A fluorescent off-on-off'' proton switch derived from natural products and further studies of first-generation fluorescent photoinduced electron transfer (PET) systems

Two new second generation fluorescent switches that are based on the chromophore-spacer receptor architecture are reported in this paper. The fluorescence modulation of these switches is a result of quenching or initiating photoinduced electron transfer ( PET) between the chromophore and the receptors due to cation binding. These two molecules utilize an alkaloid, anabasine, as the proton receptor, and function as fluorescent off-on-off switches with decreasing pH. One of these molecules also utilizes a coumarin as the chromophore, making it the first rationally designed fluorescent PET system based on natural products. Further studies of two well-known first generation fluorescent switches to achieve more complex fluorescence modulation are also reported in this paper.