TEMPSYNTHFIX · Templated synthesis and fixation of self-assembled p-conjugated oligomers using DNA and PNA

Final Activity Report Summary - TEMPSYNTHFIX (Templated synthesis and fixation of self-assembled p-conjugated oligomers using DNA and PNA)

The development of nanosized electronics will become increasingly important to modern society. Nowadays the need for nanoscale devices that can process data at high speed and store information with high density is widely recognised. Supramolecular chemistry, which makes use of self-assembling molecular units, offers an excellent tool to construct cheaply and easily electronic components in the nanometre range (Bottom-Up approach to nanostructuring). If pi-conjugated organic oligomers are used as building blocks in these nanosized components one can expect new, unprecedented electrooptical properties. The construction and properties of these objects is highly innovative and can be named as supramolecular electronics. However, any nanotechnological application of these functional self-assembled systems demands uniform and monodisperse objects having well-defined properties that remain unaltered upon transfer to solid supports. At the moment, the stack length and position of the different chromophores cannot be precisely controlled. The basic goal of this project is to find a way to control the stacking of functional organic molecules in order to obtain nanoobjects whose structure, composition and size is well-defined. For this purpose, we use commercially available oligonucleotides, whose length and sequence is well-defined. These oligomers can specifically recognise, via hydrogen bonding, different ?-conjugated oligomers, and therefore can template their assembly following the sequence of the oligonucleotide strand. This process is shown schematically in the figure below. With this novel supramolecular synthetic approach, allowing us to specifically position different chromophores in a well-defined stack, fundamental issues, such as light harvesting and excitation energy transfer or photoinduced electron transfer within the stacks, can be investigated. This innovative and ambitious approach required, first of all, a deep understanding of the binding process of chromophore-nucleobase systems to DNA oligomers in water, as well as a thorough characterisation of the supramolecular assemblies formed. The study of model systems has allowed us to identify the structural requirements for a strong binding to DNA. This is strictly necessary for the orthogonal self-assembly of donor and acceptor molecules, in order to build well-defined nanoobjects for energy and electron transfer studies. We have therefore prepared a series of chromophore-nucleobase systems that can bind to thymine-cytosine oligonucleotides. In addition, we have exploited the versatile supramolecular chemistry of guanosine (G) derivatives in both organic solvents and in water. These compounds are known to form well-defined architectures such as G-ribbons or, in the presence of certain cations, G-quartets. We have demonstrated that we can reach a control on the kind of self-assembled structure formed as a function of the experimental conditions employed. In particular, we have identified conditions in which guanosine-chromophore systems can form discrete, well-defined complexes, such as octamers or hexadecamers, or polymeric nanofibres.

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