Molecular characteristics of a fluorescent chemosensor for the recognition of ferric ion based on photoresponsive azobenzene derivative

Metal ion recognition is of great significance in biological and environmental detection. So far, there is very few research related to the ferric ion sensing based on photoresponsive azobenzene derivatives. In this work, we report a highly selective fluorescent turn-off' sensor for Fe3+ ions and the molecular sensing characteristics based on an azobenzene derivative, N-(3,4,5-octanoxyphenyI)-N'-4-[(4-hydroxyphenyl)azophenyl]1,3,4-oxadiazole (AOB-t8). The binding association constant was determined to be 6.07 x 10(3) M-1 in ethanol and the stoichiometry ratio of 2:2 was obtained from Job's plot and MS spectra. The AOB-t8 might be likely to form the dimer structure through the chelation of ferric ion with the azobenzene moiety. Meanwhile, it was found that the photoisomerization property of AOB-t8 was regulated by the binding with Fe3+. With the chelation of Fe3+, the regulated molecular rigidity and the perturbed of electronic state and molecular geometry was suggested to be responsible for the accelerated isomerization of AOB-t8 to UV irradiation and the increased fluorescence lifetime of both trans- and cis-AOB-t8-Fe(III). Moreover, the reversible sensing of AOB-t8 was successfully observed by releasing the iron ion from AOB-t8-Fe(III) with the addition of citric acid. (C) 2016 Elsevier B.V. All rights reserved.