Construction Of Cellulose Nanocrystal Chiroptical Materials And Study On Their Circularly Polarized Properties

Cellulose nanocrystals（CNC）were considered as natural renewable,low-cost green nanomaterials.Due to their excellent physical and chemical properties,they have broad application prospects in structural reinforcement materials,biomedicine,nano energy and other fields.CNC prepared by the acid hydrolysis have chiral liquid crystal optical properties,chiroptical materials can be constructed by self-assembly of CNC.However,most of the current research focused on the self-assembly mechanism and structural color control of CNC.The application research of CNC chiroptical materials is relatively simple,and there are few studies on the circularly polarized optical properties of CNC chiral liquid crystals,which limit the further development and application of chiroptical materials.This thesis using CNC as the building blocks,multifunctional chiroptical materials were prepared by adding water-soluble small molecules to assemble with CNC,and their applications in structural color sensing,photonic inks and optical coatings were investigated.By designing different luminescent guests to assemble with CNC,circularly polarized optical materials were prepared,full-color tunable circularly polarized luminescence（CPL）,tunable upconverted circularly polarized luminescence（UC-CPL）and circularly polarized room temperature phosphorescence（CPRTP）were achieved.For the first time,the CPL produced by the CNC chiral photonic film was applied to trigger azobenzene supramolecular polymers into chiral structures.This thesis clarified the structure-activity relationship between chiral structures and circularly polarized optical properties of CNC,showing the application of CNC chiroptical materials in optical encryption and asymmetric photochemistry.It has important significance for the development on biomass optical functional materials and the research on cellulose chiral sciences.Using CNC as building blocks,based on the film forming properties and chiral liquid crystal optical properties,cholesteric liquid crystal structural colored composites were prepared by adding small molecules glycerol to assemble with them.The effects of glycerol addition on the structure,optical properties and mechanical properties of CNC/glycerol composite films were studied.Results showed:as the glycerol content increased,the helical pitch of chiral nematic structure increased,and the color of the film red-shifted;The addition of glycerol improved the color uniformity and improved the mechanical properties of the composite films.Due to the hygroscopic property of glycerol,CNC/Gly20 film was used as the humidity sensor.Under different relative humidity,the film showed a fast response of structural color change,and the reflection wavelength changed from 525 nm to 820 nm.CNC/Glycerol composite suspensions were used as photonic inks to write on the substrate,dried photon writings have adjustable structural colors and unique fingerprint textures.CNC/Gly nanocomposites were also used to make iridescent coatings on different substrates.The addition of glycerol increased the adhesion strength of the iridescent coatings on ABS and wood substrate,and regulated the structural colors of iridescent coatings on the sulfuric acid paper.Based on the regulation ability of circularly polarized light by CNC films,CNC/QD chiral photonic films were prepared by the co-assembly of Zn S/Cd Se quantum dots（QD）and CNC,full-color tunable CPL emission were realized.The effects of chiral structure,QD fluorescence emission,photonic band gap（PBG）and film thickness on CPL were studied.Results showed:CNC/QD film have left-handed chiral structures and chiral photonic band gap（PBG）,which produced right-handed CPL.Tunable fluorescence emission QD resulted in full-color tunable CPL of the film.As the glycerol content increased,PBG wavelength of the CNC/QD film red shifted from 475 nm to 646 nm,which enabled CPL with adjustable intensity,and the fluorescence asymmetry factor(g_lum)value changed from-0.48 to-0.21.As the film thickness increased,CPL became stronger,and the g_lum value increased from-0.27 to-0.43.Based on the circularly polarized information in the ground state and excited state,CNC/QD photonic films were developed as optical labels to encoding and decoding information.Based on the research in the previous chapter,CNC/UCNPs chiral photonic composite films were prepared by doping upconverting nanoparticles（UCNPs）with multiple emission peaks into CNC photonic films.Under the irradiation of near-infrared light,UC-CPL was achieved.CPL spectrum showed:photonic films have right-handed,multiple wavelength（450 nm and 620 nm）UC-CPL emission.Glycerol was used to adjust the PBG of chiral photonic films,and PBG effect on UC-CPL was investigated.Results showed:as the glycerol content in the photonic film increased,PBG red shifted from 413 nm to 634 nm,which resulted in tunable UC-CPL and adjustable g_lum values at different wavelengths.When the upconverted luminescence locate in the PBG center,UC-CPL intensity is larger and the g_lum is higher at this wavelength.Moreover,because PBG and chirality of the photonic composite film can respond to relative humidity（RH）,humidity responsive UC-CPL was obtained from glycerol composite photonic film.As the RH increased,UC-CPL intensity at blue wavelength decreased,with a g_lum value decreased from-0.156 to-0.033.Based on CPL generated by the singlet luminescence of the luminescent guest in the CNC chiral photonic film,CNC/PVA/CDs hybrid chiral photonic films were prepared by the co-assembly of CNC,polyvinyl alcohol（PVA）and carbon quantum dots（CDs）,CPRTP based on the triplet luminescence were realized.Hybrid films have room temperature phosphorescence features.By changing the PVA content in the hybrid film,PBG of the hybrid film were adjusted,and the regulation of PBG on CPL and CPRTP were studied.Results showed:as the PVA content increased,PBG of hybrid film red shifted,leading to tunable CPL wavelengths and invertible CPL handedness,with the highest g_lum value of-0.19.The left-handed and right-handed CPL is generated by chiral transfer from CNC to CDs during the self-assembly process and the PBG effect of chiral photonic films,respectively.The triplet excitons generated by CDs are stabilize through the hydrogen bond networks of the film.Due to the modulation of PBG,right-handed CPRTP was generated,and the asymmetry factor(g _RTP)was up to-0.47.Long afterglow patterned photonic films with CPL and CPRTP optical properties were prepared by using silica mold as the substrate.On the basis of the above research,based on the circularly polarized optical properties of chiral CNC films,transmitted（T-）CPL and CPL emission were used to induce the formation of chiral helical structures of nonchiral azobenzene supramolecular polymers.CNC films were prepared by self-assembly to produce T-CPL.The chiral induction effect of T-CPL on azobenzene polymers with different chemical structures and different phase states was studied by CD spectroscopy.The chiral induction effect of T-CPL was enhanced on Azo polymers with longer spacers,with a asymmetric absorption factor(g_abs)increased from 2?10^-4to 1.5?10^-3.This is because the polymer chains with long spacers have stronger mobility,and it’s easier for them to arrange into chiral structures under T-CPL irradiation.After annealing treatment,the azobenzene polymer changed from an amorphous state to a liquid crystalline state.After T-CPL irradiation,a significantly amplified chirality and g_abs（21.8×10-3）were obtained due to the synergistic effect of liquid crystals.T-CPL induction strategy is recyclable,and the chirality of induced polymers have good stability.CDs/CNC films were prepared by co-assembly of CDs and CNC,CPL emission with a considerable g_lum（-0.66）was achieved.Under UV irradiation,CPL emission was applied to the chiral photo induction of azobenzene polymers.The induced polymers had high g_abs values（23.7×10-3）.