Doctor of Philosophy
Dr. Joe B. Gilroy
This thesis describes the synthesis of π-conjugated small molecules and polymers consisting of boron difluoride (BF2) formazanate dyes. It utilizes different strategies such as extended π-conjugation, planarity of the backbone, donor-acceptor interactions, etc. to modulate the frontier molecular orbitals and band gaps of these systems. The resulting materials are redox-active and exhibit rich optical properties including high molar absorptivities and low band gaps. Chapter 2 describes a series of acceptor-donor-acceptor compounds consisting of BF2 formazanates as electron acceptors bridged by a variety of π-conjugated donors. The work in this chapter demonstrates that the optoelectronic properties and the corresponding band gaps can be tuned by varying the electron donating spacers. The resulting compounds exhibited low optical band gaps (1.73−1.38 eV).
Chapter 3 describes the synthesis and characterization of a series of oligoynes with up to 10 alkyne units using BF2 formazanates as end-caps. Not only did BF2 formazanates stabilize the oligoynes, but they also introduced unique optical and redox properties. The resulting compounds exhibited a blend of properties that cannot be achieved by either oligoyne or BF2 formazanates individually (e.g., panchromatic absorption, multiple redox waves).
Chapter 4 describes the first example of a π-conjugated polymer incorporating BF2 formazanate and Pt(II)-acetylide units. This polymer exhibited reversible redox waves, low optical band gap (1.4 eV), and film forming properties. The reversible electron accepting ability of the polymer was demonstrated by chemically reducing the BF2 formazanate units using cobaltocene and subsequently oxidizing it back to the neutral form in air.
The work described in Chapter 5 is a follow-up to the work in Chapter 4. It describes a series of small molecules incorporating BF2 formazanate and Pt(II)-acetylides to thoroughly examine the effect of Pt(II)-acetylide conjugation on the optoelectronic properties of BF2 formazanates. The results presented in this chapter demonstrate improved redox properties and red-shifted absorption and emissions bands compared to parent BF2 formazanates.
Taken together, the work described in this thesis demonstrates the readily tunable optoelectronic properties of BF2 formazanate dyes. Furthermore, owing to their low band gaps, π-conjugated materials described in this thesis are promising candidates for use in the organic electronic arena.
Summary for Lay Audience
This thesis describes the preparation of new highly coloured small molecules that can absorb different colours of light. This is important for potential applications in organic electronic devices such as solar cells and light-emitting diodes (LEDs). Their broad absorption capability could allow for the efficient absorption of sunlight which can ultimately lead to better performance of the devices. What they all have in common is that they exhibit delocalization of electrons (electric charge carriers), meaning the electrons can move around the entire molecule and are not static. The delocalization of electrons results in unique properties that give rise to strong colours. This is also the reason why tomatoes are red, carrots are orange, and leaves are green. They all consists of molecules that contains a chain of alternating single and double bonds between atoms. Synthetically, the colour of molecules can be changed by varying the number of alternating single and double bonds. This is because molecules with different chain lengths will absorb different colours of light. In general, as the number of alternating single and double bonds are increased, the molecules gradually change colour from red to blue. Chapters 2 to 5 describe the preparation of several small molecules as well as a chains of small molecules (known as polymers). They exhibited broad light absorption properties, the ability to store additional electrons and subsequently donate them under appropriate conditions. In the future, the small molecules and polymers I have prepared will be useful for application in organic solar cells to efficiently convert sunlight into electricity.
Dhindsa, Jasveer S., "Exploring the Optical and Redox Properties of π-Conjugated Boron Difluoride Formazanate Dyes" (2022). Electronic Thesis and Dissertation Repository. 8990.
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