Kang En-Hua, Bu Tianjia, Jin Pengcheng, Sun Junqi, Yang Yanqiang, Shen Jiacong
Key Lab of Supramolecular Structure and Materials, College of Chemistry, Jilin University, Changchun, P. R. China 130012.
Langmuir. 2007 Jul 3;23(14):7594-601. doi: 10.1021/la700749s. Epub 2007 Jun 8.
Organic/inorganic hybrid multilayer films with noncentrosymmetrically orientated azobenzene chromophores were fabricated by the sequential deposition of ZrO2 layers by a surface sol-gel process and subsequent layer-by-layer (LbL) adsorption of the nonlinear optical (NLO)-active azobenzene-containing polyanion PAC-azoBNS and poly(diallyldimethylammonium chloride) (PDDA). Noncentrosymmetric orientation of the NLO-active azobenzene chromophores was achieved because of the strong repulsion between the negatively charged ZrO(2) and the sulfonate groups of the azobenzene chromophore in PAC-azoBNS. Regular deposition of ZrO(2)/PAC-azoBNS/PDDA multilayer films was verified by UV-vis absorption spectroscopy and quartz crystal microbalance measurements. Both UV-vis absorption spectroscopy and transmission second harmonic generation (SHG) measurements confirmed the noncentrosymmetric orientation of the azobenzene chromophores in the as-prepared ZrO2/PAC-azoBNS/PDDA multilayer films. The square root of the SHG signal (I(2omega)(1/2)) increases with the increase of the azobenzene graft ratio in PAC-azoBNS as the number of deposition cycles of the ZrO(2)/PAC-azoBNS/PDDA films remains the same, while the second-order susceptibility chi(zzz)(2) of the film decreases with the increase of the azobenzene graft ratio. Furthermore, the present method was successfully extended to realize the noncentrosymmetric orientation of azobenzene chromophores in multilayer films when small organic azobenzene compounds with carboxylic acid and/or hydroxyl groups at one end and sulfonate groups at the other end were used. The present method was characterized by its simplicity and flexibility in film preparation, and it is anticipated to be a facile way to fabricate second-order nonlinear optical film materials.
通过表面溶胶 - 凝胶法依次沉积ZrO₂层，随后将非线性光学（NLO）活性含偶氮苯聚阴离子PAC - azoBNS与聚二烯丙基二甲基氯化铵（PDDA）进行逐层（LbL）吸附，制备了具有非中心对称取向偶氮苯发色团的有机/无机杂化多层膜。由于带负电荷的ZrO₂与PAC - azoBNS中偶氮苯发色团的磺酸根基团之间存在强烈排斥作用，从而实现了NLO活性偶氮苯发色团的非中心对称取向。通过紫外 - 可见吸收光谱和石英晶体微天平测量验证了ZrO₂/PAC - azoBNS/PDDA多层膜的规则沉积。紫外 - 可见吸收光谱和透射二次谐波产生（SHG）测量均证实了所制备的ZrO₂/PAC - azoBNS/PDDA多层膜中偶氮苯发色团的非中心对称取向。当ZrO₂/PAC - azoBNS/PDDA膜的沉积循环次数保持不变时，SHG信号的平方根（I(2ω)(1/2)）随着PAC - azoBNS中偶氮苯接枝率的增加而增加，而膜的二阶极化率χ(zzz)(2)则随着偶氮苯接枝率的增加而降低。此外，当使用一端带有羧酸和/或羟基且另一端带有磺酸根基团的小有机偶氮苯化合物时，该方法成功扩展到实现多层膜中偶氮苯发色团的非中心对称取向。该方法的特点是在膜制备过程中简单且灵活，有望成为制备二阶非线性光学薄膜材料的简便方法。
