1. School of Chemistry and Biochemistry, Center for Organic Photonics, Georgia Institute of Technology, Atlanta, Georgia 30332-0400, United States
2. CREOL, The College of Optics & Photonics, University of Central Florida, Orlando, Florida 32816-2700, United States
3. Department of Materials Science and Engineering, College of Engineering, Peking University, Beijing 100871, People′s Republic of China