1. Department of Chemistry; National University of Singapore; 3 Science Drive 3 117543 Singapore Singapore
2. Department of Physics; National University of Singapore; 2 Science Drive 3 117542 Singapore Singapore
3. BNLMS; College of Chemistry and Molecular Engineering; Peking University; Beijing 100871 P. R. China
4. Science Division; Yale-NUS College; 16 College Ave. West 138529 Singapore Singapore