Synthesis And Properties Of Hyperbranched Porphyrin Arrays And Linear Porphyrin Polymers Encapsulated In Dendrimers

Artificial photosynthesis is a highly important subject, not only from the basic science point of view, but also for its possible contribution to sustainable utilization of energy resources. Biological photosynthetic systems consist mainly of two functional moieties, one of which is a light-absorbing antenna to efficiently capture visible photons. Porphyrins and their derivatives play an important role of light-absorbing antennas. Multiporphyrin arrays have a great number of chromophore units to realize a large absorption cross section. Since the chromophore units cooperate with one another, the antenna can capture photons more efficiently. Recently, several research groups have prepared conjugated multiporphyrin arrays, in which the porphyrin π-systems merge to form giant supermolecular chromophores with extraordinary electrooptical and nonlinear optical properties. Therefore,multiporphyrins are promising candidates as scaffold for molecular design of light-harvesting antenna and for potential applications in photoeletronic materials and biological mimics. In this thesis, we prepared and characterized two kinds of multiporphyrin arrays: hyperbranched multiporphyrin arrays and linear multiporphyrin arrays encapsulated in dendrimers. The three-dimensional dendritic and hyperbranched multiporphyrin arrays have attracted more and more scientific attention these days. The there-dimensional structure can strongly prevent the intermolecular aggregation. Monodisperse, well-defined, and highly branched dendrimers are prepared by time-consuming multistep reactions, whereas irregularly branched and polydisperse hyperbranched polymers possessing architectures and properties similar to those of dendritic ones are prepared by one-pot reactions, which makes the large-scale synthesis possible at a reasonable cost. However, an efficient synthesis of multiporphyrin arrays remains a challenge. Until now, only low-generation dendritic porphyrins have been prepared. Here we describe the preparation of a novel kind of hyperbranched porphyrin arrays by one-pot Suzuki polycondensations (SPC) of AB3 monomers or AB3+C4 monomers. A set of hyperbranched multiporphyrin arrays have been prepared. Fluorene-type porphyrins were used as monomers, which can form conjugated connections, and the octyl chains on fluorene units can help to increase their solubility. High molecular weight and polydisperse hyperbranched multiporphyrin arrays were obtained through self-polymerization. Recently, it has been proved that the introduction of multifunctional core molecules in the hyperbranched polymerization process can, to some extent, control the molecular weight and the molecular weight distribution. So we used a more active C4 porphyrin molecule as a core to copolymer with the AB3 monomer to tailor the structures of the hyperbranched polymers. The structure of the products were determined with NMR spectroscopy and element analysis; the molecular weight and the molecular weight distribution were determined with gel permeation chromatography (GPC); optical properties were investigated with UV-Vis and fluorescence spectroscopy; thermal properties were investigated with differential scanning calorimetry (DSC) and thermalgravimetric analysis (TGA). These experimental results indicated that...