| Selective fluorescence quenching is a photophysical process whereby an excited-state fluorophore is deactivated by a quencher molecule but other, structurally similar fluorophores remain unaffected. In this work, this phenomenon is investigated on theoretical, experimental, and applied levels.; Ab initio calculations were used to study the mechanism by which selective quenchers discriminate between alternant and nonalternant polycyclic aromatic hydrocarbons (PAHs). Calculations of the ground- and excited-state properties of four representative PAHs demonstrated that relative to their alternant isomers, nonalternant PAHs possess higher ground-state energies, lower relative excitation energies, and greater changes in their excited-state geometries. Selective quenching of pyrene (an alternant PAH) versus fluoranthene (a nonalternant PAH) by nitromethane was also studied. Although two routes existed for the deactivation of pyrene, only formation of an ion pair and its subsequent recombination to form a ground-state complex was both energetically feasible and allowed within symmetry selection rules. In contrast, fluoranthene had no energetically favorable route to deactivation via an ion pair.; More rapid and accurate methods for determining the efficiency and selectivity of quenchers have also been developed. A sensitive, multi-wavelength fluorescence detection system with a capillary flow cell was designed, built and characterized for this purpose. Flow-injection techniques that automated the preparation and mixing of fluorophore and quencher solutions were developed and validated by comparison to traditional methods. Using this apparatus, primary, secondary, and tertiary mono- and diamines were studied as selective quenchers of nonalternant PAHs. Quenching efficiency increased and selectivity decreased with the electron-donating ability of the amine. However, all compounds studied were more selective than previously reported quenchers for nonalternant PAHs. Nitrated explosives were also studied as quenchers of alternant PAHs, and found to be highly efficient quenchers of pyrene. In particular, nitroaromatic species could be identified based on their unique perturbation of the pyrene excited state.; Lastly, the use of selective fluorescence quenching for novel forms of detection in capillary liquid chromatography has been explored. Adding either nitromethane or diisopropylamine to the effluent of a capillary liquid chromatography column followed by laser-induced fluorescence detection enabled the profiling of complex mixtures of alternant and nonalternant PAHs. Conversely, adding pyrene to the column effluent allowed for indirect detection of nitrated explosives. These techniques were applied to the forensic and environmental analysis of petroleum products and explosives. Both qualitative and quantitative information about the composition and potential common origin of various samples was generated. |
