Various classic dyes have been applied as chemosensory signaling units, such as coumarin, pyrene, 1,8-naphthalimide, xanthene, boron dipyrromethene difluoride (BODIPY), and cyanine derivatives. Among them, cyanine-based platforms have gained much interest due to their remarkable spectral properties, and particularly an intense π-π* absorption which can be easily tuned from the visible to the near-infrared (NIR) region by structural modifications in the chromophore moiety. Metal-cyanine interactions can produce a color change associated with the conjugation of π-electrons, allowing for easy detection of the intended analyte in solution, making them ideal candidates as colorimetric sensors for metal recognition.

Following the research group’s interest on heterocyclic optical chemosensors for various ions, a pentamethine cyanine dye containing two sulfonic acid groups, for improved solubility in aqueous media, was evaluated as a chemosensor for the recognition of several metal cations with biological and environmental relevance. Chemosensing studies showed that this cyanine displayed a highly sensitive colorimetric response, from blue to colorless, for Cu²⁺and Fe³⁺ in acetonitrile solution.