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Title: Studies of quenching of excited states of aromatic molecules in polymer matrices
Author: Jassim, Alwan Nsayiff
Awarding Body: University of St Andrews
Current Institution: University of St Andrews
Date of Award: 1980
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The phosphorescence behaviour of a series of polycyclic aromatic compounds has been studied in different polymer matrices. Measurements have been carried out at 77K and from room temperature up to 350K. Studies at 77K have shown that the polymer matrix takes part in some quenching reaction, the rate constant depending on the additive being studied. At higher temperatures non-exponential decays were observed, for polystyrene this phenomenon is very marked. It is proposed that the cause of non-exponential decay is T-T annihilation resulting from mobile triplet exciton migration within the polymer matrix. It is proposed that the triplet levels are 285.9 and 297.4 kJ mole−1 for polystyrene and poly(methylmethacrylate) respectively. The quenching of fluorescence for the polycyclic aromatic additives by oxygen has been examined and unusual plots obtained. At low pressures of oxygen enhanced singlet emission was observed but as the pressure was increased normal Stem-Volmer plots were obtained. Simultaneously as pressure of O2 increased the triplet emission was very efficiently quenched and the increase in fluorescence was observed. When the phosphorescence ceased the intensity of singlet emission decreased with increasing pressure of O2. The mechanism proposed to account for this very unusual behaviour involves paramagnetic quenching of the singlet state by the mobile triplet exciton. The increase in fluorescence resulting from removal of the triplet exciton by oxygen is greater than the direct singlet quenching by O2.
Supervisor: MacCallum, J. R. Sponsor: Federal Government of Iraq
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QD381.9A8J2 ; Polymers