Tuning the sensitivity of fluorophore-nitroxide radicals

The synthesis of pyrene-pyrazole nitronyl and imino nitroxides is reported, along with characterization of the radicals by UV-Vis, PL and EPR techniques. The UV-Vis studies revealed that the nature of the spacer attached to the nitroxide plays a crucial role in the radical n-pi* transition intensity. This finding forms the basis for the evaluation of these nitroxides as redox-probes. The results of these investigations confirmed the preliminary assumptions of the profound sensing properties of these radicals. In fact, it was demonstrated that the sensitivity of the newly synthesized probes far surpasses known literature analogues. Hence, the strategy described here opens new horizons for the targeted design of radical sensing materials.