Conjugated dimers of nickel(II) octaethylporphyrin linked by extended meso,meso-alkynyl bridges. II Redox properties and electronic spectra of electrogenerated anions and dianions

Oligoporphyrins with One-and Two-Atom Covalent Bridges: Synthesis and Reactivity, Solid-State, Solution and Electronic Structures, Spectroscopy and Applications

“…This pattern of larger oxidative splitting applies to all conjugated porphyrin dimers reported so far. 99,139,167,168 The HOMO-LUMO gap, as expected, was much smaller (1.78 V) compared with unsubstituted ZnDPP (2.17 V), but not very different from the better model ZnDPP-C 2 SiMe 3 (1.81 V). 76 The Therien group later studied a group of dimers, trimers and pentamers, in which substituents on the terminal and lateral positions of the rings were tailored for their electronic effects.…”

“…The UV-visible spectra were not recorded >900 nm, so the near-IR IVCT bands of 65b +• and 65d +• could not be observed. The authors appear to have mis-assigned the bands observed near 850 nm as the IVCT bands, which from the work of Yeh and coworkers 99 (on analog 65f ) and Arnold and coworkers 139,167,168 are anticipated at much lower energy. In view of the rather minor changes to the Soret region after reduction of 65c, the authors suggested a strong component of Au(II) character in the mono-reduced species.…”

“…99 Their results mirror the expectations from the work of Arnold, Heath and coworkers on the C 4 MOEP and ZnDAPP dimers. 139,167,168 In particular, the dimer cation-radical of 65f exhibits a near-IR intervalence charge transfer (IVCT) band at 4950 cm −1 , similar to that of the C 4 analog of ZnDAPP dimer 65d (4090 cm −1 ). 167 As expected, this band is not present in the spectrum of the dication, being replaced by a band at 10,750 cm −1 , in accord with the interpretation of Arnold and coworkers.…”

“…The π-π overlap through the bridge in Class III (delocalized) mixed-valence diporphyrins can be expressed in pictorial terms by the eight-orbital scheme of Heath and Arnold (see next section). 139,167,168,170,174,175 The voltammetric splitting reflects the magnitude of the comproportionation constant, a thermodynamic property of the three components involved, namely the neutral, radical-cation, and dication oxidation states of the dimer (or the analogous anions on the cathodic side). In intermediate Class II/III or even less delocalized systems, such as the ethane-linked dimers, the interaction is much less pronounced by all other measures, yet clearly these dimers can have indeed the largest voltammetric splittings between the first two one-electron oxidations (assuming these are indeed one-electron per dimer processes in all cases).…”

Synthetic N-substituted metal aza-macrocyclic complexes: properties and applications

“…The preparation and electrochemical reactions of conjugated dimers of nickel(II) octaethylporphyrin linked by extended meso, mesoalkynyl bridges, i.e. NiOEP-C-2-X-C-2-NiOEP [where X ¼ (C-2)(n), for n ¼ 0, 1 or 2; trans-CH¼CH; 1,4-C 6 H 4 ; 1,3-C 6 H 4 ; 2,5-C 4 H 2 S] and trans-NiOEP-CH¼CH-YNiOEP [where Y ¼ C-2; trans-C-2-CH¼CH; trans-C-2-CH¼CH] have been reported [51]. Each [P-2](0) dimer has been converted to its electrogenerated dianion, and, as far as possible, to the intervening monoanion as well.…”