We have comprehensively established the solid-state photochemistry of o-alkylaromatic aldehydes and Norrish Type II photochemistry of disubstituted butyrophenones and the associated diastereomer-differentiating photochemistry. It is shown through nanosecond time-resolved transient absorption spectroscopy that the diastereomer-differentiating photochemistry that is observed in the product formation emanates at the triplet state and that the diastereomeric 1,4-biradicals of the precursors of the products likewise collapse with different rates. At the same time, we are exploring fundamental concepts underlying the phenomenon of photochromism in a class of compounds called chromenes. We have shown that simple arylation of diarylchromenes can lead to dramatic modification in the photochromic properties through changes in the absorption properties of o-quinonoid intermediates. Similarly, a variety of factors such as toroidal conjugation, through space interactions, phane effects and helicity are shown to influence the phenomenon of photochromism based on diarylchromenes
Supramolecular Chemistry: Crystal Engineering
In the realm of supramolecular chemistry, we have shown that sterically-hindered carboxylic acids exhibit unique synthons. With a rational design of molecular modules based on 4-fold functionalized bimesityls and pyrenes, a rich inclusion chemistry and control of molecular self-assembly based on hydrogen and coordinate covalent bonds has been developed. Our current interest focuses on guest-induced structural mimicry giving rise to multicomponent crystals and self-assembly based on charge-assisted hydrogen bonds.
Development of Porous Metal-Organic Materials
We have also been interested in the development of porous metal-organic materials based on a de novo design of building blocks that inherently feature concave shapes. Assembly of D2d-symmetric tetrapyridyl ligands in presence of metal ions has been shown to give rise to a variety of porous coordination polymers. The porous CPs containing uncoordinated pyridyl rings are shown to be efficient heterogeneous nucleophilic catalysts for acetylation of a number of phenols. Further, we have shown the site-selective metal-node metathesis in a Zn-MOF constructed from tritopic triacid leading to novel bimetallic MOFs, which are inaccessible by conventional approaches. Recently, we have shown the selective capture of CO2 gas by a Cd-MOF with nitrogen-rich channels based on triazole-functionalized tetraacid linker. Funtional utility of a paramagnetic Mn-MOF has been shown by applications in solvent polarity indicator and sensing of explosive nitroaromatics.
Development of Organic Light Emitting Materials
By exploiting the concepts of supramolecular chemistry, a novel class of amorphous materials are being developed; the functional utility of some systems has been demonstrated through OLED device fabrications with high quantum efficiencies. The design of such amorphous materials are mainly based on twisted bimesitylene and V-shaped Troger's base cores. Our current interest is focused on the development of novel host materials for Phosphorescent OLEDs.
Mechanistic Organic Chemistry
We have been endeavoring to apply the riches of supramolecular chemistry to develop novel oxidation chemistry based on IBX-a reagent that has surged into lot of prominence in the contemporary oxidation chemistry. We have also been interested in the exploitation of hydrogen bonding in stereoselective organocatalysis. In fact, we have develpoed a variety of H-bonding organocatalyst for the mechanistic studies of Biginelli Reaction, Michael addition reaction, enantioselective aldol reactions, etc.