UCLA

This dissertation describes the development of triplet Dewar benzenes for photonic amplification in the crystalline solid, verification of the quantum chain process in solution and the solid state, and further potential for the quantum chain process by addressing limitations in crystal packing and electronics. This work relied heavily upon understanding how each component of the quantum chain reaction effects its reactivity, including transient absorption spectroscopy to determine triplet lifetimes and quenching rates in solution, concentration dependence through quantum yield calculations, and computational studies to gain insight on the mechanistic photochemical isomerization of Dewar benzene. Solid state irradiation experiments were performed in nanocrystalline suspensions via reprecipitation method in surfactant to stabilize particles. Chapter One is an overview of quantum chain reactions as part of a class of nonlinear photochemical processes. This chapter outlines known quantum chain reactions, the complexity of this process as it requires several steps to occur, and seminal work that inspired exploration in expanding this reaction in crystalline Dewar benzenes. Chapter Two describes the development and study of crystalline benzophenone-linked Dewar benzene. This work demonstrates the ability to access triplet excitation and photochemical isomerization of Dewar benzene in the solid state. Lifetimes and triplet energy of the photoproduct (responsible for the energy transfer event) were determined using transient absorption spectroscopy and fluorimetry. The crystalline Dewar benzene proved to undergo quantum amplification in the solid state environment, possessing quantum yields greater in solid state than in solution. Chapter Three establishes similar reactivity in the solid state within other Dewar benzene derivatives and showcases enhanced reactivity of derivatives over the example from Chapter Two. This work demonstrated the significance of the solid state packing influence on the extent of the quantum chain process. Confirmation of suspension crystallinity was performed using pXRD. Comparisons between bulk powder and suspension packing revealed polymorphism crystalline Dewar benzenes. This work also established that the solid state reaction from Dewar benzene to H�ckel benzene proceeds via solid-to-solid transformation, starting from a polycrystalline powder reactant to give an amorphous resulting photoproduct upon irradiation. It was demonstrated that electronics play a significant role upon comparison of quantum yields between di- and mono-sensitizer linked Dewar benzenes, revealing thepotential for benzophenone surface quenching. Chapter Four focuses on exploring unique reactivity of Dewar benzenes and proposing promising new derivatives that have the potential to extend the quantum chain to 10^6. This work addresses the bulk properties and irradiation of a Dewar benzene-sensitizer salt pair, a non-sensitizer linked Dewar benzene and a mono- sensitizer linked Dewar benzene. Further exploration into the exceptional reactivity of the mono-sensitizer linked Dewar benzene was carried out via transient absorption analysis, revealing longer-lived intermediates than that of the di-sensitizer linked Dewar benzene. To further validate the presence of benzophenone self-quenching in the solid state and extending the quantum chain, four Dewar benzenes and their synthesis were proposed.