(Benzimidazolylmethyl)cyclen: A Potential Sensitive Fluorescent PET Chemosensor for Zinc

A new fluorescent probe for Zn2+, methylbenzimidazole‐pendant cyclen [LH: 1‐(benzimidazol‐2‐ylmethyl)‐1,4,7,10‐tetraazacyclododecane] was designed and synthesized. The protonation constants of (benzimidazolylmethyl)cyclen and the stability constants of the corresponding zinc complex were determined by potentiometric titrations. The single‐crystal X‐ray diffraction analysis showed that LH and Zn2+ form a 1:1 complex [ZnLH]2+. The results of potentiometric, 1H NMR and UV titrations indicated that above pH 8, [ZnLH]2+ mainly deprotonates into [ZnL]+. On addition of successive amounts of Zn2+ at pH 10.4 (2 × 10–2 mol L–1 CAPS, 25 °C), the fluorescence emission of cyclen(methylbenzimidazole) increases linearly by a factor of 3.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)