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内容記述 |
The supramolecular integration of porphyrin and its derivatives has attracted<br /> to obtain well-defined porphyrin aggregates, not only covalent bonding but also metal<br /> coordination, hydrogen-bonding and van der Waals interactions have been utilized<br /> and the obtained integrated structures have been employed for applications in various<br /> fields of materials science and technology. I have focused on the supramolecules of<br /> amphiphilic motives with rigid π-conjugated cores, which have been well employed to<br /> obtain excellent optoelectronic properties associated with the characteristic<br /> nanostructures. In this study, I have developed an asymmetrically β-substituted<br /> amphiphilic porphyrin, which is designed to be much planar and less bulky with an<br /> aim to accomplish densely packed nanostructures and induce strong intermolecular<br /> interactions between the metal centers.<br /> The triethyleneglycol(TEG)-tethered and alkyl-tethered dipyrromethanes have<br /> been prepared, and then the synthesis of the target porphyrin has been accomplished<br /> by the condensation reaction of these dipyrromethanes. In contrast to the synthesis<br /> of <i>meso</i>-aryl-type porphyrin, that of asymmetrically substituted β-alkyl-type<br /> porphyrin has not been well explored. Several conditions were examined for the<br /> condensation reaction of two different dipyrromethanes and finally, the target zinc<br /> porphyrin was successfully obtained by condensation of TEG-tethered dipyrromethane<br /> and an alkyl-tethered <i>α,α’</i>-dipropylimino-dipyrromethane in refluxing cyclohexane in<br /> the presence of Zn(OAc)<small>2</small>2H<small>2</small>O as a template. In this procedure, an isomerization<br /> reaction of porphyrin derivatives, so-called scrambling reaction, was suppressed under<br /> lower reaction temperature or in less polar solvents by hampering the pathway of this<br /> side-reaction. For the optimized synthesis, 44.8 mg of the porphyrin mixture was<br /> obtained in 18% yield and the ratio of the target compound and the isomer<br /> (isomer/target) was 0.03. The isolation of the target porphyrin 1-Zn from the<br /> isomeric mixture was accomplished by repeated recrystallizations from the solution<br /> in a CH<small>2</small>Cl<small>2</small>-MeOH mixed solvent. As a result, the isomeric mixture of 44.8 mg afforded<br /> 22.5 mg of the target 1-Zn to be pure at NMR level. The characterization of the<br /> target porphyrin has been carried out by <sup>1</sup>H and <sup>13</sup>C NMR spectroscopies and HR<br /> FAB-MS spectrometry. The central zinc atom was demetallated under the acidic<br /> condition with TFA in CH<small>2</small>C<small>l2</small> and the freebase porphyrin 1-H<small>2</small> was obtained in 98%<br /> yield. The insertion of copper ions was carried out by refluxing the solution of 1-H<small>2</small><br />in the presence of Cu(OAc)<small>2</small>・H<small>2</small>O, which resulted in target compound 1-Cu<br /> quantitatively.<br /> The supramolecular integration of the obtained porphyrins 1-H<small>2</small> and 1-Cu has been<br /> examined in some polar solvents by taking advantageous of the amphiphilic properties<br /> of the porphyrins. The UV-Vis spectral changes were observed on adding H<small>2</small>O to the<br /> solution of the freebase 1-H<small>2</small> in THF. The Soret absorption band of 1-H<small>2</small> shows red shift<br /> by 42 nm. Similar behaviors were observed for the absorption experiments of 1-H<small>2</small><br /> upon cooling the hot MeOH solution. On the other hand, when H<small>2</small>O was added to the<br /> solution of 1-Cu in THF, the Soret band of 1-Cu at 397 nm displayed clear blue shifts<br /> with a peak (<i>λ</i><small>max</small>) at 392 nm in THF : H<small>2</small>O = 1 : 9 mixed solvent. In general, Kasha’<br />s exciton theory predicts that a blue shift observed in the optical absorption indicates a<br /> face-to-face H-aggregation of the chromophores.<br /> The shapes of the nanostructures of the integrated porphyrin assemblies have been<br /> confirmed by the SEM and TEM observations. When the suspension of freebase<br /> porphyrin 1-H<small>2</small> precipitated from the hot MeOH solution was casted on a substrate, the<br /> TEM image revealed a rod structure that consists of the bundles of wires with the<br /> diameter of about 25 nm. The precipitate of 1-Cu obtained from THF-H<small>2</small>O showed short<br /> rod-like structures with the diameter of around 11 nm and the length in the range of<br /> 140－310 nm as estimated from the SEM and TEM observations. The SEM image of<br /> the precipitate of 1-Cu obtained from a hot MeOH solution afforded a helical<br /> ribbon-structure without chiral selectivity.<br /> The XRD analysis of the precipitate of 1-Cu from THF-H<small>2</small>O solution revealed that<br /> the molecules are packed in a monoclinic unit cell with the dimensions of <i>a</i> = 67.71(4), <i>b</i><br /> = 3.546(3) and c = 24.62(2) Åand β = 96.72(7)° and the π-stacked 1-D chains are aligned to the <i>b</i>-axis with the π-stacking distance of 3.55 Å.<br /> I investigated the thermal magnetic behaviors of 1-Cu with SQUID measurements<br /> in order to confirm the intermolecular metal-metal interaction induced by the<br /> supramolecular integration. The magnetic susceptibility of the precipitate obtained<br /> from THF-H<small>2</small>O solution shows a bent on decreasing temperature, which indicates a weak magnetic interaction between the Cu(II) centers. The Curie-Weiss plot of the<br /> susceptibility between 4-300 K affords the Weiss constant as -0.22 K. The induction of<br /> intermolecular magnetic interaction between metal centers with soft-material systems is<br /> rare.<br /> The supramolecular integration of the porphyrin without any solvents has been also<br /> investigated by slow cooling from the melting state. The DSC measurement and the<br /> POM observation of 1-Cu showed that the melting point was <i>ca</i>. 130 ℃ and the<br /> porphyrin was thermally stable upto this temperature region. When 1-Cu was heated<br /> over 130 ℃, fluid-like porphyrin was observed. After cooling to r. t., integrated 1-Cu<br /> was obtained easily and the UV-Vis spectrum and the XRD analysis of this aggregate<br /> suggested a similar supramolecular structure as 1-Cu precipitates obtained from the<br /> solution in polar solvents.<br /> In summary, I have succeeded in the syntheses of novel amphiphilic porphyrin<br />complexes, investigated their self-assembly behaviors and the properties of the<br />assembled nanostructures. |
要旨・審査要旨 (342.6 kB)
