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Title: Exploring rapid nuclear motion in molecular dyads
Author: Allen, Ben
ISNI:       0000 0004 2720 4388
Awarding Body: University of Newcastle Upon Tyne
Current Institution: University of Newcastle upon Tyne
Date of Award: 2008
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have found that while simple consideration of the equilibrium geometries is unable to reproduce the experimental results, we have been able to use molecular dynamics and vibrational coordinate analysis to rationalize the rapid electron transfer. Specifically, certain vibrations of MesAcr promote the electron transfer, but through an interesting mechanism. We then proceed to describe three more systems where nuclear motion is critical to explaining their photophysical properties. A C6o-Ru dyad is shown to undergo efficient electron exchange at room temperature, but with a pronounced activation energy. We use molecular dynamics to show that the CwRu dyad should not be considered as a rigid system, but that the "butterfly" motion of the molecular "dumbell" can introduce new mechanisms for electron exchange. We also present preliminary calculations on a bodipy-Co, dyad which appears to exhibit dual emrssion from both bodipy- and C60 centred triplet states. These results indicate that instead of an equilibrium existing between these two distinct states, the actual emmissive state has characteristics of both, being delocalised across the whole dyad. Finally, a bodipy-pyrene dyad which exhibits a large increase in the rate of non-radiative decay when subjected to a protic environment is investigated using theoretical techniques. We show that this effect is not due to a large distortion of the bodipy dye inherent in the excited state's properties, but is likely to be due to the increased n-stacking of the pyrene units as they orient to minimize solvent contact Constrained biphenyl and quaterphenyl molecules are potentially effective units for use in molecular electronic devices. We describe how computational chemistry can be applied to the study of their excited states, providing a sound rationalization for both the excitation and emission spectra. Specifically, the differing strap lengths used to constrain the internal torsion angle is only partially effective, due to the accessibility of many more conformations as the strap length increases. Thus, we see that the excited SI state geometries remain comparable, regardless of strap length, and that the presence of almost iso-energetic conformers leads to interesting behaviour in the ground state. Finally, we use theoretical calculations as a mainstay for the design of a molecular memory device. This work proposes a biphenyl unit constrained by a disulfide bridge as a central switching unit. Calculations are concerned with both the reversible opening/closing reactions, as induced by electrochemical methods, and the possibility of using photo-induced electron transfer as the stimulus for conformational exchange.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available