SYNTHESIS, SPECTRAL AND ELECTROCHEMICAL STUDIES OF MIXED β-SUBSTIUTED PORPHYRINS

Abstract

Porphyrins and their metal derivatives are of considerable importance owing to their applications in various fields such as catalysis, sensors, non-linear optics, light emitting diodes and dye sensitized solar cells (DSSCs). In living systems, porphyrins are very vital to many enzymes and biomolecules which perform significantly important physiological processes like photosynthesis, gas transport, redox reactions and so on. Porphyrins are chemically versatile molecules due to their conformational flexibility and rich thermal and chemical stabilities. They also have remarkable optical, photophysical and electrochemical redox properties which make them robust precursors for obtaining industrially, medicinally and scientifically suitable chemicals. On account of the above properties, porphyrins are the most studied molecules in chemistry and are made to undergo innumerable amount of reactions. Herein, we report the synthesis and characterization of β-functionalized porphyrins and their utilization in a variety of applications like catalysis, non-linear optics. The proposed thesis will consist of the following chapters Chapter 1 gives a general introduction to the field of porphyrins, their synthesis and different functionalization procedures undertaken to mould them into desirable target molecules. It also gives a peek into the material applications of porphyrins including dye sensitized solar cells, photodynamic therapy, catalysis and molecular sensing. Chapter 2 describes the synthesis of new β-arylaminoporphyrins MTPPNO2(NHPh), MTPPNO2(N-fusedPh) [where M = Co(II), Ni(II), Cu(II), (Zn(II)) and their characterization by various spectroscopic techniques, cyclic voltammetry (CV) and DFT studies are reported. The UV-Visible absorption spectra of synthesized arylaminoporphyrins were compared, which showed blue shifted Soret and Q bands as compared to parent porphyrins and showed broad emission spectra and fluorescence enhancement. These porphyrins exhibited cathodic shift in the first oxidation potentials as compared to H2TPP. The observed NMR and mass spectra of new porphyrins were matching with the proposed structures. ΔCβ and Δ24 values were higher which suggested more non-planarity. Moreover, these arylaminoporphyrins exhibited reduced HOMO-LUMO gap due to extended π-conjugation. Chapter 3 describes the synthesis of new benzoporphyrins MTPP(benzo)Br6 [where M = Co(II), Ni(II), Cu(II), (Zn(II)) and their characterization by various spectroscopic techniques, cyclic 2 voltammetry (CV) and DFT studies are reported. The UV-Visible absorption spectra of above new benzoporphyrins were compared, which showed red shifted Soret and Q bands as compared to parent porphyrins. The electron withdrawing nature of bromine groups decrease the electron density on porphyrin ring resulting anodic shift in their reduction and oxidation potentials as compared to parent porphyrins. The observed NMR and mass spectra of new porphyrins were matching with the proposed structures. Moreover, these hexabromo benzoporphyrins exhibited reduced HOMO-LUMO gap due to the presence of electron withdrawing β-substituents. Chapter 4 describes the study of catalytic activity of complex VOTPPNO2Br2. The synthesized complex VOTPPNO2Br2 has been used as catalyst to study the catalytic oxidative bromination of thymol (a monoterpene) in the presence of KBr, 70% aqueous HClO4 and 30% H2O2 in aqueous solution under appropriate reaction conditions