| Liquid crystal is a special physical form,which has both the anisotropy and order of crystal and the continuity and fluidity of liquid.Liquid crystal materials have a wide range of applications in nano-machines,display devices,sensors,artificial intelligence and other fields,regulating their internal ordered structure is the key to studying liquid crystal theory and adjusting the performance of liquid crystal materials.Liquid crystal luminescent materials organically combine the intrinsic luminescent properties of luminescent molecules and the properties of liquid crystals,which will greatly expand the application scope of liquid crystal materials in optical information storage,semiconductors,liquid crystal displays and organic light-emitting diodes.In recent years,the research of liquid crystal molecular materials with precise microstructure and the exploration of the relationship between the ordered structure of liquid crystal molecules and the luminescence behavior of materials at the molecular level have attracted strong scientific interest among researchers.In this thesis,starting from the design of monomer molecules,we explored a concise and universal sequence-controlled ring-opening metathesis polymerization(ROMP)method for the preparation of precise main-chain liquid crystal polymer materials,designed and synthesized discotic liquid crystal luminescent materials with aggregation-induced emission(AIE)effect.The liquid crystal properties,electrochemical properties and photophysical properties of these materials were investigated in depth,respectively,and their application potential in the field of artificial light-harvesting was further discussed.The main research content of the thesis is divided into three aspects as follows:(1)The first part is the study of sequence-controlled polymerization.Sequence-controlled polymerization is one of the most important scientific issues in polymer synthesis methodology.Among the various sequence-controlled polymerization methods,ROMP is a very efficient and universal strategy for the preparation of complex periodic sequence polymers.However,the two representative ROMP methods,entropy-driven ring-opening metathesis polymerization(ED-ROMP)and relay-ring closing metathesis polymerization(RRCMP),have some technical defects that cannot be ignored.Therefore,we developed a sequence-controlled ROMP based on macrobicyclic olefin monomers bearing a sacrificial silyloxide bridge in this chapter.A special class of macrobicyclic olefin monomers was designed and synthesized.The main ring is a macrocyclic olefin with all monomer modules constructed according to the sequence information,and the secondary ring is a3-substituted cyclooctene structure containing a sacrificial silyloxide bridge on theα,β’-positions of the double bond(di-tert-butylsilyl group based on a silicon-oxygen bond),both of which share a bridging double bond.During the polymerization process,the3-substituted cyclooctene can provide substantial ring tension,the ROMP based on the macrobicyclic olefin monomers can not only effectively control the molecular weight distribution but also construct high regio-and stereoselective polymer structures.In addition,the polymers prepared by the sequence-controlled polymerization method can further provide ideal periodic sequence polymers without any specific auxiliary structural groups through desilylation and deoxygenation reactions.The sequence-controlled polymerization method was compared with traditional acyclic diene metathesis polymerization(ADMET)and ED-ROMP methods.The experimental results show that the novel sequence-controlled polymerization method can effectively control the linear growth of molecular weight of polymers and provide extremely high regio-and stereoselectivity.This work provides a new perspective for the development of sequence-controlled polymerization.This work is an important guideline for the development of sequence-controllable liquid crystal polymers.(2)The second part is the research of graphdiyne-based liquid crystal luminescent materials.In this chapter,we designed and synthesized a discotic liquid crystal material GDYLC12 derived from the core of dehydrotribenzo[18]annulene,the basic building block of graphdiyne.The macrocyclic molecule dehydrotribenzo[18]annulene was used as the core of the mesogen,and six wedge-shaped 3,4,5-tris(dodecyloxy)benzoate groups bearing 18 terminal alkoxy side chains were introduced around the core periphery.Furthermore,the mesogenic properties,electrochemical properties and optical behavior of GDYLC12 were investigated.This graphdiyne-derived liquid crystal material can self-assemble into cubic and hexagonal columnar phase structures over a wide temperature range,is able to modulate the assembly state by temperature,and exhibits excellent luminescence properties and low optical bandgap energy.Most importantly,the discotic liquid crystal material exhibits tunable phase-dependent photoluminescence behavior,emitting light blue,green,and sky-blue light in the cubic,hexagonal,and isotropic phases,respectively.Such luminescent liquid crystal materials have potential applications in organic optoelectronic functional materials and devices,and also bring new perspectives for the development and application of graphdiyne-derived materials.(3)The third part is to further develop the light-harvesting function of liquid crystal luminescent materials.At present,there are still great challenges in constructing an efficient and controllable artificial light-harvesting system.Liquid crystals with the characteristics of tunable molecular order have great potential in regulating light-harvesting.Therefore,in this chapter,we designed and constructed an efficient and controllable artificial light-harvesting system based on an annulene-based anisotropic fluid.Using the non-planar structure and aggregation-induced luminescence properties of a cyclooctatetraene derivatives,a saddle-shaped discotic liquid crystal self-assembled donor containing cyclooctatetrathiophene fluorescent core and multiple peripheral alkyl chains was designed and synthesized,and Nile red was introduced as a fluorescent acceptor molecule to successfully construct a supramolecular artificial light harvesting system with controllable efficiency.Taking advantage of the thermal response property of liquid crystal self-assembled donor,the light-harvesting efficiency of this system can be adjusted by regulating the ordering of the donor molecules at different temperatures.In addition,the system achieves multi-color fluorescence regulation from green to red,by adjusting the donor/acceptor ratio or temperature of the light-harvesting system.The system has a high fluorescence donor-acceptor ratio(1000: 1),and exhibits a high antenna effect(39.1)at a donor/acceptor ratio of 100: 1,which is close to the natural light harvesting system.This work provides a new strategy for the application of fluorescent liquid crystal smart soft materials and the development of controlled artificial light-harvesting systems. |
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