To better understand the variations in yield with solvent, Stern-Volmer (SV) quenching studies were performed with some of the PCs in the four solvents, using DIPEA as the quencher. We could observe no correlation between the SV quenching results and the solvent polarity (Figures S54-S59 and Table ). Since the Stern-Volmer quenching studies surprisingly provided no additional insight into the yields obtained, we next assessed the photostability of the PCs in each solvent under the pinacol coupling reaction conditions. UV-Vis absorption spectra were acquired before and after each 24 h reaction (see Figures for all UV-Vis absorption spectra). It was observed that the absorption spectra of all the PCs changes significantly after the reaction compared to before.