G-Quadruplex Supramolecular Assemblies in Photochemical Upconversion.

Parallel, tetramolecular G-quadruplex (G4) DNA possessing TINA monomer, (R)-1-O-[4-(1-pyrenylethynyl)phenylmethyl]glycerol, were synthesised and evaluated in complexes with tris(2,2'-bipyridine)ruthenium(II), [Ru(bpy)3 ](2+) , and the Zn(2+) derivative of 5,10,15,20-tetrakis-(1-methyl-4-pyridyl)-21 H,23H-porphine, ZnTMpyP4. UV/Vis, fluorescence, and circular dichroism (CD) spectroscopy showed that the use of G4-DNA as a template resulted in the effective communication between the ligands and the TINA molecule that was covalently attached to the 5'-end and between T and dG at the 5'-end of the dTG4 T sequence. Only one G4-DNA possessing the TINA molecule at the 5'-end of the dTG4 T sequence was able to yield a green-to-blue photochemical upconversion (PUC, λem =420 nm) in the presence of [Ru(bpy)3 ](2+) upon excitation at 500 nm. Different DNA secondary structures can thus be used in DNA-based assemblies for PUC and the way of attachment of chromophores to DNA plays a pivotal role for the creation of a photosynthetic centre.

DNA-Based Assemblies for Photochemical Upconversion.

In the present study DNA was used as a scaffold for the supramolecular assembly of organic chromophores for photochemical upconversion (PUC). Initially, a green-to-blue PUC was observed using free chromophores in solution: tris(2,2'-bipyridine)ruthenium(II), [Ru(bpy)3](2+), which acts as a long-wavelength absorber (λex = 500 nm), and an in situ energy donor to an acceptor (R)-1-O-[4-(1-pyrenylethynyl)phenylmethyl]glycerol (PEPy or TINA monomer), which acts as an annihilator and short-wavelength photoemitter (λem = 420 nm). Then, DNA duplexes possessing TINA monomers were synthesized, and complexes with [Ru(bpy)3](2+) were investigated. In contrast to the dynamic interactions of [Ru(bpy)3](2+) with TINA monomer free in solution, ground-state complex formation was the predominant mechanism of interaction between [Ru(bpy)3](2+) and DNA duplexes bearing two TINA monomers at the 5' ends as shown by fluorescence, circular dichroism (CD), and UV-vis spectroscopy studies. The use of TINA-modified DNAs led to PUC occurring at concentrations significantly lower than that for free chromophores in solution: 2.5 µM [Ru(bpy)3](2+) and 5.0 µM TINA-modified duplex in the DNA-based systems in aqueous buffer versus 46 µM [Ru(bpy)3](2+) and 4.6 mM TINA monomer for the free donor and acceptor in DCM, respectively. Providing vast capabilities of DNA in the development of novel photonic systems as a result of the controllable organization of various chromophores, this study opens a new perspective for the development of DNA-based light-harvesting systems using PUC.