Figure 3.

Predicted vertical ionization energy of six prototype porous MOFs with respect to a common vacuum level (determined by the value of the electrostatic potential at the center of an internal pore). Note that for HKUST-1 values are shown for the ground-state antiferromagnetic singlet (solid lines), triplet state (black dashed lines), and the closed-shell singlet (pink dotted lines). The values were calculated using DFT, employing a hybrid exchange–correlation functional (HSE06), and with periodic boundary conditions used to represent the perfect solid. The redox potentials of water are drawn as horizontal lines, and values for the inorganic solids (wurtzite) ZnO and (rutile) TiO₂ are taken from recent embedded-cluster calculations.^15,27