Construction And Properties Of Double-Emitting Fluorescent Cellulose Composite Film

As a class of biomass based nanoparticles derived from natural cellulose,cellulose nanocrystals（CNC）exhibit many interesting characteristics compared to traditional inorganic nanoparticles,including high crystallinity and mechanical modulus,rich surface groups and charges,non-toxic,good biocompatibility,and renewability.It can be used as excellent building blocks for the preparation of composite materials.CNC can selectively reflect left-handed circularly polarized light（L-CPL）by leaving chiral nematic structures in the thin film through evaporation induced self-assembly（EISA）.CNC hybrid materials with various optical states have great potential as anti-counterfeit labels and information encryption materials.Based on the excellent optical and self-assembly properties of CNC,this thesis mainly conducts the following research:Preparation of dual-emission cellulose nanocrystalline composite materials with circular polarization luminescence for anti-counterfeiting labels:A customized shaped dual emission CPL material composed of CNC and luminescent bodies was obtained through EISA process.Eu³⁺complex with red fluorescence emission and TPE derivative4’,4’’,4’’’,4’’’’-（ethene-1,1,2,2-tetrayl）tetrabiphenyl-4-carboxylic acid（TPEC）with green fluorescence emission were selected as fluorescence guests.The composite films exhibited bright red and blue-green emissions under excitation at 254 nm and 365 nm,respectively.According to the photonic band gap effect,the wide reflective band of the thin film covers the green and red fluorescence emission centers,resulting in R-CPL emissions with different asymmetric factors(g_lum).Under 275 nm excitation,the g_lum at615 nm is-0.21,and under 365nm excitation,the g_lum at 500 nm is-0.11.Multiple optical states enable CNC materials to be used as anti-counterfeit application coatings.In addition,CNC-Eu（DA）₃-TPEC suspensions with low CNC concentrations can also be used as invisible inks.Preparation of cellulose nanocrystalline composite films with adjustable fluorescence color:Ln³⁺(Eu³⁺and Tb³⁺)was introduced into the CNC through host guest co-assembly.The"antenna effect"of the ligand was used to make Ln³⁺emit fluorescence with characteristic color.A series of composite films with adjustable fluorescence color were obtained by changing the doping ratio of Eu³⁺and Tb³⁺,and the energy transfer process between ligand and Ln³⁺was investigated.The addition of PVP further disperses lanthanide metal coordination compounds and endows the film with good optical transparency,making the composite film promising for application in LED.Due to the dynamic coordination bonds,composite films have a rapid and reversible response to p H,and are expected to be used as p H fluorescence probes.