1. Working Group Optical Spectroscopy, Federal Institute for Materials Research and Testing (BAM), Richard-Willstaetter-Strasse 11, D-12489 Berlin, Germany, National Nanotechnology Laboratory, Lecce University, Distretto Tecnologico, Via Arnesano Km 5, 73100 Lecce, Italy, Institute of Organic Chemistry, National Academy of Sciences of the Ukraine, Murmanskaya 5, 235660 Kiev-94, Ukraine, and Institut für Chemie, Humboldt Universität zu Berlin, Brook-Taylor-Strasse 2, D-12489 Berlin, Germany