Intramolecular C-H/C-D exchange in cofacially stacked polyfluorenes via electron-induced bond activation

EPR studies in hexamethylphosphoramide, along with DFT studies, reveal that the one-electron reduction of pi-stacked polyfluorenes containing two, three, and four fluorene units leads to the corresponding anion radicals where the odd electron is located exclusively on an outside fluorene moiety. These anion radicals disproportionate to form small concentrations of diamagnetic dianions, wherein there is a nonclassical pz overlap that crosses the C2 axis. The presence of the two extra electrons activates the C-H bonds in the ortho positions, and concomitant overlap of the p-orbitals involving adjacent fluorene moieties results in intramolecular hydrogen exchange at temperatures as low as 90 K.