Self-assembly of photoresponsive dendritic molecules

Abstract

Molecular self-assembly through specific interactions has provided an important basis of the bottom-up based nanotechnology for generation of nanostructures. Utilization of dendritic architectures in self-assembly is highly attractive partly because of the interesting characteristics encoded in their molecular structures, such as the cone-shape architecture, a large number of functional groups on the surface, easily tunable focal point, etc.. Also, the macromolecular nature of well-defined architecture is expected to fill the gap between polymeric and small molecular properties. By intelligent design of the molecular structure, the resulting structures can be also responsive to other external stimuli such as photochemical, chemical, or mechanochemical. Among these stimuli, light can be regarded as an ideal candidate to control the state of self-assembled structures because it acts in non-contact and site-specific fashion. Also, it is possible to precisely control the irradiation conditions by choosing proper irradiation time, intensity, wavelength, and polarizing direction. A novel photoresponsive bis-dendritic organogelator, consisting of a benzamide dendron and a diacetylene dendron, was synthesized and the physical behavior was studied. The bis-dendritic molecule showed physical gelation through self-assembled fibrillar network in solvents such as chloroform. When a chloroform solution of the compound was cast on a Si wafer in a stream of moist air, well-defined honeycomb patterns with the spherical cavities with diameter of ca. $1 \mu m$ were obtained. To utilize top-down lithographic techniques on the self-assembled structure generated by the bottom-up approach (breath figure), specific regions of the honeycomb patterns were exposed to UV using a line-patterned mask to induce selective chemical crosslinking between the diacetylene groups. Subsequent developing in acetone showed patterned honeycomb lines obtained at pre-defined locations. Fabrication of ...