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ESIPT-capable 2,6-di(1H-imidazol-2-yl)phenols with very strong fluorescent sensing signals towards Cr(III), Zn(II) and Cd(II): molecular variation effects on turn-on efficiency

Abstract

A series of structurally and electronically varied 2,6-di(1H-imidazol-2-yl)phenols that are ESIPT-capable (1–12) as well as the ESIPT-incapable 4,5-diphenyl-2-(3-(4,5-diphenyl-1H-imidazol-2-yl)phenyl)-1H-imidazole (13) have been designed and comparatively studied for molecular effects on sensitivity and selectivity characteristics as fluorescent chemosensors of Cr3+, Zn2+ and Cd2+. Single crystal structures revealed desired chain of intramolecular hydrogen bonding (ligand 12) as well as possible coordination modes. Probes 1 – 4 demonstrated very high turn-on sensitivity and selectivity as double fluorescent sensors for Cr3+ and Zn2+ at their different emission wavelengths (blue-shifted in case of Zn2+). A remarkable106-fold emission turn-on by Cr3+ was recorded for molecule 2, which is an unknown magnitude for Cr3+ sensitivity to the best of our knowledge. Results revealed that Cd2+ sensor may be developed by further derivatization of these probes. Possession of symmetrical substitution on both imidazole rings, multiple active protons involved in hydrogen intramolecular bonding relay and the consequent ESIPT capability were found to be very beneficial to successful outcomes as high fluorescent turn-on chemosensors by the studied molecules. Modification of sensor properties such as sensitivity and selectivity was achieved through substituent manipulations at certain peripheral positions. Thus, deliberate molecular derivatization was found to be a tool for manipulating interference and selectivity profiles. Job plot, single crystal result and sustained large Stoke’s shift in the presence of Cr3+ suggest a one-pocket N^O coordination in 1:1 stoichiometry rather than binuclear N^O^N two-pocket coordination. Quantum mechanical calculations on model structures suggest that successful turn-on results may be associated with coplanarity settings of the imidazole and phenol rings.

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Publication details

The article was received on 14 Mar 2018, accepted on 09 Apr 2018 and first published on 10 Apr 2018


Article type: Paper
DOI: 10.1039/C8NJ01265B
Citation: New J. Chem., 2018, Accepted Manuscript
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    ESIPT-capable 2,6-di(1H-imidazol-2-yl)phenols with very strong fluorescent sensing signals towards Cr(III), Zn(II) and Cd(II): molecular variation effects on turn-on efficiency

    A. O. Eseola, H. Görls, M. Bangesh and W. Plass, New J. Chem., 2018, Accepted Manuscript , DOI: 10.1039/C8NJ01265B

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