Chemically Mediated Fluorescence Yield Switching in Nitroxide-Fluorophore Adducts: Optical Sensors of Radical/Redox Reactions

摘要

The absorption and fluorescence emission spectra and quantum yields of a series of paramagnetic nitroxide naphthalene adducts are compared with those of diamagnetic analogues. While the absorption and emission energies of these compounds are unaffected by the presence of the nitroxyl radical substituents(s), the fluorescence quantum yields of the paramagnetic derivatives are 2.9- to 60-fold lower than the corresponding diamagnetic derivatives. Additionally, chemical reduction of the nitroxide moiety to a diamagnetic hydroxylamine produces a fluorescence yield increase that parallels nitroxyl radical loss. On the basis of this chemically mediated optical switching, compounds of this class may prove to be broadly applicable as sensitive optical probes for radicals and redox-active species in biological and chemical systems. Reprints. (MJM)