Towards DNA-chromophore supramolecular assemblies for photon upconversion

The interactions of long DNAs of biological origin with small molecules haveintrigued scientists for a while now, with particular emphasis on medical applicationslike cancer therapy. Recently, DNA’s unique highly ordered structures, selfassemblycapabilities and ease of chemical modification have led to a more broadbased approach for potential applications in photonic and electronic devices. In thisthesis, we show that DNA can be used as a scaffold for supramolecular assembly ofselected organic chromophores for tuning photon upconversion based on a triplettripletannihilation (TTA) mechanism.Green-to-blue photon upconversion was observed usingtris(bipyridine)ruthenium(II), [Ru(bpy)3]2+ as a long wavelength absorber and an insituenergy donor to an acceptor (R)-1-O-[4-(1-pyrenylethynyl)phenylmethyl]glycerol), abbreviated PEPy and also known as atwisted intercalating nucleic acid (TINA) monomer which acts as an annihilator andshort wavelength photoemitter. This result prompted us to investigate interactions ofthe 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 DNAscaffold. Zinc metallated porphyrins and ruthenium polypyridyl complexes are wellknown to act as donors in TTA-based energy upconversion. TINA-modified DNAduplexes and G-quadruplexes significantly improved the interaction between TINAand ZnTMpyP4/ [Ru(bpy)3]2+ as shown by fluorescence, circular dichroism (CD),and UV-Vis spectroscopy studies. In contrast to dynamic quenching of the TINAmonomer fluorescence by [Ru(bpy)3]2+ and ZnTMpyP4 for free monomers insolution, ground state complex formation was the predominant mechanism ofinteraction between TINA-modified DNAs and [Ru(bpy)3]2+/ ZnTMpyP4.Energy upconversion was observed with a [Ru(bpy)3]2+ donor and TINA-modifiedDNAs. The results presented in this thesis lay a foundation for further energyupconversion studies utilizing appropriate organic chromophores using DNA as ascaffold.