NIR Circular Polarization Properties Of Cellulose Nanocrystal-Based Films

Cellulose stands as the most abundant bioresource in nature.Cellulose nanocrystals(CNC),extracted from primary cellulose,exhibit a remarkable propensity for spontaneous assembly in suspensions beyond critical concentration,resulting in the formation of self-supporting chiral nematic films known as CNC-based films.These films boast left-handed meso-scale chirality,1D photonic crystal features,and adjustable photonic bandgaps(PBG)spanning from near-ultraviolet to near-infrared(NIR)band.Numerous studies have reported the embedding of diverse fluorescent guests within the CNC chiral nematic structure through evaporation-induced coassembly,resulting in a complex film.Remarkably,the emitted light can be effectively converted into right-handed circularly polarized luminescence,exhibiting dissymmetry factor values as high as ～0.8.This intriguing characteristic holds great promise in various fields such as optical anti-counterfeiting,stereoscopic imaging,sensing,and more.Circular polarized light in NIR region,particularly in NIR second window(NIRII,1000–1700 nm),offers remarkable advantages,including exceptional specificity,sensitivity,and information-carrying capacity.Moreover,it exhibits exceptional penetration ability and high resolution for biomedical imaging,while maintaining low noise levels for long-distance optical communication.However,the availability of highperformance NIR circularly polarized luminescent materials remains relatively scarce.In light of this,this study focuses on exploring the NIR circularly polarized optical properties of CNC-based films.The main results obtained in this study are presented as follows:(1)CNC-based films were successfully fabricated,demonstrating NIR PBG.The red-shifting phenomenon observed in these films was attributed to the nanochirality change of the CNC building blocks.(2)CNC-based NIR circularly polarized luminescent films were prepared.By employing a theoretical model,factors contributing to the failure of achieving high-performance were identified and analyzed.(3)Strategies aimed at enhancing the capabilities of CNC-based circularly polarized materials were proposed,with particular emphasis on those with NIR-Ⅱ PBG.(4)CNCbased circularly polarized materials with NIR-Ⅱ PBG demonstrated great potential on cancer diagnosis.The dissertation was divided into five chapters.In Chapter Ⅰ,the author introduced basic properties of CNC and provided an overview of the research status regarding CNC chirality and aggregates.The chapter also included the behavior,formation,modulation,and some applications of CNC selfassembly.Later in the chapter,circularly polarized light materials and relevant knowledge were introduced,including circularly polarization basis,circularly polarized luminescent materials,spontaneous luminescence modulation triggered by chiral nematic structure,and circular polarization capability of the structure.The advantages of NIR-Ⅱ circularly polarized light and the demand for such materials in highperformance applications were discussed then.Mechanism of circular polarity imaging were concluded.Lastly,the author proposed contents based on the current situation and problems.In Chapter Ⅱ,the research focused on investigating the nano-chirality of CNC and its influence on modulating the PBG of CNC-based films in NIR range.The nanochirality of CNC was examined,revealing its existence as nanoscale chiral aggregates in suspensions.Aggregates underwent disintegration and chirality attenuation after harsh sonication,resulting in a red-shifting behavior of the PBG towards NIR region.A statistical relationship was established between sonication power and several variables,including the aggregative morphology of CNC,the nano-chirality of CNC,and the PBG of CNC-based films.The author proposed that the nano-chirality of CNC played a crucial rule as a driving force for self-assembly.A series of CNC-based films were prepared,allowing for controllable PBG within the NIR range.Notably,these films exhibited a high degree of circular polarization,reaching 0.317 in NIR-Ⅱ region.The produced NIR-Ⅱ circularly polarized light demonstrated its potential for mouse cancer diagnosis,serving as a proof-of-concept.This advancement expanded the wavelength ranges and application areas for CNC-based circularly polarized materials,thereby opening up new possibilities in the field.In Chapter Ⅲ,NIR circularly polarized luminescent properties of CNC-based films were investigated.The films were prepared through evaporation-induced coassembly,resulting in complex structure with the highest dissymmetry factor value up to 0.33.Two key elements were identified for controlling the circularly polarized fluorescent abilities,structural defects of the films and emission properties(primarily referring to intensity and distribution),based on theoretical calculation and model construction.A precise and general proposal was formulated to enhance the circularly polarization performance,maximum dissymmetry factor value,and optimize the desired effects of the emission(including polarity reversal at the edge of PBG and oscillations at the corner of PBG).In Chapter Ⅳ,NIR-Ⅱ circularly polarized reflection properties of CNC-based films was discussed.Defects resulted in a decline in optical properties of CNC-based films.Experimental investigations revealed the emergence of embedded focal conic domains in CNC-based films with NIR-Ⅱ PBG following high-energy sonication treatment.The number of focal conic domains increased proportionally with higher sonication doses.The specific thickness of the films played a vital role in the formation of focal conic domains.It was demonstrated that reducing the film thickness below a threshold of 15 μm effectively eliminated these defects.A laminating strategy was proposed to construct CNC-based films with vertical chiral nematic helical axes and sufficient optical periods.This approach provided high performance on NIR-Ⅱ circularly polarized reflection properties,with the degree of circular polarization raising towards 0.556,which offered a valid pathway for reducing defects and preparing highperformed CNC-based materials for NIR circularly polarized optical applications.Finally,a demonstration was performed for human gastric cancer discrimination using the optimized CNC-based film,showcasing its potential in practical biomedical applications.Conclusions and outlook were presented in Chapter V.