Amino and chloro derivatives of 1,10-phenanthroline as turn-off fluorescence sensors for selective and sensitive detection of Fe(II)

Phenanthroline is a fluomphore known for its non-fluorescent complex formation with Fe(II). We present two novel turn-off fluorescence sensors developed based on 5-amino and 5-chloro derivatives of 1,10-phenanthroline for the quantification of Fe(II) with improved sensitivity and selectivity compared to pristine phenanthroline. The fluorescence intensity of 5-amino-1,10-phenanthroline at lambda(em) 512 nm when lambda(ex) 280 nm was decreased remarkably mainly due to the 1:3 static quenching by Fe(II), supported by the charge transfer spectra and the temperature studies. The formation of a stable complex with Fe(II) was observed in the range of pH 4.64 to 8.21 with a detection limit of 2.74 x 10(-7) M at 3.3 sigma and 25 degrees C. The 5-chloro derivative showed much higher sensitivity and selectivity towards Fe(II) in the range of pH 3.80 to 6.80 with a detection limit of 1.70 x 10(-8) M at 3.3 sigma and 25 degrees C when the lambda(ex) and lambda(em) were 286 nm and 379 nm, respectively. In both the fluorescence sensors, the observed interference from foreign ions was at a minimum level, indicating the sensors' specific selectivity towards Fe(II). The interference from cations; Cu(II), Ni(II), and Co(II) was comparatively higher, while the anions showed only a little to no interference.