Benzimidazole and its derivatives have been studied in ion recognition systems that display color changes or fluorescence quenching or enhancement upon binding. Acidity of the NH can be modulated by the presence of heterocycles, such as thiophene, pyrrole, and furan, electronically connected to the imidazole group, as a way to enhance intramolecular electronic delocalization. Furan, pyrrole and thiophene are also known for their interesting photophysical properties, which enable their use as fluorescent sensors and markers, among other applications.

Detecting metallic cations is of great interest as mercury, lead, and cadmium are some examples of cations that are toxic for living organisms, and easy detection in the environment is desirable. Also, many metallic cations are involved in biochemical reactions and their correct balance within cells or living systems is mandatory for health. Metallic cations can be complexed through N, O and S donor atoms in aromatic heterocycles. Hg²⁺ or its methylated derivative can be taken up in the food chain of aquatic organisms doing huge harm to humans and nature. Iron is the most abundant transition metal in cellular systems, more specifically, Fe³⁺ is an essential element in the growth and development of living systems as well as in many biochemical processes at cellular level.

Following our previous work on fluorimetric and colorimetric heterocyclic chemosensors, we now report the interaction studies of a family of benzimidazoles attached to furan, pyrrole and thiophene with biologically important cations, through spectrophotometric and spectrofluorimetric titrations.