Mechanistic studies Spectroelectrochemical analysis of TpBPA (Figure ) TCBPA and TdCBPA (see Supplementary Information) revealed the formation of their respective TPA .+ s by the disappearance of the TPA band (max = ca. 345 nm) and appearance of two broad absorption bands between 360-430 nm (max = ca. 420 nm) and between 600-900 nm (max = ca. 719, 856 nm), when the potential was increased from 0 to +1.3 V. Excellent reversibility was observed upon returning the potential to +0.0 V, indicating high stability of the TPA .+ s as e-PRCats. While TpBPA is a white solid that does not absorb 400 nm light, it possesses a strong absorption at max = 365 nm, where TpBPA .+ absorbs poorly. Performing our optimized synthetic procedure for 3aa with 365 nm LEDs afforded only 11%, suggesting photoexcitation of neutral TpBPA is not a dominant factor in the mechanism.