1. Department of Chemical, Biological and Macromolecular Sciences, and Unit for Nanoscience and Technology, S. N. Bose National Centre for Basic Sciences, JD Block, Sector III, Salt Lake City, Kolkata 700 098, India, Institute of Physical and Theoretical Chemistry, University of Regensburg, D-93040 Regensburg, Germany, and Material Science Division, North−East Institute of Science and Technology, Jorhat 785006, Assam, India