Towards DNA-chromophore supramolecular assemblies for photon upconversion : a thesis submitted in the partial fulfilment of the requirements for the degree of Doctor of Philosophy in Chemistry, Massey University, Palmerston North, New Zealand

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Massey University
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The interactions of long DNAs of biological origin with small molecules have intrigued scientists for a while now, with particular emphasis on medical applications like cancer therapy. Recently, DNA’s unique highly ordered structures, selfassembly capabilities and ease of chemical modification have led to a more broad based approach for potential applications in photonic and electronic devices. In this thesis, we show that DNA can be used as a scaffold for supramolecular assembly of selected organic chromophores for tuning photon upconversion based on a triplettriplet annihilation (TTA) mechanism. Green-to-blue photon upconversion was observed using tris(bipyridine)ruthenium(II), [Ru(bpy)3]2+ as a long wavelength absorber and an insitu energy donor to an acceptor (R)-1-O-[4-(1- pyrenylethynyl)phenylmethyl]glycerol), abbreviated PEPy and also known as a twisted intercalating nucleic acid (TINA) monomer which acts as an annihilator and short wavelength photoemitter. This result prompted us to investigate interactions of the ligands ([Ru(bpy)3]2+ and ZnTMpyP4, the Zn2+ derivative of 5,10,15,20-tetrakis- (1-methyl-4-pyridyl)-21H,23H-porphine) with TINA moieties attached to a DNA scaffold. Zinc metallated porphyrins and ruthenium polypyridyl complexes are well known to act as donors in TTA-based energy upconversion. TINA-modified DNA duplexes and G-quadruplexes significantly improved the interaction between TINA and ZnTMpyP4/ [Ru(bpy)3]2+ as shown by fluorescence, circular dichroism (CD), and UV-Vis spectroscopy studies. In contrast to dynamic quenching of the TINA monomer fluorescence by [Ru(bpy)3]2+ and ZnTMpyP4 for free monomers in solution, ground state complex formation was the predominant mechanism of interaction between TINA-modified DNAs and [Ru(bpy)3]2+/ ZnTMpyP4. Energy upconversion was observed with a [Ru(bpy)3]2+ donor and TINA-modified DNAs. The results presented in this thesis lay a foundation for further energy upconversion studies utilizing appropriate organic chromophores using DNA as a scaffold.
Supramolecular chemistry