1. Dipartimento di Chimica “G. Ciamician”, Università di Bologna, via Selmi 2, 40126 Bologna, Italy, Department of Chemistry, University of Newcastle, Newcastle upon Tyne, NE1 7RU, U.K., Ecole de Chimie, Polymères, Matériaux (ECPM), Laboratoire de Chimie, d'Electronique et de Photonique Moléculaires, associé au CNRS ESA-7008, 25 rue Becquerel, 67087 Strasbourg Cedex 02, France, and Department of Chemistry, University of Houston, Houston, Texas 77204-5641