Porphyrin nanotubes are made by ionic self-assembly of two oppositely charged synthetic porphyrin molecules. The diameter of the nanotubes can be altered by modifying the structure of one of the porphyrin tectons. The nanotubes are photocatalytically active, mechanically responsive to light, and are composed of J-aggregates that exhibit resonance light scattering.

Porphyrins and related tetrapyrroles have been extensively studied because of their importance in biological processes and they are often used in the development of artificial photosynthesis, catalysis, and sensor systems. Challenges in the development of functional nanoscale porphyrin systems are many, including the need to organize the porphyrins (e.g., to facilitate processes such as energy- and electron transfer) and to couple the porphyrin nanostructures to other nanoscale components (e.g., catalytic elements and conductors) to produce multifunctional nanoscale systems. This article summarizes recent advances in the synthesis of discrete self-assembled porphyrin nanostructures with well-defined shapes and sizes. A novel method for growing metal on the porphyrin nanostructures to produce nanocomposites with metal catalysts or interconnects is also described. Current and potential applications of these nanostructures and porphyrin-metal nanocomposites are discussed.

Porphyrin nanotubes represent a new class of nanostructures for which the molecular building blocks can be altered to control their structural and functional properties. Nanotubes containing tin(IV) porphyrins are photocatalytically active and can reduce metal ions from aqueous solution. The metal is deposited selectively onto tube surfaces, producing novel composite nanostructures that have potential applications as nanodevices. Two examples presented here are nanotubes with a continuous gold wire in the core and a gold ball at the end and nanotubes coated with platinum nanoparticles mainly on their outer surfaces. The latter are capable of photocatalytic reduction of water to hydrogen.