Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Chemistry

Supervisor

Gilroy, Joe B.

Abstract

This thesis describes the synthesis, characterization, optoelectronic, and redox properties of boron difluoride hydrazone (BODIHY) dyes. BODIHYs are part of a class of molecular materials whereby chelating N-donor ligands form complexes with a boron difluoride (BF2) moiety, which rigidifies and introduces push-pull electronic structures to the resulting dyes. This thesis demonstrates that structural modifications to the appended substituents on the BODIHY core can be used to drastically tune the optoelectronic and redox properties of the unique complexes.

BODIHYs are weakly luminescent in dilute solutions but exhibit enhanced emission in the aggregate- and solid-state due to a phenomenon known as aggregation-induced emission (AIE). AIE-active dyes, such as BODIHYs, have freely rotating substituents such as aryl rings which non-radiatively dissipate energy following electron excitation. In the aggregate state, these substituents are unable to move freely which result in reduced non-radiative relaxation pathways and thus, emission is detected. BODIHYs also exhibit reversible redox chemistry, which was reported for the first time in chapter two, where a paramagnetic BODIHY was observed following chemical oxidation. The results in chapter three describe BODIHY dimers that exhibit two one-electron oxidation and reduction events and explores how push-push, pull-pull, and push-pull electronics alter the optical properties of the dimers. Chapter four describes the first example of a BODIHY polymer that exhibits enhanced emission due to aggregation as well as changes in environment viscosity. Chapters five and six explore the use of BODIHYs as electron acceptors in donor-acceptor and acceptor donor-acceptor molecular architectures where the strength of the electron donor unit is altered. Chapter five focuses on triphenylamine electron donor groups which lead to dual-emission, charge-transfer character, and multiple reversible redox waves. In chapter six, a structure-property relationship is presented whereby altering the size and strength of an electron donor group alters the optoelectronic, redox, and band gaps of the resulting in D-A and A-D-A materials.

The work presented in this thesis serves as a basis for the continued development of molecular materials derived from BODIHYs and demonstrates the potential for these materials to be incorporated into optoelectronic-based applications such as organic electronic displays and light-harvesting materials.

Summary for Lay Audience

This thesis describes the preparation of a family of dye molecules that absorb and emit light in the solid-state and in solution. Based on structural changes introduced onto the dye core, the resulting colour of the light that they absorb and emit can be altered. The ability for these dyes to emit light (“glow”) in the solid-state is unique, as most dye molecules with similar elemental makeups can only emit light when dissolved in solution. The dye molecules presented tend to aggregate when suspended in water, which leads to their enhanced emission. Given that the human body is made up of over 55% water, these types of molecules may be useful for medical imaging techniques used for the detection of organs, cells, tumors, etc. Most commercially available dyes used for biological imaging are expensive ($40,000/g) and may contain harmful heavy metals. The dyes described in this thesis do not contain heavy metals, are cheaper and easier to prepare ($50/g), and exhibit properties comparable to the current molecules used in the aforementioned applications. An additional feature that makes these molecules attractive is their ability to accept and donate electrons and chapter two presents the first report of this property for these molecules, while also to highlighting their enhanced light emission in the solid- and aggregated-state. Chapters three, four, five, and six build on these results by demonstrating the preparation of dyes with different elements attached to the dye core that further alter their light absorbing, emitting, and electron accepting/donating properties. For display technologies such as organic light-emitting diodes (OLEDs), dyes that emit light in the solid state and can reversibly accept/donate electrons are required. In most light-emitting display technologies, expensive metals are used to achieve optimal performance. The results presented in this thesis provide an understanding of how altering the structural components of dye molecules can impact their colour, light-emitting properties, electron accepting/donating ability, and sensitivity to viscosity changes. The dye molecules presented throughout this thesis have the potential to be incorporated into, for example, electronic displays and medical imaging applications, without the use of harmful and expensive heavy metals.

Creative Commons License

Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.

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