1. School of Materials Science and Engineering; Nanyang Technological University; 50 Nanyang Avenue Singapore 639798 Singapore
2. Institute of Functional Nano and Soft Materials; Soochow University; Suzhou 215123 P. R. China
3. School of Chemical and Biomedical Engineering; Nanyang Technological University; 62 Nanyang Drive Singapore 637459 Singapore
4. Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences; Nanyang Technological University; Singapore 637371 Singapore
5. Singapore-Jiangsu Joint Research Center for Organic/Bio-Electronics and Information Displays and Institute of Advanced Materials (IAM); Nanjing Tech University; Nanjing 211816 P. R. China