Driven by Light: An Ultrafast Look into the Bright Future of Photosensitizers

Abstract

This thesis investigates various strong light-absorbing molecules that have potential applications in furthering our progress into replacing fossil fuels with clean energy resources and remediating harmful chemicals in the environment. The research presented in this thesis employs a range of spectroscopic techniques, complemented with computational predictions, to characterize the light absorption and excited state dynamics of newly developed chromophores that have shown promise in these various applications. Chapter 3 investigates a BODIPY-fullerene dyad designed to be used in organic photovoltaics as a triplet sensitizer to form longer-lived excitons. This triplet sensitization occurs via a ping-pong energy transfer mechanism between the BODIPY and fullerene, resulting in a long-lived BODIPY triplet (>1 µs). Chapters 4 and 5 investigate the MB-DIPY chromophore that could potentially displace fullerene as a strong and more versatile electron acceptor in organic photovoltaics. In Chapter 4, the redox potentials and photophysics of four MB-DIPY analogs are explored. The MB-DIPYs had comparable reduction potentials to fullerene and demonstrated efficient intersystem crossing to form long-lived triplet states (>10 µs). In Chapter 5, the MB-DIPY is functionalized with ferrocene, a strong electron donor, and demonstrated sub-ps charge-transfer from the ferrocene to the MB-DIPY followedby charge recombination in 12 ps. Chapters 6 and 7 investigate the Rh-Ga and Co-Ga heterobimetallic photocatalysts that can access challenging bonds via a photoredox mechanism. The excited state nature of these photocatalysts is first explored in Chapter 6. The results were consistent with the naked anionic catalyst being the active participant in the photocatalytic cycle. Chapter 7 investigates the reactivity of the photocatalysts with a chloroadamantane substrate. The results suggested that the substrate binds to the anionic rhodium photocatalyst and that the photocatalytic reactivity is not diffusion-limited. In contrast, the anionic cobalt catalyst was converted into the chlorinated precatalyst upon the addition of the substrate, demonstrating that the chemical reactivity of the rhodium and cobalt photocatalysts differ with this substrate.