1. Institute of Biophysics, Academy of Sciences of the Czech Republic, Královopolská 135, CZ-61265 Brno, Czech Republic, Photobiology Unit, Department of Dermatology, University of Dundee Ninewells Hospital and Medical School, Dundee DD1 9SY, UK, and School of Chemistry, University of Edinburgh, West Mains Road, Edinburgh EH9 3JJ, UK