Ring-Oxidized Zinc(II) Phthalocyanine Cations: Structure, Spectroscopy, and Decomposition Behavior

Abstract

A bromonium oxidizing agent was used to produce a ring-oxidized zinc phthalocyanine (PcZn), [PcZn(solvent)][BAr] (1·solvent), in good yield. This material is dimeric in the solid state with one axially coordinated solvent [tetrahydrofuran (THF) or 1,2-dimethoxyethane (DME)] and close intradimer ring-ring distances of 3.18 and 3.136 Å (THF and DME respectively); this proximity facilitates strong antiferromagnetic coupling to yield diamagnetic dimers. 1·THF is present in solution as a monomer and a dimer. In CHCl, the dimer is favored above 0.1 mM, and it is almost exclusively present in solvents with a high dielectric constant such as acetonitrile. The material 1·THF/DME decomposes in DME to a meso-nitrogen-protonated species, [HPcZn(DME)][BAr] (2), which was isolated and represents the first example of such a structurally characterized, protonated, unsubstituted PcM complex. A partially oxidized dimer or "pimer" [(PcZn(DME))][BAr] (3) was also structurally characterized and has a intradimer ring-ring distance of 3.192 Å, similar to 1·THF/DME. Dimer 3 also represents the first isolated PcM-based pimer. Electron paramagnetic resonance analysis of a 1.0 mM solution of 1·DME in DME showed the production of 3 over hours by the combination of 1·DME and 2 in solution.

Synthesis, structures and reduction chemistry of monophthalocyanine scandium hydroxides

“…It showed two signals, with g = 2.003 and 1.994 but no hyperfine splitting, confirming the presence of an unpaired ring-electron in 1 -. The presence of two signals is consistent with a mixture of radical-containing products, which may feature aggregation of 1with either 1 2or residual 1 (as supported by the UV-visible data); such mixed-valent aggregated species and their similar EPR spectra were recently reported in detail for a ring-oxidized PcZn-based system [36].…”

New Insight into an Old Problem: Analysis, Interpretation, and Theoretical Modeling of the Absorption and Magnetic Circular Dichroism Spectra of Monomeric and Dimeric Zinc Phthalocyanine Cation Radical

“…These two forms have been shown to possess different absorption spectra in the near-infrared (NIR) region. In particular, it has been demonstrated that the monomeric phthalocyanine cation radical has a Q -band centered at around 820–840 nm, while the diamagnetic dimer is associated with a Q -band centered around 715–730 nm and a broad NIR band observed at ∼1000 nm. , In addition, both the monomer and dimer have absorption at ∼500 nm (fingerprint band) and a set of transitions identified by UV–vis spectroscopy for [(Im)­ZnPc] +• at ∼420, ∼380, ∼330, and ∼286 nm. − …”

Preferential Formation of Side‐Pocket‐Substituted Zinc Phthalocyanines Emitting Beyond 800 nm

“…Of the few fully characterized examples of meso‐protonated PcMs, two have been PcZn complexes, including a study by Kobayashi, et. al ., of a 1,4,8,11,15,18,22,25‐octaphenylphthalocyaninium zinc chloride complex, as well as our recent report of an unsubstituted PcZn complex protonated at the meso‐N as a result of hydrogen atom transfer between dimethoxyethane and a ring‐oxidized [Pc −1 Zn] .+ to form zinc phthalocyaninium tetrakis(pentafluorophenyl)borate [31,32] . The latter of these two remains the only reported example of an unsubstituted PcM protonated at the meso ‐N, with all others using ligand functionalization to increase the stability of the bound cations.…”

“…Beyond functional groups on the periphery or metals within the Pc‐core, the addition of protons to the meso‐nitrogen of the N 8 C 8 aromatic ring has been shown to strongly decrease the energy of the LUMO and red‐shift the Q‐band and B‐band absorptions [25,26] . Though the addition of strong acids to PcM complexes has been shown to produce mono, di, tri and tetra meso ‐protonated complexes in solution, few of these species have been isolated and structurally characterized [27–32] …”

“…Not only have Zn(II)‐based phthalocyanine complexes been shown to form these meso‐ protonated PcM species, they also are particularly suited for the investigation of Pc‐ligand based properties due to the diamagnetic, redox‐inactive nature of Zn(II), which allows for unimpeded studies of ring‐centred analysis (without metal‐centred redox activity and UV‐visible absorption) and electronic structure, stability and spectroscopic characterization (e. g. NMR and cyclic voltammetry) compared to, for example, PcCu(II) and PcCo(II) systems [26,31,33–35] . Closed‐shell metals help to facilitate fluorescence in metal‐containing materials, and PcZn species are no exception.…”