Research On Preparation And Optical Properties Of Dendritic Zinc Phthalocyanines

Zinc phthalocyanines molecules and their self-assembled superstructures have attracted tremendous research interests mainly due to their rich photochemical and photophysical properties including near infrared emission,high singlet oxygen generation efficiency and excellent photostability.Therefore,zinc phthalocyanines based materials have been widely used in a variety of different scenarios,such as dyes,organic luminescence materials,chemical sensors,liquid crystal color display,nonlinear optoelectric devices,sensitizers in photodynamic therapy,and organic solar cells as well as photocatalysis for visible light driven degradation of organic dyes.In addition,zinc phthalocyanines molecules exhibit great flexibility of chemical structure modification enabled by peripheral substituents.More importantly,zinc macrocyclic phthalocyanines have been explored as building blocks to formulate H-type(face to face)or J-type(head-to-tail)superstructures via intermolecular ?-? interactions and metal-ligand coordination bonding.In this thesis,a series of highly conjugated bisphthalonitrile precursors were synthesized,and the bisphthalonitrile were utilized to prepare the photo-active zinc phthalocyanines.The chemical structures,surface morphology and photophysical properties of synthesized zinc phthalocyanines for different reaction time and chemical structures were systematically studied.Moreover,their self-assembled superstructures were successfully constructed via a facile protonation induced self-assembling of synthesized zinc phthalocyanines carboxylate molecules.(1)We synthesized dendritic zinc phthalocyanines(ZnPc)showing dual-emissive fluorescence in DMF solvent based on a facile one-step cycloaddition of conjugated bisphthalonitrile precursors.It was found that ZnPc synthesized for 4 h display the strongest dual fluorescent emission at ~440 nm and 690 nm in DMF,respectively,when excited at 365 nm.In addition,the fluorescent emission of ZnPc dramatically changed in different solvents: the red emission was amplified in solvent of strong polarity,while blue emission dominated in non-coordinated solvent.Interestingly,we found that the fluorescence of initially “dark” H-aggregates of ZnPc in DMF/H2 O mixed solvent was gradually recovered through self-assembling driven by the poor solvent,leading to a strong emission around 460 nm.(2)We designed and synthesized a new family of dendritic zinc phthalocyanines(ZnPc)showing both molecular NIR fluorescence and aggregation-induced emission characteristics based on a two-step reaction on the basis of bisphthalonitrile precursors with different electron donor-conjugation-acceptor structures.The ZnPc substituted with hydroquinone,naphthalenediol or dihydroxybiphenyl moieties exhibited an unusual luminescence changes from highly near infrared emitting in molecular state to strongly blue fluorescence in aggregated state as well as solid state.On the contrary,ZnPc bearing diphenylmethane or bisphenol A units only exhibit NIR fluorescent emission in their molecular state.The distinct fluorescent emissions of these ZnPc are rationalized in the framework of molecular configuration and electron density distribution as clarified by density functional theory calculation.Moreover,the well-organized three-dimensional microspheres composed of abundant rod-like building-blocks were discovered via the self-assembly of ZnPc molecules in DMF/H2 O mixture.(3)Carboxylated zinc phthalocyanines based organometallic microflowers and microrods have been constructed via a facile protonation induced self-assembling of dendritic zinc phthalocyanines(ZnPc)carboxylate molecules in acidic aqueous solution at room temperature.The resultant ZnPc microstructures exhibited simultaneous selective adsorption and visible light driven degradation of cationic dye molecules,leading to a quite competitive adsorption capacity of methylene blue approaching to 80 mg g-1.Their morphology evolution,crystalline structures as well as optical properties were systematically characterized,which demonstrated the formation process and mechanism of ZnPc microstructures.The morphology of ZnPc microstructures could be controlled by the time of the hydrolysis reaction,concentration of the HCl aqueous solution added,and incubation time of the protonation induced self-assembling.The ZnPc microstructures showing excellent adsorption capacity,photocatalytic degradation towards cationic dye molecules as well as the scalable fabrication will pave their way for future application in environmental remediation and water pollutant control.