配体改变法调控MOFs薄膜的光学性质（英文）

Tuning optical properties of MOF-based thin films by changing the ligands of MOFs

制备和开发新型光学薄膜材料对于功能性的光学和光电器件具有重要意义,特别是具有低折射率的光学薄膜材料.本论文选用一类典型的MOFs材料,MIL-101(Cr),为研究对象,通过水热法制备得到相应的MOFs纳米颗粒,并通过旋涂法成功制备光学薄膜.通过改变配体(对苯二甲酸)苯环上功能团的种类:氢原子(H)、给电子基团(-NH_2,-OH)和吸电子基团(-NO_2,双-NO_2),来调控对应的MOFs光学薄膜的光学性质.研究发现,MOFs薄膜的有效折射率n_(cff)随着MOFs纳米颗粒之间的孔隙的增加而减小,MOFs薄膜的消光系数k随着给电子基团的增加而增大,而随着吸电子基团的增加而减小.其中,含有吸电子基团的MOF即NO_2-MIL-101(Cr)的折射率最小,低至1.2左右,而且消光系数特别小,该MOFs薄膜有望应用于减反射器件,此外,根据孔隙率计算得到,MOFs材料的本征折射率n_(dense)随着功能基团的增加而增大,而且双硝基取代的MOFs的折射率大于硝基取代的,大于羟基取代的折射率,而羟基取代的与氨基取代的折射率差不多,MOFs材料中配体的多样性,使其有望成为新一代的光学材料.

The preparation and development of novel optical thin films are of great importance to functional optical and opto-electric components requiring a low refractive index.In this study, a typical metal-organic framework（MOF）, MIL-101（Cr）, is selected as the research model. The corresponding MOF nanoparticles are prepared by a hydrothermal method and the optical thin films are successfully prepared by spincoating. The optical properties of the corresponding MOF thin films are controlled by changing the type of functional groups on the benzene ring of the ligand（terephthalic acid） on MOFs.The functional groups are hydrogen atoms（H）,electron donating groups（-NH_2,-OH） and electron withdrawing groups（-NO_2,-（NO_2）_2 or F_4）, respectively. It is found that the effective refractive index（n_（eff）） of MOF thin films decreases along with the increasing voids among MOF nanoparticles. In addition, the extinction coefficient（k） increases with the addition of electron donating groups, and decreases with the addition of electron withdrawing groups. Among the MOFs used in this study, the n_eff of NO_2-MIL-101（Cr） containing electron withdrawing groups is as low as ~1.2, and value of k is particularly low, which suggests its potential application in antireflective devices. In addition, the intrinsic refractive index（n_（dease）） of the dense MOF materials evaluated according to their porosity increases with the number of the functional groups, and the n_（dense） of the two nitro-substituted MOFs is greater than that of the single nitro-substituted one, and the latter is bigger than that of hydroxyl-substituted one, which is close to that of amino-functionalized one. The diversity of ligands in MOFs makes them a promising new generation of optical materials.