Proton and¹²C NMR study of molecules related to retinal has been carried out. The characteristic differences in spectral behaviour among 7-trans and 7-cis isomers have been established which would be useful in determining the structure of new isomers and identifying components in a mixture. Through coupling constant measurements and DNMR study it is clearly established that 7-cis isomers of β-ionyl derivatives and in turn 7-cis isomers of retinyl derivatives prefer a non-planar arrangement and this non-planarity brings about resonance destabilisation.

Organic chemists have long recognized the important role that reaction media play in controlling rates, product distributions and stereochemistry. Recently, much effort has been directed towards the use of organized media to modify reactivity as compared to that in isotropic liquids. Judicious selection of a given organized system for a given application requires sufficient understanding of the properties of the organized media themselves and those of the substrate interactions therein. The multimolecular aggregation of hydrophobic solutes in water could prove to be of immense value to the organic chemist. The aggregation of simple olefinic systems in water, would enable photocycloaddition to compete efficiently with the various other modes of dacay of the short-lived excited state. Investigations of a few systems (dimerization of coumarins, stilbenes and alkylcinnamates), in our laboratory have been successful and they bring to light the significance of the hydrophobic effect. One of the most accepted manifestations of the hydrophobic interactions is probably the formation of micellar aggregates in aqueous solutions. Micelles provide a unique interface between aqueous and non-aqueous phases at which the non-polar solute can orient itself. While intermolecular orientation at micellar interfaces can provide selectivity in dimerization reactions, intramolecular orientation can be utilized to bring about selectivity in unimolecular photo-transformations. Such examples are presented.

Photochemical reactions are beginning to play an important role in the synthesis of complex organic molecules. The impetus to employ light initiated photoreactions as a synthetic tool derives from the fact that these reactions require no reagents except light. The abundance of sunlight has prompted the chemists to search for the visible light absorbing sensitizers (catalysts) to initiate the desired reactions. Our goal in this contextis to develop stable and readily available catalysts that would function under sunlight. In this manuscript, wepresent the results of our experiments with gold nanoclusters (AuNCs) as a visible light absorbing catalysts. AuNCs absorb and emit in the visible region, soluble in water and transfers electron to suitable acceptors. Employing a series of acceptors we found that excited AuNC can transfer one electron to any acceptor whose reduction potential is above −1.1 eV. In the excited state, AuNC does not accept electrons. Also, it did not serve as an energy transfer sensitizer even with molecular oxygen. We are optimistic that AuNP and AuNC could be developed into a stable and water-soluble visible light absorbing photocatalysts to perform useful photoreactions.