Excited state intramolecular proton transfer in hydroxy oxime-based chemical sensors
Fluorescent chemical sensors are of vital interest for the detection of chemical warfare compounds such as nerve agents. Charge-transfer contribution to the excited state (PET) has been shown to be involved in the detection mechanism of OP nerve-gas agents by chromophore-functionalized hydroxyl tertiary amine sensors ( J. Molec. Struct.: THEOCHEM 867, 64 (2008); Chem. Phys. Lett. 474, 278 (2009).
In the so-called second generation sensors, (Dale, T. J.; Rebek, J., Jr. Angew. Chem. Int. Ed. 2009, 48, 7850), a different mechanism has been found to be operative, namely the so called excited state proton transfer or ESIPT (Ioannis S. K. Kerkines, Ioannis D. Petsalakis, Giannoula Theodorakopoulos and Julius Rebek, Jr. J. Phys. Chem. A 2011, 115, 834)
Figure 1 detection of OP nerve agents by oxime→isoxasole with enhancement of fluorescence
Figure 2: oxime (1-4)/isoxasole (5-8) systems calculated.
Figure 3: experimental absorption and fluorescence spectra of the pyrene (2/6) sensor.
Figure 4: Energetics of the ground and excited state structures relevant to the sensing mechanism
