An aromatic binding unit was chosen as guest binding unit to facilitate electron transfer to the catalytically active site of the guest. With the compact design, displacement of the guests by water or solvent from the opposite face of the host should be inhibited. Higher binding constants of guests in surface-bound hosts compared to the binding in solution have been reported, and the increased binding strength was proposed to be related to further interactions between guest and surface. For hosts with long, flexible chains connecting them to the surface, studies with multi-valent guests showed that HGCs could be stable on a multi-hour time-scale.