1. Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati, Assam 781039, India
2. Department of Chemistry, Kamrup College, Chamata, Assam 781306, India
3. Tufts University, Medford, Massachusetts 02155, United States
4. Centre for Nanotechnology, Indian Institute of Technology, Guwahati, Assam 781039, India