Giant meso-meso-linked porphyrin arrays of micrometer molecular length and their fabrication

Abstract

On the basis of the Ag(I)-promoted coupling reaction of zinc(II)-5,15-bis(3,5-dioctyloxyphenyl)porphyrin Z1, chain elongation has been attempted by using a stepwise doubling approach, which provides Z2, Z4, Z8, Z16, Z32, Z64, Z128, Z256, Z384, and Z512. The porphyrin arrays up to Z128 are sufficiently soluble in CHCl3 and THF despite their very long molecular lengths and rodlike structures, while the arrays over Z128 show a significant drop in solubility and stability. The discrete porphyrin arrays thus isolated were characterized by means of (1)H NMR spectroscopy, matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry, UV/Vis spectroscopy, gel-permeation chromatography (GPC), cyclic voltammetry (CV), single-crystal X-ray crystallography, scanning tunneling microscopy (STM), and atomic force microscopy (AFM). Contrary to expected linear conformations of the arrays Z n (where n is the number of porphyrins), the single molecular images of Z128, Z256, and Z512 revealed largely bent structures; this finding indicates the substantial conformational flexibility of Z n. We also exploited an effective synthetic route by means of which Z n can be fabricated with a thiol-protected aryl group to provide Z n S(2) through Z n Br(2), by bromination with N-bromosuccinimide and subsequent Pd-catalyzed Suzuki-Miyaura arylation. Finally, the reaction of Z256 provided Z512, Z768, and Z1024. Collectively, this work provides an important milestone in the preparation of sub-microscale discrete organic molecules and the fabrication of molecular-based materials, hence significantly contributing to device applications.