Supramolecular Host–Guest System as Ratiometric Fe3+ Ion Sensor

Sep 11, 2017 - Furthermore, the supramolecular host–guest system could be a “turn-on” fluorescent probe for Fe3+ ion detection through the proce...
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Research Article Cite This: ACS Appl. Mater. Interfaces 2017, 9, 36320-36326

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Supramolecular Host−Guest System as Ratiometric Fe3+ Ion Sensor Based on Water-Soluble Pillar[5]arene Qianfang Yao, Baozhong Lü, Chendong Ji, Yang Cai, and Meizhen Yin* State Key Laboratory of Chemical Resource Engineering, Beijing Laboratory of Biomedical Materials, Beijing University of Chemical Technology, 100029 Beijing, China S Supporting Information *

ABSTRACT: Developing a specific, ratiometric, and reversible detection method for metal ions is significant to guard against the threat of metal-caused environmental pollution and organisms poisoning. Here a supramolecular host−guest system (WP5⊃G) based on water-soluble pillar[5]arene (WP5) and water-soluble quaternized perylene diimide derivative (G) was constructed. Morphological transformation was achieved during the process of adding WP5 into G aqueous solution, and a fluorescence “turn-off” phenomenon was observed which was caused by supramolecular photoinduced electron transfer (PET). Meanwhile, hydrophobic effect and electrostatic interaction played important roles in this supramolecular process, which was confirmed by isothermal titration calorimeter (ITC) and ζ potential experiments. Furthermore, the supramolecular host−guest system could be a “turn-on” fluorescent probe for Fe3+ ion detection through the process of interdicting supramolecular PET. Moreover, the Fe3+ ion detection showed specific, ratiometric, and reversible performances with a detection limit of 2.13 × 10−7 M, which might have great potentials in biological and environmental monitoring. KEYWORDS: supramolecular host−guest, morphological transformation, photoinduced electron transfer, metal detection



for ion detection in biological and environmental systems.26 Furthermore, inherent aggregation-caused fluorescence quenching (ACQ) properties of PDI derivatives in aqueous media could further hamper their sensitivity.27 Therefore, it is very important to develop water-soluble PDI derivatives with excellent detection performance in aqueous solution, and a supramolecular host−guest system should be one of the ideal candidates. In this study, we designed a supramolecular host−guest system (WP5⊃G) in aqueous media based on water-soluble hydroxyl modified PDI derivative (G) and water-soluble pillar[5]arene (WP5) (Scheme 1). G alone exhibited irregular aggregates. With the addition of WP5 to G, the aggregates transformed to regular blocks along with fluorescence “turn-off” because of photoinduced electron transfer (PET). Furthermore, the designed supramolecular host−guest system, WP5⊃G, had a specific response to Fe3+ ion through the process of interdicting supramolecular PET. WP5⊃G could promisingly be applied in environmental and biological monitoring with the advantages of selective, ratiometric, and reversible Fe3+ ion sensing in aqueous solution.

INTRODUCTION Nowadays, supramolecular host−guest systems have been widely investigated for their various advantages, such as low cost,1 convenient synthesis,2 and less time-consuming3 with noncovalent interactions and new functions (ion detection and recognition), which are different from the host or guest molecule alone.4,5 Pillar[n]arenes, as a new generation of macrocyclic host after crown ethers,6 cyclodextrins,7,8 calixarenes,9 cucurbiturils10 and other hosts,11 have raised significant studying interests in supramolecular host−guest systems with their incorporation properties.12−14 In the family of pillar[n]arenes, pillar[5]arenes and pillar[6]arenes are widely investigated due to their easy synthesis and functionalization.15−18 For example, responsive supramolecular host−guest systems based on pillar[n]arenes for ion sensing and drug controlled release have been developed recently.19−21 In environment and biological systems, metal ions, especially heavy metal ions, have caused severe environmental pollution and toxicity to biological systems. In order to find an effective way to detect metal ions, fluorescent probes have gained extensive attention due to their high sensitivity and convenience.22,23 For example, perylenediimide (PDI) derivatives are widely used as fluorophores to construct fluorescent probes due to their excellent chemical, thermal, and photoelectronic stability.24,25 However, many reported systems require the participation of organic solvents that is unfavorable © 2017 American Chemical Society

Received: August 14, 2017 Accepted: September 11, 2017 Published: September 11, 2017 36320

DOI: 10.1021/acsami.7b12063 ACS Appl. Mater. Interfaces 2017, 9, 36320−36326

Research Article

ACS Applied Materials & Interfaces

desorption ionization time-of-flight mass spectrometry (MALDITOF MS) was determined on a AXIMA-CFR plus MALDITOF mass spectrometer. Mass spectra (MS; see the Supporting Information (SI)) were measured with a XEVO-G2QTOF (Waters, USA). UV− visible spectra and fluorescence (FL) spectra were obtained with a spectrophotometer (Cintra 20, GBC, Australia) and fluorescent spectrofluorimeter (Horiba Jobin Yvon FluoroMax-4 near-IR, NJ, USA) respectively. The morphologies of G and WP5⊃G were observed with HITACHI S-4700 (Japan) scanning electron microscope (SEM) manipulated at an accelerating voltage of 10 kV. Samples (1 × 10−5 M; T = 298.15 K) were vacuum sputtered with Pt to increase the contrast before SEM observation. Isothermal titration calorimeter (ITC) experiments were conducted with Nano ITC (TA Instruments Waters, LLC, UT, USA). Dynamic light scattering (DLS) measurements and ζ potentials of samples were observed by a Malvern Zetasizer Nano instrument with compatible disposable capillary cell (DTS 1070 from Malvern). The electrochemical cyclic voltammetry curves were measured on a Zahner IM6e electrochemical workstation with Pt disk coated with the samples, Pt plate, and Ag/Ag+ electrode as working electrode, counter electrode, and reference electrode, respectively, in a 0.1 mol/L tetrabutylammonium hexafluorophosphate (Bu4NPF6) acetonitrile solution. Synthesis and Complexation of G with WP5. The detailed synthesis processes of WP5, G, and G′ are described in the SI (Schemes S1−S3). WP5 was synthesized according to previous literature.17 The structures of synthetic intermediate and final products were confirmed by NMR and MS (Figures S1−S4). For the purpose of preparing a 5:1 supramolecular host−guest system (WP5⊃G, 1 × 10−5 M), 2 μL of aqueous solution of WP5 was added into 2 mL of aqueous solution of G (1 × 10−5 M) dropwise. As for 1:1 ([G]/[WP5]), 10 μL of aqueous solution of WP5 (2 × 10−3 M) was added into 2 mL of aqueous solution of G (1 × 10−5 M) dropwise.

Scheme 1. Cartoon Representation of the Formation of Supramolecular Host−Guest System (WP5⊃G)



EXPERIMENTAL SECTION

Reagents and Materials. 1,4-Dimethoxybenzene (98%), paraformaldehyde (98%), borontribromide (98%), trifluoromethanesulfonic acid (98%), ethyl bromoacetate (98%), ammonium hydroxide (98%), perylenetetracarboxylic dianhydride (98%), N,N-dimethylpropylenediamine (98%), 2-bromoethanol (98%), N,N-dimethylbutylamine (98%) were all obtained from Alfa Aesar. Chlorizated salts of Fe3+, K+, Na+, Li+, Cu+, Zn2+, Mg2+, Cd2+, Hg2+, Fe2+, Sn2+, Cu2+, and Ca2+ were purchased from Xiya Reagent with the purity of 99%. All these reagents were used without further purification. Characterization. 1H NMR spectra were observed on a Bruker 400 spectrometer at room temperature. Matrix-assisted laser-

Figure 1. (a) Concentration-dependent UV−vis absorption spectra of G. (b) UV−vis absorption spectra and (c) fluorescence spectra of G aqueous solution with the addition of WP5 (1 × 10−5 M). (d) Dependence of the optical absorbance intensity at 560 nm on the molar ratio of [G]/[WP5] in aqueous solution. 36321

DOI: 10.1021/acsami.7b12063 ACS Appl. Mater. Interfaces 2017, 9, 36320−36326

Research Article

ACS Applied Materials & Interfaces

Figure 2. SEM images of (a) G (1 × 10−5 M) and (b) [G]/[WP5] = 5:1 (1 × 10−5 M) in aqueous media. Bar is 100 nm. Cartoon representations of (c) aggregation of G and (d) supramolecular self-assembly of [G]/[WP5] = 5:1.



RESULTS AND DISCUSSION Confirmation of Supramolecular Host−Guest System. A water-soluble PDI derivative containing two positive parts in each end was designed as a guest for WP5 to establish a supramolecular host−guest system (WP5⊃G).18,28−30 To confirm the formation of this supramolecular host−guest system, a simple G′ was used as a model guest. 1H NMR spectra of equimolar WP5 and G′ in aqueous solution were measured. As shown in 1H NMR spectra (Figure S5), the protonic peaks of Ha, Hb, Hc, Hd, He, and Hf of G′ shifted upfield and the protonic peaks of H1, H2, and H3 of WP5 shifted downfield,31,32 which indicated the complexation of G′ and WP5. Since MALDI-TOF MS was an effective method to study host−guest complexes,33 MALDI-TOF MS of an equimolar aqueous solution of WP5 and G was observed to further confirm the complexation (Figure S6), showing the construction of this host−guest system. Meanwhile, in order to estimate the stoichiometry of WP5⊃G, a Job’s plot was conducted (Figure S7),8,34−36 indicating that WP5⊃G had a 1:1 stoichiometry. All of these characterization results proved that a supramolecular host−guest system was constructed successfully. Optical and Assembling Properties of WP5⊃G. Since PDI derivatives were easily aggregated because of their strong π−π stack, the optical and assembling properties of G were first investigated. As shown in the concentration-dependent UV−vis absorption spectra of G (Figure 1a), the featured peaks at 466 nm (S0−2), 499 nm (S0−1), and 540 nm (S0−0) had been influenced on a limited basis except for an enhancement in the absorbance intensity, which indicated the existence of a predominantly monomeric form of G.37,38 The ratio of S0−0

and S0−1 could be used to provide a view into the degree of aggregation in solution. The absorbance intensity ratio of A0−0/ A0−1 < 1 suggested that aggregation of G happened in the aqueous solution.39 Therefore, both monomeric and aggregated G existed in the aqueous solution. Additionally, although G was slightly aggregated in the aqueous solution, the fluorescence in the concentration of 1 × 10−5 M was still strong (Figure 1c). The optical and assembling properties of supramolecular host−guest system (WP5⊃G) were further investigated. As shown in Figure 1b, when WP5 was added into G aqueous solution, the absorbance intensity of the characteristic peak of WP5 at 290 nm gradually enhanced, which was caused by the increase of WP5 concentration. Meanwhile, the peak at 540 nm gradually disappeared, indicating the vanishment of monomeric G. The peak at 466 nm gradually disappeared and the peak at 499 nm gradually decreased and broadened, suggesting the enhanced aggregation of G. A new peak at 560 nm appears (Figure 1b), which might indicate the formation of a new aggregation state. Furthermore, as shown in Figure 1c, a turnoff phenomenon could be observed with the addition of WP5. In summary, a host−guest system (WP5⊃G) was constructed successfully and adding WP5 into G aqueous solution could induce the change in the aggregation behavior of G. In order to further study the assembly behaviors of this supramolecular host−guest system WP5⊃G, the best molar ratio of G and WP5 was determined. The plot of the optical absorbance at 560 nm versus the molar ratio of [G]/[WP5] shows an inflection point at 5:1 ([G]/[WP5]) (Figure 1d),40 in which a sharp reduction of fluorescence intensity was observed after the inflection point (Figure 1c). Therefore, the best molar ratio of WP5⊃G was determined to be 5:1 ([G]/[WP5]). The parameters that influence the best molar ratio of G and WP5 36322

DOI: 10.1021/acsami.7b12063 ACS Appl. Mater. Interfaces 2017, 9, 36320−36326

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ACS Applied Materials & Interfaces

Figure 3. (a) ITC titration of WP5 (2 × 10−4 M) with G (1 × 10−5 M) in aqueous solution at 298.15 K. (b) Thermodynamic parameters of WP5 and G aqueous solutions. Cyclic voltammograms of (c) G and (d) WP5 on a platinum electrode in 0.1 M Bu4NPF6 CH3CN solution at a scan rate of 100 mV/s. The ferrocene/ferrocenium redox couple is used as a standard (−4.8 eV). (e) Schematic diagram of PET process between G and WP5.

interaction was also an important driving force in this supramolecular host−guest system. Therefore, the morphological transformation process and formation of the supramolecular host−guest system should be attributed to both the hydrophobic effect and electrostatic interaction between WP5 and G. PET Process of Supramolecular Host−Guest WP5⊃G. Because the interior cavity of WP5 was an electron-rich space18 and PDI derivatives were electron-deficient,45 the electron transfer process might be a significant cause of fluorescence turn-off. In order to confirm this hypothesis, electrochemistry experiments were conducted to determine the reduction potential (Ered) and oxidation potential (Eox) of G and WP5, which could be used to calculate highest occupied molecular (HOMO) and lowest unoccupied molecular (LUMO) energy levels.46 Ered of G and WP5 were −0.64 and −1.02 eV, respectively. And Eox of G and WP5 were 1.22 and 0.86 eV, respectively (Figure 3c,d). According to previous reports,47 HOMO of G and WP5 were calculated to be −6.02 and −5.66 eV, respectively. And LUMO of G and WP5 were −4.16 and −3.75 eV, respectively. According to the PET mechanism, WP5 could serve as an excellent PET donor and G as a PET acceptor.48 As presented in Figure 3e, the PET process could occur between WP5 and G, leading to the fluorescence turn-off of WP5⊃G.49 Therefore, the supramolecular PET process between WP5 and G could be used to design a reversible and responsive fluorescent probe.50 Fe3+ Ion Detection of WP5⊃G. Because metal ions could efficiently perturb the microenvironment of host−guest systems51 and interdict the PET process, the response capability of WP5⊃G to metal ions should be investigated. Metal ions, including Fe3+, K+, Na+, Li+, Cu+, Zn2+, Mg2+, Cd2+,

may be the charge numbers and the steric hindrance of host and guest. Moreover, the absorbance increase for lower ratios ([G]/[ WP5]) might be caused by the system aggregation state changes along with the addition of WP5. As shown in Figure 2a, morphological transformation at this ratio was observed. When G existed alone, the aggregate was irregular, while when WP5 was added, the aggregate was transformed into a regular block. Moreover, DLS results showed that the aggregation of WP5⊃G had two significant peaks at 78.8 and 142 nm, respectively (Figure S8a), which suggested that these aggregates were not simple spherical ones.41 Therefore, a morphological transformation process was achieved during the formation of the supramolecular host−guest accompanied by a fluorescence turn-off phenomenon. Interaction between G and WP5. In order to investigate the interaction between WP5 and G, ITC and ζ potential experiments were conducted. The ITC curve revealed a strong interaction of WP5⊃G with an association constant (Ka) of 3.059 × 105 M−1 (Figure 3a).33,42,43 Furthermore, the negative value of free energy (ΔG) suggested that the incorporation process was spontaneous. The negative value of ΔG and positive ΔH calculated with the Nano ITC software showed that the hydrophobic interaction was the leading driving force in this supramolecular host−guest system (Figure 3b).44 Additionally, due to the negative charges of WP5 and positive charges of G, electrostatic interaction between WP5 and G was confirmed by ζ potentials of G and WP5⊃G (1 × 10−5 M). The ζ potentials of G and WP5⊃G were 24.6 and 14.1 mV (Figure S8b,c), respectively. It is worth noting that the potential of WP5⊃G was varied from negative to positive. The reduction of the ζ potential after the addition of WP5 into G aqueous solution and the wide range indicated that the electrostatic 36323

DOI: 10.1021/acsami.7b12063 ACS Appl. Mater. Interfaces 2017, 9, 36320−36326

Research Article

ACS Applied Materials & Interfaces

Figure 4. Photographs of WP5⊃G (1 × 10−5 M) toward various metal ions in aqueous solutions (0.1 mM) under (a) visible light and (b) UV light. (c) Relative fluorescence at 550 nm of WP5⊃G (1 × 10−5 M) in aqueous solution in the presence of 0.10 mM various metal ions in aqueous solution (λex = 490 nm). (d) Linear relationship between the concentration of Fe3+ ion and fluorescence intensity at 550 nm (λex = 490 nm).

Figure 5. Detection mechanism of supramolecular fluorescent probe (WP5⊃G).

As shown in Figure 4d, the fluorescent intensity at 550 nm versus the concentration of Fe3+ ion conformed to the linear relationship within the range of 0.04−0.30 mM, which could be fitted as a function of

Hg2+, Fe2+, Sn2+, Cu2+, and Ca2+ were added separately into 2 mL of WP5⊃G ([WP5]/G = 1:1) aqueous solution (1 × 10−5 M). Only Fe3+ ion induced a significant change of this supramolecular host−guest system (WP5⊃G). With Fe3+ ion, the solution was transformed from light pink to orange accompanied by fluorescence turn-on (Figure 4a,b and Figure S9). Furthermore, the fluorescence regeneration (F/F0) could characterize the specific influence of Fe3+ ion, and the ratio was almost close to 100, as shown in Figure 4c. All these results suggest that the supramolecular host−guest system of WP5⊃G has a specific response to Fe3+ ion. To further assess the detection performance of WP5⊃G as a fluorescent probe, Fe3+ ion concentration-dependent emission properties were studied. An increasing trend in the fluorescence spectra could be observed when Fe3+ ion concentration was increased from 0.02 to 0.50 mM (Figure S10 and Figure S11).

F550 = 338632[Fe3 +] − 10183

The correlation coefficient was determined to be 0.9991, where F550 was the fluorescence intensity of WP5⊃G and [Fe3+] was the concentration of Fe3+ ion. Moreover, the detection limit (DL) was determined to be 2.13 × 10−7 M through a traditional method (DL = 3σ/slope).52 The reversibility of WP5⊃G in Fe3+ ion detection was then evaluated through chelating Fe3+ ions with sodium pyrophosphate (Na4P2O7). As shown in Figure S12, with alternative addition of Na4P2O7 and Fe3+ ion, the fluorescent probe (WP5⊃G) showed reversible 36324

DOI: 10.1021/acsami.7b12063 ACS Appl. Mater. Interfaces 2017, 9, 36320−36326

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ACS Applied Materials & Interfaces

51521062), Beijing Collaborative Innovative Research Center for Cardiovascular Diseases, and the Higher Education and High-Quality and World-Class Universities (Grant No. PY201605).

switch changes. Therefore, the supramolecular host−guest system (WP5⊃G) was a selective ratiometric Fe3+ ion fluorescent probe and had a great potential in ion detection application. ITC experiment showed that Fe3+ ion has a strong interaction with the supramolecular host−guest system WP5⊃G (Figure S13) with an association constant (Ka) of 1.976 × 105 M−1. As shown in Figure S14, the peak shapes of regenerated fluorescence spectra and fluorescence spectra of G were the same, suggesting that the fluorescence was regenerated with G. Aggregation enhancement of G may be one fluorescence quenching cause. However, after 0.10 mM Fe3+ ion was added into WP5⊃G aqueous solution, the absorbance spectra from 400 to 700 nm had no change, which indicated that the aggregation state of G did not change (Figure S15). Therefore, although both aggregation and PET were the causes of WP5⊃G fluorescence quenching, the Fe3+ ion added into WP5⊃G aqueous solution should mainly interdict the PET process between G and WP5 (Figure 5).



(1) Cordier, P.; Tournilhac, F.; Soulie Ziakovic, C.; Leibler, L. SelfHealing and Thermoreversible Rubber from Supramolecular Assembly. Nature 2008, 451, 977−980. (2) Tian, X. H.; Hao, X.; Liang, T. L.; Chen, C. F. TriptyceneDerived Calix[6]arenes: Synthesis, Structure and Tubular Assemblies in the Solid State. Chem. Commun. 2009, 44, 6771−6773. (3) Wu, D. Q.; Wang, T.; Lu, B.; Xu, X. D.; Cheng, S. X.; Jiang, X. J.; Zhang, X. Z.; Zhuo, R. X. Fabrication of Supramolecular Hydrogels for Drug Delivery and Stem Cell Encapsulation. Langmuir 2008, 24, 10306−10312. (4) Wang, W.; Wong, N. K.; Sun, M.; Yan, C.; Ma, S.; Yang, Q.; Li, Y. Regenerable Fluorescent Nanosensors for Monitoring and Recovering Metal Ions Based on Photoactivatable Monolayer Self-Assembly and Host−Guest Interactions. ACS Appl. Mater. Interfaces 2015, 7, 8868− 8875. (5) Li, J.; Yim, D.; Jang, W. D.; Yoon, J. Recent Progress in the Design and Applications of Fluorescence Probes Containing Crown Ethers. Chem. Soc. Rev. 2017, 46, 2437−2458. (6) Pedersen, C. J. The Discovery of Crown Ethers (Noble Lecture). Angew. Chem., Int. Ed. Engl. 1988, 27, 1021−1027. (7) Rekharsky, M. V.; Inoue, Y. Complexation Thermodynamics of Cyclodextrins. Chem. Rev. 1998, 98, 1875−1918. (8) Zhang, Q. W.; Li, D.; Li, X.; White, P. B.; Mecinović, J.; Ma, X.; Ågren, H.; Nolte, R. J. M.; Tian, H. Multicolor Photoluminescence Including White-Light Emission by a Single Host−Guest Complex. J. Am. Chem. Soc. 2016, 138, 13541−13550. (9) Böhmer, V. Calixarenes, Macrocycles with (Almost) Unlimited Possibilities. Angew. Chem., Int. Ed. Engl. 1995, 34, 713−745. (10) Kim, K.; Selvapalam, N.; Ko, Y. H.; Park, K. M.; Kim, D.; Kim, J. Functionalized Cucurbiturils and Their Applications. Chem. Soc. Rev. 2007, 36, 267−279. (11) Dai, S.; Ju, Y. H.; Barnes, C. E. Solvent Extraction of Strontium Nitrate by a Crown Ether Using Room-Temperature Ionic Liquids. J. Chem. Soc., Dalton Trans. 1999, 1201−1202. (12) Shu, X.; Chen, S.; Li, J.; Chen, Z.; Weng, L.; Jia, X.; Li, C. Highly Effective Binding of Neutral Dinitriles by Simple Pillar[5]arenes. Chem. Commun. 2012, 48, 2967−2969. (13) Hu, X.-Y.; Jia, K.; Cao, Y.; Li, Y.; Qin, S.; Zhou, F.; Lin, C.; Zhang, D.; Wang, L. Dual Photo- and pH-Responsive Supramolecular Nanocarriers Based on Water-Soluble Pillar[6]arene and Different Azobenzene Derivatives for Intracellular Anticancer Drug Delivery. Chem. - Eur. J. 2015, 21, 1208−1220. (14) Dong, S.; Yuan, J.; Huang, F. A Pillar[5]arene/Imidazolium [2] Rotaxane: Solvent- and Thermo-Driven Molecular Motions and Supramolecular Gel Formation. Chem. Sci. 2014, 5, 247−252. (15) Yu, G.; Ma, Y.; Han, C.; Yao, Y.; Tang, G.; Mao, Z.; Gao, C.; Huang, F. A Sugar-Functionalized Amphiphilic Pillar[5]arene: Synthesis, Self-Assembly in Water, and Application in Bacterial Cell Agglutination. J. Am. Chem. Soc. 2013, 135, 10310−10313. (16) Yao, Y.; Xue, M.; Chen, J.; Zhang, M.; Huang, F. An Amphiphilic Pillar[5]arene: Synthesis, Controllable Self-Assembly in Water, and Application in Calcein Release and TNT Adsorption. J. Am. Chem. Soc. 2012, 134, 15712−15715. (17) Strutt, N. L.; Forgan, R. S.; Spruell, J. M.; Botros, Y. Y.; Stoddart, J. F. Monofunctionalized Pillar[5]arene as a Host for Alkanediamines. J. Am. Chem. Soc. 2011, 133, 5668−5671. (18) Ogoshi, T.; Hashizume, M.; Yamagishi, T. a.; Nakamoto, Y. Synthesis, Conformational and Host-Guest Properties of WaterSoluble Pillar[5]arene. Chem. Commun. 2010, 46, 3708−3710. (19) Xia, D.; Wang, P.; Shi, B. Cu (II) Ion-Responsive Self-Assembly Based on a Water-Soluble Pillar[5]arene and a Rhodamine B-



CONCLUSIONS In conclusion, a supramolecular host−guest system (WP5⊃G) of a water-soluble PDI derivative (G) and pillar[5]arene (WP5) was constructed. Both morphological transformation and fluorescence response were achieved. G formed irregular aggregates with strong fluorescence in aqueous solution. Morphological transformation was achieved during the addition of WP5 into G aqueous solution and a fluorescence turn-off phenomenon was observed due to supramolecular PET reaction. The driving forces of this supramolecular host− guest system WP5⊃G were hydrophobic effect and electrostatic interaction, which were confirmed with ITC and ζ potential experiments. Furthermore, this supramolecular host−guest system (WP5⊃G) could work as a fluorescent probe to selectively and quantitatively detect Fe3+ ion through the process of interdicting supramolecular PET. With the addition of Fe3+ ion, the fluorescence of WP5⊃G was turned on gradually. This fluorescent probe showed a specific and reversible response to Fe3+ ion with a detection limit of 2.13 × 10−7 M. Therefore, this supramolecular host−guest system of WP5⊃G with specific response to metal ions has a great potential in future biological and environmental monitoring.



ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.7b12063. Experimental procedures, characterization of the macromolecules, and supporting figures and text (PDF)



REFERENCES

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Meizhen Yin: 0000-0001-8519-8578 Notes

The authors declare no competing financial interest.



ACKNOWLEDGMENTS This work was financially supported by the National Natural Science Foundation of China (Grant Nos. 21574009 and 36325

DOI: 10.1021/acsami.7b12063 ACS Appl. Mater. Interfaces 2017, 9, 36320−36326

Research Article

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DOI: 10.1021/acsami.7b12063 ACS Appl. Mater. Interfaces 2017, 9, 36320−36326