1. Department of Chemistry, Aliah University, New Town, Kolkata 700 156, India
2. Department of Physics, Jadavpur University, Jadavpur, Kolkata 700 032, India
3. Department of Chemistry, Jadavpur University, Jadavpur, Kolkata 700 032, India
4. Department of Chemistry, R. K. M. Residential College, Narendrapur, Kolkata 700 103, India