Synthesis and Electrochemical Studies of Porphyrin Dimers Linked by Metallocarbenes

The functionalization of porphyrins at the <i>meso</i> positions by azoles led, after subsequent alkylation, to several precursors of N-heterocyclic carbenes. Porphyrin dimers linked by palladium (or rhodium) bis-carbene spacers were prepared and characterized. Spectroscopic data and X-ray structures showed that the coordination geometry for the two carbenes around the palladium linker was <i>trans-anti</i>. Electrochemical studies revealed significant electronic communication between the two porphyrins, despite the absence of conjugation pathways

Synthesis and Electrochemical Studies of Porphyrin Dimers Linked by Metallocarbenes

The functionalization of porphyrins at the <i>meso</i> positions by azoles led, after subsequent alkylation, to several precursors of N-heterocyclic carbenes. Porphyrin dimers linked by palladium (or rhodium) bis-carbene spacers were prepared and characterized. Spectroscopic data and X-ray structures showed that the coordination geometry for the two carbenes around the palladium linker was <i>trans-anti</i>. Electrochemical studies revealed significant electronic communication between the two porphyrins, despite the absence of conjugation pathways

Ultrafast Singlet Energy Transfer in Porphyrin Dyads

A weakly fluorescent Pt-bridged dyad composed of zinc­(II) porphyrin (Zn; donor) and free base (Fb; acceptor) has been designed and exhibits an ultrafast singlet energy transfer between porphyrins. The use of larger atoms within the central linker significantly increases the MO coupling between the two chromophores and inherently the electronic communication

Ground and Excited State Properties of New Porphyrin Based Dyads: A Combined Theoretical and Experimental Study.

The properties of the ground and excited states of several porphyrins appended with external chelates coordinated to ruthenium-bisbipyridine units are reported. The important modification of the absorption spectrum upon coordination with the ruthenium complex showed that a significant electronic communication between the two subunits was present in the ground state. Experimental results were compared with quantum chemistry calculations performed at density functional theory and time-dependent density functional theory level. The influence of the exchange-correlation functional on the quality of the computed absorption spectrum is shown, and the better behavior of hybrid functionals over long-range corrected ones was rationalized. The excited states topology analysis, performed using natural transition orbitals, gave a more evident confirmation of the communication between the subunits and showed that these new compounds can be promising as dyes in dye-sensitized solar cells

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

A bromonium oxidizing agent was used to produce a ring-oxidized zinc phthalocyanine (PcZn), [PcZn­(solvent)]^•₂[BAr^F₄]₂ (<b>1</b>·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. <b>1</b>·THF is present in solution as a monomer and a dimer. In CH₂Cl₂, 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 <b>1</b>·THF/DME decomposes in DME to a <i>meso</i>-nitrogen-protonated species, [HPcZn­(DME)₂]­[BAr^F₄] (<b>2</b>), 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))₂]^•[BAr^F₄] (<b>3</b>) was also structurally characterized and has a intradimer ring–ring distance of 3.192 Å, similar to <b>1</b>·THF/DME. Dimer <b>3</b> also represents the first isolated PcM-based pimer. Electron paramagnetic resonance analysis of a 1.0 mM solution of <b>1</b>·DME in DME showed the production of <b>3</b> over hours by the combination of <b>1</b>·DME and <b>2</b> in solution

Inexpensive and Efficient Ullmann Methodology To Prepare Donor-Substituted Porphyrins

The preparation of porphyrins functionalized with one or two carbazoles (or phenoxazines) is described. The electron donors were introduced into one or two porphyrin <i>meso</i> positions by using the inexpensive Ullmann coupling procedure. Very good yields were obtained, and for two new compounds, the X-ray structures were solved. Preliminary electrochemical data coupled with electronic spectroscopy are also reported