Development of new Schiff based derivatives as fluorescent chemosensors, NIR emitters and catalysts (PhD)

Abstract

Schiff base molecules are gaining attention in recent years because of their ability to form compounds that are relevant to diverse areas. Schiff bases possess excellent characteristics including structural similarities with biological substances, relatively simple synthetic procedures and synthetic flexibility that allow structural design as per the requirements. Schiff bases often act as excellent chelating agents and form a variety of complexes with transition metal ions. Because of these unique properties, Schiff bases are widely used in the development of molecular sensors, catalysts, molecular switches, optical data storage devices and bio-mimetic compounds. However, there are still many areas where Schiff bases have not yet been fully explored. For example, the development of chemodosimeters for the selective detection of cations, especially in presence of interfering cations, is still a challenging task. The selective detection of biological macro anions like adenosine triphosphate (ATP), cytidine triphosphate (CTP) etc. is also a difficult task because of the larger size of such anions. Similarly, studies on Schiff base derivatives as solid state near infra-red (NIR) emitters and multifunctional materials are scarce in the literature. In the present thesis, we have tried to address some of the above issues by developing suitable Schiff base molecular systems. We have developed a pyrene based Schiff base chemodosimeter for the selective detection of Nb5+ ions in mixed aqueous media in presence of interfering cations and a series of hydroxyl-rich Schiff base receptors for the selective detection of macro anions like ATP and CTP in 100% aqueous environments. In continuation, we have developed a series of multifunctional zinc complexes for photo luminescent and catalytic applications using hydroxyl-rich compartmental Schiff base ligands. The photoluminescence properties of these zinc complexes were explored in solid state, solutions and in polymer matrix, which revealed their good potential as tunable solid state emitters. Some of these complexes acted as efficient catalysts for the transesterification of simple esters as well as vegetable oils revealing their potential in biodiesel generation. Finally, we have developed an extended piconjugated compartmental Schiff base molecule built on 2, 6-diformyl phenol derivatives that acted as deep red to NIR solid state emitter based on excited state intramolecular proton transfer (ESIPT) mechanism.