1. Key Laboratory of Functional Polymer Materials; Collaborative Innovation Center of Chemical Science and Engineering (Tianjin); Center for Nanoscale Science and Technology; Institute of Polymer Chemistry; College of Chemistry; Nankai University; Tianjin 300071 China
2. Materials Science Division; Lawrence Berkeley National Lab; Berkeley 94720 USA
3. Wuhan National Laboratory for Optoelectronics; School of Optical and Electronic Information; Huazhong University of Science and Technology; Wuhan 430074 Hubei China
4. Department of Polymer Science and Engineering; University of Massachusetts; Amherst 01003 MA USA