Design, Synthesis And Photoelectric Property Study Of PSⅡ Model Compounds With Porhphyrins As Photosensitizer

Porphyrins and their relatives are the cores of chlorophyll molecules. As the primary electron donor, they participate in a series of important process in photosynthesis. So porphyrins are the significant compounds in artificial photosynthesis. In nature photosythesis, the substance conversion and energy storage are only macroscopical phenomena, but the formation of charge-separation state and electron transfer are the determinative factors. Therefore building model compounds to investigate on the intramolecular electron transfer and charge-separated state formation attracted considerable attention of scholar. In this dissertation, a series of PSⅡmodel compounds with porphyrins as photosensitizer were design and synthesis, and the intramolecular electron and energy transfer and charge-separated state formation were studied to make theory foundation for the further modeling of PSⅡ.Quinone compound are the primary electron acceptor in nature photosynthesis, thus building model compounds of artificial photosynthesis with quinone as acceptor is the first selection to the scholar. In the dissertation, model compounds were built with porphyrin(P) as electron donor and anthraquinone(AQ) as acceptor. Firstly, a series of asymmetry porphyrins were synthesized, then 14 novel porphyrin- anthraquinone dyads were designed, synthesized and characterized by IR, 1H NMR and MS. They respectively connected with azo bond, with cyanuric chloride as bridge, with amido bond, with alkyl chain. Secondly, the photoelectric properties of the new compounds were studied in details. Fluorescence quenching of the dyads exhibit that intramolecular photoinduced electron transfer occurred in the porphyrin- anthraquinone molecules. And the great decrease of fluorescence lifetime (315ps) of compound 46 further confirms this. The P·+-AQ·-state can be observed by transient absorption spectroscopy because the absorption spectrum of the charge-separated state differs from that of the porphyrin excited triplet in 600~700nm. The experiment results of transient absorption spectroscopy illustrated that new absorption band appeared at 600nm and 650nm due to the formation of porphyrin cation in compounds 27, 34. The lifetime of charge-separated state is 1.42μs and 1.33μs respectively. The formation of long-lived charge-separated state provides theory guidance and essential idea for the optimization of dyads system. And the structure of the charge-separated state is more close to the nature. So porphyrin-anthraquinone dyads 27 and 34 are excellent PSII model compounds. 9 novel porphyrin-oxadiazole dyads connected with azo bond and with cyanuric chloride as bridge were designed, synthesized and characterized by IR, 1H NMR and MS. The molecular structures of compounds 22, 23, 36b were further identified through MM2 simulating calculation. The spectral properties of new dyads were investigated in details. The experiment results show that intramolecular photoinduced energy transfer occurred from excited oxadiazole moiety to porphyrin moiety in the dyads 36b, 36c, 23 and 37, leading to the fluorescence quenching of oxadiazole moiety and the fluorescence enhancing of porphyrin moiety. And there is no return electron transfer from excited porphyrin moiety to oxadiazole moiety. Moreover, the results obtained from the redox property indicated that the HOMO and LUMO of porphyrin moiety sandwiched between the levels of the HOMO and LUMO of oxadiazole moiety. So electron transfer from oxadiazole moiety to porphyrin moiety becomes possible. The porphyrin-oxadiazole dyads will be the fine PSII model compounds.4,4'-dimethyl-2,2'-bipyridine reacted with NBS, then alkylation with hydroxyl porphyrin at the existence of NaOH to generated porphyrin-bipyridine dyad 35. Porphyrin-bipyridine dyad 38 was prepared from amino porphyrin and 4-dimethyl-4'-carboxylchlroride-2,2'-bipyridine. The structures of new compounds were confirmed by 1H NMR and MS. And the photoelectric property of compound 35 was studied to make foundation for the further synthesis of porphyrin-bipyridine-Mn model compounds.11 novel porphyrin-aminoacid dyads and 2 triads were prepared from porphyrin and amino acid through protection of amino group of amino acid with Fmoc-OSu, then activation of carboxyl group with SOCl2, and characterized by IR, 1H NMR and MS. The photoelectric properties of compounds were studied in detail to make foundation for the further synthesis of porphyrin-bipyridine-Mn model compounds containing amino acid moiety. In addition the reaction mechanism of compounds 17, 20, 29, 30, which synthesized through esterification and included two amino acid chains, was discussed.