The aforementioned control reaction without applied potential afforded only 4% of 3aa. In contrast to TpBPA, TCBPA is a pale yellow solid that does absorb appreciably at 400 nm. Nevertheless, in the absence of an applied potential for the optimized synthesis of 3gb, only a 12% yield of 3gb was observed. The detection of small amounts of product in the aforementioned control reactions corroborates a conPET-type mechanism where photoexcitation of TpBPA or TCBPA leads to SET reduction of protons or trace O2 (reactions were bubbled by N2 for 5 min during preparation and sealed; no further strict precautions were taken) to generate the corresponding TPA .+ . In any case however, the very substantial yield differences when applied potential is present or absent confirm the pivotal role of the TPA .+ s and that e-PRC is the main product-forming pathway in both reactions. Inspecting the UV-visible absorption spectra of TpBPA .+ and TCBPA .+ , we reasoned that the longest wavelength bands (max at ca. 719 and 856 nm, respectively) must contain their D0→D1 transitions.