To increase the stimulus-responsivity of the photoswitchable aggregates, we exploited the chelating properties of ATP to study the possibility to control this assembly with ions. Knowing the strong affinity of ATP with divalent metal ions , our hypothesis was that the addition of such cations would lead to the disassembly of the aggregates and the decrease of their fluorescence (Figure ). To characterize this effect, we started from the preformed ATP/AzoDiGua aggregates and added different metal cations (M n+ ) to ensure a final molar ratio [M n+ ]/[ATP] = 2. Interestingly, it was found that the turbidity of the solution immediately disappeared for the tested divalent cations (Mg 2+ , Ca 2+ , and Cu 2+ ) but remained for the monovalent ones (Na + , K + ) (Figure ), showing that the ion-triggered disassembly was valence-selective. The color due to the presence of trans-AzoDiGua (Figure ) remained upon ion-triggered disassembly as the response was mediated by ATP chelation and not by a change of AzoDiGua isomerization state. The mechanism of the metal-mediated disassembly of the aggregates was then further investigated in the case of Cu 2+ using EPR spectroscopy, keeping all concentrations identical to that used for the assembly/disassembly experiments ([ATP] = 1 mM ; [AzoDiGua] = 1 mM ; [Cu 2+ ] = 2 mM). The EPR signal of pure Cu 2+ (2 mM) shifted to lower fields with appearance of a marked shouldering when it was mixed with ATP (1 mM) while ATP alone had no EPR signature for the same field range (Figure ). These effects, in agreement with previous reports , are attributed to the interaction between Cu 2+ and ATP upon chelation . On the contrary, the EPR signal of pure Cu 2+ did not evolve upon addition of AzoDiGua (1 mM) showing the absence of interaction between these two cationic species (Figure ). Interestingly, AzoDiGua/ATP aggregates did not have any EPR signal but, after addition of Cu 2+ , a clear paramagnetic signal appeared and displayed the same features as the one of Cu 2+ /ATP mixture (Figure ). This new signal was thus attributed to the coordination of Cu 2+ with ATP and shows that the disassembly of ATP/AzoDiGua aggregates upon Cu 2+ addition is due to the competitive complexation between ATP and Cu 2+ . Optical microscopy observations of the ATP/AzoDiGua aggregates ([ATP] = 1 mM ; [AzoDiGua] = 1 mM) exposed to increasing amounts of Cu 2+ evidenced a gradual disassembly with an increase in [Cu 2+ ] and showed that an excess of Cu 2+ (2 mM) was necessary to ensure full and permanent disassembly (Figure ). This ion-stimulated disassembly was then used to control the fluorescence of ATP/AzoDiGua co-assembly (Figure , S13), showing either a way to chemically adjust the fluorescence of the system or an original method to titrate the presence of divalent cations (here, Cu 2+ ) by fluorescence. After disassembly for a ratio [Cu 2+ ]/[ATP]=2, further addition of ATP (3 mM) led to the re-assembly of ATP/AzoDiGua aggregates and appearance of suspension turbidity (Figure ), emphasizing the reversibility of the supramolecular aggregates and the role of free ATP for the assembly to occur. By exploiting the chelating properties of ATP and its strong and specific affinity for divalent cations, we demonstrated that ATP-AzoDiGua aggregates were cation-responsive and valence-selective, offering the possibility not only to dynamically control both their assembly/disassembly behaviour and their fluorescence through a chemical stimulus but also to envision the principle of a divalent-specific ionic sensor.