“This review describes discoveries and advances in the field of fluorogenic and chromogenic sensors for anions from the first systems described in the early nineties up to the last developments in the year 2003.”

This paper is a comprehensive review about recent developments in the field of fluorogenic and chromogenic chemosensors and reagents for anions. Most likely the paper is highly cited due to the remarkable grow in interest that this interdisciplinary field has attracted in the past few years and which is reflected in the large amount of work published in this area.

This review describes discoveries and advances in the field of fluorogenic and chromogenic sensors for anions from the first systems described in the early 90’s up to the last developments taking place in the year 2003. It was our aim to provide a useful tool, via this extensive and exhaustive review article, to researchers working on the design of anion chemosensors and new sensing procedures for anion chemosensing.

Optical anion chemosensing is a relatively novel research field interested in developing sensing protocols for anions based in the transduction of the anion coordination event via a remarkable color or anion-induced fluorescence changes. Many systems are based on the use of supramolecular anion binding sites and signalling units. The binding site is responsible for the selective anion coordination process, whereas the signalling subunit transforms the coordination process into a color or fluorescence emission change of the anion-host ensemble. The paper makes a classification of optical anion chemosensors in relation to the output signal—changes in fluorescence or modifications of the color—and in relation to the use of different sensing protocols ("binding site-signalling subunit", "displacement," and "chemodosimeter" approach) and tries to give a clear perspective of the field. The paper also explains the basics involved in different optical sensing processes in relation to the transcription of the anion coordination event into macroscopic observable signals.

My research group began to work in the early 90’s on the development of synthetic receptors functionalized with redox-active groups for the electrochemical recognition and sensing of metal cations and anions. After some years working in electrochemical recognition it was quite natural for us to move on to optical sensing. When we started developing our first colorimetric system for anions this was a field which was, in some ways, unexplored. Since then, our contribution to this field has involved a number of chromogenic and fluorogenic systems containing certain binding sites and different dyes as suitable chemosensors for the chromo-fluorogenic sensing of carboxylates, ATP, cyanide, sulphide, citrate, fluoride, borate, etc. We are particularly interested in systems that work in aqueous solution, in developing new protocols for guest sensing, and in the design of smart sensory materials for anions, cations, and neutral species.