Top Master Project december 2009
Feringa group Molecular Nanotechnology and Smart Materials
Title: ‘Molecular Switches; towards molecular electronic devices’
Among the most challenging goals in contemporary material sciences and
nanotechnology is the design of molecular electronic switches and trigger elements [1]
by which properties and functions can be controlled in a fully reversible manner in order
to achieve their implementation in molecular electronic devices. In contrast to the topdown approach based on miniaturization of existing electronic devices, new alternatives
focus on the building of entirely synthetic molecular systems that feature key functions
and which rely on assembly processes using small molecular building blocks in a so called
bottom-up approach.[2] Hence, implementation of molecular switches in real working
electronic devices is a breakthrough alternative for the fabrication of new molecular
systems that among others present further supramolecular functionalities controlled
through the switching units at the molecular level (Figure 1).
S
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closed
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577 nm
313 nm
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Figure 1a Diarylethene molecular switch for reversible light-controlled conductivity
modulation
Reversible conductance switching in large array
molecular devices
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Under Irradiation
Assembled Open
Assembled Closed
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Adv. Mater. 2008
with de Boer, Blom
Figure 1b Large array electronic device based on self-asembled monolayers of molecular
switches
In recent years, the group of Feringa has explored a wide variety of molecular switches
for the control of a range of properties including changes in colour, conductance,
fluorescence, assembly, transport, viscosity and chirality.[1,3] Outstanding results have
been obtained in the field of molecular switches as electronic components or molecular
units for information storage. For instance, recently in a joined effort the Feringa, Blom,
de Boer and van Wees groups have demonstrated solid-state molecular electronic devices
that show light-control reversible conductance of switch diarylethene molecules.[4]
In the design of synthetic molecular switches, the reversible control of switch function by
light stands out as it allows non-invasive triggering and easy tuning of the switching
process. The switches that we will developed will be based on diarylethenes shown in
figure 1, where the switching process, based on a photoinduced pericyclic cyclization
reaction, changes from a non-conjugated system (open state) to the conjugated
analogue (closed state). Alternatively we have demonstrated that these systems are
excellent redox switches. This gives these switches the unique property that by light or
by applying a voltage the electronic pathway – conductivity at the molecular level- can
be controlled (switched ) in a fully reversible manner!!
The goal of the current project is to study the self-assembly and electronic conductance
properties of molecular switches and we will in particular prepare 2D patterns of
organized electronic systems that can be integrated in molecular electronic devices. The
challenge that will be pursued is to build the world first electronic devices using 2D
patterned switches with a self-assembly approach.
The master project will comprise the 2D assembly of switches on surfaces, the study of
the organization using scanning probe techniques, the study of the switching behaviour
and the construction and functioning of molecular based devices (as shown in figure 1b).
Although self-assembly on surfaces is well established, a major outstanding challenge
remains the 2D positioning of photo- and redox-active molecules. Therefore, an
important issue that we will addressed is the 2D assembly of molecular switches in a
controlled way. Recently, in the group of Feringa, it has been proved that 2D molecular
patterns of zinc porphyrins with axial ligands bound to the metal center, are readily
prepared through self-assembly[5]. In the present project, we will apply molecular
switches decorated with pyridines in order to control their assembly either, in a parallel
or in a perpendicular fashion with respect to the surface (figure 2). For the latter
approach, the major challenge will be the nano scale precise lateral pyridine positioning
of each switchable unit in order to fit perfectly with the porphyrin patterning at 1.4 nm.
2D Molecular Patterning
molecule
C12H25
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C12H25
complex
C12H25
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Zn N
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C12H25
C12H25
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C12H25
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C12H25
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surface
2D molecular patterning by surface-enhanced
Zn-porphyrin coordination on HOPG or AU
2D Molecular Self-assembly
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Zn-TDP
nitropyridine-Zn-TDP
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a) a=1.4±0.1 nm, b=1.9±0.2 nm, =100±6°.
b) a=1.4±0.2 nm, b=2.0±0.2 nm, =88±8°
c) a=1.4±0.1 nm, b = 1.9±0.1 nm,  = 86±8°.
Ka
STM image (VT = 761 mV, iT=13 pA, 20.8 nm x 20.8 nm)
Functional group
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Switch
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Par a ver est a pelí cula, debe
dis poner de Q uickTim e™ y de
un descom pr esor .
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Figure 2: 2D Molecular patterning of Zn-TDPs with metal substituted pyridine and molecular
switches assembled in different orientations with respect the surface.
This part of the programme will comprise the study their assembly upon deposition with
Zn-porphyrin using modern scanning probe techniques like scanning tunnelling
microscopy (STM). We will address the molecular switching patterns by photochemical
and electrochemical means, studying their electronic properties in a real device (see
ref.4) to measure electronic transport. Further on, we will prepare patterns of open and
close areas by selective irradiation. These will mean a breakthrough towards the
development of patterned areas, which functions can be controlled at the molecular level,
to be integrated into electronic circuits.
The molecules are available in the group; the master project will be executed in
cooperation with PhD students and postdocs as part of our subgroup efforts/program on
smart materials and surfaces.
The is ample opportunity to learn about supramolecular materials science, self-assembly,
molecular electronics, scanning probe techniques and device fabrication as part of the
exciting and highly timely field of molecular electronics.
In summary, based on the rather simple concept of a functional molecular switch our
systems will be explored in controlling molecular (optic & electronic) and
supramolecular/device properties. With proof of principle at hand we will construct the
first molecular electronic switchable device with precise 2D & 3D control of molecular
architecture.
[1] (a) Feringa, B. L. Molecular Switches, eds. Wiley-VCH, Weinheim, Germany, 2001.
(b) Feringa, B. L. “The Art of Buillding Small: From Molecular Switches to Molecular
Motors”, J. Org. Chem. 2007, 72, 6635-6652.
(c) Feringa, B. L. “From Molecules to Molecular Systems”, Chimia, 2009, 63, 254256.
[2] Whitesides, G. M.; Love, J. C. “ The Art of Building Small”, Sci. Am. 2001, 38-47.
[3] Feringa, B. L.; van Delden, R. A.; Koumura, N.; Geertsema, E. M. “Chiroptical
Molecular Switches”, Chem. Rev. 2000, 100, 1789-1816.
[4]
Kronemeijer, A. J.; Akkerman, H. B.; Kudernac, T.; van Wees, B. J.; Feringa, B.
L.; Blom P. W. M.; de Boer, B. “Reversible Conductance Switching in Molecular Devices”,
Adv. Mater. 2008, 20, 1467-1473.
[5] (a) Katsonis, N.; Vicario, J.; Kudernac, T.; Visser, J.; Pollard M. M.; Feringa, B. L.
“Self-Organized Monolayer of meso-Tetradodecylporphyrin Coordinated to Au(111)”,
J. Am. Chem. Soc. 2006, 128, 15537-15541.
(b) Visser, J.; Katsonis, N.; Vicario J.; Feringa, B. L. “Two-Dimensional Molecular
Patterning by Surface-Enhanced Zn-Porphyrin Coordination”, Langmuir, 2009, 25,
5980-5985.
For further information please contact Prof. Ben L. Feringa;
b.l.feringa@rug.nl, tel: 3634235, room 15.205