Photoalignment of poly(di-n-hexylsilane) by azobenzene monolayer.: 1.: Preparative conditions of poly(di-n-hexylsilane) spincast film

The photocontrol of the in-plane alignment of spincast poly(di-n-hexylsilane) (PDHS) film was successfully achieved on a photooriented azobenzene- (Az-) containing monolayer irradiated with linearly polarized visible light. The Si backbone of PDHS after crystallization aligned in the perpendicular direction to the polarization plane of actinic light. The preparative conditions of the PDHS film such as molecular weight of this material and thickness were examined in detail by polarized UV-visible absorption spectroscopy. The orientational order of PDHS chain was strongly dependent on the molecular weight of PDHS. Lowering of the molecular weight of PDHS gave rise to a higher orientational order of the Si backbone. With increasing film thickness, the photoalignment of the PDHS main chain became less efficient. However, successive annealing and crystallization upon cooling provided high degrees of alignment even for thicker films of the low molecular weight material. The atomic force microscopic observation revealed the formation of characteristic fibrous morphologies in the film, which was directed parallel to the electric vector of the polarization. Thus, photoinduced anisotropy in the Az monolayer controls not only the PDHS backbone alignment but also the mesoscale morphology of the film at larger hierarchies.