1. Department of Chemistry, Jadavpur University, Kolkata 700 032, India, Leiden Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands, CNR-INFM SLACS and Dipartimento di Fisica, Università di Cagliari, S.P. Monserrato-Sestu Km 0.700, I-09042 Monserrato, Italy, and Department of Chemistry, National Changhua University of Education, Changhua, Taiwan 50058