1. Department of Physics, Hamamatsu University School of Medicine, 3600 Handa-cho, Hamamatsu 431-3192, Japan, Department Organic Materials, National Institute of Materials and Chemical Research, 1-1 Higashi, Tsukuba 305-8565, Japan, and Department of Organic and Polymeric Materials, Tokyo Institute of Technology, 2-12-1, Ookayama, Meguro-ku, Tokyo 152-0033, Japan