Date of Award
Master of Science (MS)
Reid, Scott A.
Charge transfer complexes are charge separated states that are formed at donor - acceptor interfaces and play significant role in charge photogeneration. One of the main criteria for efficient charge transfer is suppression of charge recombination process. Previous experiments show that one of the most effective ways to inhibit recombination is an introduction of bridge molecules between donor and acceptor or increase the number of electron donating and withdrawing groups. These solutions are inspired by photosynthetic reaction centers where charge transfer occurs over long distances. Covalent Organic Frameworks (COFs) are advanced porous crystalline materials that can be constructed of multiple donor and acceptor building blocks. This approach improves efficiency of charge transfer by suppressing dissociation of polaron pairs. In the present work, photophysical and charge dynamics processes of various donor-acceptor systems, namely star-shaped carbazole-π-triazine organic chromophores, BTPA-cased donor-acceptor COFs, and metallophthalocyanine COFs, were investigated using the combination of steady-state spectroscopic techniques and time-resolved femtosecond transient absorption (TA) spectroscopy. The study on star-shaped carbazole-π-triazine organic chromophores showed that formation of charge transfer can be facilitated by positioning a bridging phenyl ring by creation of conjugated system. Nevertheless, the introduction of two phenyl bridge units can distort the coupling leading to weak charge migration from carbazole. Combination of BTPA (5,5',5''-(1,3,5-Benzenetriyl)tris[2-pyridinecarboxaldehyde]) and a series of three different organic precursors: 1,3,5-Tris(4-aminophenyl)benzene (TPB), 4,4',4''-Triaminotriphenylamine (TPA), and 1,3,5-Tris(4-aminophenyl)triazine (TPT) for the synthesis of COF showed that efficient charge transfer and slower recombination process can be achieved by incorporating stronger electron donating group, such as TPA, to enhance excited state dipole moment. Finally, the investigation of charge dynamics in COFs constructed using copper and nickel metallophthalocyanine linked to electron withdrawing 2,3,5,6-tetrafluoroterephthalonitrile (TFTPN) revealed the delocalization of charge between neighboring donor-acceptor units formed within 1.464 – 1.750 ps, which is further transferred between COF layers and dissociates between 0.662 – 3.383 ns.
Available for download on Friday, May 14, 2021