From the cross-fertilisation of fluorescent pH indicators and fluorescent redox switches, our group has established a new class of molecular sensor that operates as two-input molecular logic gates. These molecular sensors, known as ‘Pourbaix sensors’, are named in honour of Marcel Pourbaix, who developed the pH–potential diagrams for the various states of metal ion species in aqueous solution. This review highlights the evolution of ‘Pourbaix sensors’ based on anthracene and naphthalimide fluorophores. Potential applications of this class of molecule in fields such as corrosion science, cell biology and biomedical diagnostics are highlighted.