The background to the work discussed in this paper stems from two projects currently being pursued at the Centre for Molecular Architecture. The first is in the area of nanotechnology where we plan to build and test a new type of molecular switch. Modelled very much after a bell, it has a molecular framework with porphyrin walls which acts as the metal sides of the bell and a mobile clapper with a group X on the end. When the X-group actually interacts with the porphyrin, then a signal is emitted; when it is removed away from the wall, the signal ceases. Thus, in analogy with a bell where the signal is produced when the clapper hits the side of the bell to emit the sound (ring), so the molecular switch gives off a signal (e-transfer, light) when the mobile arm (the polymethylene chain) positions the X-group close to the porphyrin. A schematic of this system is shown in Figure 1. The key elements in this model are the rigid molecular frame to which the porphyrin walls are attached and the positioning of the clapper on the inner face of the U-shaped framework system.

A similar U-shaped molecular frame is an integral part of our second project which deals with catalyst design. Here, the molecular framework is designed with different wall units to which guest molecules X and Y can be specifically associated. Where the guests are carrying groups A and B at their termini, which have the capacity to react with one another, a termolecular species comprising the host and the two guests (Figure 2) can be envisioned. By designing the host, guest dimensions to allow A and B to attain the correct transition state for reaction, then the host should catalyse the reaction. We are presently exploring such systems to assess the reality of this proposed catalytic, enzyme-like activity.

At the commencement of each of these projects only limited methodology was available for the construction of rigid, U-shaped molecular frameworks and our first task was to address this construction deficiency. Some years down the track, we have now developed methodology which is exceptionally versatile and efficient for alicyclic framework construction (Figure 3). Aspects of this work form the basis for the present plenary.