Quantum-Mechanical Investigations of Excited State and Catalytic Properties of Organic Luminophores and Zeolites
Over the years, there has been significant interest in the conversion of methane to methanol. This has been due to the abundant nature of natural gas which is composed mainly of methane. In order to prevent over-oxidation of CO2, CO, and HCOOH, it has been demonstrated that copper-exchanged zeolites can kinetically trap activated methane as strongly bound methoxy groups. We describe the process by which over oxidation products are produced in great detail. We have investigated the impact of heterometallic extra-framework motifs on the temperature gradients of each step. We also discuss quantum-mechanical computations of activated copper-exchanged zeolites; realizing how these systems have evolved at the molecular level will open up possibilities for enhancing reactivity.Here, we used quantum-mechanical methods to study dipyrrinones. These are nonfluorescent yellow-pigmented components of bilirubin, when excited with UV/blue light experiences Z to E isomerization and produce highly fluorescent compounds like N,N-methylene-bridged dipyrrinones and xanthoglows. The first instances of dipyrrinone analogues with fluorescence without covalently bonding the nitrogen atoms of the pyrole and pyrrolidine are described in this thesis. We also considered the possibility of using quantum-mechanical calculations to develop the brightest series of pyronin fluorophores. Typically, pyronin Y and B (PY and PB, respectively) are used in staining applications. However, these dyes have low fluorophore brightness, we developed the brightest series of pyronin fluorophores ever reported, these systems outperform both pyronin Y and B through a combination of experimental and theoretical work (PY and PB). The pyronins have a low fluorophore brightness, though, and there is not a clear process in the literature for creating enhanced variants. The best agreement for this group of systems is obtained using DFT functionals with an exact Hartree-Fock exchange of 0-10%. The intensities of the pyronin fluorophores are determined by TD-DFT calculations of interconversion barriers and energies between structures on the lowest excited singlet (S1) surface and twisted intermolecular charge transfer (TICT) states. Lastly, as a capstone to this thesis, we developed a new double hybrid density functional approximation (DH-DFA), ωB88PTPSS, which incorporates the equipartition of density functional theory (DFT) and non-local correlation but with a meta-GGA correlation functional as well as the range-separated exchange of ωB2PLYP. The new density functional provides accurate excitation energies for conventional systems as well as correct prescription of negative singlet-triplet gaps for non-conventional systems with inverted gaps (INVEST). ωB88PTPSS performs quite well than recent DH-DFAs for open-shell systems, it correctly and accurately predicts negative gaps for 50 systems with inverted singlet-triplet gaps, for intramolecular charge-transfer excitations, in which its performance was achieved near-CC2 and ADC(2) quality for the QUESTDB set and also relative to EOM-CCSD reference.
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