Self-Assembly of Discrete Cyclic Nanostructures Mediated by Transition Metals

Understanding electronic communication among the constituents in multicomponent macromolecular architectures is essential for the rational design of molecular devices for photonic, electronic, or optoelectronic applications. This Account describes studies aimed at understanding the mechanisms of electronic communication in porphyrin-based architectures that undergo excited-state energy migration and ground-state hole/electron hopping. Porphyrins are ideal building blocks for such constructs owing to their attractive and versatile physical properties and amenability to synthetic control. These properties have permitted the creation of covalently linked multiporphyrin arrays wherein the rates of excited-state energy migration and ground-state hole/electron hopping can be tuned over a wide range.

Probing electronic communication in covalently linked multiporphyrin arrays. A guide to the rational design of molecular photonic devices.

Molecular Rods. 1. Simple Axial Rods.

Electron-transfer rates and electronic coupling factors for ferrocene groups attached to gold electrodes via oligo(phenylethynyl) “molecular wire” bridges of variable length and structure are reported. Attachment to gold was achieved via thiol groups at the end of the bridge opposite the ferrocene. Bridge structures were designed to promote strong coupling between gold and ferrocene, thereby promoting rapid electron transport over long distances. The effects of bridge length and of substituents on the phenyl rings in the bridge were addressed. Bridges containing between three and six phenylethynyl units were studied, and a “beta” value of 0.36 A-1 describing the exponential distance dependence of bridge-mediated electron-transfer rates was obtained. The effect on the rates of adding two propoxy groups onto one of the phenyl rings in the bridge was examined and found to be minimal. The standard electron-transfer rate constant of 350 s-1 obtained for the adsorbate with the longest bridge (six phenylethynyl ...

Electron Transfer at Electrodes through Conjugated “Molecular Wire” Bridges

Synthetic routes to multiporphyrin arrays.

Synthesis and Intramolecular Electron- and Energy-Transfer Reactions of Polyyne- or Polyene-Bridged Diporphyrins

1,4-Phenylene-bridged, linear porphyrin arrays including the dimer, trimer, pentamer, heptamer and nonamer have been synthesized by acid-catalysed condensation of formyl-substituted porphyrins with bis(3-ethyl-4-methylpyrrol-2-yl)methane in moderate yields. The molecular length of the nonamer is estimated to be as long as ca. 122 A. The Soret bands of both zinc complexes and doubly protonated free base porphyrins are split depending upon the number of the porphyrins, which can be explained in terms of exciton coupling theory. With an increase in the number of the porphyrins, the fluorescence spectra become broader and red-shifted without significant decrease in the fluorescence quantum yield, reflecting their stretched conformations that do not allow the formation of a singlet-excitation-energy trapping site.

Synthesis of 1,4-phenylene-bridged linear porphyrin arrays

Synthesis of linear porphyrin arrays of unusual length was reported. 1,4-Phenylene-bridged porphyrin oligomers up to a nonamer (ca. 122 A length) were synthesized by acid catalyzed condensation of formyl-substituted porphyrins with dipyrrylmethane. The absorption and fluorescence spectra of these molecules exhibit systematic changes upon the increase in the number of the porphyrins.

An Efficient Synthesis of Linear Porphyrin Arrays

A convenient synthetic procedure of a series of polyyne-bridged porphyrin dimers from diphenylpolyyne dialdehydes is reported. Trichloroacetic acid catalyzed double condensation of diphenylpolyyne dialdehydes with bis(3-hexyl-4-methyl-2-pyrrolyl)methane and 3,5-di-tert-butylbenzaldehyde in acctonitrile-dichloromethane followed by p-chloranil oxidation gave a set of diporphyrin model compounds (Pn, n = 0–4) bridged by conjugated triple bonds.

Nobuhiro Tanabe

Papers

Synthesis and Intramolecular Electron- and Energy-Transfer Reactions of Polyyne- or Polyene-Bridged Diporphyrins

Synthesis of 1,4-phenylene-bridged linear porphyrin arrays

An Efficient Synthesis of Linear Porphyrin Arrays

A Convenient Synthesis of Polyyne-bridged Porphyrin Dimers