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UBC Theses and Dissertations

Symmetric and non-symmetric stimuli-responsive flexible Lewis pair systems Arsenault, Nicole Evelyn


Herein an investigation of the photophysical properties of stimuli-responsive molecules incorporating a triarylborane Lewis acid and phosphine oxide Lewis base pair on a bithiophene backbone, called flexible Lewis pairs (FlexLPs), is presented. The FlexLPs change conformation between the Lewis acid-base bound adduct form and unbound open form with surrounding solvent, where strongly hydrogen bond donating solvent stabilizes the open form through formation of a hydrogen bond with the Lewis base. The ability to synthesize diverse stimuli-responsive molecular motifs incorporating FlexLPs is achieved by installing a reactive terminal alkyne functional group on a FlexLP molecule. The application of this FlexLP molecule as a versatile stimuli-responsive ligand that can be incorporated into more complex molecular architectures, such as dimers, transition-metal complexes, and functionalized nanoparticle materials, is thus demonstrated by utilizing different alkyne coupling chemistry. Synthesis of a dimeric molecule with two FlexLP pairs connected through a conjugated bithiophene-alkyne-alkyne-bithiophene backbone is described and compared to a monomeric FlexLP molecule. The monomer and dimer FlexLP demonstrate changing emission colours and lifetimes with varying solvent, proposed to be from a change in FlexLP conformation. In the closed form a π–π* energy transition occurs resulting in blue-green emission colour, while in the unbound form a charge transfer event occurs resulting in yellow-orange emission colour. Monometallic and bimetallic Pt(terpyridine)-containing complexes functionalized with the FlexLP ligand are explored as solvent-responsive optical switches. A low energy CT band between the acid-base pair ligand and terpyridine ligand appears for both complexes, Absorption spectroscopy reveals this CT band is solvent- and temperature-responsive, and is dependent on the FlexLP ligand conformation. Investigation of the photophysical properties of two emissive Pt-functionalized FlexLP complexes reveal both complexes fluoresce despite being able to populate the excited triplet states of the complexes. Transient absorption spectroscopy reveals that the FlexLP ligand conformation has a significant effect on the triplet-state lifetime. Functionalization of FlexLPs onto nanoparticles is explored for applications as water-sensing emissive fluorophore tags for biomedical imaging applications. The emission colour and lifetime change in response to water concentration in surrounding solvent, evidenced by fluorescence and emission lifetime spectroscopy. Preliminary fluorescence microscopy studies are also performed.

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