The magic of integration: Exploring the construction of dithienylethene-based infinite coordination polymers and their synergistic effect for gaseous ammonia probe applications

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Abstract

Infinite coordination polymers are recognized as excellent platform for functionalization. Dithienylethene motifs, which are one of the most attractive functional moieties, were incorporated into an infinite coordination polymer, to deliver a “smart” porous material that can response to external stimuli. The obtained dithienylethene-based infinite coordination polymers (named Cu-DTEDBA) share the advantages of both infinite coordination polymers (porosity and stability) and dithienylethene motifs (photochromism). The physical and chemical properties of Cu-DTEDBA were characterized by FTIR, TEM, SEM, XRD, TGA, UV–vis, EDX and BET. Moreover, the combination of dithienylethene and infinite coordination polymers gives rise to a synergistic effect, which induces functional behaviors of ammonia sensor applications. Both open and closed forms of Cu-DTEDBA exhibit distinct colorimetric change upon exposure to gaseous ammonia, which is not observed in dithienylethene free molecules.

Graphical abstract

The incorporation of dithienylethene motifs into the skeleton of infinite coordination polymers gives rise to a synergistic effect, inducing functional behaviors of ammonia sensing applications in addition to simple photochromism.

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Introduction

As an emerging class of inorganic–organic hybrid materials, infinite coordination polymers (ICPs) have spurred flourishing research interests in the past decade [1], [2], [3], [4]. The structure of ICPs, in which repeating organic ligands are linked together by metal nodes, are highly appealing because the numerous choices of transitional metal nodes and predefined organic linkers give rise to a high degree of tailorability for ICPs [5], [6], [7], [8], [9]. The merits of tailorablility, together with the presence of porosity that often enjoyed by ICPs provide researchers with versatile network structures which can be deliberately designed for a varieties of applications, such as catalysis [10], gas adsorption [11], bio-sensing [12] and drug delivery [13]. Apart from the above properties, ICPs still have huge potency to be further exploited to extent their applications. Specifically, the employment of functional ligand precursors can afford “smart” materials which can carry out multiple tasks under different external stimuli [14]. However, the fabrication of such functional ICPs have been rarely reported and remains a challenging subject.

Among the external stimuli, light is one of the most attractive way to manipulate molecular functions, due to its superiority in spatial, temporal and energetic resolutions and the minimum of side reactions [15], [16], [17], [18], [19], [20]. One of motifs are known as photochromism, which stars the marvellous photo-isomerizable molecules, including azobenzenes [21], [22], [23], [24], spiropyrans [25], [26] as well as dithienylethenes (DTE) [27], [28], [29]. Among these photochromic molecules, DTE derivatives, which undergo photo-induced isomerization involving ring-opening/closing reactions [30], [31], are one of the most appealing classes of molecules, due to their excellent thermal stability, rapid response, and fatigue resistance [29], [32], [33]. Moreover, the geometry of DTE derivatives undergoes limited change under isomerization, which favors their involvement in the construction of ICPs, for the isomerization exhibits negligible effect to the stability of coordination polymer structure.

In spite of limited reports of functional “smart” ICPs, their counterpart inorganic–organic hybrid materials (for example, metal–organic frameworks) have found themselves more and more involved in the construction of functional porous materials [34], [35], [36], which gave us inspiration for designing DTE-based photo-controllable ICPs. The amazing structure of ICPs, that an infinite scaffold being assembled by repeating ligands and metal nodes, gives rise to a synergistic combination of both merits of photo-switchable ligands and coordination polymer network. The synergistic effects, which induces unique performances occurred in the hybrid structures while not available in “free” molecules, results in an enhanced efficiency of both functional motifs and coordination polymer structure. Herein, not only have we fabricated photochromic DTE-based ICPs, but also have fully utilized the synergistic effect of DTE motifs and ICPs to deliver unique properties that are not applying to DTE-based small molecules. The synergistic combination of photochromic moieties and porosity would provide more space to transduce the host–guest interaction to a colorimetric probe for gaseous ammonia.

Section snippets

Experimental

Materials and methods: DMF, Cu(NO3)2·3H2O were purchased from Sinopharm Chemical Reagent Co., Ltd., China. The preparation of DTEDBA was described in supporting information. 1H NMR spectra were collected on a Bruker Avance DPS-300 spectrometer using CDCl3 or DMSO-d6 as solvent and tetra-methylsilane as an internal reference. Thermogravimetry analysis (TGA) were performed under N2 on a NETZSCH STA449F3, with a heating rate of 10 °C min−1. The morphology of the samples were characterized on a JEOL

Results and discussion

To fabricate DTE-based ICP, the DTE derivative of DTEDBA [4,4′-(4,4′-(cyclopent-1-ene-1,2-diyl)bis(5-methylthiophene-4,2-diyl))dibenzoic acid] that containing carboxylic groups were designed and synthesized to deliver ligand for the coordination with metal ion species (Scheme 1a). As illustrated in Scheme 1b, an ICP named Cu-DTEDBA was prepared from heating the mixture of DTEDBA and Cu(NO3)2·3H2O in DMF/H2O at 80 °C. Cu-DTEDBA was obtained as light green solid. Fourier transform infrared

Conclusion

We used carboxylic DTE derivatives as the organic ligand to construct novel Cu-DTEDBA with rigid structure and porosity. Rapid photochromic reaction successfully occurred for Cu-DTEDBA, in consistent with the obvious change in color. More importantly, Cu-DTEDBA exhibit detectable colorimetric change after exposure to gaseous ammonia, indicating a synergistic effect between ICPs and DTE motifs. This would lead to unique functionalities of resulting materials, thus broadening the design and

Acknowledgments

This work was financially supported by National Basic Research Program of China (No. 2013CB733501), National Natural Science Foundation of China (Nos. 91334203, 21376074, 21402050) and the Fundamental Research Funds for the Central Universities of China (No. WK1314008).

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