Photoluminescence Investigation of Fundamental Charge Transfer Processes in Stable Nitroxyl Radical-Containing Polymers
Since nitroxyl radicals are known fluorescence quenchers, we probed the charge transport in this system by the incorporation of fluorescent perylene markers into the radical-containing polymer matrix. We have investigated the interplay between collisional and static quenching processes using steady-state and time-resolved photoluminescence quenching studies of perylene by TEMPO (2,2,6,6-tetramethylpiperidinyloxyl), radical-containing species. Quenching studies for these model systems, including both free TEMPO monomers and non cross-linked, solution-phase PTMA-nitroxy polymers, (poly(4-methacryloyloxy-2,2,6,6-tetramethylpiperidine-N-oxyl) have allowed us to calculate optimal synthetic parameters for construction of polymer cathode systems. We have determined how such polymer properties as average chain length, spacing between pendant groups, proclivity for polymer folding, and solvent swelling affect both the mechanism of quenching as well as the efficiency of charge transfer. As a function of polymer length, we observe a change in quenching mechanism, while the density of radical moieties has significant affects on quenching/charge transfer efficiency. The quenching sphere of action and thus the optimal distance between radical moieties and fluorophores for the most efficient charge transfer has also been determined and will be discussed at length.