This document discusses the design and operation of molecular rotary motors at interfaces. It describes: 1) How rotary motors in biology inspired the design of an artificial molecular rotor with a photoisomerizable double bond that undergoes a light-driven unidirectional rotary cycle. 2) Methods explored to control the speed of rotation, attach the motors to surfaces, and demonstrate light-driven rotary motion of surface-bound motors. 3) Efforts to utilize the rotary motion to perform work, such as stirring molecules at the interface, which could enable applications if the random motion of the motors can be confined and directed.

1. Gregory Carroll
Stratingh Institute for Chemistry
University of Groningen
March 23, 2009
ACS National Meeting Salt Lake City
Light-driven Molecular Motors at
Interfaces
g.t.carroll@rug.nl

2. 2
Rotary Motors
Can rotary motion at the molecular level to perform useful tasks?

3. 3
Rotary Motors in Biology
ATP Synthase
Bacterial Flagellar Motor
Rotor: 6000-17 000 RPM
Alberts et al. MolecularBiology ofthe Cell
~100 r.p.s.

4. 4
Designing a Molecular Rotor
( P , P ) - t r a n s
M e a x
M e a x
DEFINITION:
A rotary motor is a device
that is able to convert
energy input into controlled,
directional, rotary motion in
a continuous fashion
REQUIREMENTS
• Controlled Motion
• Consumption of Energy
• Directional Movement
• Continuous Process
Structural Features
• Photo-isomerizable double-bond
• Two helical halves
• Two stereogenic centers on each half
cis
trans

5. 5
Rotary Cycle
(P,P)-trans
Meax
Meax
(M,M)-cis
MeeqMeeq
> 280 nm
Meeq
Meeq
(M,M)-trans
> 280 nm
N. Koumura, R.W.J.Zijlstra, R.A. van Delden,N. Harada, B.L. Feringa, Nature 1999,401,152
D 60o
C
T1/2 (4th Step) = 233 h at 20° C
Meax Meax
(P,P)-cis
20o
C
T1/2 (2nd Step) = 32 min. at 20° C

6. 6
Ideal Unidirectional Rotation

7. 7
2nd Generation Motors
• Symmetric tri-cyclic lower half
• Unidirectional rotation controlled by a single stereogenic center
• The energy barriers for the thermal steps can be adjusted (X,Y)
• Distinct chemical functionalities can be introduced into the upper and lower
halves, allowing for attachment to surface and modification of properties
KEY FEATURES:
X
Y
Me
H
Desired Properties
• Ability to control speed
• Functionality for attachment to surface

8. 8
Unidirectional Rotation
-150
-100
-50
0
+50
+100
+150
250 300 350 400 450
D
 /nm
(2’R)-(M)-trans-1
(2’R)-(P)-cis-2
(2’R)-(M)-cis-2
(2’R)-(P)-trans-1
S
S
Mea x
MeO
Hg-lamp, 365 nm
5 ~ 10°C
S
S
MeO
60°C
S
S
MeO
S
S
MeO
Meeq
MeaxMeeq
60°C
Hg-lamp, 365 nm
5 ~ 10°C
(2'R)-(M)-trans-1 (2'R)-(P)-cis-2
(2'R)-(P)-trans-1 (2'R)-(M)-cis-2
ratio 14:86
ratio 89:11
T1/2 = 233 h at 20° C

9. 9
Increasing the Speed
hn hn
D
Energy
Rotation step
stable trans stable transstable cis
unstable
trans
D
unstable cis
Size of bridging rings
Size of substituent
at stereocenter
T1/2 = 5.74 x 10-3 s at 20° CT1/2 = 3.2 min. at 20° CT1/2 = 233 h at 20° C
S
S
M e a x
M e O
(2 'R )-(M )-tra n s-1
Michael M. Pollard, Martin Klok, Dirk Pijper and Ben L. Feringa AdvancedFunctionalMaterials2007,17,718-729.

10. 10
Utilizing Motor to Perform Work
Major Hurdle: Brownian Motion
Limit random motion – Confine motor at interface
Stable attachment to surface
Adsorption on surface
Long-term Goal: Show that movement of rotor
can affect motility of motor or molecule/material
in presence of motor
Interfacial Stir Bar
hn
Crowd Surfing
Molecules

11. 11
Surface-bound Motors
Azimuthal orientation Altitudinal orientation
G.S. Kottas, L.I. Clarke, D. Horinek, J. Michl , Chemical Reviews2005, 105,1281-1376
Need two-legged attachment to prevent
rotation around single bond.

12. 12
Unidirectional rotation on Au nanoparticles
-38
-37.8
-37.6
-37.4
-37.2
-37
-36.8
-36.6
-36.4
0.0028 0.00285 0.0029 0.00295 0.003 0.00305 0.0031
1/T (K-1
)
ln((kh)/(kBT))
nanoparticles
parent motor
t1/2 = 198 h
t1/2 = 93 h
0 2 4 6 8
-20
-10
0
10
20
30
CD
(mdeg)
hn>280 nm hn365 nm hn365 nm hn365 nmD D D D
CD signal at 280 nm
through 2 rotary cycles

13. 13
Monolayer of Motors on Au Film
Au
Au

14. 14
quartz
Thin gold surfaces
Au Vapour
deposition
200 400 600 800 1000
0.0
0.2
0.4
0.6
absorbance(a.u.)
wavelength (nm)
5 nm gold
5 nm gold
quartz
quartz
OH OH OH OH OH OH
O O
Si
NH2
O O
Si
NH2
O O
Si
NH2
O O
Si
NH2
O O
Si
NH2
O O
Si
NH2
1) H2SO4 / H2O2
2)
O O
Si
NH2
Transparent Gold Surface

15. 15
Self-assembled monolayer of molecular motors
Dense SAM
Dilute SAM
No change upon irradiation
quartzquartz
5 nm gold 5 nm gold
10:1
Decanethiol:motor
S
O
O
O
O
S
S
S
OO
O
O
S
S
S
O
O
O
O
S S
S
O
O
O
O
S
S
SO
O
O
O
S
S
S
O
O
OO
S
S
S
O
O
O
O
SS
S
O O
O
O
S
S
Au Nanoparticles

16. 16
Increasing the length of the legs
• Motors function with longer tethers to gold
surface, but suffer from some quenching by
the gold.
• Results in longer irradiation times
9 9 9 9
9 9 9 9

17. 17
Grafting Motor to Quartz
M. M. Pollard, M. Lubonska, P. Rudolf,B.L. Feringa, Angewandte ChemieInt. Ed. 2007,46, 1278-1280

18. 18
Molecular motors function on quartz
on surface
in solution
in solution
on surface
D

19. 19
Altitudinal Motor on Surface
XX
• Store for extended periods without degradation or polymerization
• Motor should be stable for complete characterization prior to surface modification
• Reliable and reproducible surface modification
• Monolayer
New Strategy for Functionalization of Quartz, SiO2/Si and mica
• Difficulty introducing acid chloride into legs of some motors
• Acid chloride moisture sensitive and therefore characterization prior to surface
modification is limited
• amino silane surfaces not easy to control
Limitations of Previous Method

20. 20
Interfacial 1,3 Dipolar Cycloaddition
H R2
Cu-cat. N N
NR1
R2H
NR1 N N
T. Lummerstorfer,H. Hoffmann
Journalof PhysicalChemistryB
2004,108,3963-3966
R R'
Hartmuth C. Kolb, M. G. Finn, and K. Barry Sharpless
Angewandte Chemie InternationalEdition 2001,40,2004-2021
Mixed monolayers on Au
Monolayers on SiO2/Si wafer
Magnetic Nanoparticles
J. P. Collman, N. K. Devaraj,
C. E. D. Chidsey Langmuir 2004,20,1051-1053
M. A. White, J.A. Johnson, J. T. Koberstein,N. J. Turro
Journalof the American Chemical Society 2006,128,11356-11357

21. 21
Solution-phase
365 nm
OR
OR
OR
OR
D
O
O
O
O
stable unstable stable
t1/2 = 1.5 min (20oC)
D‡G° = 83.5 kJ/mol
R = (CH2)2OCH2CCH
300 400 500
0,0
0,1
0,2
0,3
0,4
0,5
Absorbance(a.u.)
Wavelenght (nm)
Stable, MeOH, -20C
60 min irrad, 365nm
300 400 500
-50
0
50
100
D
Wavelenght (nm)
Stable, MeOH, -20C
90 min irrad, 365 nm
UV-Vis Absorbance
CD
3:1 ratio at
photostationary state
G. London,G. T. Carroll, T. Fernández Landaluce, M. M. Pollard,
P. Rudolf and B. L. Feringa, ChemicalCommunications,2009,1712

22. 22
Azide-SAM Formation
SiO O Si O Si O
N3 N3 N3
SiO O Si O Si O
OH OH OH
Si
O
O
O
11CH2
Br
Si
O
O
O
11CH2
N3
NaN3
Cyclohexane/THF
H2O/H+
H2O Contact Angle: 73±3
Ellipsometric Thickness: 0.7 ±0.1 nm
Method 2 (Self-assembly in toluene)Method 1 (Hydrolysis in THF,
Self-assembly in cyclohexane)
H2O Contact Angle: 82±1
Ellipsometric Thickness: 1.8 ±0.1 nm
CH2
ATR IR
cm-1
1.5
1.0
0.5
x10
-3
3000 2900 2800 2700 2600
1.5
1.0
0.5
x10
-3
2200 2150 2100 2050 2000
Abs
390392394396398400402404406408410
Intensity(Arb.Units)
Binding Energy (eV)
N1s
X-ray Photo-electron Spectroscopy (XPS)
Azide 2095 cm-1
No photochemical degradation after 24 hrs irradiation
90%

23. 23
Motor-monolayer formation
800
600
400
200
x10
-6
2120 2100 2080 2060
Azide, 2095 cm-1FT-IR
H2O Contact Angle decreases: 67±2º
Ellipsometric thickness increases: 2.9 ±0.1 nm
390392394396398400402404406408410
Motor monolayer
Azide monolayerXPS
Intensity(Arb.Units)
Binding Energy (eV)
XPS
Azide
Triazole
No Cu or Na found in XPS survey
nm
8
6
4
2
0
x10
-3
460440420400380360340320300
Unmodified Quartz
Without Copper
Absorbance
Motor
SiO O Si O Si O
OO
OO
N3 N3 N3
SiO O Si O
O
O
O
O
N
N
N
N
N
N
CuSO4*5H2O (2 %)
Na-ascorbate (10%)
DMF, rt, 12h
2% Cu(SO4)
10% NaAsc
DMF

24. 24
Rotary Motion on Surface
SiO O Si O
O
O
O
O
N
N
N
N
N
N
SiO O Si O
O
O
O
O
N
N
N
N
N
N
D
365 nm
300 400 500
0,000
0,005
0,010
Abs
nm
Stable, -20C
30 min irr, 365nm
Therm Conv
1.6x10
-3
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Absorbanceat439nm
40003000200010000
Time (s)
28 C
40 C
28⁰C
40⁰C
Thermal step affected byconfinementin monolayer
Two processesoccurring?
T1/2 1st
step: 3 minutes
T1/2 2nd
step:21 minutes
Decay at 439 nm

25. 25
SEM
OO
O O
O
N
Si
O
O
N
Si
O
O
N
N
N
N
O
1111
H2O, H+
THF
OO
O O
N
Si
N
Si
OH
N
N
N
N
1111
HO
3
3
Silane-modified Motor
cyclohexane
Insoluble precipitate begins to form after
approximately 10 min.
Ellipsometric Thickness: 77±8 nm
H2O Contact Angle: 79 ±3
Robust Faint Yellow Film
0.14
0.13
0.12
0.11
0.10
0.09
Absorbanceat439nm
25x10
3
20151050
Time (s)
0.4
0.3
0.2
0.1
Abs
550500450400350
nm
60 min.
1 min.
Pre-irradiation
28 h
Very slow thermal recovery
clearly demonstrates effect of
crowding on speed

26. 26
250 300 350 400 450 500 550
0.0
0.2
0.4
0.6
0.8
1.0
Absorbance(au)
Wavelength (nm)
Stable, -20C, MeOH
PSS, 365nm
t1/2 (20oC)= 50 s (in MeOH)
The reverse reaction analogue
O
HO
O
HO
ON3
O
N3
1. Mesyl-Cl
CHCl2, 2h, rt
2. NaN3 DMF
5h, 55oC.
63 %
SiO O Si O Si O
OO
NH NH NH
O
O
O
O
O
O
N3N3
SiO O Si O Si O
NH NH NH
O
O
O
O
O
O
N
N
N
N
N
N
OO
CuSO4*5H2O (2 %)
Na-ascorbate (10%)
DMF, rt, 12h
8
6
4
2
0
x10
-3
550500450400350
Ellipsometric Thickness: 0.8 ±0.1 nm
H2O Contact Angle: 74 ± 10°
Ellipsometric Thickness: 1.9 ±0.1 nm
H2O Contact Angle: 57 ±1°
Alkyne Surface

27. 27
Two-legged Attachment
390392394396398400402404406408410
Motor monolayer
Azide monolayerXPS
Intensity(Arb.Units) Binding Energy (eV)
XPS
Azide
Triazole
S iO O S i O S i O
N H N H N H
O
O
O
O
O
O
N
N
N
N
N
N
OO
SiO O Si O Si O
NH NH NH
O
O
O
O
O
O
N3 N
N
N
OO
410 405 400 395 390
Intensity(Arb.Units)
Binding Energy (eV)
N1s
XPS after
reaction
1.4
1.2
1.0
0.8
0.6
0.4
0.2
x10
-3
3000 2900 2800 2700 2600 2500 2400
1.4
1.2
1.0
0.8
0.6
0.4
0.2
x10
-3
2300 2250 2200 2150 2100 2050 2000
ATR IR
No Azide

28. 28
H. Noji, R. Yasuda, M. Yoshida, K. Kinosita Jr. Nature,1997,386,299-302
Visualization of Rotary Motion
Group
Fluorescent
Group

29. 29
Fast Motor on Surface
Choice of motor:
Me
Br
MeO2C CO2Me
Coupling to the arm
Coupling to the surface
› Fast Motor against Brownian storm
(t1/2 nanoseconds)
0.8
0.6
0.4
0.2
0.0
DA
800700600500400
Wavelength (nm)
Increment: 1 ns
Frames: 98
Accumulations: 50
t0: 233203 ns
T: 22.3 deg C
Prof. Fred Brouwer(UniversiteitVan Amsterdam)
Rotation too fast to be measured using classical
techniques (CD, UV or NMR experiments)
O
Si
O O
Si
O
O
N N
9 9
N
N
N
N
Me
O
O
O
O
Quartz
10
8
6
4
2
0
x10
-3
440420400380360340320300280
nm
Cu, Azide SAM Lower Coverage
Cu, Unmodified Quartz
Azide SAM, No Cu
Cu, Azide SAM Higher Covarage
H2O Contact Angle: 65±2
Ellipsometric Thickness: 1.8 ±0.1 nm

30. 30
Me
OPr
OPr
MeO2C CO2Me
N
O OEt2N
O
OPr
OPr
OPr
OPr
OPr
OPr
OPr
OPr
OPr
OPr
OPr
OPr
OPr
OPr
Target Molecule
Dr. JeromeVachon
Considered to be relatively rigid structure
solubility
Converted to alkynes

31. 31
Length of Arm
Dye for visualization with wide-field
fluorescence imaging
Two alkyne moieties for attachment of
the motor ‘stator’ to the surface

32. 32
O
Si
O O
Si
O
O
N3 N3
9 9
Quartz
Attachment to Surface
Cu2SO4 (1 mol%)
Sodium Ascorbate (5 mol%)
DMF
c ~ 10-8 M
O
O
O
O
O
O
N
OPr
OPr
OEt2N
8
N
N
N N
N
N
O
Si
O
Si
O
O O
10 10

33. 33
O
O
O
O
O
O
N
OPr
OPr
OEt2N
8
N
N
N N
N
N
O
Si
O
Si
O
O O
10 10
Wide-field Microscopy
Filippo Lusitani University of Groningen
Fluorescence on Surface

34. 34
A Cholesteric (Chiral) LC
Chiral Dopant:
R. Eelkema, B. L. Feringa et al., Nature 2006, 440, 163.
ee.concHTP
1
p


pitch (p)

35. 35
Rotating Micro-scale Objects
Rienk Eelkema, et. al. Nature 2006,440,163
Texture Rotation Rotation of Micro-rod

36. 36
Motor-functionalized Polymers
O
N
N
O O
OO
C6H13H13C6
6
H17C8C8H17H17C8
* *
x y z
X : Y : Z = 10 : 11 : 1
No changes upon irradiation
hn hn

37. 37
Motor-terminated Polymer
Control over Helical
twist of single poly
(hexyl isocyanate)
macromolecule
D. Pijper et al, Angew.Chem.Int. Ed.,2007,46,3693.
Stiff helical conformations
Racemic P / M helicity (fast
dynamic equilibrium)
Subtle chiral influence can induce large preference for one helical sense:

38. 38
SurfaceAdsorption
AFM SEM
Polymer on mica
Au
Mica

39. 39
Acknowledgements
University of Groningen
Prof. Ben L. Feringa
Prof. Petra Rudolf
Dr. Michael Pollard
Gabor London
Tatiana Fernandez-Landaluce
Dr. Jerome Vachon
Filippo Lusitani
Dr. Dirk Pijper
Mahthild Jongejan
University of Amsterdam
Prof. Fred Brouwer
Nano Ned