As such, the photocatalytic pinacol coupling reaction was chosen as a model reaction, using benzaldehyde as the substrate (Figure ). This reaction has previously been described to proceed through a reductive quenching cycle, whereby the excited PC is reduced by the sacrificial reductant N,N-diisopropylethylamine (DIPEA) [(E(DIPEA•+/DIPEA) = 0.65 V vs SCE in MeCN], which then is employed to reduce the aldehyde to its radical anion. Although reduction of benzaldehyde is challenging (Ered = -1.80 V vs SCE in DMF), the weak attraction of the protonated DIPEA with the aldehyde has been proposed to render this process less thermodynamically demanding. The oxidation potential of DIPEA was first measured in each of the solvents used (Figure and Table ). There is a progressive cathodic shift of the Eox of DIPEA with increasingly solvent polarity (Eox = 0.93 V in THF and 0.65 V in MeCN). Therefore, despite the PCs generally being weaker photoreductants in more polar solvents, this is somewhat offset by DIPEA being more easily oxidised in polar media.