[1] Univ Munster, Inst Phys, D-48149 Munster, Germany
[2] Ctr NanoTechnol CeNTech, D-48149 Munster, Germany
[3] Univ Wurzburg, Inst Organ Chem, D-97074 Wurzburg, Germany
[4] Univ Wurzburg, Ctr Nanosyst Chem, D-97074 Wurzburg, Germany
[5] Delft Univ Technol, Dept Chem Engn, Optoelect Mat Sect, NL-2628 BL Delft, Netherlands
[6] Free Univ Berlin, Inst Chem & Biochem, Forschungszentrum Elektronenmikroskopie, D-14195 Berlin, Germany
[7] Max Planck Inst Bioanorgan Chem, D-45470 Mulheim, Germany