1. College of Chemistry and Molecular Sciences, Wuhan University, 430072 Wuhan, P. R. China, Fax: +86‐27‐68754067
2. Department of Chemistry, Hong Kong Baptist University, Waterloo Road, Hong Kong, P. R. China, Fax: +852‐3411‐7348
3. Centre for Advanced Luminescence Materials, Hong Kong Baptist University, Waterloo Road, Hong Kong, P. R. China
4. Department of Physics, Hong Kong Baptist University, Waterloo Road, Hong Kong, P. R. China
5. Center for Molecular Science, Institute of Chemistry, Chinese Academy of Sciences, 10080 Beijing, P. R. China