Obviously, CTPAB is more active for HER than the other two structures due to the high electron affinity of O of the C=O bridge. Upon light irradiation, the photogenerated electrons on CTPAB, OTPAB and MTPAB will contribute to a drive potential (Ue) of 0.14, 1.55 and 1.90 eV for HER, respectively (Figure ). In this case, the HER process on OTPAB and MTPAB will proceed spontaneously with all the elementary steps becoming downhill. For CTPAB, although the first step of HER is still uphill upon irradiation, the remaining energy barrier is as negligible as 0.07 eV, which can be easily overcome by adding co-catalysts (e.g. Pt) or applying external electric potential. Note that the solvation effect is not considered in this work which may quantitatively influence the calculated Gibbs free energy of different intermediates. However, the differences in photocatalytic activity as a function of the composition of the building monomers will not be qualitatively affected by the presence of water solvent.