Manipulation and assembly of small objects in liquid crystals by dynamical disorganizing effect of push-pull-azobenzene-dye

Abstract

The phase transition of a nematic liquid crystal containing a push-pull azobenzene dye could be induced efficiently during irradiation with visible light. The dynamical disorganizing effect of the push-pull azobenzene dye on the liquid crystalline order through its trans-cis-trans photoisomerizaion cycle under visible light was contributed to the efficient phase transition. Then, the effects of light irradiation on the motion of small objects dispersed in the liquid crystals containing the push-pull azobenzene were explored, and the manipulation and assembly of those objects were successfully achieved in the nematic phase but also in the smectic phase. The combination of the photo-controlled dynamical change in the liquid crystalline order and the intrinsic self-assembly property of a liquid crystal is promising for use in technologies that require not only the organization of small objects but also the photo-driving of nano- and micro-sized mechanical materials.

Nanoporous frameworks exhibiting multiple stimuli responsiveness

“…These entities have recently attracted much attention as key components of stimuli-responsive materials, examples of which include self-darkening windows 3 , self-healing coatings [4][5][6] , or silica-based delivery vesicles, which can be engineered to release cargo molecules upon activation with a variety of external stimuli 7,8 . Among these different stimuli, light is arguably the most attractive: it is a stimulus that can be delivered instantly, into a precise location, and in the form of different wavelengths, to which different photoresponsive molecules selectively respond [9][10][11] . One of the most unique examples of molecular switches is spiropyran, whose closed-ring, hydrophobic SP isomer transforms into a highly polar, open-ring merocyanine (MC) form upon exposure to ultraviolet light, whereas the reverse reaction can be induced by visible light [12][13][14] .…”

Photo-responsive traveling of small-particles modified with azobenzene groups as molecular motors in a liquid crystal

“…Therefore, considering the possibility for micro-manipulation in our previous study [16], we hypothesized that the Azo/MPs have potential applications as micro-machines driven by moving optical stimuli in a LC with an organized structure.…”

“…On the other hand, the decreasing intensity immediately recovered to its pre-irradiation level after shutoff of pumping light ('off' time). On the basis of the verification of moving behavior and the evaluation of the phase transition, the results suggest that, around the DR1USi /MPs in the irradiation area, the N-to-I phase transition of 5CB is caused by a dynamical disorganizing effect [16], which is associated with the photo-induced trans-cis-trans isomerization of the push-pull-substituted DR1, as shown in Figure 3d.The driving force for the dynamical disorganization cannot clearly suggest, at this stage, an elastic force or a force induced by interfacial tension between different phases, indicating the presence of N-phase and a disorganized phase at the A-area in LC media. Before irradiation, almost all individual Azo/MPs were aligned along the LC organizing direction by the rubbing treatment, as shown in Figure S2.…”

“…In Figure 2a, an absorption band originating from Push-Pull DR1USi on the DR1USi/MPs was observed at approximately 500 nm, corresponding to the spectrum for the DR1USi solution (Figure 2b), and the spectrum changed slightly by photo-induced isomerization after a few minutes of visible-light irradiation. This small change under visible-light irradiation indicates that the quantities of cis-DR1USi in the photo-stationary state are quite low and that reversibletrans-to-cis and cis-to-trans (trans-cis-trans) isomerization cycles [16,24] occur even on the surface of the DR1USi/MP. Therefore, considering the possibility for micro-manipulation in our previous study [16], we hypothesized that the Azo/MPs have potential applications as micro-machines driven by moving optical stimuli in a LC with an organized structure.…”

“…Using molecular motors, which are similar to bio-motors such as protein motors [4][5][6], has been a simple and promising strategy for developing these types of machines. In particular, azobenzene (Azo) derivatives [7][8][9][10][11][12][13][14][15][16][17][18][19] or other photo-responsive molecules [20][21][22][23] have been utilized as moieties that produce the driving force for photo-induced mechanical materials such as molecular motors. Several research groups have reported motive objects such as small particles [13][14][15][16]20] and liquid droplets [17,18] by using photo-responsive molecules that are sensitive to light stimuli.…”