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Synthesis of porphyrin-chromophore conjugates
thesisposted on 2022-03-28, 01:46 authored by Rajesh Kisan Raut
Several porphyrin-chromophore conjugate systems have been synthesized for future energy /electron transfer studies. This thesis discusses the systematic approach used in the synthesis of three chromophores (boranils, α-cyanostilbenes and 1,3-diketone boron complexes) linked toporphyrins via either covalent bonds or supramolecular interactions. The UV-visible absorption and fluorescence emission spectra, together with the relative quantum yields of the conjugates were examined in order to establish any structure-property relationships that may exist. Three different porphyrin frameworks were prepared for use in the syntheses of covalently linked porphyrin-chromophore conjugates. The first of these was a porphyrin ring mono-functionalised on one of the meso-aryl rings. The second framework had a functionalised phenyl ring connected to animidazole ring that was fused to the porphyrin at adjacent β-pyrrolic carbons. The third framework was functionalised on a quinoxaline ring that was fused to the porphyrin at adjacent β-pyrroliccarbons. Porphyrin-boranil conjugates were synthesized by condensation of amine-functionalised porphyrins with salicylaldehyde or 2-hydroxynaphthaldehyde to afford the corresponding 2-hydroxyaryl imines (also known as anils), followed by reaction with boron trifluoride to afford the boron complexes. Aldehyde-functionalised porphyrins were condensed with the reactive methylene group present in 4-nitrophenylacetonitrile, 4-bromophenylacetonitrile and benzyl cyanide to afford α-cyanostilbeneporphyrin conjugates. Two series of 1,3-diketone boron complexes were synthesized for future studies involving a supramolecular approach to porphyrin-chromophore conjugate assembly. One series contains a 4-hydroxyphenyl unit (for coordination to tin(IV) porphyrins) and the second series contains a 4-pyridyl unit (for coordination to zinc(II) porphyrins). A titration experiment (monitored with UV visible spectroscopy) was conducted with one of the 4-pyridyl appended 1,3-diketone boron complexes and a zinc(II) porphyrin. The results indicated that a complex was formed. The 4-pyridyl appended 1,3-diketone boron complexes were converted to their N-methylpyridinium salts, and a computational study was also conducted to calculate their non-linear optical properties.