Synthesis And Characterization Of Novel2’,2-bipyridine Derivatives Containing Diazo-naphthanol Structure And Their Ruthenium Complexes

Photosystem II （PSII） is the crucial enzyme for light-driven water oxidationreaction in natural photosynthesis. In order to construct an artificial photosystem torealize light-induced water oxidation，substantial efforts have been paid to mimic thestructure and function of the donor side of PSII. It has been proved that the electrontransfer process from oxygen evolving center to the photosensitizer P680+in PSII isalso a proton coupled electron transfer （PCET） process. But the mechanism has notbeen clearly determined until now. Therefore, some model systems are expected. Inthis thesis，two novel polypyridyl Ru（II） complexes containing intramolecular stronghydrogen bond were synthesized，aiming for mimicking the electron transfer processfrom Tyr_zto P680+assisted by a vicinal histidine His190.The work is as follows:First，ligands4and5were prepared by introducing a diazo-2-naphthanol ordiazo-1-naphthanol group to the ligand2,2’-bipyridine. Their structures werecharacterized by IR,1H NMR, MS and elemental analysis. The strong intramolecularhydrogen bond in ligand4（formed between the hydrogen of the naphtholic OH andthe bridging N=N nitrogen） was determined by1H NMR with the chemical shift of15.63ppm. In addition，the pKa values of phenolic hydroxyl groups in ligand4andligand5were measured，which are4.80and6.33respectively. The acidity of–OH inligand4is much stronger than that in ligand5. This result further confirmed theexistence of strong intramolecular hydrogen bond in ligand4.Complexes4a and5a were obtained through the reaction of ligand4and ligand5with cis-[Ru（bpy）₂]Cl₂2H₂O respectively. Complexe4b was obtained through thereaction of ligand4with [Ru（phen）₂]Cl₂2H₂O. Their structures were characterizedby IR，1H NMR，MS and elemental analysis. Chemical shifts of the hydrogen of thephenolic hydroxyl group in complex4a and complex4b are15.73ppm and15.45ppm respectively，which indicate that the strong intramolecular hydrogen bonds existin the complexes4a and4b. Additionally，the pKa value of phenolic hydroxyl groupsin the complexes4a and4b were also measured as5.18and8.13, which further confirmed the existence of strong intramolecular hydrogen bonding in the complexes4a and4b.In the UV-Vis spectra，the maximum absorbance of the MLCT band in thecomplexes4a,5a and4b are red shifted with59nm,20nm and58nm respectivelycompared with the MLCT band of the reference complex [Ru（bpy）₃]（PF6）₂. Complex4a showed high stability under irradiation with sunlight, but complex5a slowlydecomposed under irradiation which was comfirmed by UV-visible spectra and MS.Compared with the reference complex [Ru（bpy）₃]（PF6）₂, no emission was found forcomplex4a,5a and4b. It means that the3MLCT bands of complex4a,5a and4bwere quenched by an energy transfer or an electron transfer process after theintroduction of diazo-2-naphthol group. In the future work，we will further investigatethe PCET process in complex4a,5a and4b by electrochemical, nanosecond laserflash photolysis and theory calculation etc.