Synthesis of new photoactive materials for Laser Micromachining and Microfabrication

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dc.contributor.advisor Kay, A en
dc.contributor.advisor Jin, J en
dc.contributor.author Whitby, Reece en
dc.date.accessioned 2017-09-03T22:20:13Z en
dc.date.issued 2016 en
dc.identifier.uri http://hdl.handle.net/2292/35456 en
dc.description.abstract This thesis describes the synthesis of a number of novel photoinitiator materials based around triphenylamine to aid in the development and optimisation of the two-photon polymerisation technique. Such materials should allow for improved writing speeds, smaller fabricated feature sizes and low laser powers to initiate polymerisation. Two-photon polymerisation allows for the fabrication of intricate three-dimensional structures, but suffers from slow writing speeds and sufficiently optimised photoinitiators. This work starts with an introduction to the two-photon polymerisation technique, used for fabricating micro/nano-scale three-dimensional polymeric structures, and in particular when using a 780 nm femtosecond Ti:Sapphire laser. This is followed by a description of the synthesis, analysis and characterisation of a number of newly synthesised photoinitiators. The latter part consists of a detailed analysis of the two-photon polymerisation work carried out using these newly synthesised photoinitiators. An in depth analysis of the factors that allow for more efficient photoinitiators was conducted, and identified the key parameters and molecular properties that should lead to better performing materials. Following this, the design and synthesis of three suites of new photoinitiators containing a variety of electron donors and acceptors was conducted in order to maximise two-photon absorption cross-sections - a key parameter for any successful compound. The general suites of compounds prepared were: (i) branched triphenylamine-π-ester systems; (ii) triphenylamine-π-acceptor and acceptor-π-acceptor systems and (iii) triphenylamine: α,β-unsaturated ketone systems. It was found the two-photon cross sections of up to 590 GM were achievable and this is above the 500 GM that was targeted at the outset of this work. For each class of compound studied, fluorescence measurements were performed, and these showed the strong influence that solvent viscosity had on the molecular properties of the multi-branched structures reported here, particularly the fluorescence quantum yield, and ultimately, the two-photon polymerisation thresholds. Furthermore, the effect of incorporating ketone functionality as a means to reduce fluorescence quantum yields – and which leads to more efficient photoinitation (through increasing inter system crossing to the active triplet state) - was also studied. This indeed proved to be a valid approach and fluorescence quantum yields for some of the ketone containing molecules were below 1%. In-depth studies were also performed to assess the photoinitiators ability to initiate the polymerisation of acrylates when exposed to an 800 nm femtosecond Ti:Sapphire laser on a fabrication stage. It was found that high quality structures with micrometre resolutions could made using writing speeds as fast as 200 μm/s and at laser powers as low as 27 μW. Furthermore, it was shown that making use of dipolar photoinitiators is advantageous over larger multi-polar species, even though the latter species can display seemingly improved properties. It was concluded that in more complex, multibranched systems, that localisation of the excited state to a single branch effectively negates the molecular properties exhibited by larger species. Moreover, given the difficulty in synthesising larger photoinitiators this work suggests that pursing such a pathway is unlikely to yield large improvements in polymerisation thresholds. Overall it is concluded that improving dipolar species to maximise their two-photon absorption cross-sections, minimise their fluorescence quantum yields and improve their solubility in a variety of monomer materials is likely to be a more fruitful endeavour. en
dc.publisher ResearchSpace@Auckland en
dc.relation.ispartof PhD Thesis - University of Auckland en
dc.relation.isreferencedby UoA99264930502002091 en
dc.rights Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated. Previously published items are made available in accordance with the copyright policy of the publisher. en
dc.rights.uri https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm en
dc.rights.uri http://creativecommons.org/licenses/by-nc-sa/3.0/nz/ en
dc.title Synthesis of new photoactive materials for Laser Micromachining and Microfabrication en
dc.type Thesis en
thesis.degree.discipline Chemistry en
thesis.degree.grantor The University of Auckland en
thesis.degree.level Doctoral en
thesis.degree.name PhD en
dc.rights.holder Copyright: The author en
dc.rights.accessrights http://purl.org/eprint/accessRights/OpenAccess en
pubs.elements-id 657248 en
pubs.record-created-at-source-date 2017-09-04 en


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