A new optical sensor for Al3+/Fe3+ based on PET and chelation-enhanced fluorescence

A simple probe (compound 1) sensing Al3+ or Fe3+ by suppression of photoinduced electron/energy transfer (PET) process and chelation-enhanced fluorescence is described. Compound 1 was prepared from 2-(bromomethyl)benzo[d]thiazole and pyridine-2,6-diamine. Compound 1 showed a much stronger fluorescence response to Al(III) than to Fe(III). The best fluorescence response of 1 to Al3+ was found to be at pH near 7. The results indicated that 1 could be a promising fluorescent turn-on chemosensor for Al3+ or Fe3+. Ratiometric sensing of 1 to Al3+ or Fe3+ was accomplished by plotting the absorbance ratio at 338 to 310 nm versus Al3+ or Fe3+ concentration. The fluorescent turn-on response of 1 to Al3+ or Fe3+ can be attributed to suppression of PET process and chelation-enhanced fluorescence upon binding with Al3+ or Fe3+. The binding mode of 1-Al3+ or 1-Fe3+ was found to be a 1:1 complex based on Job's plot, electrospray ionization (ESI) mass spectroscopy (MS) data, and density functional theory (DFT) calculation results.