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Hindrance of the rotational relaxation in the excited singlet state of biphenyl and para-terphenyl in cooled solutions by methyl substituents
Affiliation:1. Affiliated Hospital of Beihua University, Jilin 132011, PR China;2. School of Pharmacy, Jiangsu University, Zhenjiang 212013, PR China;1. Key Laboratory of Applied Surface and Colloid Chemistry (MOE), School of Materials Science and Engineering, Shaanxi Normal University, Xi''an 710062, PR China;2. School of Chemistry & Chemical Technology, Shanghai Jiaotong University, Shanghai 200240, PR China;3. Xi''an Modern Chemistry Research Institute, Xi''an 710065, PR China;1. Université de Carthage, Laboratoire de Chimie des Matériaux, Faculté des Sciences de Bizerte, 7021 Jarzouna, Tunisia;2. CFisUC, Department of Physics, University of Coimbra, P-3004-516 Coimbra, Portugal;3. Laboratoire de Chimie Organométallique de Surface (LCOMS), Ecole Supérieure de Chimie Physique Electronique, 69626 Villeurbanne Cedex, France;1. Biomaterials Laboratory, Department of Biotechnology, Bhupat and Jyothi Mehta School of Biosciences, Indian Institute of Technology Madras, Chennai 600 036, Tamil Nadu, India;2. Chimiothérapie Antiparasitaire, UMR 8076 CNRS BioCIS, Faculté de Pharmacie, Université Paris-Sud, Rue Jean-Baptiste Clément, F-92296, Chatenay-Malabry, France
Abstract:The measured fluorescence spectra of biphenyl (BP) and para-terphenyl (PTP) in solution reveal with decreasing temperature first an increasing structure and a slight red shift and below the glass transition a loss in structure and a strong blue shift. The effect is discussed using a torsional potential scheme in agreement with QCFF/PI calculations. Comparison of the experimental blue shifts with the results of CNDOS calculations suggest an incomplete hindrance of the relaxation process of the unsubstituted molecules. A nearly perfect hindrance could be detected for the tetra-methyl substituted BP and PTP molecules.
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