Oxidative quenching of PFBT by residual Pd has been reported up to at least 50% with 1170 ppm Pd while still quenching around 25% with as low as 36 ppm Pd. However, the reductive quenching of PFBT by SDs to form reduced PFBT also seems to be an important pathway with 20-30% quenching in 30% DEA and 40% in Ascorbic acid . We can also see a clear reductive quenching of PFBT in organic media with ascorbic acid (Figure -15), since this is a condition with sufficiently acidic protons that the reduced polymer is expected to rapidly be protonated. This is even more likely with ascorbic acid as it will also release a proton as it decomposes after being oxidized and therefore works like a proton-coupled electron transfer (PCET) donor and not just a simple reductive agent . Therefore, it is also likely that electron transfer to an active Pd site could also happen from an already protonated reduced polymer. In this case, it is possible that the proton would transfer as well, as it has already been shown that BT sites will perform protoncoupled electron transfer reactions . This certainly requires that the residual Pd is close enough to the active site. It however generates a question: what is the form of residual Pd in the PFBT polymer?