1. CAS Key Laboratory of Engineering Plastics, CAS Research/Education Center for Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
2. University of Chinese Academy of Sciences, Beijing 100049, China
3. Spallation Neutron Source Science Centre, Dongguan 523803, China
4. Optoelectronics Group, Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, United Kingdom
5. Laboratoire Léon Brillouin, UMR 12 CEA-CNRS-UPSay,
CEA Saclay, 91191 Gif-sur-Yvette, France