2,6-Bis(2-Benzimidazolyl)Pyridine Fluorescent Red-Shifted Sensor for Recognition of Zinc(II) and a Calorimetric Sensor for Iron Ions.

The ability of 2,6-bis(2-benzimidazolyl)pyridine (bbp) as an optical sensor was studied by fluorescence spectroscopy, colorimetric and UV-visible techniques. The fluorescence spectra of bbp demonstrated a red-shifted upon addition of Zn(2+) ion, whereas rest of the cations did not induce any shift. Selectivity of the sensor was examined toward Zn(2+) in the presence of a wide range of cations, as interfering agents, that showed no disruption in its function. In addition, the pH effect was tested on the fluorescence response of bbp; which showed the efficiency of the sensor in a wide pH range. The limit of detection for Zn(2+) was estimated as 2.1 μM. Furthermore, the colorimetric studies were carried out and the observations showed a color change from colorless to purple by the addition of Fe(2+) ion and from colorless to yellow by the addition of Fe(3+). The UV-visible studies were carried out to confirm the colorimetric observations. The color changes occurred when Fe(2+) and Fe(3+) were added to the sensors solution, respectively. The detection limits were calculated as 2.8 × 10(-7) M and 3.5 × 10(-6) M for Fe(2+) and Fe(3+), respectively. Hence, bbp can be used as a dual mode optical sensor for detection of Zn(2+) by fluorescence and discriminately detection of Fe(2+) and Fe(3+) visually.