Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy
A luminescent lanthanide complex-based anion sensor with electron-donating methoxy groups for monitoring multiple anions in environmental and biological processes
Graphical abstract
A ternary europium (III) tris(2-thenoyltrifluoroacetonate) with 2-(3,4,5-trimethoxy phenyl)imidazo[4,5-f]-1,10-phenanthroline (1) was prepared and it can detect various anions such as F−, AcO− and . Spectroscopic studies of UV–vis, Fluorescence and NMR present that the sensor exhibits striking emission changes to fluoride (purple), acetate anions (green) and (blue), respectively. More importantly, transparent hybrid thick films (poly-methyl methacrylate) show intense red emissions and give rise to luminescence change in fluoride anion containing DMSO solution.
Highlights
► Ternary complex was strong red emissive. ► The sensor exhibits striking emission changes to anions. ► Luminescent could display luminescence change for fluoride anion.
Introduction
Since different anions such as fluoride, hydrogen sulfate and acetate are critical components in environment, biological and metabolic processes. The specific structural and reactive receptors composed of organic fluorophores were designed and prepared in monitoring particular anions [1], [2], [3], [4], [5], [6], [7], [8].
The trivalent lanthanide ions are well-known for their luminescent properties in the visible (Eu, Tb) and near-infrared region (Yb, Pr, Nd) of the electromagnetic spectrum and long emission lifetime ranging from microseconds (e.g. Yb, Nd) to milliseconds (e.g. Eu and Tb). Thus autofluorescence from the much shorter lived biomolecules (sub-microseconds) can easily be filtered via time-gated techniques and the penetration depth for imaging purposes can be maximized using NIR emitting probes. Unfortunately, trivalent lanthanide ions inherently suffer from weak light absorption capabilities because their f–f transitions are Laporte-forbidden resulting in molar absorption coefficients (ε) smaller than 10 L mol−1 cm−1 for most of the absorption transitions [9]. This is extremely low compared to organic chromophores, which are generally at least 5000 time larger [10]. Thus an obvious solution to this problem is to introduce an organic chromophore that acts as an “antenna” and has the capacity to absorb more light because of its more intense absorption bands to subsequently transfer the excitation energy to the lanthanide ion by intramolecular energy transfer (indirect excitation) [9], [11].
Not surprisingly, lanthanide-organic chromophore complexes have caught the attention of many researchers in various disciplines over the past few decades, not in the least because of their extraordinary properties. Their sharp and intense emission bands and versatile color changes are sensitive to external interaction with guest molecules such as anions. Lanthanide complexes are markedly oxophilic and positively charged, thereby providing strong electrostatic interactions with anions [12]. Furthermore, the aforementioned long emission lifetimes, obviation of practical problems associated with autofluorescence and Rayleigh scattering in biological samples make them desirable probes in biological and biomedical research.
A number of groups have previously reported various lanthanide-based luminescent sensors with various sensitivities and specificities. Parker et al. [11], Faulkner et al. [13], and Gunnlaugsson et al. [14] developed multidentate cyclen-based lanthanide complexes for the selective detection of various anions, including bicarbonate. Tsukube’s group reported lanthanide complexes of tris(2-pyridylmethyl)amines [15] and a series of N3, O-mixed donor chiral tripods that formed stabile lanthanide complexes [16] as anion-responsive luminescent compounds for anions such as chloride and nitrate. Ziessel and co-workers [12] prepared complexes of europium and terbium with bis-[(6′-carboxy-2,2′-bipyridine-6-yl)]phenylphosphine oxide donor ligands for the detection of ADP3−, ATP4−, and phosphate anions. However, because there are few sensors available that detect multiple anions and, to the best of our knowledge, no sensor that is capable of detecting dihydrogen phosphate anions, we aimed to synthesize a europium-based sensor that would accomplish this.
In this paper, we describe the two step synthesis, initial characterization, and application of a novel antenna ligand, 2-(3,4,5-trimethoxy-phenyl)imidazo[4,5-f]-1,10-phenanthroline (1) for a europium-based Eu-(TTA)3-1 anion sensor. This novel complex (Fig. 1A) could be applied as an effective receptor and sensor for the luminescent detection of acetate (AcO−), fluoride (F−) and dihydrogen phosphate () anions. Since hybrid materials of polymers and lanthanide complexes display beneficial properties, such as mechanical flexibility and durability, thermal stability, and easy processability, such configurations have attracted much attention, particularly for applications in electronics and optics [17], [18]. Because simple embedding of lanthanide ions in the polymer matrix often leads to inhomogeneous distribution of the probe and associated luminescence artifacts [9], [19], [20], such as local quenching, we opted to covalently couple the Eu-(TTA)3-1 anion sensor monomers via co-polymerization to the polymer host [9], [17], [21]. We thus managed to introduce the europium-based anion sensor into a polymeric host, poly-methyl methacrylate (PMMA), to create transparent polymeric films that were sensitive to fluoride anions and showed homogenous emission signals.
Section snippets
Materials and techniques
Tetrabutyl ammonium fluoride trihydrate (97%), tetrabutyl ammonium chloride (97%), tetrabutyl ammonium bromide (98%), tetrabutyl ammonium iodide (98%), tetrabutyl ammonium hydrogensulfate (97%), tetrabutyl ammonium dihydrogen phosphate (98%), tetrabutyl ammonium acetate (97%) were purchased from Sigma–Aldrich company. Other chemicals and materials were acquired from local commercial suppliers, used as received and were of the highest purity available. 1H-NMR spectra were recorded at 293 K on a
Results and discussion
We aimed to synthesize a lanthanide complex-based luminescent sensor for the detection of various anions relevant to biological and environmental processes. The newly synthesized lanthanide complex with electron-donating methoxy groups, Eu-(TTA)3-1, is structurally depicted in Fig. 1A. Eu-(TTA)3-1 was characterized by NMR and MS and its properties to detect various anions evaluated. The sensor’s photophysical properties were determined via UV–vis and fluorescence spectroscopy in DMSO as a
Conclusions
With the intention of exploiting the unique properties of lanthanide luminescence and based thereon to synthesize a sensor sensitive to different types of relevant anions, we prepared a red luminescent ternary europium-chromophore-sensing ligand complex (ternary europium (III) tris(2-thenoyltrifluoroacetonate) with 2-(3,4,5-trimethoxyphenyl)imidazo[4,5-f]-1,10-phenanthroline ligands). The sensor itself exhibited a bright red luminescence with an absolute quantum yield of 10% and a lifetime of
Acknowledgements
The authors acknowledge financial support from the National Natural Science Foundation of China under scheme No. 21002035 (Y.Z., C.T., and Q.W.) and an External Collaborative Research Grant FMR-1791 (G.P.D.).
References (28)
- et al.
Coord. Chem. Rev.
(2006) - et al.
Coord. Chem. Rev.
(2000) - et al.
Environ. Pollut.
(1999) Coord. Chem. Rev.
(2000)- et al.
Thin Solid Films
(2002) - et al.
J. Photochem. Photobiol. A-Chem.
(2009) - et al.
J. Photochem. Photobiol .A-Chem
(2009) - et al.
Ther.
(2009) - et al.
Biochemistry Seventh ed
(2010) - et al.
Nat. Rev. Drug Discov.
(2008)
Nat. Clin. Pract. End. Met.
Med. Res. Rev.
Ecol. Appl.
Chem. Rev.
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2022, Coordination Chemistry ReviewsCitation Excerpt :The development of reliable analytical methods for specific, sensitive, and rapid detection of the fluoride (F−) in vivo is thus demanded. Based on the F−-mediated displacement approach, numerous lanthanide(III) complexes have been developed as the probes fluorescence detection of F− [260,261]. In 2016, Wang et al. developed a Gd(III) complex as the MRI/fluorescence bimodal probe (92) for F− detection in vitro and in vivo (Fig. 51A) [262].