Persistent, Well-Defined, Monodisperse, π-Conjugated Organic Nanoparticles via G-Quadruplex Self-Assembly

摘要

Several oligo(p-phenylene-vinylene) oligomers capped with a guanosine or a guanine moietynhave been prepared via a palladium-catalyzed cross-coupling reaction. Their self-assembly, in both thenabsence and presence of alkaline salts, has been studied by means of different techniques in solutionn(NMR, MS, UV-vis, CD, fluorescence), solid state (X-ray diffraction), and on surfaces (STM, AFM). Whennno salt is added, these π-conjugated molecules self-associate in a mixture of hydrogen-bonded oligomers,namong which the G-quartet structure may be predominant if the steric hindrance around the guanine basenbecomes important. In contrast, in the presence of sodium or potassium salts, well-defined assemblies ofneight functional molecules (8mers) can be formed selectively and quantitatively. In these assemblies, thenπ-conjugated oligomers are maintained in a chirally tilted (J-type) stacking arrangement, which is manifestednby negative Cotton effects, small bathochromic absorption and emission shifts, and fluorescencenenhancements. Furthermore, these self-assembled organic nanostructures, ∼1.5-2.0 nm high and 8.5nnm wide, exhibit an extraordinary stability to temperature or concentration changes in apolar media, andnthey can be transferred and imaged over solid substrates as individual nanoparticles, showing no significantndissociation or further aggregation.