High pressure Raman studies on the structural conformation of oligophenyls |
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| Affiliation: | 1. Institute of Solid State Physics, Graz University of Technology, Graz, Austria;2. Institute of Theoretical Physics, Graz University, Graz, Austria;3. Department of Physics and Astronomy, University of Missouri, Columbia, MO, USA;4. Department of Physics, Virginia Tech, Blacksburg, VA, USA;1. Department of Medical Laboratory Techniques, Dijlah University College, Baghdad 10021, Iraq;2. Medical Laboratory Techniques Department, Al-Farahidi University, Baghdad, Iraq;3. Department of Chemistry, College of Science, University of Anbar, Anbar, Iraq;4. Department of Biomedical Engineering, Al-Mustaqbal University College, Babylon, Iraq;5. Laser and Optoelectronics Engineering Department, Kut University College, Kut, Wasit 52001, Iraq;6. College of Medical Technology, Islamic University, 54001 Najaf, Kufa Street, Iraq;7. Dentistry Department, Al-Rasheed University College, Iraq;8. Medical Laboratory Techniques Department, Al-Turath University College, Baghdad, Iraq;9. College of Technical Engineering, The Islamic University, Najaf, Iraq;10. Department of Chemistry, Govt. Nagarjuna PG College of Science, Raipur, 492010, India;1. Department of Physics, Ramapuram Campus, SRM University, Chennai, 600 089, India;2. SSN Research Centre, SSN College of Engineering, Chennai, 603 110, India;1. School of Chemistry and Physics, University of KwaZulu-Natal, Westville Campus, Private Bag X54001, Durban, 4000, South Africa;2. School of Electrical, Electronic and Computer Engineering, University of KwaZulu-Natal, King George V Avenue, Durban, 4014, South Africa;3. Department of Applied Chemistry, University of Johannesburg, P.O. Box 17011, Doornfontein, Johannesburg, 2028, South Africa;4. Department of Physics, University of Johannesburg, PO Box 524, Auckland Park, 2006, South Africa |
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| Abstract: | The goal of this combined experimental and computational study is to investigate the structural conformation of oligo(para-phenylenes) in the crystalline phase, in particular the planarity of this type of molecules. To this end we have performed Raman experiments on para-terphenyl and para-quaterphenyl in a pressure range from 0 to 70 kbar and at temperatures from 10 to 300 K. The positions and the relative intensities of the C–C interring stretch mode at 1280 cm−1 and the C–H in-plane bend mode at 1220 cm−1 have been tracked. We find that upon increasing temperature at ambient pressure the intensity ratio I1280/I1220 drops rapidly at temperatures that coincide with the crystallographic phase transition for the investigated materials. At ambient temperature also, this intensity ratio drops rapidly upon increasing pressure up to about 15 kbar. In the computational part, the Raman frequencies and activities of isolated 3P and 4P molecules were calculated within restricted Hartree–Fock formalism with the interring tilt angles varying from 0 to 90°. These calculations confirm that the I1280/I1220 intensity ratio can be related to the planarity of the molecules. Three-dimensional bandstructure calculations within density functional theory were applied to determine phonon frequencies and estimate Raman activities for the polymer poly(para-phenylene). These simulations show that the same conclusions hold for crystalline environment. |
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