1. Center for Polymers and Organic Solids, University of California at Santa Barbara; Santa Barbara CA 93106-5090 USA
2. School of Integrative Engineering, Chung-Ang University; 221 Heukseok-dong Dongjak-gu Seoul 156-756 Republic of Korea
3. Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology; Guangzhou 510640 China