Abstract
One-pot condensation reaction between 9,9-Bis(4-aminophenyl)fluorene and 9-Ethyl-9H-carbazole-3-carbaldehyde afforded a chemosensor ((N,N′)-4,4′-(9H-fluorene-9,9-diyl)bis(N-((9-ethyl-9H-carbazol-2-yl)methylene)aniline, SB) having Schiff base skeleton. The further step was the synthesis of the polymer (P-SB) via oxidative polycondesation reaction of SB. FT-IR, 1H NMR and 13C NMR instruments were used to characterize the functional groups on the monomer and polymer. Thermal stability and electrochemical features of SB and P-SB were characterized by thermogravimetric analysis-differential thermal analyses (TG-DTA) and cyclic voltammetry (CV), respectively. The glass transition and surface image of P-SB were determined from DSC and SEM measurements, respectively. UV–vis and photoluminescence spectroscopy (PL) allowed to determine the optical properties of SB and P-SB. The obtained polymer, which had the weight average molecular weight of 8400 Da identified by gel permeation chromatography (GPC), exhibited fluorescence property. The synthesized turn-on fluorogenic chemosensor SB showed high selectivity and sensitivity towards Sn2+ among the cations of Ag+, K+, Hg2+, Mn2+, Cd2+, Sn2+, Ca2+, Pb2+, Zn2+, Co2+, Ni2+, Cu2+, Fe3+, Al3+, Cr3+ and Cr6+. The fluorescence turn-on recognition process for the detection of Sn2+ was related to the restriction of CN isomerization, followed by inhibiting intramolecular charge transfer (ICT), with consequent chelation-enhanced fluorescence (CHEF) mechanism. The stoichiometry ratio of the analyte-sensor adduct in the solution was found to be 1:1 by Job's plot method concomitant with a dramatic increase in fluorescent signal at 471 nm and a marked color change from colorless to turquoise blue upon addition of Sn2+ ions. Limit of detection value for the formation of SB-Sn2+ chelation was calculated as 3.37 nM. No change in PL intensity of SB-Sn2+ chelation was observed in the company of other metal ions. Reversibility of the chemosensor in its binding towards Sn2+ was demonstrated in the presence of chelating agent EDTA. The synthesized SB could effectively detect Sn2+ ion as a fluorescent sensor.
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