1. Instituto de Fisica de Sao Carlos, Universidade de Sao Paulo, C.P. 369, 13560-970, Sao Carlos, SP, Brazil, Laboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands, and Faculty of Chemistry, Jagiellonian University, 30-060 Kraków, Poland