- ICT-Isomerization-Induced Turn-On Fluorescence Probe with a Large Emission Shift for Mercury Ion: Application in Combinational Molecular Logic
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A unique turn-on fluorescent device based on a ferrocene-aminonaphtholate derivative specific for Hg2+ cation was developed. Upon binding with Hg2+ ion, the probe shows a dramatic fluorescence enhancement (the fluorescence quantum yield increases 58-fold) along with a large red shift of 68 nm in the emission spectrum. The fluorescence enhancement with a red shift may be ascribed to the combinational effect of C=N isomerization and an extended intramolecular charge transfer (ICT) mechanism. The response was instantaneous with a detection limit of 2.7 × 10-9 M. Upon Hg2+ recognition, the ferrocene/ferrocenium redox peak was anodically shifted by ΔE1/2 = 72 mV along with a "naked eye" color change from faint yellow to pale orange for this metal cation. Further, upon protonation of the imine nitrogen, the present probe displays a high fluorescence output due to suppression of the C=N isomerization process. Upon deprotonation using strong base, the fluorescence steadily decreases, which indicates that H+ and OH- can be used to regulate the off-on-off fluorescence switching of the present probe. Density functional theory studies revealed that the addition of acid leads to protonation of the imine N (according to natural bond orbital analysis), and the resulting iminium proton forms a strong H-bond (2.307 ?) with one of the triazole N atoms to form a five-membered ring, which makes the molecule rigid; hence, enhancement of the ICT process takes place, thereby leading to a fluorescence enhancement with a red shift. The unprecedented combination of H+, OH-, and Hg2+ ions has been used to generate a molecular system exhibiting the INHIBIT-OR combinational logic operation.
- Bhatta, Sushil Ranjan,Mondal, Bijan,Vijaykumar, Gonela,Thakur, Arunabha
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p. 11577 - 11590
(2017/10/13)
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- THERAPEUTIC COMPOUNDS: PYRIDINE AS SCAFFOLD
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Compounds of formulas I, IA, and IB or IC or pharmaceutically acceptable salts thereof: wherein A, A1, A2, A3, A4, R2, R3, R4 and n are as defined in the specifications well as salts and pharmaceutical compositions including the compounds are prepared. They are useful in therapy, in particular in the management of pain.
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