Samples for SEC studies were grown on fluorine-doped tin oxide glass slides as thin films, using similar conditions to those used for the standard MOF synthesis. In a typical synthesis, the FTO glass slide was washed with alconox and water, then rinsed with acetone followed by ethanol. A monolayer of the carboxylic acid linker was prepared prior to the MOF reaction using 1 mmol of the corresponding dicarboxylate in DMF and heating in the oven at 100 o C overnight. The glass slide was then removed from the solution, rinsed briefly with DMF, and transferred into a 20-mL vial containing a stirred reaction mixture for MOF synthesis (using the same strategy as used for bulk MOF crystallisation). The vial was tightly capped and heated in the oven for 24 h. On completion of the reaction, the vial was removed from the oven and cooled to room temperature. The resulting FTO glass slide was washed with DMF to remove any unreacted starting materials and any crystals that do not adhere strongly to the surface. Further details of experimental design are described in the SI.