The excited-state chemistry of molecular assemblies and novel aromatic chromophores

Dongare, Prateek (2014) The excited-state chemistry of molecular assemblies and novel aromatic chromophores. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

This dissertation explores the spectroscopic characterization, excited-state behavior and mechanistic analysis of systematically designed molecules. Excited-states are modular in nature, they can be utilized to study electron transfer, proton transfer and concerted electron proton transfer. Furthermore, the excited-state of a molecule has an ability to respond to specific stimuli which can be detected as fluorescence quenching or enhancement. Therefore, the reactivity of an excited-state can be utilized in a variety of applications. This dissertation starts with investigation of the excited-state properties of strained pyrenophanes. The absorption and emission spectra of three inherently chiral pyrenophanes were analyzed using Franck-Condon band shape analysis and emission spectral fitting procedures. The study tested the applicability of the one-mode spectral fitting procedure and provided detailed quantitative understanding of structural, vibronic and electronic parameters. With the increased understanding of ground and excited-state properties of pyrene, effect of protonation on constrained pyridine appended pyrene based macrocycles and their half cycle counterparts was studied. Global analysis of the absorption and emission spectral data reveals sequential 1:1 and 1:2 binding equilibria in macrocycles and direct 1:2 binding equilibria in their truncated segments bearing only one pyrene chromophores. In chapter 5, the applicability of the excited-state in detection of analytes such as saccharides and metal ions was investigated. Systematically designed molecules comprised ii of triazole rings were utilized as sensors to detect saccharides and metal ions by employing fluorescence spectroscopy. The study reveals that triazole rings play a major part in the ground and excited-state properties of these molecules and teaches us how to design new sensors to be used in opto-electronic devices. In chapter 6, concerted electron proton transfer using Re(I) based MLCT excitedstates was studied. A sterically bulky phenol was employed as a combined electron/proton donor and the reductive quenching of three analogous Re(I) polypyridyl complexes was studied. Owing to the significant oxidizing power of Re(I) MLCT excited-states the concerted electron proton transfer in these molecular assemblies is feasible. Chapter 7 lists the major conclusions drawn from the individual chapters. In the end, some recommendations for the future work are outlined.

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