Monodisperse cyclic porphyrin polymers, with diameters of up to 21 nm (750 C-C bonds), have been prepared using Vernier template-directed synthesis. The ratio of the intrinsic viscosities for cyclic and linear topologies is 0.72, indicating that these polymers behave as almost ideal flexible chains in solution. When deposited on gold surfaces, the cyclic polymers display a new mode of two-dimensional supramolecular organisation, combining encapsulation and nesting: one nanoring adopts a near-circular conformation thus allowing a second nanoring to be captured within its perimeter, in a tightly folded conformation. Scanning tunnelling microscopy reveals that nesting occurs in combination with stacking when nanorings are deposited under vacuum, whereas when they are deposited directly from solution under ambient conditions, there is stacking or nesting, but not a combination of both.The tertiary structures of biological macromolecules are achieved through folding, coiling and multiplex formation, driven by the cooperative effect of many weak interactions 1 . Synthetic monodisperse macromolecules with similar cooperative folding behaviour provide a viable approach to the programmed fabrication of 3D nanostructures [2][3][4][5] . Here we show that cyclic porphyrin polymers, with molecular weights of 30-60 kDa, self-assemble into nested structures on a gold surface. These nested assemblies are only observed when the cyclic polymer has 30 or more repeat units, in keeping with the predictions of a simple geometrical model.The importance of non-covalent self-assembly in biology has inspired many studies of supramolecular organisation on surfaces [6][7][8] , generating 2D assemblies with progressively escalating complexity, from early work on simple structures such as clusters 9 and rows 10,11 , to nanoporous arrays 12,13 , host-guest architectures [14][15][16] , hierarchical arrangements 17 , and multicomponent assemblies [17][18][19] . However, cooperative conformational control has proved difficult to achieve, and this remains a significant gulf between artificial and biological systems. One reason for this difference is that biological macromolecules are much more flexible than the component molecules studied in 2D supramolecular assemblies which are small and, with some exceptions 20,21 , are often treated as quasi-rigid building blocks. Here we illustrate how interactions between large flexible molecules can result in biomimetic cooperative conformational organisation.Studies of linear and cyclic butadiyne-linked zinc porphyrin oligomers (structures l-PN THS and c-PN, Fig. 1) have shown that the distance between the centres of the porphyrin units along the chain is a = 1.35 nm 5,22,23 . Thus the contour length of a linear oligomer, or the perimeter of a nanoring, is Na, where N is the number of porphyrin repeat units. Previously we have shown that nanorings adsorbed on Au(111) exhibit flexibility [24][25][26] , and also that they can act as nanoscale traps for other adsorbed species, such as C 60 guest molecules 2...

Naphthalocyanine (Nc) thin films have been grown by sublimation on SiO2. We have used atomic force microscopy and X-ray diffraction to show that the films are disordered for room temperature deposition, but show a highly crystalline needle-like morphology for a substrate temperature of ~200 o C. Field effect transistors exhibit p-channel operation with a mobility, which has a peak value of 0.052 cm 2 /Vs, showing a high dependence on substrate temperature. Exposure to atmosphere results in an increase in current and mobility and a reduction in threshold voltage. We compare our results with films formed from analogue molecules such as phthalocyanines and naphthalocyanine functionalised with solubilising sidegroups and discuss the potential of Nc for applications in organic electronics and sensors.