Taffa Derejehailu, Kathiresan Murugavel, Walder Lorenz
Institute of Chemistry, University of Osnabruck, Barbarastrasse. 7, D-49069 Osnabruck, Germany.
Langmuir. 2009 May 5;25(9):5371-9. doi: 10.1021/la8038126.
Alkyl phosphonic acids (Pho-C(n)-R) of different chain length (6, 10, and 14 carbons) bearing neutral, positive, and negatively charged head groups (R = -H, R(-) = sulfonate, R(+) = pyridinium) were prepared and anchored to the inner walls of randomly sintered mesoporous TiO(2) thin films. Quartz crystal microbalance (QCM) and Fourier transform infrared (FT-IR) measurements show that a monolayer coverage was achieved. The monolayer crystallinity is lower as compared to alkyl thiols on gold, but it increases with the length of the carbon chain. The neutral phosphonic acid modifier makes the TiO(2) highly hydrophobic and suppresses electrochemistry in aqueous media, and the alkyl phosphonic acids with charged head groups render the TiO(2) film as an ion exchanger with a phase separated hydrophilic and hydrophobic portion. Different charged guest molecules were incorporated on top or into the supported membranes. The host-guest interactions were found to be electrostatic, hydrophobic, or both. Highly charged electroactive metal complexes (Fe(CN)(6), IrCl(6)) and purpose-synthesized organic electrochromophores (dialkylated viologens with variable chain length, C(1)-V(+2)-C(n), C(n)-V(+2)-C(n), n = 6, 10, and 14) were used as molecular guests, and the assemblies were characterized by cyclic voltammetry and FT-IR. Using the preconcentration phenomenon, Fe(CN)(6) concentration as low as 200 nM can be detected on a Pho-C(14)-R(+) modified TiO(2) electrode by conventional cyclic voltammetry. The new surface modification technique simplifies the molecular requirements for functional surface modifiers considerably. Using a limited set of organic anchors with orthogonal coordination properties and adjustable hydrophobicity, a broad range of electrochromophores, redox active wiring compounds, or sensitizers can be adsorbed onto TiO(2).
制备了具有不同链长（6、10和14个碳）且带有中性、正电荷和负电荷头基（R = -H，R(-) = 磺酸盐，R(+) = 吡啶鎓）的烷基膦酸（Pho-C(n)-R），并将其锚定在随机烧结的介孔TiO₂薄膜内壁上。石英晶体微天平（QCM）和傅里叶变换红外（FT-IR）测量表明实现了单层覆盖。与金表面的烷基硫醇相比，单层的结晶度较低，但随着碳链长度的增加而提高。中性膦酸改性剂使TiO₂具有高度疏水性，并抑制了在水性介质中的电化学作用，而带有电荷头基的烷基膦酸使TiO₂薄膜成为具有相分离的亲水和疏水部分的离子交换剂。不同电荷的客体分子被引入到支撑膜的顶部或内部。发现主体-客体相互作用是静电的、疏水的或两者兼有的。高电荷的电活性金属配合物（[Fe(CN)₆]⁴⁻、[IrCl₆]²⁻）和专门合成的有机电致变色发色团（具有可变链长的二烷基紫精，C₁-V⁺²-Cₙ、Cₙ-V⁺²-Cₙ，n = 6、10和14）被用作分子客体，并且通过循环伏安法和FT-IR对组装体进行了表征。利用预富集现象，通过传统循环伏安法可以在Pho-C₁₄-R⁺修饰的TiO₂电极上检测到低至200 nM的[Fe(CN)₆]⁴⁻浓度。这种新的表面改性技术极大地简化了对功能性表面改性剂的分子要求。使用一组具有正交配位性质和可调节疏水性的有限有机锚定剂，可以将广泛的电致变色发色团、氧化还原活性布线化合物或敏化剂吸附到TiO₂上。
