Ahmed Adawi - Academia.edu (original) (raw)
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Pacific Northwest National Labortory
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Papers by Ahmed Adawi
Chemical Physics, 2009
Single molecule fluorescence spectroscopy is used to study the optical properties of two polymers... more Single molecule fluorescence spectroscopy is used to study the optical properties of two polymers: a fluorene-based statistical copolymer that contains a low fraction (10%) of a red-emitting thiophene group, and the green-emitting polymer poly(9,9-dioctylfluorene-alt-benzothiadiazole). These polymers were studied when isolated at a low concentration in a polymer matrix (either polynorbornene or polystyrene). For the red-emitting polymer, we compare the relative emission intensity from the green-emitting benzothiadiazole groups with the red-emitting thiophene. We find that red emission from the thiophenes is significantly suppressed in the single molecule regime, suggesting that interchain energy transfer dominates intrachain processes in such polyfluorene copolymers. We then use fluorescence spectroscopy and polarization anisotropy measurements to show that the conformations of both polymers are dependent on their host matrix, adopting a more collapsed, globular conformation in polystyrene and a more extended chain conformation in polynorbornene.
Advanced Functional Materials, 2008
The polymer poly(9,9-dioctylfluorene) (PF8) can be driven into a morphological form termed the β-... more The polymer poly(9,9-dioctylfluorene) (PF8) can be driven into a morphological form termed the β-phase that has enhanced planarity and increased structural rigidity. We show that the β-phase can be generated in two different fluorene oligomers; a fluorene pentamer, and a short (statistical) oligomer composed of chains having a maximum length of 19 monomer units. By comparing the energy of the zero-zero phonon line in fluorescence from the β-phase oligomers with that in the PF8 polymer, we show that the electronic conjugation length of the β-phase is (30 ± 12) monomer-units, a value consistent with the persistence length of the molecular chain.
Chemical Physics, 2009
Single molecule fluorescence spectroscopy is used to study the optical properties of two polymers... more Single molecule fluorescence spectroscopy is used to study the optical properties of two polymers: a fluorene-based statistical copolymer that contains a low fraction (10%) of a red-emitting thiophene group, and the green-emitting polymer poly(9,9-dioctylfluorene-alt-benzothiadiazole). These polymers were studied when isolated at a low concentration in a polymer matrix (either polynorbornene or polystyrene). For the red-emitting polymer, we compare the relative emission intensity from the green-emitting benzothiadiazole groups with the red-emitting thiophene. We find that red emission from the thiophenes is significantly suppressed in the single molecule regime, suggesting that interchain energy transfer dominates intrachain processes in such polyfluorene copolymers. We then use fluorescence spectroscopy and polarization anisotropy measurements to show that the conformations of both polymers are dependent on their host matrix, adopting a more collapsed, globular conformation in polystyrene and a more extended chain conformation in polynorbornene.
Advanced Functional Materials, 2008
The polymer poly(9,9-dioctylfluorene) (PF8) can be driven into a morphological form termed the β-... more The polymer poly(9,9-dioctylfluorene) (PF8) can be driven into a morphological form termed the β-phase that has enhanced planarity and increased structural rigidity. We show that the β-phase can be generated in two different fluorene oligomers; a fluorene pentamer, and a short (statistical) oligomer composed of chains having a maximum length of 19 monomer units. By comparing the energy of the zero-zero phonon line in fluorescence from the β-phase oligomers with that in the PF8 polymer, we show that the electronic conjugation length of the β-phase is (30 ± 12) monomer-units, a value consistent with the persistence length of the molecular chain.