[1] Univ Erlangen Nurnberg, D-91058 Erlangen, Germany
[2] Bayer Zentrum Angew Energieforsch ZAE Bayern, D-91058 Erlangen, Germany
[3] Univ London Imperial Coll Sci Technol & Med, Ctr Plast Elect, London SW7 2AZ, England
[4] Univ London Imperial Coll Sci Technol & Med, Dept Chem, London SW7 2AZ, England
[5] Univ London Imperial Coll Sci Technol & Med, Dept Phys, London SW7 2AZ, England