Theoretical and experimental investigations of photoresponsive and biomimetic supramolecular materials

A new approach for design and fabrication of new photoresponsive and biomimetic materials is described using theoretical predictions and experimental characterisations. Novel discrete hydrogen-bonded aggregates are formed from photoresponsive azodibenzoic acid building blocks, which can undergo a reversible cis-trans photoisomerisation. In trans-p-azodibenzoic acid, the two carboxylic groups are aligned parallel to each other while, in the cis isomer, they are almost perpendicular. This structural difference between the two isomers leads to different hydrogen-bonded geometries: the trans isomer aggregates linearly whereas its cis counterpart forms cyclic tetramers. Molecular and bulk material characterisation are used to identify a higher-order self-organisation from the cis-isomers, which results in long, unidimensional rod-like structures.; A new understanding of hydrogen-bonded aggregates is developed, where the thermodynamics of azodibenzoic acid self-assembly are identified using vibrational properties, molecular orbital wavefunctions, and density matrix analysis. Quantum mechanical properties of hydrogen-bonded azodibenzoic acids establish the relative stabilities of the self-assembly products, validating the formation of trans-linear tapes and cis-cyclic tetramers.; A molecular modelling strategy is implemented to provide detailed information on packing within cis-azodibenzoic acid rod-like nanostructures. Energy scans determine face-packing as the preferred macrocycle arrangement. Quantum mechanical optimisation of this face-packed structure shows little deviation from predicted molecular models, highlighting the strength of this modelling technique. Electronic properties exhibit significant pi-electron delocalisation throughout the entire arrays, along with a HOMO-LUMO band gap narrowing towards values typical of non-doped, organic semi-conducting materials.; Dicyano-, ditriazene- and diureido-azobenzene derivatives are introduced to design tightly bound supramolecular structures by multiple hydrogen-bonding and metal-coordination. Using geometric arguments, the conservation of recognition site orientations and electronic properties upon substitution allows the use of the trans- and cis-azodibenzoic acids as model monomers for the prediction of self-assembly for these new photoresponsive units.; Finally, new triaminopyrimidine nucleosides are synthesised to generate hydrogen-bonded supramolecular structures from DNA-base analogues. Experimental characterisation shows that hydrogen-bonding of the triaminopyrimidine monomer with barbiturates leads to oligomeric species. Using sterically encumbered cyanuric acid nucleosides dramatically alters the hydrogen-bond self-assembly of these molecules, giving rise to discrete hexameric macrocycles which further associate to form elongated nanostructures.