@Article{C8NJ01265B,
author ="Eseola, Abiodun O. and Görls, Helmar and Bangesh, Masroor and Plass, Winfried",
title  ="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",
journal  ="New J. Chem.",
year  ="2018",
volume  ="42",
issue  ="10",
pages  ="7884-7900",
publisher  ="The Royal Society of Chemistry",
doi  ="10.1039/C8NJ01265B",
url  ="http://dx.doi.org/10.1039/C8NJ01265B",
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) were designed and comparatively studied for their molecular effects on their sensitivity and selectivity characteristics as fluorescent chemosensors of Cr3+{,} Zn2+{,} and Cd2+. Their single-crystal structures revealed a 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 the case of Zn2+). A remarkable 106-fold emission turn-on by Cr3+ was recorded for molecule 2{,} which{,} to the best of our knowledge{,} is an unheard of magnitude for Cr3+ sensitivity. The results suggested that a Cd2+ sensor could be developed by further derivatization of these probes. The possession of symmetrical substitution on both imidazole rings{,} multiple active protons involved in hydrogen intramolecular bonding relays{,} and the consequent ESIPT capability of the studied molecules were found to be very beneficial to their successful outcomes as high fluorescent turn-on chemosensors. Modification of the 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 the interference and selectivity profiles. The Job plot{,} single-crystal results{,} and sustained large Stoke{'}s shift in the presence of Cr3+ suggest a one-pocket N^O coordination in a 1 : 1 stoichiometry rather than a binuclear N^O^N two-pocket coordination. Quantum mechanical calculations on the model structures suggested that the successful turn-on results may be associated with the coplanarity settings of the imidazole and phenol r