Porphyrin-based molecular wires: From polaron delocalization to phase-coherent single-molecule transport — a Woodward Career Award paper

Molecular wires are the most fundamental type of single-molecule electronic device and they are the components of organic semiconductors. Porphyrins are excellent building blocks for constructing molecular wires because their small reorganization energies and rich redox activity lead to low barriers for charge transport. This short review summarizes work on three types of porphyrin-based molecular wires: (a) axially coordinated shish-kebab complexes, (b) alkyne-linked chains, and (c) edgefused nanoribbons. The techniques used to probe wire-like behavior are introduced, including singlemolecule conductance measurements and non-contact ensemble measurements, such as time-resolved microwave/terahertz spectroscopy and electron paramagnetic resonance spectroscopy (EPR). Experimental results indicate that edge-fused porphyrin nanoribbons, with lengths in the range 5-10 nm, are the most wire-like molecules yet created by solution-phase organic synthesis. This is evident from their highly delocalized and mobile polarons, high single-molecule conductances and their phase-coherent, wave-like charge transport.