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15 October 2012 Correlation between molecular structure and self-healing in a series of Anthraquinone derivatives doped in PMMA polymer
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We observe that many different derivatives of anthraquinone chromophores doped in PMMA self heal after undergoing photodegradation. We are interested to know the mechanisms that are responsible for photodegradation and photorecovery, which are not yet fully understood. We used fluorescence and absorption spectroscopy as a probe of the photodegradation and recovery process while the temperature dependence is used to determine the energies of the species involved. We hypothesize that the host polymer mediates the formation of a quasi-stable state. In this scenario, once photo - damaged by intense pump laser, the molecules non radiatively decay into a tautomer state by intra molecule proton transfer, which subsequently leads to the formation of a damaged species - leading to decay of the fluorescence intensity. This hypothesis is consistent with our observation. The temperature dependent fluorescence decay and recovery studies give an insight about the different energy levels participating in optical excitation, decay and recovery. Comparing the experimental parameters such as decay and recovery rates of the fluorescence signal associated with the evolution of peaks in the fluorescence and absorbance spectrum helps us understand correlations between the efficiency of the recovery process and the structures of the dye molecules. Based on the temperature and the time-dependent observations of fluorescence and absorption, we validate qualitatively a new theoretical model which qualitatively takes into account the observed behavior and sheds light on the underlying mechanism. Preliminary measurements show good agreement with the theoretical model. More careful experiments and calculations are in process for further validation of the model.
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P. Dhakal, S. K. Ramini, and Mark G. Kuzyk "Correlation between molecular structure and self-healing in a series of Anthraquinone derivatives doped in PMMA polymer", Proc. SPIE 8519, Nanophotonics and Macrophotonics for Space Environments VI, 85190F (15 October 2012); doi: 10.1117/12.929424;

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