Molecular switches get wired: Synthesis of diarylethenes containing one or two sulphurs

Article abstract of DOI:10.1080/15421400590946398

Two series of novel diarylethenes, the first containing one and the second two acetyl protected thiol groups, were synthesised in two and three steps from an easily available known intermediate. Newly synthesised compounds present ideal examples of model

Full text of DOI:10.1080/15421400590946398

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Molecular Switches Get Wired:
Synthesis of Diarylethenes
Containing One or Two
Sulphurs
T. Kudernac a , J. J. De Jong a , J. Van Esch a , B. L.
b
Feringa a , D. Dulić , S. J. Van Der Molen b & B. J.
Van Wees b
a Department of Organic and Molecular Inorganic
Chemistry , Straitingh Institute , Material Science
Centre, University of Groningen, Nijenborgh
Groningen, The Netherlands
b Physics of Nanodevices , Material Science Centre ,
University of Groningen, Nijenborgh, Groningen, The
Netherlands
Published online: 31 Aug 2006.
To cite this article: T. Kudernac , J. J. De Jong , J. Van Esch , B. L. Feringa , D.
Dulić , S. J. Van Der Molen & B. J. Van Wees (2005) Molecular Switches Get Wired:
Synthesis of Diarylethenes Containing One or Two Sulphurs, Molecular Crystals and
Liquid Crystals, 430:1, 205-210, DOI: 10.1080/15421400590946398
To link to this article: http://dx.doi.org/10.1080/15421400590946398
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Mol. Cryst. Liq. Cryst., Vol. 430, pp. 205–210, 2005
Copyright # Taylor & Francis Inc.
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400590946398
Molecular Switches Get Wired: Synthesis of
Diarylethenes Containing One or Two Sulphurs
T. Kudernac
J. J. De Jong
J. Van Esch
B. L. Feringa
Department of Organic and Molecular Inorganic Chemistry,
Straitingh Institute, Material Science Centre, University of
Groningen, Nijenborgh Groningen, The Netherlands
´
D. Dulic
S. J. Van Der Molen
B. J. Van Wees
Physics of Nanodevices, Material Science Centre, University of
Groningen, Nijenborgh, Groningen, The Netherlands
Two series of novel diarylethenes, the first containing one and the second two
acetyl protected thiol groups, were synthesised in two and three steps from an eas-
ily available known intermediate. Newly synthesised compounds present ideal
examples of model substrates for photochromic studies on metal surfaces.
Keywords: diarylethene; gold surface; photochromism; synthesis
INTRODUCTION
There has been an increasing interest in the implementation of small
organic molecules into the field of nanoelectronics in the last decades
[1]. In the infinite ‘‘pool’’ of organic compounds, a replacement for con-
ventional switches [2], rectifiers [3], wires [4] and transistors [5] has
been found. The necessity to respond to external stimuli makes
switches the most challenging part of these efforts. Photochromic
Address correspondence to BL Feringa, Department of Organic and Molecular Inor-
ganic Chemistry, Straitingh Institute, Material Science Centre, University of Gronin-
gen, Nijenborgh 4, 9747 AG Groningen, The Netherlands. E-mail: feringa@chem.rug.nl
205

206
T. Kudernac et al.
FIGURE 1 Typical photoreaction of dithienylethenes.
switches exhibit reversible photo-induced transformation between
their two isomeric forms whose absorption spectra are different [6].
Among these, 1,2-dithienylethenes maintain a prominent position
because of their exceptional thermal stability and fatigue resistance
[7] of the photochromic reaction (Fig. 1), and they seem to be promis-
ing candidates for various photo-devices.
The incorporation of small molecules into the integrated circuit
remains an unsolved task. Employing single-molecule techniques such
as Mechanically controllable break junction [8] and Scanning electron
microscopy (STM) [9], researchers have been able to combine a single
molecule with metallic electrodes and thus simulate the integration.
We have published a first attempt to incorporate dithienylethenes
between two nanoscopic gold electrodes and to study their electronic
and photochromic properties on a single molecule level [10].
In order to explore the published system more, we synthesised two
new molecules. The design of the recently studied molecule 1a and the
two new molecules 1b, c incorporating two sulphur atoms proposed for
these experiments, was mainly influenced by the necessity to create a
strong bond between gold and molecules and by the possibility to vary
the conducting character of the spacer from the well-conducting thio-
phene to the meta substituted benzene ring providing only cross-
conjugation. Moreover, molecules 2a, b, c incorporating one sulphur
atom were synthesised and these might be used for further experi-
ments, better explaining the events happening in the metal-molecule
system, such as STM measurement or the use of absorption spec-
troscopy on the monolayer protected gold nanoparticles modified by
those sulphur derivatives.
RESULTS AND DISCUSSION
The synthetic strategy for both symmetrical and asymmetrical mole-
cules was based on a palladium catalysed cross-coupling reaction
between arylhalides and arylboronic acid [11]. Starting from the
known 1,2-Bis(5-chloro-2-methylthien-3-yl)cyclopentene 3 [11], the

Molecular Switches Get Wired
207
FIGURE 2 Synthetic route to compounds 1. i) a) n-BuLi, THF, b) B(OBu)4, c)
ArBr, Pd(PPh3)4, Na2CO3, THF, reflux, ii) a) t-BuLi, THF, ꢀ78ꢁC, b) Sg,
ꢀ78ꢁC, c) AcCl. (for R see Table 1).
TABLE 1 Substituents and Yields of Compounds 4 and 1
Compd.
4a
4b
4c
1a
1b
1c
R
Yield[%]
66
53
56
33
41
39
series of compounds 4a, b, c (Fig. 2) was prepared with satisfactory
yields (Table 1). The final products 1a, b, c were synthesised by treat-
ment with n-butyllithium followed by the addition of sulphur and the
protection with acetyl chloride giving moderate yields.
The general procedure for the preparation of 4 and 1 is as follows.
To a solution of compound 3 (0.729 mmol) in THF (7 ml), kept under
an inert atmosphere, n-BuLi (1.92 mmol, 1.6 M in hexane) was added.
FIGURE 3 Synthetic route to compounds 2. i) and ii) a) n-BuLi, THF, b)
B(OBu)4, c)ArBr, Pd(PPh3)4, Na2CO3, THF, reflux; iii) a) t-BuLi, THF,
ꢀ 78ꢁC, b) Sg, ꢀ 78ꢁC, c) AcCl. (for R see TABLE 2).

208

Molecular Switches Get Wired
209
After 1 h, B(OBu)3 (2.19 mmol) was added to produce a bis-boronic
ester intermediate. A separate flask was charged with aromatic halide
(2.98 mmol), Pd(PPh3)4 (0.083 mmol), THF (5 ml), (aq.) 2 M Na2CO3
o
(4 ml) and ethylene glycol (5 drops). The mixture was heated to 80 C
and the performed boronic ester was added slowly. The reaction mix-
ture was boiled under reflux overnight, diluted with diethyl ether
(50 ml) and washed with water (50 ml). The water layer was washed
with an additional volume of ether (50 ml) and the combined organic
phases were dried over Na2SO4 and concentrated. Subsequent chro-
matography on silica gel (hexane) afforded compounds 4 [12].
Compounds 4 (0.236 mmol) were dissolved in THF (5 ml) and
the solution was cooled down to ꢀ78ꢁC. To this solution t-BuLi
(0.520 mmol, 1.5 M in pentane) was added dropwise and the mixture
was stirred for 2 h, after which S8 (0.472 mmol) dissolved in a small
portion of THF was added. The reaction mixture was stirred at
ꢀ 78ꢁC for 1 h and then allowed to reach room temperature and stir-
red for an additional 1 h. The reaction mixture was cooled down to
ꢀ 20ꢁC and acetyl chloride (0.944 mmol) was added. The reaction
was allowed to slowly reach room temperature and stirred overnight.
The reaction was diluted with dichloromethane (50 ml) and the
organic phase was washed with water and brine. The organic phase
was dried and concentrated. Subsequent chromatography on silica
gel (hexane=dichloromethane) afforded 1. All compounds were ident-
1
ified by H NMR, 13C NMR and MS.
The synthesis of the asymmetrical derivatives 2a, b, c follows
exactly the same sequence of the two palladium catalysed couplings
and sulphuration (Fig. 3). However, the first coupling step requires
four times higher dilution to provide products 5a, b with good yields
(Table 2) and high selectivity for the mono substitution.
In conclusion, the general synthetic strategy leading to either sym-
metrical or asymmetrical derivatives incorporating one or two sul-
phurs can be adopted to many new compounds, taking into account
the final desired properties, by varying the spacer unit and changing
the position of sulphur groups. The newly synthesised compounds
are currently being subjected to various photochemical experiments
on gold surfaces. Relevant information will be reported.
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[2] Feringa, B. L. (2001). Molecular Switches. Wiley-VCH: Weinheim, Germany.
[3] Metzger, R. M. (2003). Chem. Rev., 103, 3803.
[4] Robertson, N. & McGowan, C. A. (2003). Chem. Soc. Rev., 32, 96.

210
T. Kudernac et al.
´
[5] Kubatkin, S., Danilov, A., Hjort, M., Cornil, J., Bredas, J.-L., Stuhr-Hansen, N.,
Hedegard, P., & Bjornholm, T. (2003). Nature, 425, 698.
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´
[10] (a) Dulic, D., van der Molen, S. J., Kudernac, T., Jonkman, H. T., de Jong, J. J. D.,
Bowden, T. N., van Esch, J., Feringa, B. L., & van Wees, B. J. (2003). Phys. Rev.
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(b) for a single molecule switching also see: Irie, M., Fukaminto, T., Sasaki, T.,
Tamai, N., & Kawai, T. (2002). Nature, 420, 759.
[11] Lucas, L. N., van Esch, J., Kellogg, R. M., & Feringa, B. L. (1998). Chem. Commun.,
2313.
[12] 4a) mp. 204–208ꢁC decomp. 1H NMR (500 MHz, CDCl3) d 1.94 (s, 6H), 2.04 (m, 2H),
2.79 (t, J ¼ 12.5, 4H), 6.87 (s, 2H), 6.95 (t, J ¼ 6.5, 2H), 7.03 (d, J ¼ 4.5, 2H),
7.13 (d, J ¼ 8.5, 2H) ppm. 13C NMR (75.4 MHz, CDCl3): d 14.3 (q), 22.9 (t),
38.5 (t), 122.9 (d), 123.7 (d), 124.5 (d), 127.6 (d), 133.0 (s), 134.0 (s), 134.5 (s),
136.3 (s) ppm. HRMS calcd. for C23H20S4 424.045, found 424.045.
[13] 4b) 1H NMR (300 MHz, CDCl3) d 1.99 (s, 6H), 2.09 (m, 2H), 2.84 (t, J ¼ 7.3, 4H),
7.02 (s, 2H), 7.19–7.21 (m, 2H), 7.33–7.41 (m, 4H), 7.64 (s, 2H) ppm. 13C
NMR (75.4 MHz, CDCl3): d 14.4 (q), 23.0 (t), 38.4 (t), 122.9 (s), 123.9 (d),
124.8 (d), 128. 2 (d), 129.7 (d), 130.3 (d), 134.7 (s), 135.4 (s), 136.5 (s), 136.8
(s) ppm. HRMS: calcd. for C27H22S2Br2 567.953, found 567.953.
[14] 4c) de Jong, J. D., Lucas, L. N., Hania, R., Pugzlys, A., Kellogg, R. M., Feringa,
B. L., Duppen, K., & van Esch, J. H. (2003). Eur. J. Org. Chem., 1887–1893.