Light irradiation process has the feature of being able to control and switch the structure and functional characteristics of material systems by non-contact mode, and is diverse for the construction of new devices for the future. The photoalignment technology already used in the fabrication of liquid crystal (LC) displays is a typical example as the practical application. The method of imparting light response functions to soft materials such as polymers and LC materials is currently a major trend in smart material chemistry. Dr. Takahiro Seki started research on polymers and LC systems using azobenzene from the dawn of this trend, and have led the field by proposing and demonstrating many types of photocontrol of soft material systems. The followings are his major contributions.

1. Photoalignment of polymer thin film systems with hierarchical structure
The photoalignment technology for LC display manufacturing utilizes photoinduced molecular orientation on a photoresponsive polymer film by irradiation with linearly polarized light or oblique irradiation. Dr. Seki extended this principle to the molecular orientation control of various types of hierarchical structures.
When a polymer film of a side-chain type LC polymer is prepared on a substrate, mesogens are oriented in the direction perpendicular to the substrate. This is a drawback that the probability of light absorption is not efficient. Dr. Seki prepared a high-density brush-type side-chain type LC polymer by living polymerization initiating from the substrate surface. This strategy orients the mesogen parallel to the substrate, which allows an efficient light response with linearly polarized light for the in-plane orientation characteristics. Furthermore, a simple high-density LC polymer brush forming method was proposed based on self-assembly by surface segregating of a LC block copolymer added in a small amount to an amorphous polymer. The polymer brush preparative method obtained by this method is not limited to a flat substrate but can be applied to curved surfaces. For example, by forming an azobenzene polymer brush on the surface of a honeycomb-shaped polymer film, a spherical nematic LC droplet embedded in the honeycomb cavity is prepared. This can be a new example of optical element where the orientation mode of the LC droplet (bipolar/radial) is switched by light.
The development of a method for controlling the on-demand alignment of the microphase-separated structure of block copolymers is important for their practical applications. Dr. Seki realized the photoalignent and its realignment of the microphase-separated structure by linearly polarized light using a LC block copolymer having an azobenzene unit. The photoalignment is advantageous in that the hierarchical structure can be easily oriented with a simple low-cost light source setup. Characterizations of structural changes in real time were successfully performed using a synchrotron radiation X-ray facility. The hierarchical alignment is found to proceed in a strongly cooperative way between the structures of different feature sizes.

2. Photocontrol from the free surface.
The surface photoalignment phenomenon of LC molecules has long been performed using solid substrate surfaces. On the other hand, Dr. Seki proposed a process using the free (air-side) surface for side chain LC polymer films. In this method, a new class of photoalignment processes can be envisioned. For example, LC alignment can be achieved on demand at a local part where a photoresponsive ink is drawn by the inkjet printing method.
In addition, Dr. Seki has proposed a method for surface microfabrication by controlling the light-induced Marangoni convection generated by the surface tension gradient. A side-chain azobenzene LC polymer film shows the smectic LC phase to isotropic phase transition by ultraviolet light irradiation. Thus, the large viscosity reduction of the phase transition can initiates the Marangoni convection at designed parts where inkjet-printing is drawn. Marangoni convection is technically troublesome that prevents its flatness during painting and spin coating, but this strategy contrastingly demonstrates that it can be a useful process as a new surface microfabrication procedure. Marangoni convection has been a well-known physical process since the 19th century, and this work is also significant in showing that this process can be controlled by light spatiotemporally.
The surface effect on the mass migration is further emphasized. Onto a light-passive LC polymer film, a molecular Langmuir film of a photoresponsive azobenzene polymer was transferred from the water surface, and then a patterned UV irradiation was performed. A large mass migration was induced in this system, which means that surface tension change at the outermost surface has a critical role in the mass migration. So far, photoinduced mass mgration motions has been interpreted by the gradient force of light, molecular volume change, mutual diffusion, mean field theory, phase change, etc., but the effect of surface tension at the outermost surface has hardly been considered. The photoinduced mass migration has been studied for more than 25 years, and this work proposes a new aspect in this field. Furthermore, the photocontrol of wrinkle formation with an azobenzene LC polymer placed on the surface of an elastomer film was achieved based on the light modification of Young's modulus of the surface photoresponsive film.

In summary, Dr. Seki's long lasting effort proposed new aspects of photoresponsive LC polymer film systems that show various molecular amplification effects, and created new innovations in this field. The proposal of polymer systems of photoresponsive polymer materials based on the interplay between the interface and the hierarchical structure has a great impact on the soft matter research area, and is expected to open the way to industrial technology. Therefore, his achievements were recognized as worthy of the Chemical Society of Japan Award.