Reversible acidochromism and thermo-responsive luminescence properties of a novel Zn(II)/Eu(III) coordination polymer.
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2020
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Elsevier Ltd.
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Dyes and Pigments 181 (2020) 108587
Abstract
A new Zn(II)/Eu(III) compound with the N,N′-ethylenebis(5-carboxysalicylideneamino) ligand (H4Salendc) has been synthesised and its photophysical behaviour studied. This species, [Zn(Salendc)Eu(CH3COO)(DMSO)]·xH2O·0.5CH3CN (x = 3.5–4), has been characterised by XRD, XEDS and SEM and HTEM microscopies. Experimental results suggest the formation of a one-dimensional polymeric compound. The compound behaves as a luminescent material in the solid state. Moreover, it exhibits acidochromic properties upon the addition of a few drops of HCl and in the presence of its vapours. The emission intensity of the bands attributed to the Eu(III) ion can be also modulated by the temperature and by the presence of water, so that this species is a good candidate for its use as a luminescent acid, temperature and water sensor.
Description
Eu(III) complexes exhibit a high quantum yield and a long-live emission, which make them suitable candidates for the preparation of novel advanced functional materials with sensorial abilities. It is well-known that the coordination of water, can cause a quenching of the Eu(III) emission bands by the antenna effect blocking, this effect is useful to detect water via luminescence spectroscopy in certain solvents or humid environments. However, it has also allowed to developed novel Eu(III) complexes with stimuli-responsive properties. The application of an external stimulus can induce the establishment of new intermolecular interactions, and coordinated water can be replaced by other chromophore ligands in order to revival the antenna effect.
In this work, a new polymeric Zn(II)/Eu(III) compound with a flexible dicarboxylic salen-type ligand, N,N0 -ethylenebis(5-carboxysalicylideneamino), H4Salendc, has been obtained and its photophysical behaviour studied. The salen compound used as the ligand has been strategically functionalised with terminal carboxylic groups to favour the formation of coordinative –COO⋅⋅⋅Eu⋅⋅⋅OOC– bonds. Interestingly, it is possible to break and form again these short contacts upon exposure to several external stimuli, which originates dramatic changes in the luminescence properties of the complex. Structure/properties relationships have been studied in deep to understand the mechanisms of these processes; results could be of great interest for potential application in the field of thermo and acid sensors.