Photomodulated Self-Assembly of Hydrophobic Thiol Monolayer-Protected Gold Nanorods and Their Alignment in Thermotropic Liquid Crystal

Abstract

Three terminal thiols possessing azobenzene and perylene diimide (PDI) segments covalently linked by alkylene spacers of different lengths (PnSH, n = 4, 6, and 8) were synthesized to stabilize and functionalize gold nanorods (GNRs) via strong covalent Au–S bonds onto the gold surface. The resulting hydrophobic thiol monolayer-protected GNRs (PnGNRs) were stable in both organic solvent and the solid state and exhibited fascinating photoresponsive self-assembly behavior. The PDI moieties provided π–π interactions to promote GNR self-assemblies while the photoresponsive azobenzene moieties offered a way to phototune the assemblies in a reversible manner. Interestingly, when PnGNRs were mixed with a structurally similar room-temperature thermotropic liquid-crystal perylene diimide (LCP), the UV-irradiated PnGNRs showed more compatibility with the LCP host than their corresponding unirradiated ones. Furthermore, the PnGNRs with varied alkylene chain lengths showed different dispersion abilities in LCP. The UV-irradiated P4GNRs did not disperse well in LCP, whereas the UV-irradiated P6GNRs and P8GNRs dispersed well in LCP and were further aligned upon mechanical shearing. In addition, preliminary molecular simulation was performed to explain this interesting photomodulated self-assembly of the GNRs.