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Author: search.filters.author.Grover, NitikaSubject: search.filters.subject.Density Functional Theory (DFT)

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    β-substituted donor-acceptor porphyrins: Synthesis, energy transfer and electrochemical redox properties
    (Elsevier, 2019-02) Grover, Nitika
    β-substituted D-A porphyrins have been synthesized via Suzuki coupling reaction and characterized by various spectroscopic techniques. Two different electron donating moieties i.e. 4-(carbazol-9-ylmethyl)phenyl and 4-(phenothiazin-10-ylmethyl)phenyl were appended at antipodal β-positions of electron acceptor moiety i.e. H2TPP(NO2). The absorption and emission data suggested an interaction between the donor and acceptor subunits. An efficient energy transfer (78–88%) from β-substituents to macrocyclic core was supported by steady state and time resolved fluorescence measurements. Density functional theory (DFT) and time dependent-density functional theory (TD-DFT) studies support the existence of intramolecular energy and charge transfer from β-donor substituents to macrocyclic core in the dyads. Förster energy transfer studies revealed that the nature of energy transfer was mainly through bond (χTB = 0.71–0.83) in nature. The basic nature of porphyrin core was elucidated by very high protonation constants (logβ2 = 9.59–10.45). The first and second oxidation potentials of 1, 2 and their Zn(II) complexes (1a and 2a) were cathodically shifted as compared to H2TPP(NO2) and ZnTPP(NO2) due to effective electron donating nature of β-substituents which led to lower HOMO-LUMO gap.
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    Incremental Introduction of Organocatalytic Activity into Conformationally Engineered Porphyrins
    (Wiley, 2019-01) Grover, Nitika
    To study the correlation of macrocycle nonplanarity and catalytic activity of free base porphyrins in detail, a series of six tetraphenylporphyrins with graded degree of β-ethyl substitution (“H2EtxTPPs” 1–6; x = 0, 2, 4, 6, 8) was applied in organocatalyzed reactions. The macrocycles display incrementally increasing nonplanarity due to repulsive peri-interactions. This creates an out-of-plane vector and better accessibility of the core amine and imine groups as the number of alkyl substituents increases. Following such a molecular engineering approach, the inner core system could be used to activate small molecules as a result of significant saddle distortion. The potential organocatalyst “H2EtxTPPs” were used in benchmark sulfa-Michael reactions and we found a distinct relationship between nonplanarity and conversion. These observations were attributed to the combined effect of enhanced basicity and increased H-bonding potential that could facilitate bifunctional organocatalysis. Ultimately, density functional theory (DFT) calculations were performed on 1–6 to monitor some electronic properties of the title compounds.