A Novel Selective "Turn-On" Fluorescent Chemosensor Based on Thiophene Appended Cyclotriphosphazene Schiff Base for Detection of Ag+ Ions

The salicylaldehyde-functionalized cyclotriphosphazene (1) and thiophene appended cyclotriphosphazene based Schiff base (2) were designed and synthesized. The characterizations were carried out via MALDI-TOF, FTIR, C-13, P-31 and H-1 NMR. The photophysical behavior of compound 2 was evaluated by UV-Vis absorption, time-resolved fluorescence, excitation-emission matrix (EEM) analysis, steady-state fluorescence, and 3D-fluorescence spectroscopies. Compound 2 demonstrated selective fluorescence "turn-on" response at 427 nm towards to Ag+ ion when the tested competitive species did not affect fluorescence signal. The binding and sensing mechanisms were evaluated by DFT calculations which approved that the PET process between C=N and fluorophore groups was inhibited, and the fluorescence "turn-on" response was obtained with the contribution of CHEF after 1 : 1 coordination of compound 2 with Ag+ ion. The LOD and LOQ were calculated as 3.15 and 9.45 mu mol L-1, respectively in the linear range of 9.35-210.00 mu mol L-1 Ag+ ions. The practical application of compound 2 for Ag+ determination was successfully performed in environmental waters after optimization of measurement conditions. The obtained results approved that compound 2 is a selective fluorescent sensor for Ag+ ions and it can be used for spectrofluorimetric Ag+ determination in real samples. Importantly, according to the literature, this report is the first example of cyclotriphosphazene based fluorescent sensor for Ag+ ion.