Abstract
A series of rhodamine derivatives L1–L3 have been prepared and characterized by IR, 1H-NMR, 13C-NMR and ESI-MS. These compounds exhibited selective and sensitive “turn-on” fluorescent and colorimetric responses to Al3+ in methanol. Upon the addition of Al(III), the spiro ring was opened and a metal-probe complex was formed in a 1:1 stoichiometry, as was further confirmed by ESI-MS spectroscopy. The chemo-dosimeters L1–L3 exhibited good binding constants and low detection limits towards Al(III). We also successfully demonstrate the reversibility of the metal to ligand complexation (opened ring to spirolactam ring).
Highlights
Aluminum is the third most abundant element in the Earth's crust and second most widely used metal after iron for the manufacture of electrical equipment, automobiles, building construction, water purification, clinical drugs [1] and packaging materials [2], etc
A weak absorption peak was observed with Cr3+ and Cu2+, while no peak appeared with the other metal ions even when in excess
Under a UV lamp, a spectacular color change of the probe solution from colorless to fluorescent pink occurred upon addition of Al3+, which could be detected by the naked-eye (Figure 2a, inset). This involves a delactonization process of the spirocyclic form of rhodamine to its ring opened form which is induced by metal ion coordination
Summary
Aluminum is the third most abundant element in the Earth's crust and second most widely used metal after iron for the manufacture of electrical equipment, automobiles, building construction, water purification, clinical drugs [1] and packaging materials [2], etc. Among the various detection methods, the fluorescence sensing technique [19,20,21,22,23,24,25,26,27] has become the most useful and popular in clinical, biology and environmental chemistry due to its non-destructive nature, high selectivity and sensitivity, real-time response and possible naked eye detection. Rhodamine derivatives are used widely as a fluorescent signal transducers due to their excellent photophysical properties such as long absorption and emission wavelengths, large absorption coefficients and high fluorescence quantum yields. Several rhodamine-based fluorescent chemosensors have been developed for different chemical species [33,34,35]. We report the synthesis of a series of rhodamine-derived chemosensors L1–L3 using the synthetic route outlined in Scheme 1. Upon further refluxing with dialdehydes (a, b and c) compound 1 yielded the sensors L1, L2 and L3, which show a reversible, selective and sensitive fluorescence enhancement response to Al(III) in alcoholic media
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