Abstract:
Porphyrins and its derivatives have been well studied for their potential application in biology, medicine and catalysis. Porphyrin derivatives have also been used as artificial light harvesting systems to capture and store energy. Porphyrins ae important for its rich photophysical properties and coordination chemistry. Inspired by these interesting properties of porphyrin derivatives, venture has been made to synthesize and characterize novel difuctionalized porphyrins, Functionalized N-confused porphyrins (NCPs) and metal dipyrrinato complexes have drawn attention in recent times due to various applications. All the synthesized molecules have been thoroughly studied for understanding the photophysical and electrochemical, more specifically, redox properties. The present thesis consists of three main chapters viz. synthesis and studies of di- and mono- functionalized NCPs. Energy donor-acceptor type trans-A2B2 type porphyrins and triphenylamine dipyrrinato metal complexes. Along with these, an initial chapter consisting of the synthesis of common precursors which has been utilized in various projects has been drafted.
The second chapter accounts for the synthesis, characterization photophysical and electrochemical studies of functionalized NCPs. Even though, there are several reports of the synthesis of tetra meso substituted NCPs, only few studies have been reported where synthesis of asymmetric of functionalized NCPs have been carried out. Moreover, unlike porphyrins, NCPs are less explored as light harvesting systems and in energy donor-acceptor based conjugates. Therefore an attempt has been made to synthesize di- and mono-functionalized NCPs which can be utilized in the synthesis of energy donor-acceptor type dyads or triads. Synthesis of these functionalized NCPs are challenging and therefore our first objective was to synthesize the molecules with modified synthetic strategy which is versatile to produce functional NCPs in better yield. Finally, a detailed study has been made to synthesize donor-NCP-donor (D-π-A) type triads employing the difunctionalized NCPs.
The third chapter consists of the synthesis, characterization and studies of energy donor- acceptor (D-A) type trans- A2B2 type porphyrins where sterically bulky and electron rich meso substituents have been chosen as donor. There are several reports of the synthesis and studies of trans- A2B2 type porphyrind, however, such bulky meso substituent based donor-acceptor system are novel of its kind. These molecules have been studies thoroughly by UV-Vis, steady state and time resolved fluorescence spectroscopy and cyclic voltammetry, Zn(II) and Pd(II) metal complexes have also been synthesized and studies especially for photophysical studies. The energy-transfer efficiencies of the different donors viz. N-butylcarbazole. N-butylphenothoiazine and triphenylamine have also been studied qualitatively and quantitatively. The final aim of this work is to employ these molecules for bioimaging studies which require few more synthetic steps and is beyond the scope of the present work.
The fourth chapter presents the synthesis, characterization, photophysical and electrochemical studies of the triphenylamine dipyrrinato metal complexes. Dipyrrins structurally resemble to be the half part of porphyrins. However, their photophysical and electrochemical properties are very much different compared to the porphyrins. In the last decade metal dipyrrinato complexes have been wells studied and much of its potential applications in luminescent materials, sensing, sensitized solar cells and metal organic frameworks have been revealed. In the present context, our interest lied in the understanding of the role of different metals on the same dipyrrinato ligand and studying the photophysical and electrochemical properties of the complexes. A set of homoleptic, heteroleptic and bimetallic type metal complexes have been synthesized and studied. The metals have been chosen on the ground of their coordination [Ni(II), Co(II)] and photophysical [Zn(II), Pd(II), In(III)] properties.
Finally, the experimental results have been summarized and conclusions have been drawn which is certainly a juxtaposition of objectives accomplished and future scopes.