Reversible on/off conductance switching of single diarylethene immobilized on a silicon surface

Article abstract of DOI:10.1021/ja203269t

The chemical functionalization of hydrogen-terminated silicon(111) surfaces with photochromic diarylethene using an ethylene anchoring group was achieved. Conductive atomic force microscopy measurements showed the current changes on modified silicon elect

Full text of DOI:10.1021/ja203269t

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Reversible On/Off Conductance Switching of Single Diarylethene
Immobilized on a Silicon Surface
Kazuki Uchida, Yoshinori Yamanoi, Tetsu Yonezawa, and Hiroshi Nishihara*
Department of Chemistry, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
S Supporting Information
b
with n-BuLi and subsequent reaction with trin-butylborate
ABSTRACT: The chemical functionalization of hydrogen-
terminated silicon(111) surfaces with photochromic diary-
lethene using an ethylene anchoring group was achieved.
Conductive atomic force microscopy measurements
showed the current changes on modified silicon electrodes
caused by light-induced isomerization of the diarylethene
between an open form and a closed form.
provided a boronic ester intermediate, which was reacted with
(4-iodophenylethynyl)trimethylsilane in the presence of a palla-
dium catalyst to provide 2 in 91% yield. Introduction of 2 to
1-(2,4-dimethyl-5-phenyl-3-thienyl)heptafluorocyclopentene11
gave compound 3 in 73% yield. Deprotection of the trimethylsilyl
group proceeded using K2CO3 in an ether-ethanol mixture to
afford the desired unsymmetrical diarylethene 1o in 95%.12
Scheme 2 shows the photochromic reaction between the
open-ring isomer 1o and the closed-ring isomer 1c. π-Conjuga-
tion extended over the entire molecule in the closed form,
whereas it was restricted to each half of the molecule in the
open form. The molecule photoisomerized from an open form
1o (colorless) to a closed form 1c (deep blue) in 78% yield upon
exposure to UV light (313 nm). The reverse transition to the
open form was driven by exposure to visible light (578 nm).
Next, we sought to determine the extent to which the
transition between isomers occurred on the silicon surface and
to measure the differences in the electrical conductance of the
two forms (Figure 1a). The photochromic diarylethene 1o was
anchored onto a hydrogen-terminated silicon(111) surface via a
thermal hydrosilylation reaction.8 Anchoring of the molecule to
the silicon surface was ensured by the ethylene anchoring
group.13 The resulting surface was characterized by measuring
the water contact angle as well as by AFM, after sonicating the
silicon wafers in a nonpolar solvent (toluene) and a polar solvent
(ethanol) for 10 min.
hotochromism is the photochemical process by which a
P
photoactive compound transitions between two isomers
having different absorption spectra.1 Among the various photo-
chromic compounds, diarylethenes are promising photoswitch-
able molecules because both isomers are thermally stable and
fatigue resistant, and the photoinduced transition is highly
reversible, sensitive, and responsive.2 The functionalization of
surfaces using diarylethenes has been suggested as a method for
information strorage,3 optical switching,4 and the design of
optoelectronic devices.5 Despite much progress, photochromic
studies of diarylethenes with switching units linked to the
electrode surface have posed several challenges, and few reports
describe attempts to switch the conductance of electrode surface-
bound molecules using light.6 A major hurdle to such studies has
been the difficulties associated with synthesizing surface mod-
ified organic molecules.
Modification of silicon surfaces with organic groups via hydro-
silylation has attracted much attention.7 The hydrosilyla-
tion reaction offers mild reaction conditions for producing
high-quality monolayers that are more stable than those formed
on other commonly used substrates. Recently, we reported the
immobilization of gold nanoparticles on hydrogen-terminated
silicon(111) surfaces using the thermal hydrosilylation reaction.8
Although Uosaki described the diarylethene connected to a
silicon surface via viologen derivatives linkers,9 the direct attach-
ment of diarylethene has not been reported. Here, we report the
direct immobilization of diarylethene having an acetylene moiety
onto a silicon surface via a π-conjugated system, and we describe
electrical characterization studies using conductive AFM. The
closed form of diarylethene on a silicon surface is expected to
exhibit better electrical conductance than the open form. We
refer to the two forms as the on (closed) and off (open) states of
the switch.
Water contact angle measurements provide a simple and
direct method for evaluating surface modifications. The water
contact angle on the hydrogen-terminated silicon(111) surface
was 89° in agreement with previously reported data.14 The con-
tact angle decreased to 66° upon SAM formation (Figure 1b),
indicating that the surface was terminated with close-packed
phenyl groups.15 AFM images of the modified surface showed
that the fully formed monolayer was continuous (see Sup-
porting Information). Holes extending to the silicon substrate
were not observed at this resolution. Accordingly, we con-
cluded that a highly packed monolayer was prepared using this
process.
The currentÀvoltage (IÀV) curves of the modified layer were
evaluated by forming a junction with the metallic tip of a con-
ductive AFM instrument. Typical IÀV curves are presented in
Figure 1 for the 1o-Si SAM and after irradiation at 313 nm (for 0.5 h),
which switched the molecules to the ring-closed form, 1c-Si. The
closed form corresponded to the more conductive state and the
Photochromic diarylethene molecule 1o was prepared in three
steps from 2,4-dibromo-3,5-dimethylthiophene.10 This molecule
bears an acetylene moiety at the terminus for bonding to the
hydrogen-terminated silicon surface. The synthesis is outlined in
Scheme 1. Treatment of 2,4-dibromo-3,5-dimethylthiophene
Received: April 9, 2011
Published: May 27, 2011
r
2011 American Chemical Society
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dx.doi.org/10.1021/ja203269t J. Am. Chem. Soc. 2011, 133, 9239–9241
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Scheme 1. Synthetic Route of Ethynyldiarylethene 1oa
a Reagents and conditions: (i) n-BuLi, THF, À78 °C; (ii) B(O(n-Bu))3, À78 °C to rt; (iii) (4-iodophenylethynyl)trimethylsilane, Pd(PPh3)4, Na2CO3,
THF-H2O, reflux, 91% (in 3 steps); (iv) n-BuLi, THF, À78 °C; (v) 1-(2,4-dimethyl-5-phenyl-3-thienyl)heptafluorocyclopentene, À78 °C to rt, 73%
(in 2 steps); (vi) K2CO3, ether-ethanol, rt, 95%.
Scheme 2. Photochromic Reaction between Open-Ring
Isomer 1o and Closed-Ring Isomer 1c
Figure 2. Current changes of the 1o-Si and 1c-Si surfaces due to
photoisomerization by alternate photoillumination with UV and visible
light. Tunnel current on a silicon(111) surface modified with ethynyl-
diarylethene after 313 and 578 nm photoillumination, which was
measured by conductive AFM at a voltage of 2 V.
We investigated the influence of alternating photoillumination
on the current changes of 1-Si under a fixed tip bias of 2 V
(Figure 2). During UV (313 nm) illumination, the initial current
of the silicon surface increased. Irradiation of the 1c-Si SAM with
visible light (578 nm) for 2 h restored the 1o-Si surface, and the
current decreased near the value for the initial state. After this
process, the UV light-induced increase and the visible light-
induced decrease in current were repeated without attenuation.
The stability of the response over time was attributed to the high
stability of the covalent attachment to the silicon surface through
Figure 1. (a) Diarylethene switch bound through a CdC bond to
Si(111). Reagents and conditions: (i) toluene, reflux, 18 h. (ii) 313 nm,
the anchoring π-conjugated group. This experiment showed that
the structureÀproperty relationships were preserved upon self-
assembly of the switch on Si(111).
In conclusion, we designed and synthesized a new diary-
lethene bearing an acetylene moiety at the terminus, and we
demonstrated light-controlled reversible conductance switching
of the monolayers prepared on silicon surfaces. This system under-
went photochemically reversible current changes upon alternate
irradiation with UV and visible light, which drove a reversible
0.5 h. (b) Progress of the hydrosilylation reaction over time during the
formation of the 1o-Si SAM, measured by water contact angle. (c)
Typical currentÀvoltage (IÀV) curves measured by conductive AFM
on the 1o-Si SAM immediately after its formation and following
irradiation at 313 nm for 0.5 h (1c-Si SAM).
open form corresponds to the less conductive state (Figure 1c).
These measurements allowed us to associate the ring open form
with the off state and the ring closed form with the on state.
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photocyclization reaction. Understanding the interplay between
the molecular structures and the switching properties can provide
firm design principles for the creation of optoelectronics devices.
The reversibility of switching was directly related to π-conjugation
between the switching unit and the substrate.
(14) Okubo, T.; Tsuchiya, H.; Sadakata, M.; Yasuda, T.; Tanaka, K.
Appl. Surf. Chem. 2001, 171, 252.
(15) Liu, Y.; Yamazaki, S.; Yamabe, S.; Nakato, Y. J. Mater. Chem.
2005, 15, 4096.
’ ASSOCIATED CONTENT
Supporting Information. 1H and 13C NMR spectra of
S
b
1o, UVÀvis spectra of 1o and 1c, and AFM images of 1o-Si and
1c-Si surfaces. This material is available free of charge via the
Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
nisihara@chem.s.u-tokyo.ac.jp
’ ACKNOWLEDGMENT
We thank Ms. Kimiyo Saeki and Dr. Aiko Sakamoto of the
Elemental Analysis Center of the University of Tokyo for
elemental analysis. This work was financially supported by Grant-
in-Aids for Scientific Research on Innovative Areas “Coordina-
tion Programming” (area 2107, No. 21108002) and the Global
COE Program for “Chemistry Innovation through the Coopera-
tion of Science and Engineering” from the Ministry of Education,
Culture, Sports, Science, and Technology, Japan.
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