Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy
Nitrogen atom free polythiophene derivative as an efficient chemosensor for highly selective and sensitive Cu2+ and Ag+ detection
Graphical abstract
Introduction
Along with economic development, metal ion pollution is becoming more and more serious through wastewater discharge, especially for these heavy metal ions, such as Cr3+, Cu2+, Hg2+, Ni2+, Zn2+ and so on [1,2]. This is because that these metal ions are easily enriched through the food chain, which constitutes a severe threat to the health of human beings, like menke syndrome, anaemia and minamata disease, etc. [3,4] Therefore, it is of great significance to effectively monitor metal ions concentration in wastewater for the implementation of environmental protection policies.
Traditional detection methods are usually based on experimental apparatuses, such as X-Ray Fluorescence (XRF), X-ray Photoelectron Spectroscopy (XPS), etc. [5,6] However, these measurement machines require a lot of instruments and equipments, which are expensive and inconvenient for wide application. Based on the current researches of metal ions detection, it is urgent to develop simple, fast-response and cheap method to detect metal ions. As a new sensing means, chemosensors are more and more active in the field of detection because of their low price [7,8]. Rapid development in exploiting and designing novel chemosensors for detecting metal ions has been made over these years. Nowadays, lots of materials have been successfully applied as chemosensors. For instance, Wang et al. developed a new kind of CdTe QDs for metal cations detection, which was a highly sensitive and selective chemosensor, showing a promising application in the detection field [9]. Lv and his coauthors successfully prepared an enhanced MOF-based material chemosensor in detecting metal ions, and this brilliant optical performance enabled it to be one of these candidates of metal ions sensors [10]. Besides, Hai et al. built a nanoscale Ag particles sensor doping on wood for metal ions sensing for the first time, and this material showed a lower detection limit of 32 pM for detecting Hg2+. This result was even lower than the detecting standards in water [11]. Through the study of rotaxane, Denis et al. found that this sort of interlocked molecules could be well applied to the design of the molecular structure, thus expressing remarkable sensitive fluorescence quenching to metal ions [12]. Furthermore, Wu and coauthors prepared a new fluorescent chemosensor CMCA, and it was highly sensitive to existence of N2H4 or HSO3−. The detection of CMCA for HSO3− could even reach 20 nM, which also showed a wide application in the living cells [13]. Sakunkaewkasem et al. prepared a new chemosensor based on [5] helicene derivative. This probe could highly recognize Cu2+ and Zn2+ in aqueous system, and detection of this sensor for Cu2+ and Zn2+ were calculated as 5.6 and 3.8 ppb, respectively [14]. Through the analysis of intramolecular atomic sites, Huang et al. firstly synthesized several bisbenzimidazole-based chemosensors. The three sensors were very sensitive and selective to Fe3+ or Ag+ under different pH, which were also stable in the environment [15]. Wu's group constructed one “on-off” model NBS-CDs chemosensor, and successfully applied it to the detection of L-Cys and Ag+ in cells. This simple and high standard material would greatly expand its application in other detection fields [16]. With the enhancement of people awareness of environmental protection, the requirements for metal ions detection has become higher than past [17]. Thus, it is crucial to develop novel chemosensors with excellent performance in this field.
Recently, the investigation and application of conjugated polymers (CPs) have developed rapidly [18,19]. This is a kind of macromolecule composed of conjugated groups with π-electrons. Because of the transition of π − π* electrons between polymer chains, CPs exhibit an excellent light capture ability [20]. This characteristic enables them to be widely studied in electro-optic field [21,22]. Among different CPs, polythiophene and its derivatives have attracted broad attention due to their low price and high thermal stability and excellent electroconductivity [23]. All these prominent features enable polythiophene-based polymers to be ideal materials in the electro-optic field, such as electroluminescent devices and solar cells, etc. [24,25] Nevertheless, in addition to mainstream field of electrochemical, there is also a small number of polythiophene-based polymers applications in sensing area. Xing et al. synthesized a polymer with the base of thiophene and the thiophene-based material showed an excellent selectivity for Cu2+. This special detection to metal ions has greatly expanded the application of polythiophene derivatives [26]. Guo and co-workers have successfully achieved a new polythiophene derivative containing N/O ligand, and they further applied it in the detection for Cu2+ and amino acids. The detecting level for Cu2+ of this material was far below the international standard. The results showed that these polythiophene derivatives had great potential application in sensing field [27]. Yao and co-workers have successfully prepared a supramolecular complex based on polythiophene derivative, and they applied it to Cu2+ detection in aqueous system. It was based on a thiophene structure, and the detecting level for Cu2+ of this material was 0.05 mM. The results showed that these polythiophene derivatives had great potential application in sensing field [28]. In addition, Yao et al. synthesized the poly(2-(4-methyl-3-thienyloxy)propanesulfonate and they applied it as the Cu2+ sensor, which surprisingly exhibited a detection limit of 3 μM [29]. However, to the best of our knowledge, most of these CPs chemosensors applied to the metal ions detecting field are basically introduced with N atom because of its particular coordination properties with metal ions [27,30]. Few reports are focused on crown-ether-polythiophene derivatives applied in metal ions detection. This is due to the difficulty in introducing polyether bond groups and further polymerization through oxidation or metal catalysis.
In this work, on account of current circumstances of the researches for polythiophene derivatives in sensing area, a novel poly{3-[2-(2-methoxy-ethoxy)-ethoxy]-thiophene} (PM) is successfully synthesized and applied in the field of metal ions detection. Moreover, this material presents excellent fluorescent sensing properties to Cu2+ and Ag+ when they are in a tiny concentration range, and the detection limit of it for Cu2+ even reaches only 0.45 μM. We believe that it will largely broaden the application of these polymers in sensing field.
Section snippets
Materials
The first-step product (3-[2-(2-methoxy-ethoxy)-ethoxy]-thiophene) was synthesized according to the following procedures [31]. 40 mL degme and 2.3 g Na were added into a flask under 60 °C. Then put 0.955 g CuI, 5 mL DMF and 16.1 g 3-bromothiophene into the mixture for 12 h under 135 °C. Eventually, the product (3-[2-(2-methoxy-ethoxy)-ethoxy]-thiophene) was prepared and separated by chromatography and other ways. Later, (3-[2-(2-methoxy-ethoxy)-ethoxy]-thiophene), 4.41 g NBS and 50 mL DMF were
Structural properties
The structural and optical characteristics of PM were characterized by FT-IR and Fluorometric spectra. As seen from Fig. 1(a), a large peak range from 2800 cm−1 to 3000 cm−1 is assigned to stretching of aliphatic hydrocarbon [32]. Besides, CC and CC bands on thiophene ring appear in these positions (1636 cm−1, 1511 cm−1, 1337 cm−1) [33]. Furthermore, one peak at 1078 cm−1 is relevant to the band of COC stretching in the sample [34]. Another characteristic peak at around 695 cm−1 is associated
Conclusions
In brief, we have synthesized a fluorescence chemosensor based on nitrogen atom free polythiophene derivatives poly{3-[2-(2-methoxy-ethoxy)-ethoxy]-thiophene}, which is much easier on synthesis than N-containing polythiophene derivatives. This polythiophene-based polymer containing methoxy-ethoxy units can interact well with Cu2+ and Ag+ through the coordination characteristics, generating specific fluorescence changes and visible color changes to naked eyes. Furthermore, it performs low DL for
Acknowledgements
We thank the Natural Science Foundation of China (21875173), the Fundamental Research Funds for the Central Universities (2042015kf0180) of China and Large-scale Instrument And Equipment Sharing Foundation of Wuhan University for supporting this research.
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2021, Coordination Chemistry ReviewsCitation Excerpt :The limit of detection for Cu2+ is calculated to be 10 nM. Several other turn-off fluorescent conjugated polymer probes (P45 [95], P46 [96], and P47 [97]) based on polythiophene backbone are also designed for Cu2+ detection (Scheme 10). When Cu2+ is added, the nitrogen atom of the amino and oxygen atom of the carbonyl group of P45 can coordinate with Cu2+, and leads to the quenching response of P45.