Porphyrins

Water Soluble Porphyrin Receptors (Cardiff University)

We are investigating the synthesis of porphyrin dimers that are designed to sandwich hydrophobic molecules in aqueous solvent. The new receptors will feature quaternary ammonium salts to enhance their water solubility.


	Left - Design of water soluble porphyrin receptors for complexing hydrophobic guests in water.

Multi-metallic porphyrin arrays (Ph.D. with Prof. Jeremy Sanders)

Metallo-porphyrins are ideal building blocks for self-assembled structures due to their rigid geometry, ease of substitution and selective axial ligand coordination chemistry. Rh(III) porphyrins were exploited as they display strong binding to nitrogenous bases and are diamagnetic which facilitates characterization by NMR spectroscopy. Dimeric Rh(III) porphyrin complexes were formed with ligands such as bipyridine, bipyrimidine, hydrazines, methyl sulfide and methyl selenide.


	In contrast the oxophilic Sn(IV) porphyrins have little affinity for nitrogen donors, but tightly bind carboxylates. A combination of Rh(III) and Sn(IV) porphyrins enables large structures to be selectively prepared.

Above - a Sn(IV) and Rh(III) porphyrin complex with isonicotinic acid, and the structure as determined by x-ray crystallography (with porphyrin alkyl substituents omitted for clarity).

Wedge shaped building blocks were synthesized from acetylene and iodo-aryl substituted porphyrins using Pd catalyzed couplings. Wedges were coordinated through a carboxylate group to a Sn(IV) porphyrin core, and Rh(III) porphyrins bound to peripheral pyridyl groups to create 11 porphyrin arrays with up to four different metallation states.

Self Assembled Monolayers (with Prof. J. K. M. Sanders, Dr T. Rayment)

Porphyrin thiols and disulfides were used for preparation of self assembled monolayers on gold surfaces.


	Cyclic porphyrin disulfides avoided the problems associated with photosensitized oxidation of the corresponding dithiols. Contact angle and electrochemical measurements indicated that these two classes of compound formed layers of different structures on gold surfaces


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