1. Department of Materials Science and Engineering University of Washington Seattle WA 98195‐2120 USA
2. Center for Molecular Systems and Organic Devices (CMSOD) Key Laboratory for Organic Electronics and Information Displays and Institute of Advanced Materials (IAM) Nanjing University of Posts and Telecommunications Nanjing 210023 China
3. Department of Chemistry University of Washington Seattle WA 98195 USA
4. Department of Chemistry City University of Hong Kong Kowloon Hong Kong China
5. Department of Materials Science & Engineering City University of Hong Kong Kowloon Hong Kong China