1. Department of Chemistry, Hong Kong Baptist University Waterloo Road, Kowloon Tong, Hong Kong, P. R. China, Fax: (internat.) + 852‐3411‐5862
2. Department of Applied Chemistry, National Huaqiao University Quanzhou 362011, P. R. China
3. Department of Physics, Hong Kong Baptist University Waterloo Road, Kowloon Tong, Hong Kong, P. R. China