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The use of dipyrromethene and polydipyrromethene ligands in supramolecular chemistry Zhang, Yongjun

Abstract

The main objective of this work was to study the use of dipynomethene and polydipyrromethene ligands in supramolecular chemistry. Numerous poly-dipyrromethene metal complexes were synthesized via selfassembly and characterized by mass and NMR spectrometry and X-ray crystallography. Some of their structures were simulated using Hyperchem release 5.01 MM+ force field. Methylene and directly linked bis(dipyrromethene) coordinated to metal ions to form complexes 60a, 60b and 59 which are dimer ((ligands^Mo). X-ray structures of these complexes showed them to have helical geometry. Ethylene-linked bis(dipyrromethene) once coordinated to metal ion, gave a mixture of monomer ((ligand)M) 61a and dimmer 61b ((ligand)2M2). Molecular modeling showed that simulated complex 61a possess a helical double-stranded geometry and 61b a distorted tetrahedral geometry. The methylene-linked tris(dipyrromethene) zinc complex 87 was also synthesized and shown to contain helical double-stranded structure by X-ray crystallography. Dipyrromethenes which contain a raeso-phenyl group and are free at α and β positions coordinated to trivalent metal ions forming octahedral complexes 131-135. The oxidation reaction of porphyrins with oxaziridines was studied and this leads to a new synthetic method towards the synthesis of chlorins which are potential photosensitizers in photodynamic therapy. Chlorins 179 and 180 were synthesized and characterized. The longest wavelength absorptions of these chlorins have an approximate 20 nm bathochromic shift and a significant increase in intensity as compared with octaethyl porphyrin. Their structures were determined by ¹H and ¹³C NMR spectrometry. A mechanistic proposal for this reaction will be presented.

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