1. Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of Ministry of Education College of Chemistry and Materials Science Northwest University Xi'an Shaanxi 710127 P. R. China
2. Division of Chemistry and Biological Chemistry Nanyang Technological University 21 Nanyang Link 637371 Singapore Singapore
3. Science and Mathematics Cluster Singapore University of Technology and Design 8 Somapah Road Singapore 487372 Singapore