Viswanathan’s research interests have spanned the areas of molecular conformations and weak non-covalent interactions, particularly the hydrogen bonding interactions, which pervades through all of chemistry, physics and biology. Matrix isolation spectroscopy, a method where isolated molecules are trapped in a cryogenic solid inert gas matrix, was the experimental technique used for these studies. The trapped molecules were then probed using infrared spectroscopy. The experimental results were corroborated using ab initio quantum chemical computations. These studies resulted in a detailed understanding of the structure and energetics of hydrogen bonded complexes. Recent studies of his group on conformations of amino acids, an important class of biomolecules, revealed a very interesting and restrictive structural preference that these molecules adopt, with respect to their backbone, comprising of the COOH and NH2 moieties. In addition, his research group has also been interested in lanthanide fluorescence, specifically to develop methods for the enhancement of fluorescence in an attempt to develop sensitive analytical methods. Enhancement of fluorescence by a factor of over 10,000 was achieved by choosing appropriate ligands as energy transfer agents. He has also been interested in the use of mass spectroscopy for analytical applications.
He subscribes to the adage that research and teaching must coexist since there is a definite synergy between the two. At IISER, Mohali, he enjoyed teaching courses at all levels – from introductory to the advanced, with each level presenting its own challenges. He has also coordinated a number of summer science programmes for school and university students. It is also his conviction that courses in universities must not be restricted to just learning; there must be a small component where students get to teach during their final years.

While it is important for students to study well, he believes it is also important for them not just to study well, but have multiple interests apart from their major area of study, for a wholesome growth. He has practiced this philosophy himself. Apart from teaching and research, he is interested in sports and music. He is an avid player of cricket, tennis and table-tennis and enjoys music.