the basis of the facts that the fluorescence intensity of the target compound could be effectively controlled by base/acid, Zn2+, and UV/vis stimuli (Schemes 2 and 3), we constructed two types of logic circuits by using pH, light irradiation, and cations as the input signals and the change of fluorescence intensity as the output signal (Figure 8). One logic circuit had four inputs (TBAH (In1), TFA (In2), UV (297 nm, In3), and vis (λ > 450 nm, In4)) and an output (fluorescence intensity at 566 nm (O1)), and the other had three inputs (UV (297 nm, In3), vis (λ > 450 nm, In4), and Zn2+(In5)) and an output (fluorescence intensity at 549 nm (O2)). As shown in Figure 8A, the four inputs could be either “on” or “off” state with different Boolean values. When TBAH was employed, In1 was switched to “on” state with a Boolean value of “1”. In the same way, In2 was “1” corresponding to the addition of TFA, In3 was “1” corresponding to irradiation with 297 nm UV, and In4 was “1” corresponding to irradiation with appropriate visible light (λ > 450 nm). Diarylethene 1O exhibited strong fluorescence by the addition of TBAH, and its fluorescence intensity at 566 nm was used as an initial state. The output signal could serve as “on”, when the fluorescence intensity at 566 nm was 2 times higher than the initial value. Otherwise, it was regarded as “off”. Under the stimuli of different inputs, the diarylethene exhibited an on−off−on fluorescent switching behavior. As a result, 1O could read a string of four inputs and write one output (Table 1). Similarly, the fluorescence of 1O could be triggered by Zn2+ and quenched by UV light, so that the other circuit could be G

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Table 2. Truth Table for All Possible Strings of Three Binary-Input Data and the Corresponding Output Digit input In3 (UV)

In4 (Vis)

In5 (Zn2+)

outputa λem = 549 nm

0 0 1 0 1 0 1 1

0 0 0 1 0 1 1 1

0 1 0 0 1 1 0 1

0 1 0 0 0 1 0 0

a

At 549 nm, the emission intensity more than 5 times the original value is defined as 1, otherwise defined as 0.

4. CONCLUSION In conclusion, a novel diarylethene with a thiocarbamide unit via a salicylidene Schiff base linkage was synthesized, and its multicontrollable fluorescent switching behaviors with light, base/acid, and Zn2+ were investigated systematically. The results demonstrated that the diarylethene was highly selective toward Zn2+. Induced by the stimulation of Zn2+, it also showed a gated photochromic reaction that could be potentially applied in optical memory technology with nondestructive readout methods. Moreover, the diarylethene exhibited different absorption and fluorescence behaviors in basic and acid environments. On the basis of the mentioned facts, two logic circuits were constructed by using the fluorescence intensity as the output signal with the inputs of TBAH/TFA, Zn2+, and UV/vis stimuli. Our experimental results are useful for the design and construction of new fluorescent sensors based on photochromic diarylethenes with multicontrollable functional groups and high selectivity for special metal ions of interest.

Figure 8. Two logic circuits based on the diarylethene with various inputs: (A) The combinational logic circuits equivalent to the truth table given in Table 1: In1 (TBAH), In2 (TFA), In3 (297 nm UV light), In4 (450 nm visible light), and O1. (B) Combinational logic circuits equivalent to the truth table given in Table 2: In3 (297 nm UV light), In4 (450 nm visible light), In5 (Zn2+), and O2.

Table 1. Truth Table for All Possible Strings of Four BinaryInput Data and the Corresponding Output Digit input In1 (TBAH)

In2 (TFA)

In3 (UV)

In4 (Vis)

outputa λem = 584 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 0 0 0 0 1 0 0 0 0 0 1 0 0

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AUTHOR INFORMATION

Corresponding Author

*E-mail [email protected]; Fax +86-791-83831996 (S.P.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors are grateful for the financial support from the National Natural Science Foundation of China (51373072, 21363009, and 21262015), the Project of Jiangxi Advantage Sci-Tech Innovative Team (20142BCB24012), the Science Funds of Natural Science Foundation of Jiangxi Province (20132BAB203005 and 20142BAB203005), and the Project of the Science Funds of Jiangxi Education Office (KJLD13069 and KJLD12035).

a

At 566 nm, the emission intensity overtop 100% of the original value is defined as 1, otherwise defined as 0.

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REFERENCES

(1) Evans, R. A.; Hanley, T. L.; Skidmore, M. A.; Davis, T. P.; Such, G. K.; Yee, L. H.; Ball, G. E.; Lewis, D. A. The Generic Enhancement of Photochromic Dye Switching Speeds in A Rigid Polymer Matrix. Nat. Mater. 2005, 4, 249−253. (2) Kärnbratt, J.; Hammarson, M.; Li, S.; Harry, L.; Albinsson, B.; Andréasson, J. Photochromic Supramolecular Memory with Nondestructive Readout. Angew. Chem., Int. Ed. 2010, 49, 1854−1857. (3) Yoon, J. Encoding Optical Signals. Angew. Chem., Int. Ed. 2014, 53, 6600−6601.

constructed. The output signal O2 could serve as “on” when the fluorescence intensity at 549 nm was 5-fold higher than the initial value. Otherwise, it was regarded as “off”. All of the possible logic strings of the three inputs are listed in Table 2, and the logic circuit equivalent to the truth table is shown in Figure 8B. H

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DOI: 10.1021/acs.jpcb.5b01390 J. Phys. Chem. B XXXX, XXX, XXX−XXX