Coulombic screening in polydiacetylene crystals |
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| Affiliation: | 1. Institute of Chemistry, Far-Eastern Branch of the Russian Academy of Sciences, 159, Prosp. 100-letiya Vladivostoka, Vladivostok 690022, Russia;2. A.V. Zhirmunsky National Scientific Center of Marine Biology, Far Eastern Branch, Russian Academy of Sciences, 17 Palchevskogo Street, Vladivostok 690041, Russia;1. Department of Chemistry, Sapienza University of Rome, P.le A. Moro 5, 00185 Rome, Italy;2. Department of Biochemical Sciences, Sapienza University of Rome, P.le Aldo Moro 5, 00185 Rome, Italy;1. Department of Chemistry, Sapienza University of Rome, P.le Aldo Moro 5, 00185 Rome, Italy;2. Department of Haematology, Oncology and Molecular Medicine, Istituto Superiore di Sanità, Rome, Italy;3. ENEA-UTTAMB, C.R. Casaccia, Via Anguillarese 301, 00100 Rome, Italy;1. Department of Chemistry, Sapienza University of Rome, Rome, Italy;2. Department of Chemistry, Faculty of Science, Helwan University, Cairo, Egypt;1. State Key Laboratory of Fine Chemicals, Institute of Artificial Photosynthesis, Dalian University of Technology, Dalian, 116024, People’s Republic of China;2. Division of Materials Science, School of Materials Science and Engineering, Nanyang Technological University, 639798, Singapore;3. Department of Chemistry, School of Engineering Sciences in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, Stockholm, 10044, Sweden |
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| Abstract: | The strong colour of polydiacetylene polymer crystals is due to the backbone exciton. The energy of the exciton is strongly affected by Coulombic interactions with the surrounding crystalline environment. X-ray diffraction and optical absorption measurements of the blue phase polymer crystals of 4BCMU show that a change in the energy of the polydiacetylene backbone exciton can be related to a change in the inter-backbone spacing within the crystals. Over the range of inter-backbone spacings measured, this variation is in very good agreement with Coulombic screening theory. It is calculated from these results that inter-backbone Coulombic screening lowers the value of the exciton energy in the blue phase polymer crystals of 4BCMU by −0.362eV, which is 15.4% of the total exciton energy. Coulombic screening is shown to have an important effect on the optical absorption properties of other polydiacetylene derivatives. Calculations and resonant Raman spectroscopy measurements show that a combination of a low level of Coulombic screening and strain in the crystal lattice accounts for the red colour of the polymer crystals of PTS-12 and TCDU. |
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