The central objective of our group is to use single and two laser based spectroscopic techniques to study molecular properties. In the area of molecular nonlinear optics our aim is to exploit second harmonic generation (SHG) as a probe for bulk physical properties of molecules in solution. Intensity of SHG is proportional to the molecular hyperpolarizability (b) which changes with a physical process as well as symmetry of the molecular specie in solution. Using this principle we measure second harmonic light scattering intensity and relate it to the property which is responsible for causing the change. Chemical application of second harmonic light scattering is a very active area in our group. Polarization resolved second harmonic scattering has been used to probe geometry of weak (1-10 kcal/mol) molecular complexes in solution for which no technique other than small angle neutron scattering is available to probe the geometry in solution. The origin of large second harmonic generation in noble metal nanoparticles of 5-100 nm diameter is another area of investigation where we probe the origin of nonlinearity in these systems.

In the area of atmospheric and environmental chemistry our research efforts are currently directed to detection of polycyclic aromatic hydrocarbons and their photolysis products at low concentrations by time resolved FTIR spectroscopy. A series of dimethyl naphthalenes and phenanthrenes have been studied in the gas phase. We are currently trying to identify photochemical products generated from them upon ultraviolet irradiation by ir spectroscopy, which will help us understand the type and identity of radicals that are formed in the upper atmosphere from PAHs by solar radiation.

In the area of biophysical chemistry we are studying molecular association/interaction by surface plasmon resonance spectroscopy. Binding of small molecules (lipids, carbohydrates, etc.) to proteins, polypeptides, and DNAs are areas of interest.

Representative Publications

Chandra . M, Puspendu K. Das, Size dependence and dispersion behavior of the first hyperpolarizability of copper nanoparticles , Chem.Phys.Lett., B 476, 62-64 (2009).

Ghosh .S, Ranjini A.S, Pandey .R and Puspendu K. Das,First hyperpolarizability of bacteriorhodopsin, retinal and related molecules revisited, Chem.Phys.Lett., C 474,307-310 (2009).

Chandra . M, Puspendu K. Das,"Small-particle limit" in the second harmonic generation from noble metal nanoparticles, Chem.Phys., B 358, 203-208 (2009)

Prasanta Das, E. Arunan, Puspendu K. Das, Infrared spectra of dimethyl naphthalenes in the gas phase, Vibrational Spectroscopy, 47, 1-9,(2008).

Abdul Wahab, Mily Bhattacharyya, Sampa Ghosh, A.G.Samuelson, and Puspendu K. Das, Quadratic nonlinearity of one-and two-electron oxidized metalloporphyrins and its switching in solution, J. Phys. Chem. B 112, 2842-2847 (2008)