A fluorescent AND logic gate based on a ferrocene-naphthalimide-piperazine format responsive to acidity and oxidizability

A novel fluorescent molecular logic gate 1 is demonstrated as a two-input AND logic gate for the detection of acidity and oxidizability. Designed according to an electron-donor-spacer fluorophore-spacer-receptor' format, the modules are represented by ferrocene as the electron donor, 1,8-naphthalimide as the fluorophore and piperazine as the proton receptor. In the presence of elevated concentrations of H+ and Fe3+, the molecule switches 'on' emitting at lambda(max), = 530 nm with Phi(f) = 0.060 at 10(-4) MH+ and 50 mu M Fe3+. The H+ binding and apparent Fe3+ binding constants determined by fluorimetric titrations in 1:1 (v/v) methanol/water are log beta(H+) = 8.1 and log beta(Fe3+) = 4.7. Modulation of the fluorescence output results from controlling competing photoinduced electron transfer (PET) at the ferrocene end and internal charge transfer (ICT) at the piperazine end. Time-resolved fluorescence spectroscopy reveals a single fluorescent lifetime of 5.8 ns, while from absorption transient spectroscopy a remarkable fast decay signal < 2 ps is observed. Comparison is made with methylpiperazine 2 and piperazine fluorescent pH indicator 3 as model compounds.