1. The State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210093, P. R. China, Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, Nanyang Avenue, Singapore 639798, Solid State Microstruct Lab, Department of Physics, Nanjing University, Nanjing 210093, P. R. China, and Chemistry Department, Kent State University, Kent, Ohio 44240