Design,Synthesis And Characterization Of Second-Order Nonlinear Optical Polymers Containing Janus Dendritic Unit

Information and materials are the foundation of modern civilization.Second-order nonlinear optical(NLO)materials have shown great application prospects in high-speed optical communication,data storage,information processing and laser frequency conversion.As a key research field of optoelectronic technology,the acquisition of NLO materials with excellent comprehensive properties plays a vital role in the fabrication of optoelectronic devices and the development of optical information technology.Compared to traditional inorganic crystal materials,organic/polymer NLO materials usually possess merits with large NLO coefficient,low dielectric constant,fast response time,high laser damage threshold,strong electromagnetic interference resistance,superior chemical flexibility and good fabricability,and has gradually become the research hotspot in the field of NLO materials in recent years.Of these,how efficiently translate the large??value of organic chromophores into the macroscopic NLO coefficient of the polymers is still the major problem in this field.Therefore,how to design and prepare organic NLO polymers with excellent comprehensive properties by simple synthetic routes is still one of the important topics in this field.NLO polymers with dendritic structure possess good site-isolation effect and spacer effect,which is beneficial to the improvement of the macroscopic NLO effect of the materials,and can also improve solubility,fabricability and stability of the material.Reviewing of the development of organic NLO polymers with dendritic structure in recent decades,it could be found that the control of spatial topological structure is very important for these polymers to achieve high NLO effect,good stability and optical transparency.Among all kinds of macromolecules with dendritic structure,dendrimers tend to possess higher macroscopic NLO effect,especially the Janus dendrimers developed in recent years have unique advantages and show great potential,but their synthetic routes needs to be further simplified,thermal stability remains to be further improved and structure-properties relationship needs to be further explored.In order to obtain NLO materials with excellent comprehensive properties(high macroscopic NLO effect,good thermal stability and optical transparency)in simplified synthetic routes,in this thesis,base on Janus dendritic unit,three aspects of research has been carried out,including dendrimers,dendronized polymers and dendronized hyperbranched polymers.Chapter 1:firstly,the theoretical basis of NLO and the application of NLO materials were introduced.Next,some design ideas and resolution strategies of the NLO materials were summarized.Then,the development of organic NLO polymer materials with dendritic structure were introduced.Finally,the design idea of this thesis was proposed base on the current research hotspots and difficulties in the field.The first part is about the Janus dendrimers,including the Chapter 2 to 4.Chapter 2:the synthetic route of Janus dendrimers were simplified.By using the“Click Chemistry”reaction,a series of Janus dendrimers with different peripheral groups were designed and synthesized to investigate the Ar-Ar^F self-assembly effect and the content of pentapfluorophenyl groups on the NLO proformance of Janus dendrimers.Chapter 3:by using the“Click chemistry”reaction,a series of Janus dendrimers which possess ordered chromophore orientation molecular design,were designed and synthesized through the“convergent and divergent”approach.It was found that the molecular design with a certain ordered arrangement of chromophores in the natural state was indeed conducive to achieving higher NLO effects,among them,d₃₃ values(NLO coefficient)of D2-Ph,D2 and D2-PFPh of the second generation dendrimers were as high as 197.7,202.5 and 214.4 pm/V,respectively.Chapter 4:the concept of“isolation chromophore”was introduced into the Janus dendrimers.By using the similar synthetic method of Chapter 3,a series of Janus dendrimers containing isolation chromophores with ordered chromophore orientation were densigned and synthesized.The result demonstrated that the introduction of isolation chromophore into Janus dendrimers can further improve the macroscopic NLO effects.The d₃₃ value of the D2-Ph-NS,D2-NS and D2-PFPh-NS were as high as 221.3,226.8,and 213.3 pm/V,respectively,and their optical transparency and NLO thermal stability were also improved comparing with their corresponding dendrimers in Chapter 3.The second part is about dendronized polymers containing Janus dendritic unit,including Chapter 5 and 6.Chapter 5:by extending the Janus dendrimers horizontally,two main chain dendronized polymers were construct through the Suzuki coupling reaction.It was found that in addition to basically maintaining the macroscopic NLO effect of their corresponding low generation dendrimers,the NLO thermal stability of the obtained dendronized polymers were also significantly improved.Chapter 6:the concept of“isolation chromophore”was further introduced into dendronized polymers,and two main chain dendronized polymers containing isolation chromophore were synthesized.It was found that the NLO effects,optical transparency and NLO thermal stability of the obtained dendronized polymers were improved compare with their corresponding dendronized polymers in Chapter 5.The third part is about dendronized hyperbranched polymers containing Janus dendritic unit,including Chapter 7 and 8.Chapter 7:by expanding the Janus dendrimers into 3D space,two main chain dendronized hyperbranched polymers were construct through the“A₃+B₂”type Suzuki coupling reaction.It was found that the NLO effects of the dendronized hyperbranched polymers were almost the same as their corresponding monomers and dendronized polymers,and their NLO thermal stability has also obviously improved.Chapter 8:the concept of“isolation chromophore”was further introduced into dendronized hyperbranched polymers,and two dendronized hyperbranched polymers containing isolation chromophore were synthesized.It was found that the NLO thermal stability of dendronized hyperbranched polymers was higher than their corresponding dendronized hyperbranched polymers in Chapter 7.Their d₃₃ values were higher than 150 pm/V,and decay temperature higher 110 ^oC,which solved the“nonlinear-transparency trade-off”and“nonlinear-stability trade-off”to a certain extent.