Dimers and Model Monomers of Nickel(II) Octaethylporphyrin Substituted by Conjugated Groups Comprising Combinations of Triple Bonds with Double Bonds and Arenes. 1. Synthesis and Electronic Spectra

Abstract

Porphyrin dimers linked in the meso-positions by bridges containing alkynes conjugated with the porphyrin π-systems display highly perturbed electronic absorption spectra. We have prepared a series of such dimers using meso-ethynyl nickel(II) octaethylporphyrin as the primary building block. The bridging units include diethynylbenzenes, 2,5-diethynylthiophene, hexenediyne, octatetrayne, butenyne, hexenediyne, and octadienediyne. Some meso-to-β dimers were also made. The dimers are complemented by a set of monomers containing the bridging units as mesosubstituents. The compounds were prepared by a combination of palladium-catalyzed couplings of alkynes with unsaturated halides and oxidative alkyne couplings. The separate effects of the substituents and the presence of the second porphyrin chromophore are delineated by comparisons of the visible absorption spectra for the various monomers and dimers. The dimers fit into three spectral classes: (i) those displaying strongly split Soret bands indicative of inter-porphyrin conjugation (diyne, tetrayne, enediyne, enyne, diethynylthiophene), (ii) those in which this conjugation is interrupted (diethynylbenzenes), and (iii) those with double bonds attached to the meso-carbons, which exhibit broad, low-energy bands, but small splittings of the Soret band. These illustrate some of the promising light-harvesting properties which can be achieved by tailoring the composition of the conjugating bridges linking the units in multi-porphyrin arrays.

A Cyclic Porphyrin Tetramer Linked by Azo and Butadiyne Bridges

“…This was observed in earlier work done by the Arnold group involving porphyrins with acetylene linkers, [53] and by others working in different fields. [54][55][56][57][58][59] We find it to be a very convenient and highyielding method.…”

PELDOR on an exchange coupled nitroxide copper(II) spin pair

“…1-Oxyl-2,2,5,5-tetramethylpyrrolin-3-acetylene (TPA) 4 [29] and 3-(4 0 -Iodo-biphenyl-4-ylethynyl)-2,2,5,5-tetramethylpyrrolin-1-oxyl 5 [10] were prepared by procedures described earlier. Cu(meso-ethynyl-OEP) 6 and Ni(meso-ethynyl-OEP) 7 were prepared according to references [16,30] and used as obtained, due to the products susceptibility to spontaneous oxidative dimerisation [31].…”

One-pot synthesis of nickel porphyrins with 2-pyridine-acetyl substituents: the unexpected Sonogashira cross-coupling products

“…This method has been widely used to synthesize porphyrins with ethyne-linked functional groups [11][12][13][14][15]. Although porphyrins with 2-pyridine-ethynyl substituents were expected to be the products according to the method, we found that nickel porphyrins with 2-pyridine-acetyl substituents were in fact the major products (Fig.…”