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.

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.

For reverse photochromism JACS. 2006, 128, 15938-15939 Christopher J. Bardeen et.al For reverse photochromism K3 ≥ k4 Journal of Photochemistry, 28 (1985) 103 - 110 MAKIKO ISSHIKI et. al

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

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).

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

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°

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

Dependence of bending motion… 5 s ~ 30 s 9° ~ 25° No UV- 500 s ~ 1400 s 530 nm at 10 mWcm-2- 63 s

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

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 0.905 (2): 0.095 (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 -172.4(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’)

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.

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.

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

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.