Key Laboratory of Mesoscopic Chemistry of MOE, School of Chemistry & Chemical Engineering, Nanjing University, 22 Hankou Road, Nanjing, 210093, People's Republic of China.
Nanoscale. 2017 Nov 9;9(43):16700-16710. doi: 10.1039/c7nr03421k.
The combination of photo-responsive azobenzene (AB) and biocompatible Au nanomaterials possesses potential applications in diverse fields such as biosensing and thermotherapy. To explore the influence of azobenzene moieties and Au substrates on the collective switching behavior, two different azobenzene derivatives (rigid biphenyl-controlled versus flexible alkoxyl chain-linked) and three different Au substrates (a planar Au(111) surface, curved Au(SR) and Au(SR) clusters) were chosen to form six Au@AB combinations. A reactive molecular dynamics (RMD) model considering both the torsion and inversion path was implemented to simulate the collective photo-induced cis-to-trans switching process of AB monolayers on Au substrates. The major driving force for isomerization is demonstrated to be the torsion of the C-N[double bond, length as m-dash]N-C dihedral angle, in addition to the minor contribution from an inversion pathway. The isomerization process can be divided into the preliminary conformation switching stage and the later relaxation stage, in which a gradual self-organization is observed for 40 ps. The Au substrate affects the packing structure of the AB monolayer, while the choice of different kinds of ABs tunes the intermolecular interaction in the monolayer. Flexible alkoxyl-linked F-AB may achieve much faster conversion on Au clusters than on the surface. For rigid biphenyl-based R-AB anchored on Au nanoparticles (AuNPs), a competitive torsion between the biphenyl and C-N[double bond, length as m-dash]N-C dihedral may delay the C-N[double bond, length as m-dash]N-C dihedral torsion and the following isomerization process. After the R-AB molecules were anchored on the Au(111) surface, the strong π-π stacking between biphenyl units accelerates the collective isomerization process. A curvature-dependent effect is observed for R-AB SAMs on different-sized substrates. The cooperation between functional AB monolayers and the Au substrate determines the collective switching behavior of Au@AB materials. These results are expected to guide rational designs of Au@AB hybrid materials for different uses.
光响应偶氮苯（AB）与生物相容的 Au 纳米材料的组合在生物传感和热疗等多个领域具有潜在的应用。为了探究偶氮苯基团和 Au 基底对集体开关行为的影响，选择了两种不同的偶氮苯衍生物（刚性联苯控制与柔性烷氧基链连接）和三种不同的 Au 基底（平面 Au(111)表面、弯曲 Au(SR)和 Au(SR)团簇）来形成六个 Au@AB 组合。实施了考虑扭转和反转路径的反应分子动力学（RMD）模型，以模拟 AB 单层在 Au 基底上的集体光诱导顺反异构转换过程。结果表明，异构化的主要驱动力是 C-N[双键，长度为破折号]N-C 二面角的扭转，此外还有较小的反转途径贡献。异构化过程可以分为初步构象转换阶段和后期松弛阶段，在 40 ps 内观察到逐渐的自组织。Au 基底影响 AB 单层的堆积结构，而不同种类的 AB 则调节单层中的分子间相互作用。柔性烷氧基连接的 F-AB 可能在 Au 团簇上比在表面上实现更快的转换。对于刚性联苯为基础的 R-AB 锚定在 Au 纳米颗粒（AuNPs）上，联苯和 C-N[双键，长度为破折号]N-C 二面角之间的竞争扭转可能会延迟 C-N[双键，长度为破折号]N-C 二面角的扭转和随后的异构化过程。R-AB 分子在 Au(111)表面上锚定后，联苯单元之间的强 π-π 堆积加速了集体异构化过程。在不同尺寸的基底上观察到 R-AB SAMs 的曲率相关效应。功能 AB 单层与 Au 基底的协同作用决定了 Au@AB 材料的集体开关行为。这些结果有望指导不同用途的 Au@AB 杂化材料的合理设计。
