Synthesis of Porphyrin-Based Nanostructures By Ionic Self-Assembly: Exploring Novel Tectons

Self-assembly of porphyrins is a powerful method for the production of highly functionalized nanomaterials. Porphyrin-based nanomaterials can be self-assembled using a number of procedures including ionic self-assembly (ISA), re-precipitation and coordination polymerization.¹ ISA has proven to be a particularly flexible synthetic method and can be used to couple oppositely-charged porphyrin ions (tectons) in a range of environments such as at liquid-liquid interfaces,² on templates,³ or spontaneously in water.^4,5 The resulting materials have been investigated as catalysts for the reduction of O₂ to H₂O,² as photosensitizers for the reduction of H₂O to H₂,⁶ as adsorbed pigments for functionalizing carbon nanotubes,⁷ as H₂ storage materials,⁸ and as photoconductors.⁵

Despite these considerable advances, little is known about the ISA of structurally modified porphyrin tectons that may be useful for producing nanomaterials with specific properties. It is well established that extension of the π-system or nonplanar deformation of the macrocycle significantly alter many properties of porphyrins, including their optical and electronic behaviour. In this talk, we describe recent investigations of the self-assembly of tecton 1 (M = Ni)⁹ which contains both of these structural modifications, with the standard tecton TPPS 2(M = Sn, Fe, Mn, Cu or 4H) (see Graphic).

Porphyrins 1 and 2 are shown to react to produce nanoscale materials together with porous micron-sized wafers, although the reactions are significantly different than those previously reported for ISA of standard water-soluble porphyrins based on the TPP framework. Of particular note are the  reactions of 1 with the diprotonated form of 2 (M = 4H) which can yield precipitates with stoichiometries lower than or much higher than those expected for ISA. Reasons for the formation of these unusual products are discussed, together with the potential applications of this chemistry to the formation of ternary systems containing 1, a metal complex of 2, and the diprotonated form of 2.

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