Syntheses, Structural Characterizations, and Optical and Electrochemical Properties of Directly Fused Diporphyrins

Abstract

Directly fused diporphyrins display the extensive pi conjugation as evinced by highly perturbed electronic absorption spectra as well as lowered and largely split first oxidation potentials. Such diporphyrins prepared include meso-beta doubly linked diporphyrins 7, meso-meso beta-beta beta-beta triply linked diporphyrins 8, and meso-meso beta-beta doubly linked diporphyrins 9. Oxidation of 5,15-diaryl-substituted and 5,10,15-triaryl-substituted Ni(II)-, Cu(II)-, and Pd(II)-porphyrins with tris(4-bromophenyl)aminium hexachloroantimonate (BAHA) in CHCl(3) afforded 7, and triply linked Cu(II)-diporphyrins 8a and 8g were respectively prepared by the oxidation of meso-meso singly linked Cu(II)-diporphyrins 5c and 5f with BAHA. Meso-meso beta-beta doubly linked Ni(II)-diporphyrin 9a was isolated along with triply linked Ni(II)-diporphyrin 8e from the similar oxidation of meso-meso singly linked Ni(II)-diporphyrin 5a. Doubly linked diporphyrins 7 and 9a both exhibit significantly perturbed electronic absorption spectra, in which the Soret-like bands are largely split at around 405-418 and 500-616 nm and the Q-bandlike absorption bands are substantially intensified and red-shifted at 748-820 nm, probably as a consequence of symmetry lowering. Triply linked diporphyrins 8 display more strongly perturbed electronic absorption spectra with split Soret-like bands at 408-419 and 567-582 nm and Q-bandlike absorption bands reaching far-infrared region. Structures of three types of fused diporphyrins 7b and 7c, 8g and 8j, and 9a have been unambiguously determined by X-ray crystallography to be nearly coplanar. Both the triply linked diporphyrins 8g and 8j exhibit very flat structures, whereas the doubly linked diporphyrins 7b and 7c exhibit ruffled structures. The doubly linked diporphyrin 9a shows a helically twisted conformation with larger ruffling toward the opposite directions and has been actually separated into two enantiomers, which display strong Cotton effects in the CD spectra. The first oxidation potentials (E(OX1)) decrease in the order of 5 > 7 > or = 9 > 8, indicating lift-up of HOMO orbital in this order, and split potential differences DeltaE = E(OX1) - E(OX2), in turn, increase in the reverse order of 5 < 7< or = 9 < 8. The (1)H NMR spectra have indicated that the aromatic porphyrin ring current becomes weakened in the order of 5 > 7 > 8. Collectively, the electronic interactions between the diporphyrins have been concluded to increase in the other of 5 << 7 < or = 9 < 8.

Supramolecular Chirality in Porphyrin Chemistry

“…The molecular and crystallographic structure of the bis-porphyrin, 51, covalently linked by a meso-meso and a beta-beta bond. Reproduced with permission from Tsuda, A. et al [46].…”

“…The chiral structures were also stabilized either via the intermolecular self-assembly assisted by an Ag cation [44] or via the formation of an intramolecular helical arrangement of two porphyrinoids, which could then be optically separated [45]. Another approach to fix asymmetry in the bis-porphyrin structures was used in the case of 51, where the porphyrin moieties were covalently linked by a meso-meso and a beta-beta bond ( Figure 14) [46]. This double strapping resulted in the opposite ruffling of two macrocycles in 51, thus producing a helical structure with nearly C 2 symmetry.…”

Subporphyrins: A Legitimate Ring-Contracted Porphyrin with Versatile Electronic and Optical Properties

“…Along this strategy three-dimensional porphyrin boxes and other interesting architectures have been constructed through rigorous self-sorting assembly of pyridineappended or cinchomeronimide-appended mesomeso-linked Zn(II) diporphyrins. 1720 In the meanwhile, we explored an effective oxidative ring-closure reaction initially with tris(4-bromophenyl)aminium hexachloroantimonate 21,22 and later with the combined use of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and Sc(OTf) 3 . 23 The latter method is superior to the former because of the absence of serious halogenation side products, and allows the conversion of long mesomesolinked Zn(II) porphyrin arrays to corresponding mesomeso, ¢¢, ¢¢ triply linked porphyrin arrays that are called porphyrin tapes.…”

Design of Porphyrin Nanoclusters toward Discovery of Novel Properties and Functions

“…18 The oxidation potentials of the bismetalloporphyrins change systematically upon increment of the linkage between the porphyrin components. 16 The directly mesoÍmeso linked Zn II Í bisporphyrin [Ar 3 P] 2 (I) mm underwent two reversible redox in oxidation at E OX1 = 0.47 and E OX2 = 0.59 V (ËÅE (=E OX1 Õ E OX2 )Ë = 0.12 V) versus Ag/AgClO 4 due probably to oneelectron redox in each porphyrin unit. The redox potentials in the first/second oxidation were also detected at 0.…”