Formation of two-dimensionally ordered diarylethene annulated isomer at the liquid/hopg interface upon in situ UV irradiation

Full text of DOI:10.1246/cl.130705

doi:10.1246/cl.130705
Published on the web August 31, 2013
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Formation of Two-dimensionally Ordered Diarylethene Annulated Isomer
at the Liquid/HOPG Interface upon In Situ UV Irradiation
Takeshi Sakano, Yohei Imaizumi, Takashi Hirose, and Kenji Matsuda*
Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering,
Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510
(Received July 30, 2013; CL-130705; E-mail: kmatsuda@sbchem.kyoto-u.ac.jp)
A unique photoinduced change in the molecular ordering of
a photochromic diarylethene derivative having amide groups
was investigated at the liquid/highly oriented pyrolytic graphite
(HOPG) interface by scanning tunneling microscopy (STM).
Ordering of the diarylethene was stabilized by the hydrogen-
bonded network of amide groups. The open- and the closed
isomers formed characteristic stripe-patterned orderings; a
different hydrogen-bonding network was formed in each case.
In situ UV irradiation resulted in the exclusive formation of a
third molecular ordering γ that is composed of the photo-
irreversible annulated isomer. No photoisomerized molecule was
detected in the 2-D orderings, i.e., the open-ring isomer in the
ordering of the closed-ring isomer and vice versa, despite the
similarity in their molecular structures.
dynamics, even if the amount of the generated isomer is tiny.
The results in this study revealed that one of the orderings is
photoirreversible and showed an overwhelming preference of
ordering formation at the liquid/solid interface upon in situ UV
irradiation.
We chose diarylethene as the photoresponsive core because
of its well-studied photochromic properties, showing a dramatic
change in the electronic properties such as orbital energies and
electronic transitions.7 Molecular design of diarylethene deriv-
atives to optimize their isomerization properties, such as
photoisomerization quantum yield and thermal stability of
photogenerated isomer, has been thoroughly investigated over
the last decade. In addition, a small change in molecular
geometry upon photoisomerization between the open- and the
closed isomers8 would be an important advantage to develop
spatially resolved single molecule isomerization in a well-
ordered molecular ordering on a 2-D surface.
From the viewpoint of 2-D crystal engineering at the liquid/
HOPG interface, introduction of both long alkyl chains and
intermolecular interacting groups is an effective approach to
fabricate a desired molecular ordering.1a,9 Hydrogen-bonding
(H-bonding) of amide groups is often used in supramolecular
chemistry,10 inspired by biological systems where an amide
group is commonly used as an interacting group, such as α-helix
or β-sheet in proteins. Diarylethene derivatives 1-3 were
systematically examined to evaluate the effect of the number
of amide groups, which is designed to form intermolecular H-
bonding network with adjacent molecules (Scheme 1). Alkyl
side chains were introduced on both sides of the photochromic
core to ensure sufficient van der Waals interaction with the
HOPG surface.11 The dynamic nature of the noncovalent
interactions guides the system to a specific columnar ordering
through adsorption-desorption dynamics.
Compounds 1-3 were synthesized via a general amide-ester
condensation and Suzuki-Miyaura coupling reaction.12 The
compounds showed a good photochromic reactivity in common
organic solvents, including octanoic acid which is used as
a solvent in STM measurements. UV irradiation (365 nm) to a
solution of 1o in ethyl acetate generates a new absorption
band at ca. 596 nm with an isosbestic point at 327 nm. Upon
successive visible-light irradiation (- > 460 nm), the original
spectrum of the open-ring isomer was regenerated. The
conversion ratio of the open- to the closed-ring isomer was
4:96 in ethyl acetate and 5:95 in octanoic acid at the photosta-
tionary state (PSS) under the UV irradiation (365 nm). The
photoisomerization cycle between the open- and the closed-ring
isomers can be repeated many times; however, it is reported that
the formation of the annulated isomer becomes detectable when
the closed-ring isomer is exposed to UV illumination for a long
time.13
As molecular ordering can be visualized at the single
molecular resolution by using scanning tunneling microscopy
(STM), the design of molecular ordering on surfaces has been
intensively investigated in recent years.1 Stimuli-responsive
two-dimensional (2-D) surfaces are of great potential to realize
optoelectronic molecular devices such as high-density recording
media and power-saving integrated switches. Although apparent
changes in ordering pattern by external stimuli such as temper-
ature,2 addition of guest molecules,3 tip voltage,4 or photo-
irradiation,5 have been investigated by many research groups,6
the rational control of multistep ordering changes induced by a
combination of photochemical and chemical reactions remains a
challenge.
In this study, we report photoresponsive molecular ordering
involving three different photogenerated isomers (Scheme 1).
When the ordering of one photogenerated isomer is considerably
stable over the others, the existing order is replaced with the
new energetically stable ordering via adsorption-desorption
F
F
H
N
F
F
F
F
1: R1 = R2
=
C16H33
O
H
N
1
R2 =
C12H25
S
S
2
: R =
R1
R2
C16H33
O
O
open isomer (o)
3: R1 = R2
=
C12H25
O
UV vis.
F
F
F
F
F
F
F
F
F
F
F
F
UV
vis.
S
S
S
S
R1
R2
R1
R2
closed isomer (c)
annulated isomer (a)
Scheme 1. Chemical structure of diarylethenes 1-3.
Chem. Lett. 2013, 42, 1537-1539
© 2013 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/

1538
Figure 1. STM images of (a) the open-ring isomer 1o (the ordering α, Iset = 60 pA, Vbias = ¹1.0 V, a = 5.71 nm, b = 0.89 nm,
¡ = 88°), (b) the closed-ring isomer 1c (the ordering β, Iset = 20 pA, Vbias = ¹0.9 V, a = 4.82 nm, b = 0.56 nm, ¡ = 85°) at the
octanoic acid/HOPG interface. (c) The ordering after UV irradiation for 15 min (the ordering γ, Iset = 30 pA, Vbias = ¹1.0 V, a = 10.2
nm, b = 0.48 nm, ¡ = 87°). (d) Enlarged molecular model of the open-ring isomer 1o and (e) that of the closed-ring isomer 1c.
Hydrogen-bond network of amide groups is highlighted in green.
The molecular ordering of both the open- and the closed-
ring isomers was carefully investigated using the sample isolated
by HPLC. Compounds 1o and 1c, having two amide groups,
formed characteristic stripe structures at the octanoic acid/
HOPG interface as expected (Figures 1a and 1b), while no
ordering was observed with compounds 2 or 3 under the same
condition before photoirradiation. The result clearly indicates
the effect of the amide group in stabilizing molecular ordering
via an intermolecularly H-bonded network. Note that, in our
previous study, a large interacting group of a planar polycyclic
aromatic hydrocarbon (PAH), i.e., pyrene, was necessary to
observe the molecular ordering of diarylethene.14 The width of
the bright rows was 3.5 nm for 1o (ordering α) and 1.5 nm for 1c
(ordering β), suggesting different ordering patterns for the two
isomers. The width of the bright row in ordering α corresponds
to two molecular columns of 1o with an alternating H-bonding
network at the central axis of the bright row, whereas that in
ordering β corresponds to one column of 1c with twofold
H-bonding networks on both sides of photochromic core
(Figures 1d and 1e).15 Besides the difference in the number of
columns, a prominent difference was found in the intermolecular
distance. Considering the lattice parameter of the shorter axis b,
the intermolecular distance of adjacent molecules in ordering
α (0.89 nm) was significantly larger than that of ordering β
(0.56 nm). This indicates a face-on arrangement of 1o and an
edge-on arrangement of 1c. The difference in the arrangement
could be attributed to the rigid core framework of the closed-ring
isomer whose delocalized π-conjugation system prefers to form
a face-to-face π-π stacking assembly. Average domain size of
ordering β was larger than 4 © 104 nm2, which was almost
one order of magnitude larger than that of the ordering α
(4.4 © 103 « 1.8 © 103 nm2). It is plausible that the π-π stacking
interaction of the rigid conjugated core and twofold H-bonding
networks contribute to enlarging the domain size of the ordering
of the closed-ring isomer.
Although the structural transformation from ordering β
to ordering α was reasonably induced by in situ visible-light
irradiation (Figure S6), in situ UV irradiation resulted in an
entirely different ordering γ, regardless of whether the initial
ordering was α or β (Figure 1c). Ordering γ can be distinguished
from the other orderings by the following properties; (i) the
width of the bright row was 1.5 nm and corresponds to the
width of one molecular column of diarylethene core, similar to
ordering β, (ii) the bright rows lie between the alternating dark
brown and yellow ocher rows,16 (iii) no periodical bright pattern
is found in the dark brown rows in contrast to ordering β.
Ordering γ could not be obtained either by simple premixing of
1o and 1c in any fraction or by the addition of 1c solution to an
existing ordering of 1o. Instead, ordering γ emerged either by
in situ UV irradiation on HOPG or by preirradiation with UV
light in a glass tube followed by drop cast on a HOPG
substrate.12 In addition, ordering γ never reverts to the initial
ordering upon photoirradiation (UV or visible) once it is
constructed. These results clearly indicate the following three
features; (i) UV irradiation is necessary for the formation of
ordering γ, (ii) another molecular component, neither 1o nor 1c,
is generated by UV irradiation, and (iii) the photogenerated
ordering is photoirreversible.
According to previous research, UV irradiation to the
closed-ring isomer of 2-methyl-5-phenylthiophene-based diary-
lethenes induces not only a cycloreversion reaction to the open-
ring isomer but also a ring-annulation reaction to the annulated
isomer, although the quantum yield of the side reaction is
expected to be very low.13b It is also reported that the annulated
Chem. Lett. 2013, 42, 1537-1539
© 2013 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/

1539
Tobe, S. De Feyter, J. Am. Chem. Soc. 2008, 130, 7119.
isomer never converts back to the closed-ring isomer
(Scheme 1). In order to assess the ordering of the annulated
isomer, 1a was photochemically synthesized on a milligram
scale by UV irradiation to a solution of 1o overnight, and
subsequently isolated by HPLC. The ordering of 1a was
confirmed to be identical to ordering γ that was observed after
in situ UV irradiation.12 From these results, we concluded that
the ordering γ is composed of the annulated isomer 1a.
In a manner similar to 1, photoirreversible orderings were
also observed for 2 and 3 after in situ UV irradiation although
no ordering was observed prior to UV irradiation, as mentioned
above. This corresponds to the formation of the corresponding
annulated isomers 2a and 3a. An important finding is that the
presence of only 5% of 1a was enough to predominantly form
ordering γ on the HOPG substrate.12 The reason why ordering
β was not observed upon in situ UV irradiation is the strong
preferential formation of ordering γ, which may be attributed
to the rigid and highly symmetric structure of the annulated
isomer.17
Although considerable effort has been made to observe a
spatially-resolved photoisomerization reaction upon in situ UV-
visible light irradiation to ordering α or β, a prominent change in
the contrast of the diarylethene core was unfortunately not
observed; nonetheless a change in domain size of each domain
was observed.18 Considering that photoisomerization of di-
arylethene occurs even in a close-packed single crystal,8 the
reason why no photoisomerized molecule was detected in the
2-D orderings (i.e., 1o in the ordering β or 1c in the ordering α)
would be due to rapid adsorption-desorption dynamics of
molecular components between the substrate surface and the
supernatant solution. Research on photoisomerization at the
single-molecule level in a 2-D ordering on a surface is currently
underway in our group.
4
5
6
L. Xu, X. Miao, X. Ying, W. Deng, J. Phys. Chem. C 2012, 116,
1061; A. Miura, S. De Feyter, M. M. S. Abdel-Mottaleb, A.
Gesquière, P. C. M. Grim, G. Moessner, M. Sieffert, M. Klapper, K.
Müllen, F. C. De Schryver, Langmuir 2003, 19, 6474.
a) K. Tahara, K. Inukai, J. Adisoejoso, H. Yamaga, T. Balandina,
M. O. Blunt, S. De Feyter, Y. Tobe, Angew. Chem. Int. Ed. 2013, 52,
8373. b) Y. Kikkawa, Polym. J. 2013, 45, 255. c) X. Zhang, S. Wang,
Y. Shen, Y. Guo, Q. Zeng, C. Wang, Nanoscale 2012, 4, 5039.
Molecular orderings also related to the condition of supernatant
solution, such as concentration, pH, or solvent. For concentration: a)
A. Ciesielski, P. J. Szabelski, W. Rżysko, A. Cadeddu, T. R. Cook,
P. J. Stang, P. Samorì, J. Am. Chem. Soc. 2013, 135, 6942. For pH: b)
T. El Malah, A. Ciesielski, L. Piot, S. I. Troyanov, U. Mueller, S.
Weidner, P. Samorì, S. Hecht, Nanoscale 2012, 4, 467. For solvent:
c) Y. Kikkawa, K. Omori, M. Takahashi, M. Kanesato, K. Hiratani,
Org. Biomol. Chem. 2012, 10, 8087. d) L. Xu, X. Miao, B. Zha, W.
Deng, J. Phys. Chem. C 2012, 116, 16014. e) X. Miao, L. Xu, Z. Li,
W. Deng, J. Phys. Chem. C 2011, 115, 3358.
a) K. Matsuda, M. Irie, J. Photochem. Photobiol., C 2004, 5, 169. b)
M. Irie, Chem. Rev. 2000, 100, 1685.
a) M. Irie, Bull. Chem. Soc. Jpn. 2008, 81, 917. b) S. Kobatake, S.
Takami, H. Muto, T. Ishikawa, M. Irie, Nature 2007, 446, 778. c) M.
Irie, S. Kobatake, M. Horichi, Science 2001, 291, 1769.
a) L. E. Heller, J. Whitleigh, D. F. Roth, E. M. Oherlein, F. R. Lucci,
K. J. Kolonko, K. E. Plass, Langmuir 2012, 28, 14855. b) A.
Ciesielski, C.-A. Palma, M. Bonini, P. Samorì, Adv. Mater. 2010, 22,
3506. c) S. Uemura, S. Sengupta, F. Würthner, Angew. Chem., Int.
Ed. 2009, 48, 7825. d) K. Kim, K. E. Plass, A. J. Matzger, J. Am.
Chem. Soc. 2005, 127, 4879. e) N. Schuurmans, H. Uji-i, W.
Mamdouh, F. C. De Schryver, B. L. Feringa, J. van Esch, S.
De Feyter, J. Am. Chem. Soc. 2004, 126, 13884.
7
8
9
10 I. A. W. Filot, A. R. A. Palmans, P. A. J. Hilbers, R. A. van Santen,
E. A. Pidko, T. F. A. de Greef, J. Phys. Chem. B 2010, 114, 13667.
11 a) B. Ilan, G. M. Florio, M. S. Hybertsen, B. J. Berne, G. W. Flynn,
Nano Lett. 2008, 8, 3160. b) D. M. Cyr, B. Venkataraman, G. W.
Flynn, Chem. Mater. 1996, 8, 1600.
12 See Supporting Information. Supporting Information is available
electronically on the CSJ-Journal Web site, http://www.csj.jp/
journals/chem-lett/index.html.
In conclusion, we have synthesized the diarylethene
derivative having alkyl side chains linked via amide groups
that forms stripe-type molecular orderings at the liquid/HOPG
interface with three different molecular arrangements. In situ
UV irradiation exclusively forms the ordered annulated isomer
1a. To the best of our knowledge, this is the first report of a 2-D
ordering of the annulated isomer of diarylethene formed by
in situ photoirradiation. The observations presented in this study
gives a new direction for developing stimuli-responsive surfaces
by utilizing photochemical and chemical reactions.
13 a) K. Higashiguchi, K. Matsuda, S. Kobatake, T. Yamada, T. Kawai,
M. Irie, Bull. Chem. Soc. Jpn. 2000, 73, 2389. b) M. Irie, T. Lifka, K.
Uchida, S. Kobatake, Y. Shindo, Chem. Commun. 1999, 747.
14 R. Arai, S. Uemura, M. Irie, K. Matsuda, J. Am. Chem. Soc. 2008,
130, 9371.
15 According to an X-ray crystal structure, the size of the diarylethene
core is ca. 1.6 nm in the antiparallel conformation. M. Irie, T. Lifka,
S. Kobatake, N. Kato, J. Am. Chem. Soc. 2000, 122, 4871.
16 The difference in color of alkyl chain domains, yellow ocher and
dark brown, would originate from the different orientation of alkyl
chains with respect to the lattice of HOPG substrate underneath. For
this reason, unit cell parameter of longer axis a in the ordering γ is
about twice as large as that in the ordering α or β because of the
different angle of alkyl side chains. a) T. Sakano, J.-y. Hasegawa, K.
Higashiguchi, K. Matsuda, Chem.®Asian J. 2012, 7, 394. b) J.-R.
Gong, L.-J. Wan, J. Phys. Chem. B 2005, 109, 18733.
This work was supported by NEXT program (No. GR062)
from JSPS, Japan. This work was also supported by a Grant-in-
Aid for Young Scientists (B) (No. 25810048).
17 The open-ring isomer has two stable conformations, i.e., parallel-
and antiparallel conformer, due to rotatable C-C bond of the core,
which are in thermal equilibrium in a solution. The closed-ring
isomer has rigid core with chiral C2 symmetry. In contrast to the two
isomers, the annulated-isomer is the rigid meso-isomer that has no
enantiomer or conformer.
18 Some spots having different contrast should be detectable if different
isomer of diarylethene is immobilized in the ordering within the time
scale of STM scans. a) Arramel, T. C. Pijper, T. Kudernac, N.
Katsonis, M. van der Maas, B. L. Feringa, B. J. van Wees, J. Appl.
Phys. 2012, 111, 083716. b) C. Coudret, G. Guirado, N. Estrampes,
R. Coratger, Phys. Chem. Chem. Phys. 2011, 13, 20946. c) S. V.
Snegir, A. A. Marchenko, P. Yu, F. Maurel, O. L. Kapitanchuk, S.
Mazerat, M. Lepeltier, A. Léaustic, E. Lacaze, J. Phys. Chem. Lett.
2011, 2, 2433.
References and Notes
1
a) K. S. Mali, J. Adisoejoso, E. Ghijsens, I. De Cat, S. De Feyter,
Acc. Chem. Res. 2012, 45, 1309. b) L. Gross, Nat. Chem. 2011, 3,
273. c) D. Bonifazi, S. Mohnani, A. Llanes-Pallas, Chem.®Eur. J.
2009, 15, 7004. d) X. Ma, Y. Yang, K. Deng, Q. Zeng, K. Zhao, C.
Wang, C. Bai, J. Mater. Chem. 2008, 18, 2074. e) S. De Feyter, F. C.
De Schryver, Chem. Soc. Rev. 2003, 32, 139.
2
3
a) Y. Li, C. Liu, Y. Xie, X. Li, X. Li, X. Fan, K. Deng, Q. Zeng, C.
Wang, Phys. Chem. Chem. Phys. 2013, 15, 125. b) J. Adisoejoso, K.
Tahara, S. Lei, P. Szabelski, W. Rżysko, K. Inukai, M. O. Blunt, Y.
Tobe, S. De Feyter, ACS Nano 2012, 6, 897.
a) X. Zhang, Q. Zeng, C. Wang, RSC Adv. 2013, 3, 11351. b) S. Ahn,
A. J. Matzger, J. Am. Chem. Soc. 2012, 134, 3208. c) S. Lei, K.
Tahara, X. Feng, S. Furukawa, F. C. De Schryver, K. Müllen, Y.
Chem. Lett. 2013, 42, 1537-1539
© 2013 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/