Title: Synthesis and spectroscopic properties of dendritic porphyrins
Other Titles: Synthese en spectroscopische eigenschappen van dendritische porfyrinen
Authors: Nguyen, Tran Nguyen
Issue Date: 19-Aug-2014
Abstract: Porphyrins and their metallo derivatives have been synthesized because of various applications in catalytic chemistry, photodynamic therapy, electronic devices, mimicking enzymes and solar energy conversion. The development of dendritic porphyrin chemistry has been prompted by the biological activities of natural porphyrin derivatives including hemes in hemoglobin, myoglobin and chlorophyll in plants. In recent years, more and more porphyrin core dendrimers have been reported for applications in biomedicine and industry. Dendritic encapsulation brings to the core molecule new features and allows to enhance/suppress several of their own properties. Therefore, the choice of the dendron type is substantial for the structure and functional properties of the designed dendrimer molecules. Carbazole derivatives and boron-dipyrromethene dyes could be considered as promising dendron molecules to prepare new functional dendrimers with a porphyrin core.Carbazole derivatives were linked to the porphyrin core via copper(I)-catalyzed azide-alkyne cycloaddition. Carbazole-based terminal alkynes were synthesized using Ullmann coupling. In order to avoid the formation of Cu(II)-porphyrin core dendrimers, zinc was inserted into the porphyrin macrocycle before the click reaction was conducted. There were six dendrimers of the first and second generation synthesized in which the largest dendrimer contains 16 carbazole units at the outer periphery. Porphyrin core dendrimers with O-linked carbazole dendrons were also obtained via the condensation between carbazole-based benzaldehydes and 5-mesityldipyrromethane or pyrrole. The aldehyde precursors were synthesized using the nucleophilic substitution reaction between carbazole-based phenols and substituted benzaldehydes. The structure of the target dendrimers was confirmed by NMR, mass spectrometry and FTIR. Photophysical properties of the porphyrin core dendrimers with 1,2,3-triazole- or O-linked carbazole dendrons were also investigated.The binding ability of the porphyrin core dendrimers toward small heterocyclic substrates was measured using spectrophotometric and 1H NMR titration methods. The largest dendrimers of the first and the second generation which were made via click reaction showed the highest binding constants of the 1:1 complexes with the monodentate ligands in toluene. However, these two dendrimers did not form 2:1 complexes with the bidentate ligand DABCO in toluene.Porphyrins and BODIPYs possess complementary photophysical properties in the visible region and BODIPYs could be promising antenna groups to improve the light-harvesting potential of porphyrins. The conjugated system of a boron-dipyrromethene dye was extended at the 3-position using a tandem reversible Michael addition/VNS (Vicarious nucleophilic substitution) of hydrogen with nitrostyrene to yield the 3-styrylated product. This latter dye was then combined with a Zn(II)-porphyrin by Cu(I)-catalyzed click reaction to afford a conjugate consisting of a porphyrin and a boron-dipyrrin dye. The absorption spectrum of this conjugate contains bands belonging to both the porphyrin and the BODIPY moieties. The fluorescence of the conjugate was found to originate from the BODIPY moiety independently of the excitation wavelength. In addition, there were three more conjugates in which each of them contains one BODIPY and two porphyrin moieties synthesized by click chemistry. A boron-dipyrromethene with two azide groups in an aryl ring located at the meso position was linked with two Zn(II)-porphyrins to obtain a conjugate which possesses an efficient energy transfer from BODIPY to porphyrin. The other conjugates in which the BODIPY part was lengthened at the 3,5-positions or at the 2,6-positions displayed an overlap between the Q bands and the boron complex S0→S1 transition in the absorption spectrum.
Publication status: published
KU Leuven publication type: TH
Appears in Collections:Molecular Design and Synthesis

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