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| - Efficient Synthesis of Porphyrin-Containing,Benzoquinone-Terminated, Rigid Polyphenylene Dendrimers
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| - A series of rigid polyphenylene, free-base porphyrin-containing dendrimers terminated with eitherdimethoxybenzene or benzoquinone end-groups were prepared by a combined divergent andconvergent synthesis. Unlike previous routes for preparing polyphenylene dendrimers that areincompatible with end-groups bearing certain functional moieties, the synthetic methodology chosenfor this work enables incorporation of functional groups on the dendrimer end-groups duringpreparation of the dendrimer wedges and during synthesis of the final dendrimer. The basic strategyutilized a convergent preparation of dendrimer wedges using Suzuki coupling conditions, whichwere then either attached to a porphyrin core in a divergent coupling step or cyclized to form theporphyrin dendrimer in a convergent step. The latter approach was found to be more general andresulted in higher yields and more readily separated products. Steady-state absorption measurements for these dendrimers showed Soret and Q-band absorptions typical of free-base porphyrins.Preliminary steady-state fluorescence measurements of these dendrimers indicate quenching ofthe S1 state of the free-base porphyrin in all benzoquinone-containing dendrimers that is attributedto efficient electron-transfer from the excited porphyrin to the benzoquinone end-groups. The amountof fluorescence quenching was in good agreement with the number of benzoquinone groups at thedendrimer periphery and the distance between the porphyrin and benzoquinone groups as calculatedby semiempirical (AM1) molecular orbital calculations.
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