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UBC Theses and Dissertations

Thiophene-containing photofunctional molecules : Pacman complexes, metallacycles and flexible Lewis pairs Cao, Yang


Three types of photofunctional molecules based on thiophene-containing conjugated backbones have been designed, synthesized and characterized. It is shown that their light absorption and emission properties can be manipulated and applied for applications such as fluorescent imaging. Binuclear Pt(II) terpyridine Pacman complexes with flexible thiophene-containing bisacetylide ligands are shown to exhibit structural folding/unfolding controllable by temperature change and different solvent environments. The structural folding and unfolding give rise to structural changes of the thiophene-containing backbone and different interactions between two metal-containing moieties, which are analyzed by DFT calculations and evidenced by UV-Vis and NMR spectroscopy. Metallacycles with a cis-diphosphino Pt(II) metal center and different thiophene-containing bisacetylides are designed to show room-temperature fluorescence and phosphorescence dual emission with different intensity ratios. Their absorption and emission properties are explained by DFT and TD-DFT analysis of ground state and singlet and triplet state energies and geometries. An intramolecular Lewis pair system between a Lewis acidic -BMes2 group and a Lewis basic phosphine oxide group based on a flexible bithiophene backbone is reported. Evidenced by NMR and IR spectra, the system is found to exhibit fast equilibrium between an open structure with unbound Lewis acid and a closed structure with Lewis adduct. The equilibrium is manipulated by lowering the temperature to favor the closed structures, or adding strong hydrogen bond donors that favor the open forms. The difference in coordination state of the boron center in these two states gives rise to an interesting single-component-two-state system with drastically different emission colors between states. The scope of such system was explored and different emission colors of the open and closed forms of the Lewis pairs are achieved by changing the backbone conjugation or strength of electron-donating groups. Furthermore, this system has been used as a two-color fluorescent dye system for fluorescence imaging of hydrophobic/hydrophilic environments in biological or medical applications.

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