1. Department of Chemistry, Institute of Polymer Science and Engineering, Department of Electrical Engineering and Graduate Institute of Photonics and Optoelectronics, National Taiwan University, 1 Roosevelt Road Section 4, Taipei 106, Taiwan, R.O.C., and Department of Photonics Engineering, Yuan Ze University, 135 Yuan-Tung Road, Chung-Li 32003, Taiwan, R.O.C.