Fluorescent Molecular Logic Gates and Pourbaix Sensors in Polyacrylamide Hydrogels.

Polyacrylamide hydrogels formed by free radical polymerisation were formed by entrapping anthracene and 4-amino-1,8-naphthalimide fluorescent logic gates based on photoinduced electron transfer (PET) and/or internal charge transfer (ICT). The non-covalent immobilisation of the molecules in the hydrogels resulted in semi-solid YES, NOT, and AND logic gates. Two molecular AND gates, examples of Pourbaix sensors, were tested in acidic aqueous methanol with ammonium persulfate, a strong oxidant, and displayed greater fluorescence quantum yields than previously reported. The logic hydrogels were exposed to aqueous solutions with chemical inputs, and the fluorescence output response was viewed under 365 nm UV light. All of the molecular logic gates diffuse out of the hydrogels to some extent when placed in solution, particularly those with secondary basic amines. The study exemplifies an effort of taking molecular logic gates from homogeneous solutions into the realm of solid-solution environments. We demonstrate the use of Pourbaix sensors as pE-pH indicators for monitoring oxidative and acidic conditions, notably for excess ammonium persulfate, a reagent used in the polymerisation of SDS-polyacrylamide gels.

Enhanced ion binding by the benzocrown receptor and a carbonyl of the aminonaphthalimide fluorophore in water-soluble logic gates.

Two fluorescent logic gates 1 and 2 were designed and synthesised with a 'receptor1-spacer1-fluorophore-spacer2-receptor2' format. The molecules comprise of an aminonaphthalimide fluorophore, methylpiperazine and either benzo-15-crown-5 or benzo-18-crown-6. Model 3, with a weakly binding 3,4-dimethoxyphenyl moiety, was also synthesised. The compounds were studied both in 1 : 1 (v/v) methanol/water and water by UV-visible absorption and steady-state fluorescence spectroscopy. The green fluorescence of 1-3 is modulated by photoinduced electron transfer (PET) and internal charge transfer (ICT) mechanisms, and by solvent polarity. In 1 : 1 (v/v) methanol/water, logic gates 1 and 2 emit with Φf = 0.21 and 0.28, and bind with pßNa+ = 1.6 and pßK+ = 2.6, respectively, and pßH+ = 7.4 ± 0.1. In water, logic gates 1 and 2 emit with Φf = 0.14 and 0.26, and bind with pßNa+ = 0.86 and pßK+ = 1.6, respectively, and pßH+ = 8.1 ± 0.1. The measured pßNa+ are significantly lower than reported for analogous classic anthracene-based Na+, H+-driven AND logic gates indicating a stronger Na+ binding interaction, which is attributed to direct interaction with one carbonyl moiety within the aminonaphthalimide. Supporting evidence is provided by DFT calculations. Furthermore, we illustrate an example of logic function modulation by a change in solvent polarity. In 1 : 1 (v/v) methanol/water, molecules 1 and 2 function as Na+, H+ and K+, H+-driven AND logic gates. In water, the molecules function as single input H+-driven YES logic gates, while consideration as two-input devices, 1 and 2 function as AND-INH-OR logic arrays.