1. Clausthal University of Technology Institute of Organic Chemistry Leibnizstrasse 6 38678 Clausthal-Zellerfeld Germany
2. Fraunhofer Heinrich Hertz Institute HHI Fiber Optical Sensor Systems Am Stollen 19H 38640 Goslar Germany
3. Department of Chemistry University of Helsinki P. O. Box 55 A.I. Virtasen aukio 1 00014 Helsinki Finland