Molecular scale patterning of photonic structures via conformational control

This thesis comprises a number of studies into controlling the photonic properties of materials by way of controlling their molecular conformation. The absorption and emission behaviours of fundamental AIE molecules TPE and HPS were probed in solutions with varying degrees of aggregation. It was found, in contrast to the existing RIR hypothesis, that the monomers were able to emit in good solutions with minimal aggregation, and continued to do so upon low levels of aggregation. The monomer emission of TPE was found to be more prevalent than that of HPS due to the difference in conjugation pathways offered by each molecule. These results suggested that the term AIE is misleading, with the assumption that the molecular emission 'switches on' upon aggregation disregarding the fact that the more efficient fluorescence actually results from a quenching process (excimer formation), with RIR causing the increase in efficiency. A new method for controlling the aggregation in fluorene/fluorenone oligomers was also investigated. Water was found to be highly effective for screening the fluorenone aggregation, with fractions of only 10% sufficient to eliminate the excimer emission. The fluorenone was then successfully reaggregated to varying degrees as the water fraction was increased, due to non-solvent effects. Investigating solutions of thermally oxidised FFF also revealed the method's ability to identify the presence of fluorenone moieties when there was no indication of oxidation in the absorption or PL. Lastly, dip-pen nanolithography was employed to pattern photonic structures in PFO thin films. Beta phase dots with diameter 548nm were achieved, demonstrating the potential of DPN in photonic device fabrication, however there were issues with consistency of feature size and damage to the film. An outline of the development of the microscale PL set-up used to analyse the patterns, and the steps taken to maximise its resolution and spectral contrast is also given. The set-up was found to be well suited to highlight the beta phase of PFO, however there were issues with reproducibility of the PL maps, as well as a trade-off between signal strength and photodegradation of the sample. When compared to patterns imaged on a different set-up, it was clear that the set-up designed here produced too low a signal to accurately compare the new patterns. Further work in sample fabrication, DPN operation and microscale PL optimisation was therefore identified to improve the quality and reproducibility of the patterns.