2015.06.09 Yuna Kim Adv. Funct. Mater. 2015, early view DOI: 10.1002/adfm.201500942 Fascinating photoresponsive thin films are well prepared from the first synthesized pillararene-based macrocyclic azobenzene liquid crystals, which demonstrate rapid reversible photoisomerization and on–off switching property, with further excellent light-triggered modulation of surface free energy, wettability, and even photoalignment-mediated orientation of discotic liquid crystal columnar mesophase. Such well-defined photoresponsive materials provide a promising platform for constructing various novel photoresponsive systems.

photochromic mesogenic unit – azobenzene - self-assembling capability and ordered characteristic of LC system; manipulating photoalignment due to their amplifying photoinduced orientation of photochromic moieties and stabilizing the oriented states. promising platform for constructing photoresponsive smart surfaces combination of long-range ordering, mobility, and response to light stimulation Trans/cis isomerization PC transformation requires sufficient free volume - low molar mass azobenzene molecules in the bulk state; the photo-responsiveness is usually remarkably weakened or even completely suppressed due to severe H-aggregation. - azobenzene containing polymer films; Self-healing capability but ill-defined composition due to the intrinsic polydispersity of the synthetic polymers A sound solution; 1) well-defined side-chain azobenzene dendritic LC systems 2) introducing a rigid or semi-rigid framework with a cavity to provide sufficient free volume

Command surface- regulating the orientation of calamitic mesogens by surface-assisted photoalignment calixarene-based macrocyclic amphiphiles with photochromic azobenzene units tethered asymmetrically on one side were immobilized on a substrate Photocontrolled Orientation of Discotic Liquid Crystals Authors gave attention on to the commander surface system DLC Limited research; mostly aiming on Low orderly discotic nematic phase - photo-triggered surface contact angle change - a light-driven directional movement of a liquid droplet Ichimura et al Adv. Mater. 2000, 12, 950 Furumi et al J. Phys. Chem. B 2007, 111, 1277 K. Ichimura , S. Oh , M. Nakagawa , Science 2000 , 288 , 1624 . K. Ichimura , Chem. Rev. 2000 , 100 , 1847 .

intermolecular p–p interactions between neighboring pillar[5]arene cores play an important role in the stabilization of the smectic A phase Nierengarten et al pentagon-shaped subunits within closely packed smectic layers may result in orientational and/or positional disorder. As a result, the crystalline phase may be destabilized but, at the same time, the intermolecular interactions between neighboring pentagon-shaped moieties should contribute to the stabilization of the liquid-crystalline phase.

Pillar9arene based Tubular framework to provide free volume

Thermotropic LC Phase Behaviors and Bulk State Packing Structures shorter spacer; less flexibility and more compact packing No crystalline phase but phase transition to glass

Thermotropic LC Phase Behaviors and Bulk State Packing Structures Lamellar periods

Thin Film Photoisomerization Comparison of Pillararene- Based Macrocyclic Azobenzenes with Variant Length Spacers Trans to cis isomerization No big difference but shorter chain length showed lower conversion extent; shoulder peak

Photoalignment of Pillararene-Based Macrocyclic Azobenzene Thin Films 2D and 3D Alignment Slantwise orientation 1h Irr. for homeotropic orientation Oblique irr. Exposed part; bright LP light; azo orientation perpendicular to the polarization direction

Readily Achievable homeotropic On–Off Switching of Photoalignment Pristine; strongest p-p absorption-totally random orientation 365->450 vs pristine historical imprint Destroying homeotropic alignment

Photo-regulated interfacial properties: oil contact angle Surface free energy increment by increasing cis isomers 450 nm; homeotropic alignment-> dewetting 41 deg; reduced surface free energy Why not comparing those on oblique aligned surface??

Photoaligned Surface-Mediated Migration and Orientation of DLC Columnar Mesophases 2,3,6,7,10,11-hexakis(hexyloxy)triphenylene exhibiting typical hexagonal columnar phase surface tension gradient due to free energy difference of underlying different directionally photoaligned azobenzene layer to LC phase Denser; Preferred wetting on oblique aligned area The main driving factor for the migration that leads to denser POM texture in obliquely aligned stripes is supposed to be the Still somewhat random Homeotropic orientation of TP6 columns

Conclusions - The tubular pillar[5]arene-based macrocyclic framework provides sufficient free volume for azobenzene moieties to achieve reversible photoisomerization and light-induced alignment. Both Pillar[5]-S10-Azo and Pillar[5]-S4-Azo with variant length spacers showed wide temperature range lamellar LC mesophases and excellent film-formation property. Pillar[5]-S10-Azo films of longer spacers displayed better photoresponse performance as demonstrated by light-triggered modulation of surface free energy, wettability, and even photoaligned surface-mediated orientation of TP6-based DLC columnar mesophases. In view of their readily achievement of alignment via simple actinic light irradiation of selected wavelengths or just changing incident directions, pillararene-based macrocyclic azobenzenes represent novel promising well-defi ned LC PRMs for film surface modulation and fascinating photoalignment directing agents.