The Synthesis And Properties Of Artificial Photosynthetic Reaction Center On Basis Of Tetrapyrrolic Macrocycles

In this paper, the porphyrin-fullerene compounds linked by meso-position oraxial of porphyrins, corrole-fullerene compounds linked through meso-or-positionof corrole and the porpyrin-anthraquinone dyad have been designed and synthesized.The photo-induced electron transfer of these artificial photosynthetic reaction centershave been investigated by the steady-and transient-spectroscopy. In addition, anunexpected rearrangement has been found during the amindation reaction ofo-carboxyazobenzene in the presence of dehydrating agents e.g. DCC, EDCI, HBTU.in which amino-substituted indazol-3,5-dione is formed.Three unsymmetry porphyrins with CHO group have been synthesized usingATPP as the starting materials. Make use of the1,3-dipolar cycloadditon reactionbetween the porphyrin with CHO, sarcosine and fullerene, three porphyrin-fullerenedyads with different linkers and configuration are obtained and characterized by¹HNMR and MALDI-Tof. The photophysical properties of these porphyrin-fullereneartificial photosynthetic reaction centers have been investigated by UV-Vis,fluorescence, time-solved fluorescence and transient absorption spectra. In compound2C3, the electron donor and acceptor are very close to each other, thus electrontransfer both through bond and space, which will result in the highest electron transferefficiency and the strongest fluorescence quenching （96%）, could take place.Furthermore, the DFT calculation is employed to obtain insight into the structuralaspects and molecular obitals which have been used to explain the results of theexperiments.Using the “two point” coordinate points of the pyrazine, we prepare twofullerene-pyrazine and one anthraquinone-pyrazine electron-acceptor ligands. Theintermolecular interaction has been detected by the emission spectra and¹H NMRbetween TPPZn and ligands, while the job’s plot obtained from the UV-Vis confirmsthe1:1complex between TPPZn and3C₁.The ferrocene-porphyrin-ferrocene through axial position has been designed andsynthesized. Meanwhile, the porphyrin-fullerene2C2is employed as the startingmaterial for the metallization to give its Tin complex which will be treated withferrocene with COOH to obtain the ferrocene-porphyrin-fullerene compound Fc-PSn-C60. In its nanosecond transient absorption spectrum, the peak at620nm witha life time of29.01s could be corresponding to the ferrocene cation radical （Fc+）.The observation of the cation radical provides proofs of the existence ofcharge-separated state after excitation. This long lived charge separation state couldresult from both the long distance between the cation and anion and the interferenceof the electron recombination due to the axial position of ferrocene.The reactive of the pyrrilic rings in corrole framework has been studied. Thesulfolenopyrrole is used as the starting material to condense with aldehyde to form thedisufolenopyrromethane4DPMS, this reaction has been optimized on theconcentration of the HCl, reaction time and temperature. Then threetetrasulfolenocorrole have been prepared by using4DPMSand aldehyde via [2+1]condensation. Thermolysis of the corrole4C1in presence of an excess of fullerenegave a difullereno-corrole selectively after9min. The2D NMR （ROESY）spectroscopic data indicated attachment of the two fullerene units at the ‘western’,directly connected pyrrole rings （ring A and D）. This result indicates that the ring Aand D is more reactive for the loss of SO₂group. In addition, the absence offluorescence in the spectrum of4C1should be taken as a sign of efficient quenchingof the excited corrole by the closely attached C60moieties. Thus this corrole-fullerenecompound could be the potential artificial photosynthetic reaction center.Three corroles containing the anthracene moiety linking at meso position havebeen prepared by the condensation between the dipyrromethanes and4A. Then thecorrole-fullerene dyad4C₄-C₆₀is prepared by treating4C4and C60at roomtemperature and characterized by¹H NMR and MALDI-Tof. In its nanosecondtransient absorption spectrum, the peak at670nm could be assigned to the corrolecation radical （Cor+） with a life time of0.98s. The observation of the cation radicalproves the existence of photo-induced charge-separated state in this compound.Meanwhile, the DFT calculation predicts that the HOMO and LUMO are mainlylocalize on the corrole and fullerene, respectively. Thus the electron transfer fromexcited corrole to fullerene could be further demonstrated in theory.One novel porphyrin-anthraquinone dyad P-Q1with a indazolone as the linkerhas been obtained by condensation between ATPP and5A. Its structure is clearlysupported with X-ray diffraction analysis. Strong fluorescence quenching is observedin the preliminary emission spectrum due to the proposed electron transfer from theexcited porphyrin to the acceptor moiety. With the help DFT calculation, we find the LUMO localizes on the indazolone instead of the anthraquinone. This unexpectedresult indicates that the indazolone could become a new type of electron-acceptor inthe construction of artificial photosynthetic reaction center in the future.The rearrangement in the amidation reaction of o-caroxyazobenzene have beeninvestigated and optimized about dehydrating agents, solvents and molar ratio.Meanwhile, the intermediate has been isolated and a possible reaction mechanism hasbeen proposed on basis of the product’s structure and the intermediate. Afterestablishing the optimization condition, we investigated the limitation of thisrearrangement reaction and find a range of electron-rich and electron-deficiento-carboxyazobenzenes and amines can be used. It should be pointed out that the sterichindrance effect could be the main reason of poor performance. This newrearrangement offers a potential way to build up the amino substitutedindazole-3,5-dione with conveniently obtainable starting materials in mild conditionsgiving rise to an appropriate yield.