Ghosh has contributed to many areas of porphyrin-related research. His early contributions include the use of X-ray photoelectron spectroscopy (XPS) to study short-strong hydrogen bonds in porphyrin-type molecules and also some of the first large-scale ab initio calculations applied to porphyrins and other bioinorganic systems. He has had an abiding interest in the phenomenon of ligand noninnocence and has contributed substantially to studying the phenomenon in transition metal nitrosyl and corrole derivatives. In recent years, he has developed the field of heavy element corrole derivatives, which are unusual size-mismatched metal-ligand assemblies that incorporate a large 4d or 5d transition metal ion within the sterically compressed central cavity of a corrole. In this area he has reported some of the first examples of Tc, rhenium, osmium, platinum, and gold corroles. Despite their size-mismatched character, many of these complexes have proved  rugged and found applications as near-IR phosphorescent photosensitizers in oxygen sensing and photodynamic therapy as well as in dye-sensitized solar cells. Ghosh's work on 4d and 5d elements has also led to new insights into metal-metal bonds (quadruple bonds) and relativistic effects.
In 2017, Ghosh and coworkers reported the first example of a stable cis tautomer of a free-base porphyrin in the form of a termolecular hydrogen-bonded complex. Subsequently, they found additional examples of porphyrin cis tautomers, proving that they can be reliably obtained from virtually any strongly saddled porphyrin co-crystallized with two molecules of a hydrogen donor (typically water or an alcohol).