Synthesis And Properties Study Of Hyperbranched Second-order Nonlinear Optical Polymers

Second-order nonlinear optical(NLO)materials have important applications in the fields of all-optical communication,optical storage and optical information processing due to their good response time and large optical coefficients.Compared with inorganic NLO counterparts,organic polymeric NLO materials generally have higher NLO effects and faster response speed beyond 10^-15s.In addition,they also have the advantages such as low dielectric constant,easy integration,high optical damage threshold,low cost,and tunable structure.At present,the major challenge in this field is how to efficiently convert the high??value(microscopic second-order NLO coefficient)of chromophores into large macroscopic second-order NLO effects of materials.To tackle this challenge,one of the major molecular design strategies is to introduce organic NLO chromophores into three-dimensional(3D)dendritic structures such as dendrimers and hyperbranched polymers(HPs),which can alleviate the strong intermolecular interactions between chromophores to improve the poling efficiency.Nonetheless,the relationship between dendritic structure and materials properties is still unclear.Furthermore,attributed to the high chemo-sensitivity of high??chromophores,there is a lack of effective synthetic approaches to introduce them into HPs.To address the above problems,in this thesis,we have totally synthesized 6 new polymeric NLO materials including 1 dendrimer and 5 HPs.The effects of dendritic structure on the macroscopic properties of materials have been carefully studied.The main contents and conclusions of each chapter of this thesis are as follows:In Chapter 1,after a brief introduction of the principle of second-order NLO effects and the NLO materials with dendritic structure,we focus on reviewing the research progress of second-order nonlinear optical HPs.Also,the design idea of this thesis is clarified at the end.In Chapter 2,we developed a simple synthetic route to prepare a new series of second-order NLO materials with the same isophorone-bridged chromophore moieties but different dendritic structures,including AB₂-type dendrimer(D1),AB₂-type HP1,“A₃+B₂”-type HP2 and“A₃+AB₂”-type HP3.The effects of dendritic structure on the material properties were systematically studied,and the results show that the AB₂-type self-polymerization with proper post-end-capping modification through post-functionalization reaction is an effective synthesis strategy for constructing high-performance second-order nonlinear optical materials.Thus,the AB₂-type dendritic materials,D1 and HP1,show much enhanced macroscopic NLO effects compared to HP2 and HP3,and particularly HP1 exhibits the largest second-harmonic generation(SHG)coefficient(d₃₃)of 77.6 pm/V.In order to introduce high??value chromophore into AB₂-type hyperbranched structure,in Chapter 3,we designed a facile synthetic route to prepare a new AB₂-type second-order NLO HP6 containing the TCBD-based chromophores with high??value by integrating double click-type postfunctionalization reactions including Cu(I)-catalyzed Huisgen's 1,3-dipolar cycloaddition and alkyne-TCNE[2+2]cycloaddition.HP6 can show a d₃₃value of 55.6 pm/V with a high depoling temperature of 125 ^oC.In Chapter 4,to further improve the material's second-order NLO performance,combined with the research contents in the Chapters 2 and 3,we prepared a new“A₃+B₂”-type HP8 through a polymer postfunctionalization based on alkyne-TCNE[2+2]cycloaddition,in which the TCBD-based chromophores in the side-chains are used as the major chromophores while the isophorone-bridged ones in the main-chains as“isolation chromophores”.The d₃₃value of HP8 was measured to be up to 96.6 pm/V,much higher than that of HP6.