In light of the tremendous versatility of porphyrins and metalloporphyrins in mediating electron and energy transfer, their utility as redox catalysts, and their dynamic photophysical properties, there have been considerable efforts made in the design and synthesis of oligoporphyrins. These covalent compounds yield information on the mechanisms of electron and energy transfer, and demonstrate the possibility to use these chromophores in photonic devices.[1] In the synthesis of discrete ordered arrays of covalently linked porphyrins, there now seems to be a practical limit of about ten macrocycles.[2] To create ever larger arrays in reasonable yields, a supramolecular approach has been employed to design a variety of discrete porphyrin arrays; [3±6] self-assembly makes use of molecular recognition through hydrogen bonds, [3] coordination of transition metal ions, [4] electrostatic interactions, [5] and self-coordination of metallo derivatives. [6] Notably, the largest designed discrete assemblies containing six or more components have been squares made up of four porphyrins assembled by four transition metal ions, [4] and a rosette containing six porphyrins assembled by hydrogen bonding.[3b]Herein we push the methodology into the next level of complexity and present the design of a discrete supramolecular array of nine porphyrins (Figure 1). Self-assembly is accomplished by coordination of exocyclic pyridyl groups on three different porphyrin derivatives to 12 palladium(ii) dichloride units: Four different types of molecules selfassemble to a 21-membered, array that is 25 nm 2 large.[7]These types of systems are expected to further our understanding of photonic communication between chromophores mediated by noncovalent interactions, serve a guide for the formation of molecular channels or receptors, and be a foundation for the development of molecular photonic materials such for use in nonlinear optics. [1, 2] The wellcharacterized photophysical behavior of these macrocycles provides a tool for the examination of the kinetics, mecha- nism, and thermodynamics of self-assembly. The formation and characterization of porphyrin squares, whose self-assembly is mediated by one or two different transition metals, have been well documented. [4] We designed the nonameric arrays 5 and 6 by appropriate choice of trans coordination by the relatively labile squareplanar bis(benzonitrile)palladium(ii) dichloride (4), the correct stoichiometries of the components, and the correct substitution patterns of three different porphyrins: one central X-shaped unit (porphyrin 1), four T-shaped units on the sides (porphyrin 2), and four L-shaped units in the corners (porphyrin 3; Scheme 1). The ªmolecular informationº inherent in the individual molecules and the stoichiometry (12 Pd, 1 ªXº, 4 ªLº, and 4 ªTº) favors the formation of the desired arrays, but the reversibility of pyridyl ± palladium bond formation is also crucial for reaching what appears to be the thermodynamic product. Thus, the desired arrays are formed in approxim...

Atomic force microscopy and solid-state nuclear magnetic resonance have been used to investigate the effect of water absorption on the nanoscale elastic properties of the biopolyester, cutin, isolated from tomato fruit cuticle. Changes in the humidity and temperature at which fruits are grown or stored can affect the plant surface (cuticle) and modify its susceptibility to pathogenic attack by altering the cuticle's rheological properties. In this work, atomic force microscopy measurements of the surface mechanical properties of isolated plant cutin have been made as a first step to probing the impact of water uptake from the environment on surface flexibility. A dramatic decrease in surface elastic modulus (from approximately 32 to approximately 6 MPa) accompanies increases in water content as small as 2 wt %. Complementary solid-state nuclear magnetic resonance measurements reveal enhanced local mobility of the acyl chain segments with increasing water content, even at molecular sites remote from the covalent cross-links that are likely to play a crucial role in cutin's elastic properties.

No abstract