1. Yuna Kim
Adv. Funct. Mater. 2015, early view DOI: /adfm
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.

2. 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

3. 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 ,
K. Ichimura , Chem. Rev , 100 ,

4. 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.

5. Pillar9arene based Tubular framework to provide free volume

6. 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

7. Thermotropic LC Phase Behaviors and Bulk State Packing Structures
Lamellar periods

8. 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

9. 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

10. 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

11. 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??

12. 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

13. 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.