[1] Tsinghua Univ, Dept Chem, Beijing, Peoples R China
[2] Tsinghua Univ, Lab Organ Optoelect & Mol Engn, Minist Educ, Beijing, Peoples R China
[3] Arizona State Univ, Dept Phys, Tempe, AZ 85287 USA
[4] Chinese Acad Sci, Dalian Inst Chem Phys, Dalian, Peoples R China