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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Date
2015
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Massey University
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Abstract
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.
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Supramolecular chemistry