A novel supramolecular three-input AND logic gate is demonstrated as a ‘lab-on-a-molecule’ for monitoring the Na⁺, pH and pE levels in solution by communicating a fluorescence signal. The fluorescence signal is modulated by three photoinduced electron transfer reactions that are controlled by an unprecedented combination of two cation binding events and one redox reaction.

A novel anthracene-based molecular AND logic gate displays a fluorescence output in methanol after chemical oxidation of the ferrocene moiety with Fe(III) and protonation of the tertiary amine. This new class of probes could have practical applications in corrosion science and living cell imaging.

A molecular logic gate with a ‘receptor–spacer–fluorophore–spacer–redox-unit’ format emits a fluorescent signal on simultaneous oxidation and protonation in aqueous methanol solution.

A molecular three-input AND logic gate with a naphthalimide fluorophore communicates the presence of a congregation of three biologically relevant cations in aqueous methanol with a 25-fold fluorescence enhancement and Φ_Fmax of 0.203.

Two novel naphthalimide-based ‘Pourbaix sensors’ for redox potential and pH were designed based on a ‘fluorophore–spacer₁–receptor–spacer₂–electron-donor’ configuration. The synthesised molecular logic gates consist of an alkylated 1,8-naphthalimide fluorophore connected to a tertiary amine by a flexible ethylene spacer to a ferrocene moiety via a methylene spacer. The UV-visible absorption and steady state fluorescent properties were examined in methanol and 1 : 1 (v/v) methanol/water. The spectroscopic properties are modulated by internal charge transfer (ICT) and photoinduced electron transfer (PET) mechanisms. A log β_H⁺ of 9.2 and 8.7 were determined in 1 : 1 (v/v) methanol/water for the methylated 1 and butylated 2 compounds, respectively. An apparent log β_Fe³⁺ of 4.2 was determined in 1 : 1 (v/v) methanol/water at pH 4. Time-resolved spectroscopic studies elucidated the stimulus-modulated photoinduced electron transfer pathways. In the oxidised and protonated state, 1 exhibits a single fluorescence lifetime of 8.5 ns, while an efficient photoinduced electron transfer characterised by a time constant of 20 ps is revealed by femtosecond transient absorption spectroscopy in the absence of a perturbing stimulus.

The exploitation of photoinduced electron transfer as a general design principle for the development of luminescent redox indicators and logic gates is described. Potential future applications in biology, environmental analysis, biomedical diagnostics, corrosion science and materials science are mentioned.