1. Photomechanical bending of salicylideneaniline crystals
Hideko Koshima, Kyoko Takechi, Hidetaka Uchimoto, Motoo Shiro and Daisuke Hashizume
Department of Materials Science and Biotechnology, Graduate School of Science and Engineering, Ehime University, Matsuyama, Japan.

2. Introduction
External stimuli using as molecular scale mechanical motion.
No macroscale mechanical motion based on molecular level shape changes.
Only in nematic elastomers, due to order-disorder phase transition as driving force.
JACS. 2010, 132, 14172–14178
Mechanical bending of diarylethene crystals by Irie et al.
Diarylethene derivative + perfluoronaphthalene
Due to elongation of b-axis
Cantilevers can lift very heavy metal balls.
Maximum deflection of 5 μm after 0.2 s.
The degree of deflection
along the a -axis < than that along the b
JACS. 2009, 131, 6890–6891
Hideko Koshima et al.

3. For reverse photochromism
JACS. 2006, 128,
Christopher J. Bardeen et.al
For reverse photochromism
K3 ≥ k4
Journal of Photochemistry, 28 (1985)
MAKIKO ISSHIKI et. al

4. N-3,5-di-tert-butylsalicylidene-3-nitroaniline
enol-1
trans-keto-1

5. Microcrystal synthesis…
On the surface and b) On the edge of the silanated glass plate.
Sublimed in a platinum pan, covered with silanated glass plate and grew the glass crystal by heating at a temperature 10 0C below melting point (132 0C).

6. X-ray diffractograms…
Before irradiation
During UV irradiation
Top surface is (001) face with longitudinal direction along the a -axis

7. 530 nm (10 mWcm-2) with halogen lamp
365 nm (40 mWcm-2) with UV-LED
45°after 5 s
530 nm (10 mWcm-2) with halogen lamp
Initial after 10 s
Video
2 s UV on and 5 s off, displacement is 37°

8. 365 nm
2.6 s
530 nm
63 s
In dark
42 day s
k = 2.8 ✕10- 7s-1 at 25 °C
Intermolecular hydrogen bonding

9. Dependence of bending motion…
5 s ~ 30 s
9° ~ 25°
No UV- 500 s ~ s
530 nm at 10 mWcm s

10. Dependence of degree of tip displacement…
Aspect ratio (length/thickness)
25° for 25 (50✕ 6.3 ✕2.1 μm)
52° for 71 (120✕ 7.1 ✕1.7 μm)
70° for 132 (159✕ 6.8 ✕1.2 μm)
Movement of silica gel particle…
Crystal on silanated surface bent
120✕ 7.1 ✕1.7 μm
50 fold heavier than microcrystal
Mechanical force generated is large
Video
Video

11. before and after successive UV irradiation
Crystallographic analysis…
200✕ 30 ✕20 μm3 microcrystal at 123 K
A disordered structure with ratio of enol-1 and trans-keto-1 is (2): (2)
before and after successive UV irradiation
The Oak Ridge Thermal Ellipsoid Plot (ORTEP)…
Bond length of trans-keto-1 b/w C(2’)-O(1’ ), C(1’)-C(7’) and C(7’)-N(1’) are 1.305(9), 1.415(9), and 1.349(9) A° which differs significantly from those 1.355(4), 1.441(5) and 1.273(4) A° of enol-1
enol-1
trans-keto-1
Torsion angle of trans-keto-1 b/w C(8’)-N(1’ )-C(7’)-C(1’) was (18)° and that of enol-1 was 177.2(3)°
O(1’) and N(1’) are in trans position w.r.t C(1’)- C(7’)

12. Changes of unit cell upon UV…
Photoisomerisation elongates crystal length along a-axis near the (001) crystal surface. ✓
In the absence of light , dimension of unit cell remains constant at the non illuminated surface, which result bending of microcrystal away from the light source.

13. AFM… (001) Surface of enol-1
Small dent with depth 1.5 nm up on 40 s UV
Smooth before
Overall morphology same
Overall morphology same
This result suggest minimal molecular movement like pedaling motion during photo isomerization is the reason for excellent 200 times repeatability.

14. Conclusion…
The photomechanical bending of plate like microcrystals of N-3,5-di-tert-butylsalicylidene-3-nitroaniline was repeated upon alternate irradiation.
The mechanism of bending was elucidated by X-ray crystallographic analyses.
thank you

15. External stimuli using as molecular scale mechanical motion.
No macroscale mechanical motion based on molecular level shape changes.
Only in nematic elastomers, due to order-disorder phase transition as driving force.