Modulation of the photochromic property in an organoboron-based diarylethene by a fluoride ion

Article abstract of DOI:10.1021/ol061370g

Organoboron-based diarylethene was successfully synthesized and exhibited photochromic property. Furthermore, its photochromic property can be modulated by a fluoride ion. The absorption maximum of the photostationary state shifted from 655 to 490 nm upon

Full text of DOI:10.1021/ol061370g

ORGANIC
LETTERS
2006
Vol. 8, No. 18
3911-3914
Modulation of the Photochromic
Property in an Organoboron-Based
Diarylethene by a Fluoride Ion
Zhiguo Zhou, Shuzhang Xiao, Jia Xu, Zhiqiang Liu, Mei Shi, Fuyou Li,*
Tao Yi, and Chunhui Huang*
Department of Chemistry & Laboratory of AdVanced Materials, Fudan UniVersity,
Shanghai 200433, P. R. China
fyli@fudan.edu.cn; chhuang@pku.edu.cn
Received June 5, 2006
ABSTRACT
Organoboron-based diarylethene was successfully synthesized and exhibited photochromic property. Furthermore, its photochromic property
can be modulated by a fluoride ion. The absorption maximum of the photostationary state shifted from 655 to 490 nm upon addition of a
fluoride ion. The modulation mechanism is attributed to the special Lewis acid
ion.
−base interaction between a trivalent boron atom and a fluoride
Photochromic materials have recently received remarkable
attention for their potential applications of optoelectronic
devices such as optical memories and photoinduced switches.1
Diarylethene derivatives are the most promising candidates
for their notable thermal irreversible photochromic behavior
and outstanding fatigue resistance.2 The open and closed
isomers of diarylethenes have not only different absorption
spectra but also many different physical and chemical
properties such as photoluminescence,3 refractive index,4
electrical carrier injection, and transport characteristics.5
These differences have been utilized to control their functions
such as electrical conductivity,6 alignment of liquid crystals,7
light-driven organogelators,8 and photocontrolled release and
uptake.9
For practical applications, modulation of photochromic
property is indispensable. The conventional approaches have
been used by controlling their conformations (parallel or
antiparallel),10 changing the acid strength,11 tuning the
intramolecular proton transfer,12 and coordinating with metal
ions.13 For example, Lehn et al.11 reported a proton-gated
photochromic reaction. At low and high pH values, the
relative rates of photocyclization were found to be 1 and
0.003, respectively. Irie et al.10 described the reactivity
control of diarylethenes by introducing intralocking arms,
which were able to form hydrogen bonds or a disulfide
linkage. Recently, they12 also investigated the modulation
(1) Feringa, B. L. Molecular Swtiches; Wiley-VCH: New York, 2001.
(2) Irie, M. Chem. ReV. 2000, 100, 1685.
(3) (a) Acebes, A. F.; Lehn, J. M. AdV. Mater. 1998, 10, 1519. (b)
Norsten, T. B.; Branda, N. R. J. Am. Chem. Soc. 2001, 123, 1784. (c) Tian,
H.; Chen, B. Z.; Tu, H. Y.; Mu¨llen, K. AdV. Mater. 2002, 14, 918. (d)
Giordano, L.; Jovin, T. M.; Irie, M.; Jares-Erijman, E. A. J. Am. Chem.
Soc. 2002, 124, 7481. (e) Yam, V. W. W.; Ko, C. C.; Zhu, N. Y. J. Am.
Chem. Soc. 2004, 126, 12734.
(4) (a) Biteau, J.; Chaput, F.; Lahlil, K.; Boilot, J. P. Chem. Mater. 1998,
10, 1945. (b) Kim, E. Y.; Choi, Y. K.; Lee, M. H. Macromolecules 1999,
32, 4855. (c) Bertarelli, C.; Bianco, A.; Zerbi, G. AdV. Funct. Mater. 2004,
14, 357.
(5) (a) Tsujioka, T.; Kondo, H. Appl. Phys. Lett. 2003, 83, 937. (b)
Tsujioka, T.; Masuda, K. Appl. Phys. Lett. 2003, 83, 4978.
10.1021/ol061370g CCC: $33.50
© 2006 American Chemical Society
Published on Web 08/10/2006

of the photochromic property of diarylethenes by esterifi-
cation and a hydrolysis reaction.
dimesitylboron fluoride (FBMes2) in 75% yield. The structure
was identified with 1H NMR, 13C NMR, MS spectra
(Supporting Information), and X-ray single-crystal diffrac-
tion.
Generally, organoboron compounds bearing π-conjugated
groups have a unique LUMO on a boron atom in which the
π-conjugation is divergently extended through the vacant
p-orbital of the boron atom. Physical and chemical properties
of organoborons are modified as the vacant p-orbital of the
boron atom is disturbed. Tamao et al. and Gabbai et al.14
have reported organoborons as colorimetric and fluorogenic
sensors for a fluoride ion, respectively. Recently, our group
has also reported the two-photon fluorescent sensors derived
from boranes for a fluoride ion by means of the special Lewis
acid-base interaction between a boron atom and a fluoride
ion.15 In this communication, we synthesized a diarylethene
derivative 1,2-bis-(5′-dimesitylboryl-2′-methylthieny-3′-yl)-
cyclopentene (1) (Scheme 1) by introducing the dimesityl-
The absorption spectra for the open (1O) and closed (1C)
ring isomers at the photostationary state are shown in Figure
1. The open isomer in THF solution was colorless, and its
Scheme 1. Concept of Photochromic Property Modulated by a
Fluoride Ion
Figure 1. UV-vis absorption spectra. Solid line: 1O (2.0 × 10-5
M) in THF solution. Dashed line: the photostationary state of 1O.
absorption maximum was at 344 nm assigned to the π f
π* transition of the 5-dimesitylboryl-2-methylthienyl group
(Figure 1). Upon illumination at a wavelength of 365 nm of
light, the colorless solution of 1O turned green quickly, and
new absorption bands centered at 428 and 655 nm were
observed with a clear isosbestic point at 368 nm. The
1
boryl group and found that the photochromic property was
modulated by a fluoride ion.
Compound 1 was prepared from 1,2-bis-(5′-chloro-2′-
methylthieny-3′-yl)cyclopentene16 in a one-step reaction with
photocyclization reaction was monitored by H NMR. The
signals of the methyl proton of thiophene were shifted to a
lower magnetic field from 1.90 to 2.21 ppm. After 30 min
illuminating, the increase in the absorbance leveled off. The
conversion from 1O to 1C in the photostationary state was
calculated to be about 94% by 1H NMR spectra. The closed
isomer (1C) was completely reverted to its open isomer (1O)
by photoexcitation with visible light of a wavelength greater
than 500 nm. The cyclization and cycloreversion quantum
yields17 were determined to be 0.27 irradiating with 365 nm
and 0.063 irradiating with 650 nm, respectively.
(6) Kawai, T.; Nakashima, Y.; Irie, M. AdV. Mater. 2005, 17, 309.
(7) (a) Denekamp, C.; Feringa, B. L. AdV. Mater. 1998, 10, 1080. (b)
Maly, K. E.; Michael, D.; Lemieux, R. P. J. Am. Chem. Soc. 2002, 124,
7898. (c) Chen, S. H.; Philip Chen, H. M.; Geng, Y. H.; Jacobs, S. D.;
Marshall, K. L. AdV. Mater. 2003, 15, 1061. (d) Michel, F.; Georg, H. M.
Chem.-Eur. J. 2004, 10, 5243.
(8) (a) De Jong, J. J. D.; Lucas, L. N.; Kellogg, R. M.; van Esch, J. H.;
Feringa, B. L. Science 2004, 304, 278. (b) De Jong, J. J. D.; Hania, P. R.;
Pugzlys, R.; Lucas, N.; De Loos, M.; Kellogg, R. M.; Feringa, B. L.;
Duppen, K.; Van Esch, J. H. Angew. Chem., Int. Ed. 2005, 44, 2373. (c)
De Jong, J. J. D.; Theodora, D.; Wegma, T.; Van Esch, J. H.; Feringa, B.
L. J. Am. Chem. Soc. 2005, 127, 13804. (d) Tian H.; Yang S. J. Chem.
Soc. ReV. 2004, 33, 85. (e) Wang, S.; Shen, W.; Feng, Y. L.; Tian, H.
Chem. Commun. 2006, 1497.
(9) (a) Mulder, A.; Jukovic, A.; Van Leeuwen, F. W. B.; Kooijman, H.;
Spek, A. L.; Huskens, J.; Reinhoudt, D. N. Chem.-Eur. J. 2004, 10, 1114.
(b) Malval, J. P.; Gosse, I.; Lapouyade, R. J. Am. Chem. Soc. 2002, 124,
904. (c) Takeshita, M.; Irie, M. J. Org. Chem. 1998, 63, 6643.
(10) Irie, M.; Miyatake, O.; Uchida, K.; Eriguchi, T. J. Am. Chem. Soc.
1994, 116, 9894.
The single crystal of 1O was obtained by recrystallization
from dichloromethane/acetonitrile. The ORTEP drawing is
shown in Figure 2, which indicated that 1O was packed in
a distorted antiparallel conformation in the crystal. The
distance between the two reactive carbons was 5.05 Å, which
is too large to photocyclize in the single crystal according
to the literature.18 This is verified by the fact that irradiating
a single crystal of 1O with 365 nm of light for 24 h resulted
in no observable color change. In the crystal state, it was
completely symmetrical, and the boron atom adopted a
trigonal planar geometry (Σ(C-B-C) ) 360.7°), as expected
(11) Kawai, S. H.; Gilat, S. L.; Lehn, J. M. Eur. J. Org. Chem. 1999,
2359.
(12) Miyatake, O.; Fukaminato, T.; Irie, M. Chem. Commun. 2005, 3921.
(13) (a) Qin, B.; Yao, R. X.; Zhao, X. L.; Tian, H. Org. Biomol. Chem.
2003, 1, 2187. (b) Kopelman, R. A.; Snyder, S. M.; Frank, N. L. J. Am.
Chem. Soc. 2003, 125, 13684.
(14) (a) Yamaguchi, S.; Akiyama, S.; Tamao, K. J. Am. Chem. Soc. 2001,
123, 11372. (b) Sole, S.; Kubo, Y.; Yamamoto, M.; Ikeda, M.; Takeuchi,
M.; Shinkai, S.; Yamaguchi, S.; Tamao, K. Angew. Chem., Int. Ed. 2003,
42, 2036. (c) Gabbai, F. P. Chem. Commun. 2004, 1284. (d) Melaimi, M.;
Gabbai, F. P. J. Am. Chem. Soc. 2005, 127, 9680.
(15) Liu, Z. Q.; Shi, M.; Li, F. Y.; Fang, Q.; Chen, Z. H.; Yi, T.; Huang,
C. H. Org. Lett. 2005, 7, 5481.
(16) Lucas, L.; Esch, J.; Kellogg, R. M.; Feringa, B. L. Chem. Commun.
1998, 2313.
(17) Uchida, K.; Tsuchida, E.; Aoi, Y.; Nakamura, S.; Irie, M. Chem.
Lett. 1999, 63.
(18) Kobatake, S.; Uchida, K.; Tsuchida, E.; Irie, M. Chem. Commun.
2002, 2804.
3912
Org. Lett., Vol. 8, No. 18, 2006

Figure 2. ORTEP drawing of 1O (30% ellipsoid). H atoms omitted
for clarity.20
Figure 3. Changes in UV-vis absorption spectra of 1O (2.0 ×
10-5 M) in THF solution upon addition of 0.1-3.0 equiv of TBAF.
Inset: plots of absorbance at 344 nm as a function of [F-]/[1O].
from previous work on the structurally characterized dimesi-
tylboryl group.19
The reaction between the boron atom (Lewis acid) and
the fluoride ion (Lewis base) has been reported in some
systems.21 Herein, the interaction between a boron atom of
1O and a fluoride ion was investigated by 1H and 19F NMR
spectra.22 Upon addition of a n-Bu4NF salt (TBAF, as a
source of a fluoride ion) in CDCl3 solution, large shifts were
observed for the signals of the thienyl proton (from 7.18 to
6.41 ppm), the phenyl proton (from 6.79 to 6.51 ppm), and
the methyl proton (from 1.90 to 1.82 ppm). Moreover, the
signal from 19F NMR was upshifted to -162.1 ppm from
-114.5 ppm of the free fluoride ion. These facts suggested
a strong affinity of the boron atom for the fluoride ion. Upon
complexation of the boron atom with the fluoride ion, the
electron negativity increased, resulting in the increasing
shield effects of the boron atom and the upshift of the proton
signal. Furthermore, the methyl proton’s peak of the dimesi-
tylboryl group was split into multipeaks due to the coupling
interaction between the fluoride ion and the methyl proton
of the dimesityl group.
The binding property of 1O with the fluoride ion was also
investigated by UV-vis absorption spectra. When TBAF was
added to the THF solution of 1O, the absorbance centered
at 344 nm of 1O was decreased gradually and then reached
the saturation after a total addition of about 3 equiv of the
fluoride ion (Figure 3). These facts indicated that the strong
B-F interaction resulted in sp3 hybridization of the boron
atom and subsequently interrupted the extended p-π con-
jugation beween 2-methylthienyl groups and dimesitylboryl
groups, thereby causing a dramatic change in the photo-
physical properties.
with exchange correction functionals of B3LYP based on
the 3-21+G* set. The examination of the DFT orbitals
revealed that the pz orbitals of the boron atom contributed
to the LUMO of 1C (Figure 4), which was close to the
Figure 4. DFT orbital picture of LUMO in 1C.
observed other organoborons bearing two dimesitylboryl
groups.23 Therefore, any events disrupting the LUMO should
greatly affect the absorption specta of 1C. In the case of
1C, the combination of the fluoride ion, which generates
anionic charge on the boron atom, should change the
conjugation of the dipole moment of diarylethene and the
dimesitylboryl substituent, so it could be expected that the
absorption property of 1C was modulated upon addition of
the fluoride ion.14b
The modulation of the photochromic property of 1C by a
fluoride ion was recorded by UV-vis absorption techniques.
Figure 5 showed the changes in absorption spectra of the
photostationary states (PSS) irradiated with 365 nm when
TBAF was added in THF solution. Upon addition of less
than 1.0 equiv of TBAF, the absorption maximum of PSS
was red shifted from 655 to 670 nm with an isobestic point
of 705 nm (Figure 5a); consequently, the absorption edge
was greatly red shifted. However, when more than 1.0 equiv
of TBAF was added, the absorption maximum of PSS was
blue shifted to 490 nm (Figure 5b), and the solution turned
from green to orange. It was attributed to the formation of
The geometry structure of the closed-ring isomer 1C was
computationally optimized with density functional theory
(19) Liu, Z. Q.; Fang, Q.; Wang, D.; Cao, D. X.; Xue, G.; Yu, W. T.;
Lei, H. Chem.-Eur. J. 2003, 9, 5074.
(20) Crystal data for C51H58B2S2: fw ) 756.71, monoclinic (C2/C), a
) 14.231(3) Å, b ) 11.851(2) Å, c ) 27.763(6) Å, R ) 90°, â ) 90.34-
(3)°, γ ) 90°, V ) 4682.2(16) Å3, Fcalcd ) 1.073 g cm-3, Z ) 4, µ ) 0.145
mm-1, R1 [I > 2σ(I)] ) 0.0459, wR2 [I > 2σ(I)] ) 0.1330, R1 (all data)
) 0.0665, wR2 (all data) ) 0.1468, GOF ) 1.046. The CCDC number of
compound 1O is 296303.
(21) Katz, H. E. J. Org. Chem. 1985, 50, 5027. Katz, H. E. J. Am. Chem.
Soc. 1986, 108, 7640.
(22) Uchida, K.; Matsuoka, T.; Kobatake, S.; Yamaguchi, T.; Irie, M.
Tetrahedron 2001, 57, 4559.
(23) Jia, W. L.; Bai, D. R.; Motala, M.; Wang, R. Y.; Seward, C.; Tao,
Y.; Wang, S. N. Chem.-Eur. J. 2004, 10, 994.
Org. Lett., Vol. 8, No. 18, 2006
3913

Figure 6. Comparison of the percent decrease of absorbance of
1O (2.0 × 10-5 M) in THF solution at 344 nm in the presence of
3 equiv of different ions.
“cage”, only allow a small “base” such as a fluoride ion to
break through this “cage” and react with the boron atom. In
addition, this steric effect has also been noted by other
researchers in their previous work.2c,3a,b,14,15
Figure 5. Changes in UV-vis absorption spectra of 1 in PSS (2.0
× 10-5 M) in THF solution upon addition of (a) 0.1-0.9 equiv
and (b) 1.0-2.0 equiv of TBAF.
In summary, we have synthesized an organoboron-based
diarylethene derivative 1 and demonstrated the modulation
of its photochromic property by a fluoride ion. The interac-
tion of a boron atom with a fluoride ion caused obvious
spectral changes of 1 in both open-ring and closed-ring form.
Moreover, the structural feature of dimesitylboryl groups
benefits the high selectivity of the fluoride ion. The results
provide a useful design strategy for the tuning of photo-
chromic properties for further applications.
a fluoride adduct with photochromic property. Furthermore,
the solution turned colorless completely by photoexcitation
with visible light at 490 nm, which was in agreement with
the observation that the THF solution of a bis(fluoride)
adduct of 1O ([1OF2]2-) turned orange upon illumination
with UV (254 nm) light.
As depicted in Figure 6, the fluoride binding property of
1O is remarkably selective. 1O showed scarcely any response
with other halide ions and weak complexation with AcO-,
Acknowledgment. The authors thank NSFC of China
(20490210, 20501006, and 20571016), Huo Yingdong
Education Foundation (104012), and Shanghai Sci. Tech.
Comm. (05DJ14004) for financial support.
-
-
-
NO3 , H2PO4 , and ClO4 . The high selective binding
property of 1O to a fluoride ion is coincident with the
previous work on other organoboranes.14,15 Generally, the
high selectivity of the fluoride ion can be probably attributed
to two factors. First, the trivalent boron atom and the fluoride
ion are a typical Lewis acid and base, respectively; therefore,
they have very strong affinity.21 Second, with sterically
congested surroundings around the central boron atom
(Figure 2), four o-methyls on the two mesityls, just like a
Supporting Information Available: Synthetic and ex-
perimental details, CIF of 1O, and computational chemistry
of 1C. This material is available free of charge via the
Internet at http://pubs.acs.org.
OL061370G
3914
Org. Lett., Vol. 8, No. 18, 2006