Preparation And Characterization Of A New Photoinduced Electron Transfer System Based On Metal Halide Complexes

Solar energy is the best renewable energy sources without any negative impacts onenvironment. Photochromic materials that involve electron transfer process have attractedincreasing attentions due to their potential application in solar energy materials, photocatalyticelectrolysis and pollutants degradation.Herein, supramolecular self-assembly and crystal engineering principles are applied asthe synthetic strategy to design and construct a series of photoactive polyhalite materials thatinvolve electron transfer process. In order to investigate the impact of electron withdrawingsubstituted groups in viologen ligands and halogen atoms as electron donors, great efforts havebeen direct to characterize the structure and optical properties of the compounds. The resultsare listed as follows:1. A one dimensional coordination polymer chain [Zn2Cl2(CNPBPY)2(BTEC)]n(compound1) are obtained by the reaction of Zn(NO3)2·6H2O, benzenetetracarboxylic acid,CNPBPY (N-(3-cyanophenyl)-4,4’-bipyridinium chloride). Viologen molecules CNPBPY areattached to the main chain as side groups. This combination mode creates an interestingfluorescent-photochromic molecular system that involves energy and electron transfer betweenthe mixed ligands. In1, fluorescence quenching takes place with light irradiation. And it iscoupling with the photochromic reaction. Yellow crystals of1turn their color from yellow toblue at the same time. With cyano substituted viologen ligand as side group, the framework of1retains its robust structure up to240°C. It shows a stable donor-acceptor photoactivesystem.2. Three hybrid inorganic-organic compounds Zn(CNPBPY)Cl3(compound2),Zn(ClPBPY)Cl3(compound3), and Zn(HPBPY)Cl3(compound4) have been successfullysynthesized by an in-situ solvothermal reaction. UV-vis and XRD data reveal that compounds1-3have different photochromic behaviors. With cyano and chlorine substituted viologen asligands, compound2and compound3show a faster photoresponsive rate than that ofcompound1. With cyano substituted viologen as ligand, the framework of2retains its robuststructure up to350°C.3. A porous metal-organic framework [Zn(HBTC)]n(compound5) is obtained by reactingZn(NO3)2·6H2O,1,3,5-H3BTC, CNPBPY (N-(3-cyanophenyl)-4,4’-bipyridinium chloride)together in an situ solvothermal reaction. CNPBPY are included into the porous MOFs. Uponlight irradiation, the photochromic reaction is activated. Electron transfer takes place from theoxygen atoms of polymer backbone to the viologen molecules. Yellow crystals of5turn their color to black at the same time. UV-vis-NIR data support that5shows absorption andreactivity in the near-infrared (NIR) region, increasing the absorption region of photochromicmaterials.4. Two mixed ligands photo-responsive molecular systems6and7were obtained bysolvothermal reactions. With similar viologens as acceptors and different combination ofelectron donors,6and7show different photochromic behaviors. It gives an ideal model forinvestigating the photochromic properties of the hybrid functional materials with two electrondonors.